John Singer

Robert De Montesquiou

Judith Gautier

Marcel Proust

Oscar Wilde

Claude Monet

Vernon Lee

The eruption, which is of a mauve colour, soon spreads, until in some cases the sufferer becomes completely covered with it. Arms, hands, and even feet are rapidly disfigured by the one prevailing hue, and strange as it

This quotation is not taken from a medical treatise but from a satirical article published in Punch, commenting upon the 'catching' craze for mauve, the first coal-tar based aniline dye accidentally discovered in 1856 by William Henry Perkin. Ironically the English chemist initially called his artificial dye 'Tyrian purple' but the term was soon replaced by 'mauve', the French name for the common mallow plant, which seemed more marketable than the antique reference, conjuring up instead the prestige of contemporary French haute-couture. ii Consequently the colour epithet 'mauve', which had existed in French only since 1829, officially entered the English language in 1859, the year of Perkin's patent and of the Punch article on the 'Mauve Measles'. The connection with France was so strong that Punch described the contaminating dye as being of French origin:

There are many who regard it as of purely English growth, and from the effect it produces on the mind contend it must be treated as a form of mild insanity. Other learned men, however, including Dr. Punch, are disposed to view it as a kind of epidemic and to ascribe its origin entirely to the French. iii Twenty-five years later, on 22 May 1886, a reviewer from the Illustrated London News, described John Singer Sargent's The Misses Vickers (1884) as 'an admirable specimen' of 'vivid portraiture', wherein the artist 'has attempted to engraft French method and dash upon the solid principles on which Velazquez worked'. The critic deemed the exercise an utter failure since 'the aniline dyes, which seem to have such an attraction for the Misses Vickers, are precisely those colours which accord least with the black and white that play so important a part of Velazquez' colouring'. iv Here the 'solid', serious, and almost achromatic black and white palette of Velazquez is contrasted with Sargent's modern 'French method' relying on the use of artificial, aniline-looking colours. Not only are the new dyes presented as both French and fake, they are also feminised by the critic's gendered rhetoric, which etablishes a clear parallel between the title of Sargent's painting and the Misses Vickers themselves who supposedly felt such a strong 'attraction' to the gaudy hues of modernity.

The rainbow colours devised by the modern chemical industry, from aniline mauve to the cobalt violet of the Impressionists, elicited mixed responses in artistic circles in France and in England, two countries which actively competed in the chromatic revolution of the industrial age. John Ruskin, William Holman Hunt and William Morris who witnessed the discovery of the new dyes, had been particularly wary of these new fugitive colours described as 'pestilential'. v However, by the 1880s and 1890s, the colours progressively became creative material for both poets and painters. This is particularly striking in the works of some of Sargent's French acquaintances, like Robert de Montesquiou and Judith Gautier, who described the painter's early works from that formative period using the new chromatic terminology and notably the colour epithet 'mauve' or its variants such as lilac or heliotrope. To paraphrase Sabine Doran's essay on the 'culture of yellow', it is this 'culture of mauve' vi as the subversive colour of modernity which I will be exploring in this article, in connection with the early oils of Sargent. My contention is that for the French and English avant-gardes of the 1880s and 1890s, who were then in close contact, mauve became a colour metaphorically encoding the modern, the liminal, and the artificial. It inaugurated a new type of chromatic syntax, which further strengthened the links between text and image as 'the chemical mimesis of the colours of the rainbow (…) enabled the creation of a virtual world, homologuous to that of language '. vii Sargent was a great admirer of French literature. viii As noted by Elaine Kilmurray, the cosmopolitan painter spoke fluent French and, 'throughout his life, his taste was for French literature, his library biased towards the French classics. He was sensitized to the rarefied aspects of early Decadent or Symbolist strain of French aesthetics rather than to the more literal, documentary concerns of the realist and naturalist schools.' ix This francophilia is well illustrated by the contents of his personal library, which included numerous French contemporary novels and volumes of poetry, from Charles Baudelaire to Joris-Karl Huysmans. x Although Sargent never wrote any poetry himself, references to the poetic quality of his early paintings are strikingly recurrent in the works of his literary friends. Judith Gautier, the daughter of Théophile Gautier, even claimed that it was because of Sargent's poetic sensibility that she agreed to be painted by him after he came to visit her and Mme Gautreau in Brittany: 'John Sargent seduces us even more; there is in his manner a nervous grace, a unique poetry which makes us favour him over all others. He will therefore be the one granted the honour of painting us'. xi Judith Gautier was a close friend of Robert de Montesquiou, the wife of the Parnassien poet Catulle Mendès, as well as the muse of Richard Wagner whom poets and painters of the fin de siècle were still adulating. Sargent was not only a Wagner enthusiast himself, he also shared the modern poetic tastes of his literary friends with a particular interest in Théophile Gautier, Baudelaire, Gustave Flaubert, Paul Verlaine or José Maria de Heredia whose works he often evokes in his correspondence, notably with Vernon Lee. In her essay In Memoriam, Lee directly connected the 'bizarre' and 'curious' beauty of Sargent's early works with this love for French poetry: In keeping with these literary acquaintances on both sides of the Channel, I will discuss the poetic dimension of Sargent's use of new colours and their contemporary literary reception. The poetry of Baudelaire and Gautier, in particular, was a great source of inspiration to painters with literary affinities. For instance, James McNeill Whistler's non-narrative Symphony in White echoed both Baudelaire's poem 'À une mendiante rousse' and Gautier's 'Symphonie en blanc majeur'. The literary reference to Emaux et Camées would later be applied in 1880 to Sargent's Fumée d'ambregris by Louis Leroy. In a satirical piece published in Le Charivari, Leroy has Manet say that the painting 'is a complete symphony in White Major. White on white, white everywhere'. xix Some critics were more favourable to Sargent's literary chromatic compositions, such as Paul Mantz, a disciple of Gautier, who celebrated the painting that same year as a 'melodic fantasy, a game like those which the impeccable master, Theophile Gautier, liked to play. He alone could have described this delicate and unique painting by M. John Sargent'. xx Such poetic and synaesthetic allusions were often a means for art critics to set off their own literary skills. However, more conservative commentators, especially in England, were suspicious of these 'beastly French' xxi literary connections, as shown by this anonymous review from the Academy describing La Carmencita in 1891 as 'a creation sprung from the artificial soil of the expiring century, a veritable "Fleur du Mal", such as would have delighted Baudelaire himself.' xxii Focusing on Sargent's eccentric chromatic and literary tastes, my aim will be to situate the early works of the painter within this specific fin-de-siècle zeitgeist. 'I like white for a bedroom', said I 'White ?' said Sarah, in tones of deep amazement, 'white ?' 'Well, why not ?' I asked. 'White !' repeated Sarah who seemed unable to get over the suggestion. 'Why, it would be ridiculous. People would laugh. They would find it absurd!' 'I was thinking of this pattern of violets', said Sarah, who had of course made up her mind before asking advice. 'Or this with the bunch of lilac' 'But' I began 'I don't see why lilac -' 'It's mauve' said Sarah 'Mauve and violet are half-mourning, and if a woman of my age is not a widow she ought to be.' xxix This quotation is interesting because it sheds light on the avant-garde's reappropriation of what was also then an established colour for half-mourning, here subverted into a chromatic signal of aesthetic elitism and sophistication. xxx The colour mauve had of course existed before 1856 but the invention of its aniline version not only increased its visual presence and raised it to the prominent and yet ambiguous status of the artificial colour par excellence. Thanks to this scientific transformation, mauve became a cultural event, a social fact xxxi . However, the aniline revolution not only affected the textile industry but also the materials of artists and the terminology of poets, as somehow anticipated by Théophile Gautier in his definition of the style of decadence: … a style that is ingenious, complicated, learned, full of shades of meaning and research, always pushing further the limits of language, borrowing from all the technical vocabularies, taking colours from all palettes, notes from all key-boards. (…) Such is the inevitable and fatal idiom of peoples and civilizations where factitious life has replaced the natural life, and developed in man unknown wants. (…) This style (…) expresses new ideas with new forms and words that have not yet been heard. xxxii How did Sargent respond to this new language, articulating colour and artifice?

According to his artist friend Edwin Blashfield (in his 1925 recollections), Sargent enthused about the chromatic potentialities offered by the aniline revolution: Apropos of breakfast things, one morning in English Broadway he exclaimed with delight over the table where the white cloth was covered with magenta colored flowers, dazzling silver shining among the buds, and said "Oh, I MUST make a study of that!" Just at that time (1887) he seemed to have a predilection for the aniline suggestion in colors. One evening at a birthday party in the big garden we had been ordered by the hostess to wear wreaths, ladies, men, and all. The rest of us were contented with roses except Alma Tadema, who wove big leaves together in a manner so skilful as to provoke attention, but Sargent was splendid in a garland of big dahlias of the color that in 1860 or thereabouts was a new creation of the dyers dubbed Solferino. In fact, he was not only able in everything, but also a little original. xxxiii Of course (the carnations) are dyed. That is why they are original. Mr Amarinth says Nature will soon begin to imitate them, as she always imitates everything, being naturally uninventive. xxxvii Following this discussion, Sargent's name is evoked to suggest a sinful deviation away from nature in favour of chromatic artifice: How exquisitely coloured these stawberries are, yet if Sargent painted them he would idealize them, would give to them a beauty such as Nature never gave to anything. So it is with the artist in sinning. He improves upon the sins that Nature has put, as it were, ready to his hand. He idealizes, he invents, he develops. xxxviii Like Sargent's sinful but inventive aniline colours, Hichens's green carnation, imitated by a less inventive Nature, illustrates Wilde's aesthetic credo exposed in The Decay of Lying (1889):

That white quivering sunlight that one sees now in France, with its strange blotches of mauve, and its restless violet shadows, is (Art's) latest fancy, and, on the whole, Nature reproduces it quite admirably. Where she used to give us Corots and Daubignys, she gives us now exquisite Monets and entrancing Pisaros (sic). 'The Impressionist analines (I can't even spell it) seem to have been spilled over all the palettes -Even the man Dannat, who by the way is right next to the really holy Valparaiso has mauve and ultramarine running into the huge legs of his Spaniard -and, by the same token, there is no B -to be found any where -They must have got through with her! -But beyond this, the drawing is marvellous in its blatant badness! -The men seem to [have] thrown all tradition and discipline to the winds, in the crazy hope that something else shall take its place -Sargent's 'Boy' that was supposed to be a masterpiece is horrible! -Boldini has some bad paintings & some hysterically clever pastels -but wildly out of drawing.' xlii Here Sargent is implicitly associated with this mauve, Impressionist clique, alongside Dannat or Boldini. In the 1880s, the American painter was indeed very much under the influence of Monet who may have encouraged him to shun black. As noted by Elaine Kilmurray, a recorded conversation between the dealer Georges Bernheim and Monet reveals that Sargent did not whole-heartedly embrace the Impressionist notion of 'pure colour' which jarred with his master Carolus-Duran's emphasis on tonal relationships.

Monet recalled: 'One day the American painter Sargent came here to paint with me. I gave him my colors and he wanted black, and I told him: 'But I haven't any' 'Then I can't paint' he cried, and added, 'how do you do it?' xliii However Monet certainly helped Sargent experiment with a new chromatic syntax, as noted by Trevor Fairbrother:

Impressionism exerted its greatest impact on Sargent's use of colour. He experimented with brighter, less black-inflected palettes and sought to capture the colors of highlights, shadows and reflections in all their varieties. An element of paradox often came into play, for the artist's emphasis on the natural effects of light -blue and lavender shadows on a sunlit white dresscould produce a pictorial effect that struck some viewers as forced or unnatural. xliv This impressionistic use of 'lavender' shadows is well reflected in his artfully staged Carnation, Lily, Lily, Rose although a luminous sheen of soft mauve had already pervaded Sargent's early twilight landscapes of the Luxembourg gardens in Paris.

The choice of an evanescent mauve certainly emphasized the liminality of the twilight hour as suggested by the poet Alice Meynell who singled out Sargent's 'system of shadows' and 'violet tints' as worthy of particular interest:

Portraits of childhood and an exquisite study of twilight and lantern-light, with the fine violet tints that artificial light lends to evening air, and with white as lovely in its coolness as the white of Titian in its gold, are united in the Garden picture Carnation, Lily, Lily, Rose. xlv Having noticed that, in a garden, for instance in summer, the human figure turns purple (se violace) in the light filtering through the green leaves and that, in the evening particularly, in gas lighting, the faces of women who use white powder called blanc de perle, become slightly violet, when the blood rushes to their cheeks, (these painters) have daubed their faces with lumps of intense violet, pressing heavily where the hue was only a hint, where the nuance was only barely perceptible. (…) The study of these works required physiological or medical competence. (…) This man saw violet ; land, sky, water, flesh -everything in his work looked either lilac or aubergine ; most of (these painters) confirm Dr Charcot's experiments on the alteration of colour perception which he noted in several hysterical patients of La Salpétrière. li Huysmans here strangely conflates the diseased perception of Impressionist artists and the decomposed complexion of their models, particularly that of the made-up women with violet faces. As this quotation reveals, the debate was not limited to violet shadows but pertained to all of the Impressionists's chromatic effects. These new colours, just like Sargent's aniline suggestions or the recherché syntax of Parnassien poets, were evidently perceived as eccentric.

'Improbable-looking' colours or Le cheveu mauve

Having stigmatised the diseased violet cheeks of Impressionist ladies, Huysmans lii was certainly not prepared to welcome the portrait of Mme Gautreau. In his review of the 1884 Salon, published in La Revue Indépendante (which Jacques-Emile Blanche would later fictionalize as 'La Revue Mauve' in his autobiographical novel Aymeris) liii he mentions Sargent only in passing as 'insidieux et brut', liv totally ignoring the portrait. Did Huysmans object to Mme Gautreau's white powder turned mauve? At the time, the peculiar colours of both the painting and the model were perceived as almost more scandalous than her risqué cleavage, as noted by Sargent's friend, the artist Ralph Curtis:

All the women jeer. (…) Then the blagueur club man -'C'est une copie !' 'Comment une copie ?' 'Mais oui -la peinture d'après un autre morceau de peinture s'appelle une copie.' lv Sargent himself commented upon the excessive chromatic matter used by Mme Gautreau to construct her social persona, in a letter to Vernon Lee:

In a few days I shall be back in Paris, tackling my other 'envoi' the portrait of a Great Beauty. Do you object to people who are 'fardées' to the extent of being a uniform lavender or blotting-paper colour all over ? If so you would not care for my sitter; but she has the most beautiful lines, and if the lavender or chlorate of potash-lozenge colour be pretty in itself I should be more than pleased. lvi As suggested by Susan Sidlauskas in her discussion of the portrait as a mise en abyme of painting, chlorate of potash may have been one of the toxic components of Mme Gautreau's lavender face powder. lvii Sargent's use of the French word 'fardée' seems to further corroborate the correlation between Frenchness, colour and artifice, as if the painting were a direct illustration of Baudelaire's L'Éloge du Maquillage.

The anglophile Jacques-Emile Blanche, himself a novelist and a painter, may have had Baudelaire's text in mind when he stressed Sargent's sense of 'glamour' in his 1926 ambiguous tribute to the artist, entitled 'Un Grand Américain à Paris'. The English word 'glamour' -which we associate today with the elegance of Hollywood stars, did not then exist in French and yet Blanche twice evokes the modern 'glamour' of Sargent's early works. lviii As the term was particularly recherché at the time, Blanche was certainly aware that a glamour originally meant 'a spell cast by a witch to deceive eyes', 'a way of 'altering the true appearance of things, ontologically on the side of seeming, (…) counterfeiters, and cosmetics'. lix His description of Sargent's works indeed suggests that the painter's art was too much a matter of surfaces and 'masks', adding that: 'His theatrical decors, his props, he never treated them firmly (…) His paint (pâte) is already cracking, thinning, losing its freshness'. lx Blanche's discussion here almost metaphorically conflates thinning pictorial matter and ageing skin ('perd sa fraîcheur')-possibly that of some of his made-up models, such as the fardées performers Ellen Terry, the Carmencita, or the professional beauty, Madame Gautreau.

In the BNF papers of Robert de Montesquiou, one finds colour reproductions of some these beauties lxi who exerted a particular fascination over the French poet and aesthete.

Montesquiou, who was an artist himself, even copied the profile of Sargent's Mme Gautreau, which he admired. The two men knew each other well in the 1880s as their correspondence reveals. They may even have visited the 1889 Exposition Universelle together as Sargent wrote to Montesquiou that he would send him a sketch of one of his Javanese dancers whose performance, involving a lilac shawl, had 'charmed' them both.

Montesquiou also sent the painter some of his poems -which Sargent alludes to as 'vos vers curieux et charmants.' lxii Even though Montesquiou remained an admirer of 'l'étrange beauté' lxiii (another Baudelairian expression) of the painter's early works, lxiv their relations eventually cooled. In Le Pavé Rouge (1905), a scathing response to the red volume on Sargent's works prefaced by Meynell, the French poet denigrates most of the painter's later portraits. He is also particularly harsh on his use of colour: Are all these paintings better off in their black and white reproductions? (…) Is the suppression of their colours a diminishing, almost a degradation as it should be? I regret I have to admit that I am not so sure of this (…) In particular for the portrait of Miss Terry, whose wounding peacock blue (blessant bleu-paon) and all its theatrical showiness I have not been able to forget. lxv Despite the French poet's stigmatisation of the excessive theatricality of Sargent's colourful models, the reference to the 'blessant bleu-paon' may not be as negative as it seems at first, given Montesquiou's personal taste for Whistlerian blue peacocks. The colour mauve is here made to suggest the 'uncertain' transition between day and night, a fragile and ephemeral balance that brings about a form of eroticism ('le mystère de l'alcove') as well as a heightened sensitivity to sounds ('la sonorité du mauve'). The poem ends with the palpitation of bats, Montesquiou's tutelary animal, suggesting again that mauve was indeed his emblematic hue, possibly a variation on the artificial blue of hydrangeas, which Sargent, Blanche and Helleu equally cherished, as Alison Symes has noted. lxxi Montesquiou even wrote all his correspondence in violet ink as in this letter to Graham Robertson in which the French poets explains how impatient he is to see

Carnation, Lily, Lily, Rose (FIG). lxxii

Montesquiou's evocation of Mme Gautreau and her 'cheveu mauve' is certainly an allusion to Baudelaire's synaesthetic praise of les 'cheveux bleux' lxxiii of his mistress in the poem 'La Chevelure'. lxxiv Like Baudelaire or Montesquiou, Sargent seems to have been drawn to what Lee describes as 'improbable-looking colours', falling on 'skin, hair and stuffs' in her essay 'In Memoriam'. lxxv Mme X's chromatic eccentricities strangely anticipate Sargent's Broadway palette, her lavender skin and dyed hair paving the way for the mauve streaks found in the hair of the Barnard children. Sargent certainly had a strange obsession with improbably coloured hair during that period lxxvi -as shown by his portraits of the Francophile and Parnassien enthusiast Edmund Gosse and his daughter Teresa. Sargent painted Teresa on her 8th birthday, in September 1885. Teresa described her portrait in a letter of 1948 to David Mckibbin: 'He was so pleased with the colour of the mauve flowers, my red hair, white dress, that he quickly painted a sketch on canvas over a landscape'. lxxvii Writing about the Broadway summer he spent with Sargent, her father Edmund Gosse also recalled:

As I approached him, Sargent looked at me, gave a compulsive plunge in the air with his brush, and said 'oh ! what lovely lilac hair, no one ever saw such beautiful lilac hair !' The blue sky, reflected on my sleek dun locks, which no one had every thought 'beautiful' before, had glazed them with colour, and Sargent, grasping another canvas, painted me as I stood laughing, while he ejaculated at intervals 'Oh ! what lovely hair !' The real colour of the hair was nothing, it existed only in the violet varnish which a single step into the shade would destroy for ever. lxxviii Although the lilac colour of Gosse's hair is not visible in Sargent's portrait, it nonetheless plays a central role in the chromatic harmony of Carnation, Lily, Lily, Rose, where the mauve flowers blend harmoniously with the lavender shadows of the children's white dresses and the mauve twilight sheen falling on their hair. But other paintings from that Broadway period seem to illustrate this mauve phase, like the portrait of Mrs Frank Millet for whom Sargent specifically selected the mauve breakfast shawl lxxix just as he chose the lilac dress of Mrs Archibald Douglas Dick painted that same year. lxxx If mauve was Sargent's and Montesquiou's cherished hue during this period, it also coloured the fictional world of Marcel Proust who depicted the French society of the Belle Époque in À la Recherche du Temps Perdu. Mauve and its variations, from lilac to Parma violet, are recurrent chromatic motifs throughout the seven volumes composing La Recherche, which induced synaesthetic writer Vladimir Nabokov to celebrate 'the mauve shades of Monsieur Proust'. lxxxi Not only did this hue offer rich connections between chromatics and onomastics, it was also an erotically charged epiteth, closely associated with the coquette Odette in the eyes of both Swann and the narrator: 'La couleur délavée, liquide, mauve et dissolue des violettes de Parme' lxxxii , with a pun on 'dissolue' suggesting a diluted as well as a dissolute colour. As noted by Butor, in Proust's works mauve is indeed closely linked to 'sexual secrecy', it is 'the catleya colour' lxxxiii -Swann and Odette's coded expression for sex. It is also the colour of the homosexual baron de Charlus, inspired by Robert de Montesquiou and described as a 'figure mauve' associated with 'sodomist scandals' in Le Temps Retrouvé. lxxxiv Could this colour have been meant also as a sign of Sargent's and Gosse's own secret sexual inclinations? lxxxv Be that as it may, the specific mention of mauve hair is found twice in connection with Elstir, the painter of ambiguity. lxxxvi In Du côté de chez Swann, the chromatic choices of Elstir (nicknamed M. Biche by the Verdurin circle) are totally misunderstood by M. and Mme Cottard who believe that: …the painter simply flung the colours haphazard upon his canvas. When, on one of these, they were able to distinguish a human form, they always found it coarsened and vulgarised (…) and devoid of truth, as though M. Biche had not known how the human shoulder was constructed, or that a woman's hair was not, ordinarily, mauve. lxxxvii Proust may have been thinking of Sargent here, and of the mauve hair and shocking shoulder of Mme Gautreau, whose poetic evocation by Montesquiou he certainly knew better than Sargent's works. lxxxviii

Conclusion

Mauve was therefore a transitional, liminal hue which Sargent and the French literary avant-garde of the fin de siècle embraced in all its infinite synaesthetic variations. But this 'mauve mania' lxxxix was only a short-lived vogue, soon replaced by more clear-cut chromatic contrasts of Mediterranean colours, favoured by artists like Henri Matisse or André Derain. Contrary to the culture of yellow, which Doran argues persisted well into the 20th century, mauve, by the 1920s, thus appeared as a passée colour, a modern colour relegated to the decadent past, in keeping with the 'mauve remoteness' xc which Nabokov so poignantly associated with the vanishing world of the turn of the century. Since she has pink tendrils, a nose that knows no limit, The portrait by Sargent, the unicorn's profile, And at night, she sleeps beneath the high four-poster canopy, With a resounding pillow in Marocco leather, In order to be warned in time, of a mauve hair Just getting ready to come through, on her temple, and it is saved Since she has the golden trowel, decorated with enamel To coat her face, with exquisite workmanship, Of scented and smooth mortars, She still walks around, a fine-looking wreck, And her famous curves leave each night, Gaining in Caran d'Ache and losing some of their Canova.

Bibliography

I

  have spoken, almost overmuch, of his love for the bizarre. (…) It may also have been connected with the Parnassian, the Heredia and Leconte de Lisle movement in literature. (…) The boyish hankering after the 'curious' would have been entirely transmuted into the particular imaginative habit, poetical, yet of almost scientific insight, which distinguishes Sargent as much as his individual quality of line and colour. xii The first Parnassien poets, like Leconte de Lisle, were the direct heirs of Théophile Gautier. They emulated his formalism, his passion for recherché words as well as for poetic craftsmanship, exemplified in the poem 'L'Art' in Emaux et Camées (1852). The Symbolist movement also sprang from the Parnasse although the Symbolists were more indebted to the sensual and synaesthetic écriture artiste propounded by Baudelaire, who had heralded the works of Eugène Delacroix, 'the alchemist of colour', as the index of the new Romantic sensibility. This celebration of colour over academic drawing (in particular in Baudelaire's article on 'Colour' in the Salon de 1846) paved the way for its autonomization and liberation from all forms of mimetic injunctions: 'Colour (…) thinks by itself, independently of the object it clothes.' xiii But Gautier and Baudelaire also influenced the apostles of l'art pour l'art in England, like Walter Pater or Algernon Charles Swinburne, who in turn supported the younger generation of French poets, from Heredia to Mallarmé. xiv They too experimented with the new sensuous chromatic syntax advocated by contemporary French poets, embracing their 'strange dyes, strange colours' xv to use Pater's Baudelairean expression in The Renaissance which Sargent, himself an advocate of art for art's sake at the time, xvi references in a letter to Lee in 1881. xvii Such cultural exchanges between France and England were frequent from the 1860s till the end of the 19 th century as shown by the francophilia of Graham Robertson, Oscar Wilde, Edmund Gosse or George Moore, whom Sargent frequented during these formative years. But the painter was also a cultural passeur himself, as he introduced Paul Bourget and Montesquiou to his English artist friends when they visited London in the mid 1880s. xviii

  figure paintings-the artificially-coloured 'cheveu mauve' of some of Sargent's sitters of the 1880s which Lee described as of an 'improbable-looking colour'

  Here Sargent's eccentricity is directly related to his interest in artificial colours, such as Solferino or Magenta, two new French dyes named after Italian battles fought and won by Napoleon III in 1859. The question here is not whether Sargent's materials were aniline-based or not, but what these colours suggested to the painter himself and to his literary commentators. xxxiv As noted by Blashfield, the flowers favoured by Sargent may well have been artifically 'colored' -the dyer's art here competing with that of the painter. This not only anticipates Sargent's enthusiastic response to Ellen Terry's 'Magenta' wig xxxv , it equally paves the way for Oscar Wilde's green carnation. The artificial colour of this flower was obtained by plunging its stem into aniline malachite green. xxxvi The flower was then worn at the première of Lady Windermere's Fan by Wilde himself and his acolytes, such as the 'jade-d' Graham Robertson (Punch's chromatic pun referring to the gem on his cane in the Sargent portrait). Robert Hichens turned this aniline green carnation into a symbol of decadent aesthetics in his eponymous novel published in 1894, another roman à clef featuring Mr Amarinth as the witty Oscar Wilde figure. The novel openswith Reggie Turner -a Lord Alfred Douglas epigone -admiring his reflection in the mirror as he is wearing a green carnation and a pair of 'lavender gloves'. In order to justify his eccentric outfit, he explains:

  xxxix

'

  Strange blotches of mauve': Impressionist shadows and Parnassien twilightsWilde's emphasis on the 'mauve' 'blotches' and 'shadows' found in French Impressionist painting reinforces the idea that mauve was the modern colour par excellence, not only because it had been invented thanks to new scientific means, but also because it entailed new ways of seeing, often perceived as deviant and bizarre. This signals a clear shift away from the empirical observations about violet shadows and complementary colours formulated by earlier painters like Eugène Delacroix. But following the aniline revolution, these shadows suddenly became 'strange' as shown by Wilde's use of the Paterian or rather Baudelairian adjective to describe the 'blotches of mauve' of the Impressionists. The French novelist and essayist Michel Butor in his analysis of Proust's Vinteuil Sonata also connects the literary predilection for mauve at the turn of the century with the Impressionist practice: 'the colour mauve, characteristic of the time, of the art of 1900, was also the colour of shadows (Monet was defined as the one who had discovered that 'all shadows are violet') -that is to say the colour of what cannot be seen, cannot be spoken' -in a word, a literary and pictorial challenge. xl Jean Carré in his 1912 'Notes sur Renoir' recalled that these violet shadows were discovered fortuitously by Monet, Renoir, Pissaro and Sisley one day when they had run out of black which they were no longer able to afford. xli The violet 'purée' described by Carré would elicit endless controversy in the art journals of the late 19th century, both in France and in England, including by James McNeill Whistler who denounced the so-called 'Impressionist anal-ines', which he deliberately misspelt as if to underline their excremental coal-tar provenance:

  Such twilight scenes were equally favoured by the Parnassien and Symbolist poets like Mallarmé as 'l'heure souverainement ambiguë', xlvi an hour touched with 'mauve, and undecided purple' xlvii recalling Paul Verlaine's Fêtes Galantes, according to George Moore, whom Monet visited with Sargent in 1901. xlviii However, this new chromatic syntax was often as misunderstood as that of the Parnassien poets whom Sargent so much admired. In a review published in Le Gaulois, an anonymous critic thus explained that 'the impressionism of the intransigeant painters of 1880' was as 'unreasonable' as that of contemporary poets who used 'vague words, connected to one another not by meaning but by sonority' and which substituted 'onomatopea to the logical development of ideas and facts'. The text ends with the following recommendation: 'the time for such eccentricities is now over (…) We only have one piece of advice to give to Messieurs Les Intransigeants: if they want to be taken seriously, they have to be serious. Men are not tatooed in green, red, yellow or violet. (…) These (painters) are lost, mad or sick'. xlix The French writer Huysmans also analysed the spreading use of mauve and violet as symptomatic of both deviance and disease in modern art, anticipating Max Nordau's stigmatization of the decadent violettomania of Manet: l

  lxvi In Les Quarante Bergères published in 1919 but written over 20 years earlier, Montesquiou dedicates a satirical poem to Sargent's portrait of Mme Gautreau which is just as ambiguous. The text is entitled 'Vénus' -possibly a reference to Mme Gautreau's nickname 'la Vénus de la République' following her affair with the President Jules Grévy: lxvii Comme elle eut les frisons roses, le nez sans borne, Le portrait de Sargent, le profil de licorne Et, la nuit, pour dormir sous le haut baldaquin, Un oreiller sonore et tout en maroquin Afin d'être avertie, à temps, d'un cheveu mauve Tout près de se briser sur la tempe, et qu'on sauve ! Comme elle eut la truelle en or garni d'émail Pour enduire sa face, en un exquis travail, De mortiers odorants et de crépit suave Elle promène encor de beaux restes d'épaves, Et son galbe fameux, chaque jour qui s'en va, Gagne du Caran d'Ache et perd du Canova. lxviii Like Blanche, Montesquiou questions the freshness of the complexion of Mme Gautreau who is described as having to 'coat her face, with exquisite workmanship' possibly to hide the 'wreck' of her ageing features. Cosmetic glamour, if not witchcraft, is presented as the beauty's means to defy the onslaught of time. Initially depicted as a chimeric Oriental princess, with the profile of an impossible unicorn, she has become by the end of the poem a caricature of herself, more similar to Montesquiou's friend Caran D'Ache's satirical cartoons, than to Canova's impeccable neo-classical Venus -to whom Mme Gautreau apparently liked to compare herself. The poem certainly sounds a little cruel at first and yet when one analyses it more closely, it is quite clear that Montesquiou celebrates Mme Gautreau's talents as a painter -possibly a greater artist than Sargent himself, who only managed a 'copie d'une peinture'. Moreover, the synaesthetic images referring to smells and sounds which pervade the poem are typical of Montesquiou's own Baudelairian affinities. The rhyming pattern stresses some of his sensual key words, such as 'suaves' (meaning soft or smooth) -which he uses in the title of one of his early volumes of poetry (Le chef des odeurs suaves). lxix But another detail in the poem is revealing: Montesquiou's rather odd reference to Mme Gautreau's 'cheveu mauve'. The fact that 'mauve' rhymes with the positive 'sauve' recalls another poem of his, entitled 'salve malva' and published in the very Verlainian Demiteinte section of Les Chauve-Souris in 1892, which the novelist Matilde Serao, who was a close friend of Montesquiou, considered as the most representative of the poet's aesthetics. The poem opens with an epigraph by the Romantic poet Lamartine, celebrating the twilight hour: 'Entre la nuit qui tombe et le jour qui s'enfuit' Dirai-je tout ce que j'entends Dans la sonorité du mauve, Et que j'y vois, en même temps ? Rose qui vient, bleu qui se sauve, Livrent des assauts hésitants Dans le ton incertain du mauve. Puis ce sont des rêves flottants Par le mystère de l'alcôve Aux crépuscules invitants. Et, sous les clairs de lune mauves, Voici les vols inquiétants Et tournoyants des souris-chauves Qui palpitent sur des étangs. lxx

Manuscripts consulted: Bibliothèque Nationale de France, Paris The

  Robert de Montesquiou papers (including le Pavé Rouge and a selection of letters from, to and about Sargent): NAF 15141-5 F72-84x Sargent's personal library (private collection) contained innumerable works by Stendhal, Flaubert, Balzac, Dumas, Fromentin, Goncourt, De Vigny, Banville, Leconte de Lisle, Verlaine, Huysmans, Gautier, Baudelaire, Anatole France. I am very grateful to the cataloguer,Richard Ormond, for this information. xi My translation. Gautier, 'Le Salon', Le Rappel, 1 May 1888. Gautier's use of the future tense may suggest that Sargent's portrait of her (in the Detroit Institute of Art) dates back to 1888 or 1889. Gautier certainly looks older -and more fardée -than in A Gust of Wind (c. 1883-5, private collection). xii Lee, In Memoriam, reproduced in extenso in Charteris, pp. 252-3. xiii My translation. Baudelaire, 'Exposition Universelle, 1855', Oeuvres Complètes, vol.2, p. 241. xiv On Swinburne and France see Ribeyrol, 'A Channel Passage : Swinburne and France' (2010). Lee wrote to her mother on 21 June 1881: 'John is extremely serious, a great maker of theories ; he goes in for art for art's sake, says that the subject of a picture is something not always in the way etc. he is quite emancipated from all religious ideas. He speaks English without accent but has to help himself out with French words'. Quoted in Ormond, 'John Singer Sargent and Vernon Lee', p. 170. xvii 'Your book Belcaro has at last arrived. I have been expecting it for weeks and it only came yesterday. I am going to read it at once. Tell me what you think of Pater's Essays. I like one or two of them very much' Quoted in Ormond, 'John Singer Sargent and Vernon Lee', p. 168.xviii Sargent, then residing in Paris, wrote Henry James the following collective letter of introduction on June 29 1885: 'Dear James, I remember that you once said that an occasional Frenchman was not an unpleasurable diversion to you in London, and I have been so bold as to give a card of introduction to you to two friends of mine. One is Dr. S. Pozzi the man in the red gown (not always), a very brilliant creature ! and the other is the unique extrahuman Montesquiou of whom you may have heard Bourget speak with bitterness, but who was to Bourget to a certain extent what Whistler is to Oscar Wilde. (Take warning and do not bring them together). They are going to spend a week in London and I fancy Montesquiou will be anxious to see as much as Rossetti's and Burne-Jones's work as he can. I have given him a card to B.J., to the Comyns Carrs and to Tadema.' Quoted in Munhall, Whistler and Montesquiou, p. 58. Bleu, p. 8 : 'la couleur se définit d'abord comme un fait de société. C'est la société qui 'fait' la couleur'.xxxii This translation of Gautier's essay on Baudelaire appears in the English version of Nordau's Degeneration, p. 299. This emphasis on the suggestiveness of colour echoes Mallarmé's symbolist credo: 'suggérer voilà le rêve'. The chemical composition of Sargent's mauve pigments is unknown, as noted by Shelley in her analysis of Sargent's materials found at his death: 'Two colors that must be presumed missing from this collection are mauve and Chinese white. The former, for which Sargent showed a marked proclivity -and which since its introduction in 1856 had become widely popular -was available in various purples and violets', p. 21. xxxv Letter to Mrs Gardner, 1st January 1889, quoted in Charteris, pp. 100-1. My translation.Butor, Répertoire II : 1959-1963, p. 259. xli Carré, 'Notes sur Renoir', pp. 408-410. xlii Letter from Whistler to Beatrix Whistler [11 June 1891?] Glasgow University Library, MS Whistler W584. xliii Quoted in Elaine Kilmurray, 'Sargent, Monet…and Manet' (no page number). xliv Fairbrother, John Singer Sargent: The Sensualist, p. 126. xlv See Meynell's introduction to The Work of John Singer Sargent (1903). xlvi Jean-Pierre Richard, L'Univers imaginaire de Mallarmé, Paris: Éditions du Seuil, 1961, 155. xlvii Moore, Confessions of a Young Man, p. 64. xlviii Monet, Lettres de laTamise, 1901Tamise, (2004)). xlix My translation. Tout-Paris, 'La Journée parisienne: Les Impressionnistes' Le Gaulois, 2 April 1880, quoted in The NewPainting, Impressionism 1874-1886, vol.1, pp. 311-312. l SeeNordau, Degeneration (1892) and Oskar Reutersvard 'The violettomania of the impressionists', (1950). li My translation. Huysmans, 'L'Exposition des indépendants en 1880', pp. 103-104. lii Huysmans would, however, change his mind about Pissarro and Monet and eventually embrace the colour 'mauve'. In À Rebours (1884), he particularly singles out the colour as the sign of aesthetic refinement in the following description inspired by the aesthetic tastes of Robert de Montesquiou who was the model for his decadent hero, Des Esseintes: …en ne conservant plus alors que les gens aux pupilles raffinées, exercées par la littérature et par l'art, il lui semblait certain que l'oeil de celui d'entre eux qui rêve d'idéal, qui réclame des illusions, sollicite des voiles dans le coucher, est généralement caressé par le bleu et ses dérivés, tels que le mauve, le lilas, le gris de perle. (p. 16) liii In his autobiographical novel Aymeris (1922), Blanche uses this colour extensively, referring to the 'revue mauve' as being famous amongst fin de siècle 'littérateurs'. A 'revue mauve' actually existed at the time which published prominent fin de siècle authors such as Mallarmé, Verlaine, Montesquiou. The 'Revue mauve' was also the nickname of Le Mercure de France due to the colour of its cover which Rachilde, another key decadent figure, claimed to have been chosen in her honour.liv Huysmans, 'Le Salon de 1884', La Revue indépendante, vol. 1, 1884, p. 123. lv Ralph Curtis's letter to his mother quoted in Charteris, p. 61. lvi The letter, dated 10 February 1883, is quoted in Ormond 'John Singer Sargent and Vernon Lee', p. 174. lvii Sidlauskas, 'Painting skin', p. 23. lviii Blanche, 'Un Grand Américain à Paris', p. 61. lix Wygant, Medea, Magic and Modernity, pp. 41-2. lx My translation. Blanche, 'Un Grand Américain à Paris', p. 76. lxi In particular La Carmencita and Mme Gautreau. lxii See the Robert de Montesquiou papers in the Bibliothèque Nationale de France, in particular NAF 15141-5 F79-82. lxiii Montesquiou, Le Pavé Rouge, p. 342. lxiv Montesquiou also dedicated a poem to Sargent's portrait of Mme Paul Escudier (1882), a blue portrait matching the French poet's own 'fleurs d'azur' in Les Paroles Diaprées (1910). lxv Montesquiou, Le Pavé Rouge, p. 342. lxvi In 1901 Montesquiou wrote a volume of poems entitled Paons. lxvii Noël, Parisiana, p. 103. lxviii This poem is translated in Davis's Strapless, p. 212:

xv

Pater, The Renaissance, p. 189. xvi xix My translation. 13 May 1880, quoted in CP, 4: 303. xx My translation. Mantz, 'Le Salon VII', Le Temps 20 June 1880. xxi The expression is Sargent's, quoted in CP, 5: 46. xxii 'Fine Art. The Royal Academy II' 16 May 1891, p. 471, quoted in CP, 2: 13. xxiii Delevoy, Symbolism, p.45 et sq. xxiv Beer, The mauve decade, p.119. xxv Mauve and marshmallow. xxvi My translation. Morand, 1900, p. 5. xxvii Robertson, Time Was, p. 241. xxviii Emily Sargent's letter to Robertson, dated 8 November 1931 (The Graham Robertson Correspondence, mssWR 512). xxix Robertson, Time Was, p. 121. xxx Sarah Bernardt's tastes may have been influenced by Montesquiou whose enthusiasm for modern chromatic harmonies in clothing as well as in interior decoration he shared with most of his friends. On mauve as the colour for mourning see Taylor, Mourning Dress, pp. 146-7. xxxi Pastoureau, xxxiii Blashfield, 'John Singer Sargent -recollections', p. 648. xxxiv xxxvi The chemical process is described in The Artist, 1st April 1892, pp. 114-5. I wish to thank Catherine Maxwell for this reference. xxxvii Hichens, The Green Carnation, p. 18. xxxviii Hichens, The Green Carnation, p. 27. xxxix Wilde, 'The Decay of Lying', in Intentions, p. 48.

xl

xc Nabokov, Speak, Memory, p. 29.


Fengchun Yang

Yan Wang
email: wangyan405@gmail.com

Hongli Li
email: lihongli1225@163.com

Minmin Yang

Tao Li

Fangfang Cao

Jianmin Chen

Zhe Wang

Influence of Cloud/Fog on Atmospheric VOCs in the Free Troposphere: A Case Study at Mount Tai in Eastern China

Keywords: Atmospheric VOCs, Mount Tai, Cloud, Fog, Photochemical reactions

Field measurements of volatile organic compounds (VOCs) were conducted in July of 2015 at Mount Tai, where 63 species of VOCs were measured using GC-MS. In this study, air samples were collected in two different weather conditions: cloud/fog and non-cloud/fog respectively and influences of the cloud/fog on VOCs species were analyzed. The sources of air masses were calculated by back trajectories with HYSPLIT model. Five main kinds of VOCs were analyzed and oxy-VOCs (OVOCs) had the largest contribution (67% on the cloudy/foggy days and 72% on the non-cloudy/foggy days) to total measured VOCs among all of the samples collected at Mount Tai. Acetone was the most abundant compound (18 ppb on the cloudy/foggy days and 15 ppb on the non-cloudy/foggy days) among the VOCs. The concentrations of VOCs collected in cloudy/foggy days were higher than those measured in non-cloudy/foggy days and indicated that cloudy/foggy days favoured the accumulation of atmospheric VOCs. However, the concentrations of most OVOCs in noncloud/fog conditions were higher than those in cloud/fog conditions. Atmospheric photochemical reactions may partly account for this result. Air mass trajectory analysis shows that most air masses from heavily polluted areas results in the increase of atmospheric VOCs. OVOCs and aromatics provided the main contribution to ozone formation potential. Besides cloud and fog, VOC concentration is concerned with integrated factors including temperature, relative humidity, wind speed and direction.

INTRODUCTION

Meteorological conditions, such as cloud and fog, have a significant effect on the dispersion, chemical/physical transformation and removal of atmospheric pollutants [START_REF] David | Diurnal and seasonal variability of surface ozone and NO x at a tropical coastal site: Association with mesoscale and synoptic meteorological conditions[END_REF][START_REF] Sahu | Source identification of VOCs at an urban site of western India: Effect of marathon events and anthropogenic emissions[END_REF]. Clouds have an important effect on tropospheric photochemistry, and further influence the concentrations of tropospheric compounds [START_REF] Tie | Effect of clouds on photolysis and oxidants in the troposphere[END_REF]. [START_REF] Prather | A persistent imbalance in HO x and NO x photochemistry of the upper troposphere driven by deep tropical convection[END_REF] found that the upper troposphere is more active in producing ozone (O 3 ) by convective injection of peroxides, aldehydes and ketones. [START_REF] Barth | Effect of marine boundary layer clouds on tropospheric chemistry as analyzed in a regional chemistry transport model[END_REF] found that the aqueous phase chemistry in clouds plays an important role in the variation of O 3 concentrations in the troposphere. Moreover, clouds alter the actinic flux by scattering solar radiation, which consequently impact the photolysis rates of several key oxidant species [START_REF] Tie | Effect of clouds on photolysis and oxidants in the troposphere[END_REF].

Fog is an aerosol system composed of liquid or solid hydrometeor particles that are suspended in the air near the ground [START_REF] Taylor | The formation of fog and mist[END_REF][START_REF] Yang | Ion composition of fog water and its relation to air pollutants during winter fog events in Nanjing, China[END_REF]. Fog, which usually forms under circumstances of stable stratification, weak winds and a shallow mixing layer, will result in the increase of the concentration of pollutants in the atmosphere by the accumulations in the surface layer. In addition, the droplets in fog work as the "micro-reactors" in the air because of their small size, high humidity, large specific surface area and long residence time. Therefore, they are conducive to producing secondary pollutants by transforming some primary pollutants [START_REF] Yang | Ion composition of fog water and its relation to air pollutants during winter fog events in Nanjing, China[END_REF].

VOCs, one of the principal trace constituents in the atmosphere, play an important role in atmospheric chemistry [START_REF] Barletta | Mixing ratios of volatile organic compounds (VOCs) in the atmosphere of Karachi, Pakistan[END_REF]Guo et al., 2004a, b). They contain a wide range of organic compounds with many different functional groups [START_REF] Yu | A review of the emission of VOCs from polymeric materials used in buildings[END_REF][START_REF] Sahu | Volatile organic compounds and their measurements in the troposphere[END_REF]. Some of the VOCs and their photochemical products, such as benzene, toluene, formaldehyde and acraldehyde, have adverse effects on human health. By entering through the respiratory tract or skin into the human body, they may lead to acute or chronic health problems, such as inflammation, heart and lung diseases and even cancer [START_REF] Ras | Vo latile organic compounds in air at urban and industrial areas in the Tarragona region by thermal desorption and gas chromatography-mass spectrometry[END_REF][START_REF] Chen | Investigating the differences between receptor and dispersion modeling for concentration prediction and health risk assessment of volatile organic compounds from petrochemical industrial complexes[END_REF]. VOCs also have negative impacts on natural environment in a large extent. They have a significant contribution to forming atmospheric fine particles and influencing the oxidizing capacity of the atmosphere by reacting with OH radicals. In addition, atmospheric chemical reaction cycles consisting of VOCs and NO x (NO x = NO + NO 2 ) in the presence of solar radiation lead to the formation of ozone and secondary organic aerosols (SOA) [START_REF] Liu | Source profiles of volatile organic compounds (VOCs) measured in China: Part I[END_REF][START_REF] Sahu | Source identification of VOCs at an urban site of western India: Effect of marathon events and anthropogenic emissions[END_REF], indirectly influencing the radiation balance of the earth's surface and consequently contributing to climate change [START_REF] Pandis | Secondary organic aerosol formation and transport[END_REF][START_REF] Kroll | Chemistry of secondary organic aerosol: Formation and evolution of low-volatility organics in the atmosphere[END_REF][START_REF] Derwent | Secondary organic aerosol formation from a large number of reactive man-made organic compounds[END_REF][START_REF] Wang | Analysis of atmospheric organic compounds by thermal desorption-comprehensive two-dimensional gas chromatography-flame ionization detection[END_REF].

In addition to anthropogenic and biogenic sources, VOCs may also be formed by atmospheric transformations of other kinds of VOCs in the atmosphere [START_REF] Atkinson | Atmospheric degradation of volatile organic compounds[END_REF], e.g., the oxidation of hydrocarbons in the atmosphere is an important source of OVOCs [START_REF] Mellouki | Atmospheric chemistry of oxygenated volatile organic compounds: Impacts on air quality and climate[END_REF]. Anthropogenic sources dominate as urban sources of VOCs, such as emissions from vehicles, landfills, refineries, petrochemical sources, solvent usage and industrial facilities [START_REF] Atkinson | Atmospheric degradation of volatile organic compounds[END_REF].

Researches on VOCs in China are mainly focused on metropolises and urban agglomeration, such as Beijing, the Pearl River Delta and the Yangtze River Delta (Zhang et al., 2014). And there is relatively little information about VOCs in remote areas, especially in the high mountains. Research on VOCs in the high mountains is of great significance to the study of global temporal and spatial variation of VOCs. Studies now have been performed on the concentration characteristics, seasonal and diurnal variations and source identification of VOCs at the summit of some mountains in China [START_REF] Tang | Characteristics and diurnal variations of NMHCs at urban, suburban, and rural sites in the Pearl River Delta and a remote site in South China[END_REF][START_REF] Tang | Implications of changing urban and rural emissions on non-methane hydrocarbons in the Pearl River Delta region of China[END_REF][START_REF] Zhang | The characteristics, seasonal variation and source apportionment of VOCs at Gongga Mountain, China[END_REF][START_REF] Yang | Aromatic hydrocarbons and halocarbons at a mountaintop in southern China[END_REF].

Many studies have concentrated on characterizing the deposition of pollutants in cloud/fog water. However, relatively fewer researches were focused on variations in gaseous pollutants during cloud/fog events, especially in the high mountains. [START_REF] Yang | Ion composition of fog water and its relation to air pollutants during winter fog events in Nanjing, China[END_REF] found VOCs concentration had significantly negative correlation with visibility during winter fog events in Nanjing. [START_REF] Sahu | Source identification of VOCs at an urban site of western India: Effect of marathon events and anthropogenic emissions[END_REF] found that the stagnant weather conditions, such as fog and drizzle, favoured the accumulation of VOCs. It was also stated in some papers that the existence of clouds has an impact on photolysis and oxidants in the troposphere [START_REF] Barth | Effect of marine boundary layer clouds on tropospheric chemistry as analyzed in a regional chemistry transport model[END_REF][START_REF] Tie | Effect of clouds on photolysis and oxidants in the troposphere[END_REF], and then it will affect the atmospheric pollutants. In addition, field investigations of VOCs have been conducted at Mount Tai in June 2006 [START_REF] Ting | A study of the atmospheric VOCs of Mount Tai in June 2006[END_REF]. Based on earlier research studies about VOCs in the high mountains or cloud/fog events, targeted sampling in foggy (cloudy/foggy condition) and sunny (non-cloudy/foggy condition) days at Mount Tai in July 2015 was conducted to mainly study the influence of cloud and fog on the characteristics of atmospheric VOCs in the free troposphere.

EXPERIMENT AND METHODS

Sample Collection

The sampling campaign was carried out in the meteorological observation station (36.25°N, 117.10°E) at an elevation of 1,534 m a.s.l on Mount Tai, which is the highest mountain in the North China (Huabei) Plain. Mount Tai is located in the eastern part of the North China Plain, one of the major agricultural areas in China, in the middle of the Shandong province. Industrial cities and coal-producing areas, such as Jinan, Weifang, Laiwu and Yanzhou, are within 200 kilometres of Mount Tai. Located in a warm temperature zone and characterized by a continental monsoon climate, summers in Mount Tai are hot and rainy. Because of high altitude, the temperature at the mountaintop is generally much lower than that at the foot of Mount Tai. Rising from the ground, Mount Tai obstructs the warm and moist air masses from plain areas during their horizon transmission. And then the air masses forced to rise in the windward slope cool easily and condense into cloud/fog. Cloud and fog are important weather phenomena in the atmosphere, and they are thought to have similar physical/chemical mechanism. With low water content, pollutant levels in cloud/fog are generally much higher than precipitation. Enveloped cloud/fog is the noted natural splendor at Mount Tai and attracts millions of tourists each year. Therefore, Mount Tai is a representative mountain site for cloud/fog observation in summer.

Targeted air samples on cloudy/foggy days and noncloudy/foggy days were collected into SUMMA canisters with a capacity of 3.2 litres from July 10-25, 2015. The sampling time of the collected samples ranged from 0.5 h to 4 h. The flow rate was controlled by a CS1200 flow-limiting valve. The sampling process and analysis were conducted according to the US EPA Methods TO-14 and TO-15. The concentrations of O 3 , NO and NO 2 as well as meteorological data, such as the atmospheric pressure, wind speed, relative humidity (RH) and temperature (T), were continuously recorded. The SUMMA canisters were cleaned and evacuated three times by Entech 3100A Canister Cleaner before sampling. In addition, field blanks of pure nitrogen were collected periodically and processed by the same analytical procedures as the samples.

Sample Analysis

Analyses of all of the samples were performed by a preconcentrator instrument (Entech7100A) and then followed by a GC-MS system (GC/MS QP 2010). The details of the analytical procedures of VOCs have been described previously by [START_REF] Yang | Aromatic hydrocarbons and halocarbons at a mountaintop in southern China[END_REF] and will be described here briefly.

A 400-mL sample was concentrated in an Entech7100A preconcentrator, where nitrogen, oxygen, argon, water and carbon dioxide were removed by a three-stage preconcentration. Finally, the highly concentrated compounds were rapidly desorbed and then swept into the column of the GC for separation and analysis.

Each target VOC was identified by its retention time and m/z (mass to charge ratio) based on USEPA standard gases, and analysis was conducted under the SIM mode.

Quantification of the target VOCs was performed using the internal standard curves method with four internal standards (bromochloromethane, 1,4-difluorobenzene, chlorobenzene-d5 and 3-bromofluorobenzene), and the corresponding VOCs of each internal standard see [START_REF] Yang | Aromatic hydrocarbons and halocarbons at a mountaintop in southern China[END_REF]. The correlation coefficients of the curves ranged from 0.900 to 1.000. In this study, 63 VOCs were measured in atmospheric samples from Mount Tai in July 2015, including alkanes, alkenes, aromatics, halocarbons and OVOCs, as shown in Table 1.

HYSPLIT Model

Long-range transport can carry air pollutants including VOCs emitted from source regions to the study site [START_REF] Gao | Observational study of ozone and carbon monoxide at the summit of mount Tai (1534 m a.s.l.) in central-eastern China[END_REF][START_REF] Zhang | The characteristics, seasonal variation and source apportionment of VOCs at Gongga Mountain, China[END_REF]. The pollutants emitted in the planetary boundary layer (PBL) are transported from PBL to free troposphere by strong convections in summer. Pollutants transported within the free troposphere can travel long distances and strongly influence the concentrations of trace gases [START_REF] Gao | Observational study of ozone and carbon monoxide at the summit of mount Tai (1534 m a.s.l.) in central-eastern China[END_REF][START_REF] Ting | A study of the atmospheric VOCs of Mount Tai in June 2006[END_REF]. To study the impact of back trajectories on the VOC concentrations of the samples in this study, an online version of the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, whose website is http://ready.arl.noaa.gov/HYSPL IT.php, was used to study the influence of the long-range transport of air masses. Back trajectories with 48 h duration were calculated for each day during sampling.

RESULTS AND DISCUSSION

Impact of Fog on the General Characteristics of Atmospheric VOCs

In this study, 63 VOCs were measured in atmospheric samples from Mount Tai in July 2015 as shown in Table 1. Some samples were collected on cloudy/foggy days and others on non-cloudy/foggy days during our sampling period. The distributions of the 5 types of VOCs measured on cloudy/foggy and non-cloudy/foggy days are shown in Fig. 1. The measurements indicated that the dominant VOC species are primarily OVOCs (67% on the cloudy/foggy days and 72% on the non-cloudy/foggy days) and halocarbons (20% on the cloudy/foggy days and 17% on the noncloudy/foggy days) among all of the samples collected at Mount Tai. OVOCs also had the largest contribution (67-85%) in the previous study [START_REF] Sahu | Source identification of VOCs at an urban site of western India: Effect of marathon events and anthropogenic emissions[END_REF]. OVOCs, which had the largest contribution to total measured VOCs in this study, may mainly originate from both photochemical oxidation of non-methane hydrocarbons (NMHCs) and direct emissions by biogenic and anthropogenic sources [START_REF] Legreid | Measurements of organic trace gases including oxygenated volatile organic compounds at the high alpine site Jungfraujoch (Switzerland): Seasonal variation and source allocations[END_REF][START_REF] Tanimoto | Measurement of air-sea exchange of dimethyl sulfide and acetone by PTR-MS coupled with gradient flux technique[END_REF][START_REF] Sahu | Source identification of VOCs at an urban site of western India: Effect of marathon events and anthropogenic emissions[END_REF].

As shown in Fig. 1(b), all of the VOC concentrations on the cloudy/foggy days were higher than those on the noncloudy/foggy days. The result agrees with [START_REF] Sun | Chemical characteristics of PM 2.5 and PM 10 in haze-fog episodes in Beijing[END_REF]. Poor dispersion of VOCs and weak photochemical reactions on the cloudy/foggy days is the most likely explanation for this result. Alkanes had the greatest contribution to this difference, and their concentration under cloudy/foggy conditions was 46% higher than that under non-cloudy/foggy conditions.

Tiny droplets or ice crystals from heavy cloud/fog can reflect or scatter sunlight, which reduces the amount of solar radiation that reaches the earth's surface as well as the ground temperature. Under this circumstance, the change in temperature is negligible along the vertical gradient, which is conducive to generating an inversion layer and static weather conditions [START_REF] Zhou | Cause of the haze weather[END_REF]. Consequently, stagnant weather condition discourages further diffusion of air pollutants and favours the accumulation of VOCs. In addition, heavy cloud/fog days tend to be paired with stable stratification and weak winds, leading to greater difficulty in further atmospheric pollutant dispersion [START_REF] Yang | Ion composition of fog water and its relation to air pollutants during winter fog events in Nanjing, China[END_REF]. And since solar radiation has been weakened from the cloud/fog, the photochemical reactions consuming VOCs could not take place effectively [START_REF] Yang | Ion composition of fog water and its relation to air pollutants during winter fog events in Nanjing, China[END_REF].

On non-cloudy/foggy days, such as sunny days, strong solar radiation can cause the mixing height of the PBL to increase. Therefore, the measurements of VOCs under noncloud/fog conditions were generally lower due to efficient dispersion and photochemical reactions. Consequently, the VOC concentrations were generally higher on cloudy/foggy days.

Fig. 1. Contributions and comparison of VOCs concentrations on cloudy/foggy and non-cloudy/foggy days at Mount

Tai. in Fig. 2(b). These industrial cities are the most heavily polluted areas. Apart from this, the vertical components of the trajectories revealed an upward transport of pollutants from heavy polluted areas, as indicated by the blue air masses in Fig. 2(b), and thus, the concentration of pollutants at the sampling site will increase accordingly. Hence, higher levels of VOCs during the period of sampling were observed on that day, which is related to the transport of mixed air masses from polluted areas as well as the rising of tropospheric air masses. The relationship between VOCs and other meteorological parameters (e.g., T, RH, wind speed and direction) was also discussed as shown in Fig. 3. The relative humidity was above 60% and the temperature was between 15 and 25°C during the sampling period. Fig. 3 also shows the south wind and wind speed (> 2 m s -1 ) played a dominant role during the measurements. In our study, a single meteorological parameter doesn't have a definite impact on the characteristics of VOCs. The measured VOC concentration is a consequence of interactions among all the meteorological factors and chemical reactions.

Impact of Cloud and Fog on OVOCs

As described above, OVOCs had the largest contribution to the total measured VOCs; thus, the impact of cloud/fog on OVOCs formed the main discussion. [START_REF] Sahu | Source identification of VOCs at an urban site of western India: Effect of marathon events and anthropogenic emissions[END_REF] compared the mixing ratios of VOCs measured under 7 different kinds of different weather conditions, such as clear sky, fog, drizzle and so on and found that OVOCs showed strong dependence on weather conditions. In our study, the difference in the concentration of OVOCs seems to show a more significant variation due to different weather conditions than other types of VOCs as shown in Fig. 1(a). This result shows that cloudy and foggy conditions may have a significant impact on the characteristics of OVOCs.

Although nearly all of the VOC concentrations were generally higher on cloudy/foggy days, most of the OVOC concentrations except for MMA, acrolein and acetone were higher on non-cloudy/foggy days, as shown in Fig. 4. On non-cloudy/foggy days, such as sunny days with stronger solar radiation, VOCs may react with OH radicals, NO 3 radicals and O 3 to produce a series of complicated photochemical reactions. Some OVOCs may also be formed in the atmosphere as products of atmospheric transformations of other VOCs. For example, alcohols and aldehydes are produced by photochemical reactions of alkanes, and part of its reaction mechanism is shown below (Eqs. ( 1)-( 5)). In the equations, hv is the photon energy with a wavelength between 280 and 430 nm [START_REF] Seinfeld | Urban air pollution: State of the science[END_REF], R is an organic moiety (e.g., CH 3 , C 2 H 5 ). In addition, a comparison of the concentrations between alkanes and alcohols on cloudy/foggy and non-cloudy/foggy days, as presented in Table 1, shows that the data agree with the reactions. Generally speaking, the concentration of alkanes was relatively higher on cloudy/foggy days, while most of OVOCs mainly except for acetone was higher on non-cloudy/foggy days. In the presence of cloud/fog, VOCs may partially dissolve into the aqueous phase according to their solubility. Dissolved organic compounds can take part in various isomerization, oligomerization and hydrolysis reactions in fog droplets. In addition, microbial activity may also contribute to the oxidation of dissolved organics in cloud droplets during periods with low free radical load [START_REF] Vaïtilingom | Contribution of microbial activity to carbon chemistry in clouds[END_REF]. However, most importantly, aqueous photolysis and its reaction with dissolved OH radicals are significant chemical sinks of VOCs in cloud and fog droplets [START_REF] Epstein | A comparison of the chemical sinks of atmospheric organics in the gas and aqueous phase[END_REF]. [START_REF] Saxena | Water-soluble organics in atmospheric particles: A critical review of the literature and application of thermodynamics to identify candidate compounds[END_REF] found that highly water-soluble organics could be produced by the photo-oxidation of VOCs in the atmosphere. The functional groups of water-soluble fraction contain carboxyls, carbonyls, hydroxyls, etc. [START_REF] Epstein | Direct photolysis of carbonyl compounds dissolved in cloud and fog droplets[END_REF]. Therefore, OVOCs dissolved in atmospheric water droplets may react with dissolved OH radicals or undergo direct photolysis by actinic radiation. [START_REF] Epstein | A comparison of the chemical sinks of atmospheric organics in the gas and aqueous phase[END_REF] found aqueous photolysis and aqueous phase OH oxidation are significant sinks for some organic compounds, including organic acids, aldehydes, ketones and ethers. [START_REF] Tie | Effect of clouds on photolysis and oxidants in the troposphere[END_REF] used FTUV and MOZART-2 models to estimate the impacts of clouds on photolysis and tropospheric chemistry. The results suggested that clouds have an important impact on the tropospheric oxidation capacity and increase global mean OH concentration. In addition, wet and/or dry deposition of OVOCs in the troposphere is also an important loss mechanism [START_REF] Mellouki | Atmospheric chemistry of oxygenated volatile organic compounds: Impacts on air quality and climate[END_REF]. Consequently, OVOCs concentration was generally lower in cloudy/foggy days.

NO 2 + hv → NO + O (1) 2 O 22 RH NO RO H O     (2) RO 2 + NO → RO + NO 2 (3) 2 O 2 RO RCHO HO    (4) RCH 2 O 2 -+ RCH 2 O 2 -→ RCHO + RCH 2 OH + O 2 (5)
As shown in Table 1, it is significant that acetone (18 ppb on the cloudy/foggy days; 15 ppb on the non-cloudy/foggy days) was the most abundant compound among the 63 VOCs on the cloudy/foggy as well as non-cloudy/foggy samples, which was then followed by chloromethane (1.2 ppb) on cloudy/foggy days and isopropanol (1.8 ppb) on non-cloudy/foggy days. Similar results were found in a previous study [START_REF] Garzón | Volatile organic compounds in the atmosphere of Mexico city[END_REF]. Atmospheric acetone plays an important role in atmospheric chemistry, acting as a principal source of hydrogen oxide radicals (HO x = OH + HO 2 ) [START_REF] Jaeglé | Chemistry of HO x radicals in the upper troposphere[END_REF][START_REF] Fischer | The role of the ocean in the global atmospheric budget of acetone[END_REF][START_REF] Hu | North American acetone sources determined from tall tower measurements and inverse modeling[END_REF], and is thought to originate from the photochemical oxidation reaction of VOCs [START_REF] Chatfield | Sources and sinks of acetone in the troposphere: Behavior of reactive hydrocarbons and a stable product[END_REF][START_REF] Reissell | Formation of acetone from the OH radicaland O 3 -initiated reactions of a series of monoterpenes[END_REF][START_REF] Garzón | Volatile organic compounds in the atmosphere of Mexico city[END_REF]. Acetone can also be emitted by the metabolic process and plant decay of terrestrial vegetation [START_REF] Warneke | Acetone, methanol, and other partially oxidized volatile organic emissions from dead plant matter by abiological processes: Significance for atmospheric HO x chemistry[END_REF][START_REF] Fall | Abundant oxygenates in the atmosphere: A biochemical perspective[END_REF]. This may account for the high acetone levels at Mount Tai, which is rich with vegetation. In addition, acetone has relatively stable chemical properties and a longer mean tropospheric lifetime, which is estimated to be between 14 and 35 days, and its photolysis rate and reaction rate with OH radicals are 60 and 53 days [START_REF] Atkinson | Atmospheric chemistry of VOCs and NO x[END_REF][START_REF] Fischer | The role of the ocean in the global atmospheric budget of acetone[END_REF][START_REF] Hu | North American acetone sources determined from tall tower measurements and inverse modeling[END_REF], respectively. Therefore, emissions of acetone have a cumulative effect in the atmosphere among various sources, which also results in a higher concentration of acetone. Lastly, there is a local source of ketone compounds from incense burning at temples on Mount Tai [START_REF] Chen | Determination of formaldehyde and benzene series of the smoke from natural incense burning[END_REF], which may also contribute to the high concentration of acetone at Mount Tai.

Comparison of Ozone Formation Potential (OFP) in the Conditions of Cloud/Fog and Non-Cloud/Fog

OFP is used as an index to quantify the potential of a VOC compound in ozone production [START_REF] Carter | Development of ozone reactivity scales for volatile organic compounds[END_REF][START_REF] Yang | Aromatic hydrocarbons and halocarbons at a mountaintop in southern China[END_REF]. The actual production of ozone is eventually produced by a specific hydrocarbon and dependent on its particular oxidation mechanism, the amount of VOCs and NO x concentrations [START_REF] Carter | Development of ozone reactivity scales for volatile organic compounds[END_REF][START_REF] Carter | Updated maximum incremental reactivity scale for regulatory applications[END_REF][START_REF] Goldan | Nonmethane hydrocarbon and oxy hydrocarbon measurements during the 2002 New England Air Quality Study[END_REF]. Therefore, OFP does not fully account for the entire atmospheric chemistry of the related compounds, but it does provide a simple way to measure the relative contribution assessment of individual VOCs to photochemistry [START_REF] Goldan | Nonmethane hydrocarbon and oxy hydrocarbon measurements during the 2002 New England Air Quality Study[END_REF].

The OFP is used to quantify the contribution of each type of VOC to ozone formation. The formula used to calculate OFP for each type of VOC is as follows:

OFP i = c i × MIR i (6)
In the formula, c i denotes the environmental concentration of each type of VOC and the constant MIR i denotes the maximum ozone incremental reaction coefficient for each type of VOCs [START_REF] Carter | Updated maximum incremental reactivity scale and hydrocarbon bin reactivities for regulatory applications[END_REF]. Not every VOC has a constant MIR, so only VOCs that have a constant MIR were selected for comparison. Fig. 5 shows the OFP for each species of VOCs measured in the air. Acetone and propene contributed more to the total calculated OFP, with contributions of 26% and 16%, respectively. Based on the results, VOCs with higher concentrations will not necessarily contribute more to the total calculated OFP. For example, the concentration of chloromethane is the second highest, accounting for 4.0% of the VOCs; however, it only contributes 0.17% of the total calculated OFP. While propene only accounts for 1.2% of the total measured VOC concentration, it contributes to 16% of the total calculated OFP.

For all five types of VOCs, the concentrations and photochemical reactivities of OVOCs and aromatics are comparatively higher; thus, they have the largest contributions to ozone production. On the contrary, the concentrations and photochemical reactivity of alkanes and halocarbons are comparatively lower; thus, they have little contribution to ozone production. Moreover, the concentrations of each type of alkenes are generally lower, but the OFP of alkenes (5.3 ppb) was higher than those of alkanes (0.17 ppb) and halocarbons (0.33 ppb). The results for aromatics, alkenes and alkanes agree with the findings of [START_REF] Zhou | Potential ozone formation and emission sources of atmospheric VOCs in Heshan during typical pollution episode[END_REF] whose contributions of aromatics, alkenes and alkanes to OFP are 42%, 39% and 17%, respectively. The C=C double bonds of alkenes enable them to be more reactive in photochemical reactions and have higher values of the constant MIR and therefore contribute more to the total OFP than alkanes and halocarbons.

The OFP are calculated on the cloudy/foggy and noncloudy/foggy days, and the contributions of VOCs to OFP are shown in Fig. 6. The OFP of cloudy/foggy days is generally higher than that of non-cloudy/foggy days, which shows that cloudy/foggy days have the potential to form more ozone. This result is also in accordance with the findings in section 3.1. [START_REF] Tie | Effect of clouds on photolysis and oxidants in the troposphere[END_REF] also found that tropospheric O 3 concentrations increased by 8% because of the impact of clouds in their study. For the samples collected on cloudy/foggy days, aromatic hydrocarbons (40%) had the largest contribution to the total OFP, while OVOCs had the largest contribution (41%) on non-cloudy/foggy days. The results obtained also coincide with the findings in section 3.2. OVOCs, which had the largest contribution to ozone formation on non-cloudy/foggy days, may be related to the photochemical reactions that produce OVOCs. Since the photochemical reactions were weakened on cloudy/foggy days due to the lack of solar radiation, the OFP of OVOCs was relatively low.

On cloudy/foggy days, the main ozone precursor was aromatics, while OVOCs were the main ozone precursor on non-cloudy/foggy days. The value of total calculated OFP increased from 21 ppb on non-cloudy/foggy days to 24 ppb on cloudy/foggy days. Therefore, cloud/fog has an impact on the dispersion and removal of atmospheric VOCs.

As we mentioned before, O 3 and NO x are also measured at Mount Tai. VOC and NO x are two main precursors of O 3 , and O 3 -NO x -VOC chemistry has an impact on the evaluation of ozone formation [START_REF] Sillman | Some theoretical results concerning O 3 -NO x -VOC chemistry and NO x -VOC indicators[END_REF]. These measurements provide more detailed information to analyze the O 3 formation [START_REF] Geng | Characterizations of ozone, NO x , and VOCs measured in Shanghai, China[END_REF]. Numerical simulations of ozone pollution in Los Angeles in the 1980s [START_REF] Seinfeld | Urban air pollution: State of the science[END_REF] provided an indicator (VOC/NO x ratio) to evaluate VOC-or NO x -limited regimes leading to ozone formation. At VOC/NO x ratios of about 8 or less, VOC control is generally more effective, otherwise NO x control is generally more effective. In our study, we just use this ratio to determine whether ozone formation was VOC-limited or NO x -limited. Fig. 7 shows the diurnal variations of five kinds of VOC concentration, VOC/NO x ratio, O 3 concentration measured and OFP calculated during the sampling period. It's clearly shown that each kind of VOC concentration, NO x concentration and total OFP all had an anti-correlation with O 3 concentration before Day 4 and then had the same trend. VOC/NO x ratios were lower than 8 between Day 4 and Day 7, which suggested that ozone formation was mainly VOC-limited during these days. It should be noted that the VOC/NO x ratio is an approximate not accurate value in Los Angeles, and there may be different situations in different regions. A photochemical model and more measurements are needed to get a more accurate analysis.

CONCLUSIONS

VOCs measurements were conducted at the peak of Mount Tai (1534 m a.s.l) in July 2015 to study the influence of cloud/fog on atmospheric VOCs in the free troposphere. Sixty-three species of VOCs were measured, including alkanes, alkenes, aromatics, halocarbons and OVOCs.

In this study, samples were collected on cloudy/foggy and non-cloudy/foggy days. Acetone was the most abundant pollutant among all of the VOCs. OVOCs had the largest contribution to total measured VOCs among all of the samples, which may be due to the photochemical oxidation of NMHCs as well as biogenic or anthropogenic source emissions.

In the presence of cloud/fog, the weather is generally stable and conducive to the accumulation of atmospheric pollutants. Moreover, cloud/fog reduces the photochemical oxidation of VOCs because of the reduction of solar radiation. Therefore, the VOCs concentrations on cloudy/foggy days were higher than those on the non-cloudy/foggy days. However, the concentrations of most OVOCs on noncloudy/foggy days are substantially higher, which may be due to the gas phase reactions on non-cloudy/foggy days as well as the aqueous phase reactions in the presence of cloud/fog.

OFP was calculated to assess the contribution of VOCs to potential ozone production. The OFP on cloudy/foggy days is generally higher than that on non-cloudy/foggy days, which is in accordance with the higher VOC concentrations on cloudy/foggy than non-cloudy/foggy days. Aromatics had the largest contribution to the total OFP on cloudy/foggy days, while OVOCs had the largest contribution on noncloudy/foggy days. This agrees with the comparison of the OVOCs concentration between cloudy/foggy and noncloudy/foggy days. In addition, the main ozone precursor and the value of OFP differ between cloudy/foggy and noncloudy/foggy days, changing from aromatics to OVOCs and from 24 ppb to 21 ppb.

Overall, cloud and fog have an impact on the deposition and removal of atmospheric VOCs by a series of physical and chemical processes. This process has a significant effect on the characteristics of VOCs at high mountains under special weather conditions. However, to get more accurate result, specific model simulation study and longer field measurements are needed.

Fig. 2

 2 Fig. 2(a). The results of the backward trajectory model during the measurement.

Fig. 2

 2 Fig. 2(b).The results of the backward trajectory model on July 14. The relationship between VOCs and other meteorological parameters (e.g., T, RH, wind speed and direction) was also discussed as shown in Fig.3. The relative humidity was above 60% and the temperature was between 15 and 25°C during the sampling period. Fig.3also shows the south wind and wind speed (> 2 m s -1 ) played a dominant role during the measurements. In our study, a single meteorological parameter doesn't have a definite impact on the characteristics of VOCs. The measured VOC concentration is a consequence of interactions among all the meteorological factors and chemical reactions.

Fig. 3 .

 3 Fig. 3. Diurnal variation of mean values of RH, T, wind speed and direction and VOC concentration.

Fig. 4 .

 4 Fig. 4. Contributions of the concentrations of OVOCs under cloud/fog and non-cloud/fog conditions.

Fig. 5 .

 5 Fig. 5. OFP distributions of each type of VOC measured in the air at Mount Tai.

Fig. 6 .

 6 Fig. 6. Contributions of five species of VOCs to OFP in the air on the cloudy/foggy and non-cloudy/foggy days at Mount Tai.

Fig. 7 .

 7 Fig. 7. The variation patterns of VOC/NO x ratio, five kinds of VOC concentration and their OFP, NO x and O 3 concentration.

Table 1 .

 1 The average mixing ratios of VOCs under cloud/fog and non-cloud/fog conditions on Mount Tai.

	Compound	mixing ratio (ppb)	Compound	mixing ratio (ppb)
		cloud/fog	non-cloud/fog		cloud/fog	non-cloud/fog
	Alkanes			Chloroethane	0.057 ± 0.04	0.090 ± 0.01
	Hexane	0.069 ± 0.08	0.088 ± 0.01	DCM	0.230 ± 0.06	0.163 ± 0.02
	Cyclohexane	0.064 ± 0.03	0.012 ± 0.02	Chloroform	0.575 ± 0.34	0.303 ± 0.12
	Heptane	0.038 ± 0.03	0.016 ± 0.03	CTC	0.063 ± 0.07	0.002 ± 0.00
	Alkenes			1,1-DCA	0.041 ± 0.01	0.021 ± 0.02
	Propene	0.337 ± 0.32	0.322 ± 0.06	1,2-DCA	0.396 ± 0.16	0.329 ± 0.14
	Chloroethylene	0.077 ± 0.02	0.074 ± 0.01	1,2-DCP	0.130 ± 0.11	0.091 ± 0.08
	1,3-Butadiene	0.066 ± 0.00	0.045 ± 0.04	1,1,1-TCA	0.022 ± 0.02	0.015 ± 0.01
	1,1-DCE	0.035 ± 0.02	0.014 ± 0.02	1,1,2-TCA	0.051 ± 0.05	0.034 ± 0.02
	(E)-1,2-DCE	0.027 ± 0.02	0.012 ± 0.01	1,1,2,2-TeCA	0.213 ± 0.03	0.063 ± 0.10
	(Z)-1,2-DCE	0.079 ± 0.09	0.062 ± 0.02	1,2-EDB	0.015 ± 0.03	0.018 ± 0.03
	(E)-1,3-DCp	0.038 ± 0.05	0.024 ± 0.02	BDCM	0.019 ± 0.02	0.033 ± 0.01
	(Z)-1,3-DCp	0.101 ± 0.15	0.032 ± 0.03	DBCM	0.058 ± 0.01	0.021 ± 0.03
	TCE	0.032 ± 0.04	0.009 ± 0.01	Bromoform	0.066 ± 0.05	0.071 ± 0.06
	PCE	0.001 ± 0.00	0.024 ± 0.02	Chlorobenzene	0.107 ± 0.13	0.002 ± 0.00
	HCBD	0.450 ± 0.30	0.342 ± 0.30	1,2-DCB	0.239 ± 0.20	0.214 ± 0.02
	Aromatics			1,3-DCB	0.262 ± 0.21	0.154 ± 0.02
	Benzene	0.406 ± 0.33	0.465 ± 0.23	1,4-DCB	0.237 ± 0.26	0.198 ± 0.11
	Toluene	0.356 ± 0.14	0.197 ± 0.22	1,2,4-TCB	0.286 ± 0.53	0.025 ± 0.01
	Ethylbenzene	0.148 ± 0.10	0.130 ± 0.02	Benzyl chloride	0.366 ± 0.24	0.501 ± 0.08
	m/p-Xylene	0.167 ± 0.12	0.059 ± 0.10	OVOCs
	o-Xylene	0.005 ± 0.01	0.003 ± 0.00	Ethanol	0.114 ± 0.08	0.311 ± 0.54
	p-Ethyltoluene	0.135 ± 0.09	0.146 ± 0.01	Isopropanol	0.049 ± 0.10	1.828 ± 1.77
	1,3,5-TMB	0.158 ± 0.02	0.099 ± 0.08	Acrolein	0.046 ± 0.03	0.031 ± 0.01
	1,2,4-TMB	0.200 ± 0.13	0.187 ± 0.15	Acetone	18.064 ± 13.96	15.216 ± 8.39
	Styrene	0.134 ± 0.08	0.073 ± 0.06	2-Butanone	0.141 ± 0.16	0.203 ± 0.17
	Naphthalene	0.502 ± 0.68	0.369 ± 0.46	MTBE	0.001 ± 0.00	0.028 ± 0.02
	Halocarbons			Vinyl acetate	0.002 ± 0.00	0.029 ± 0.02
	CFC-11	0.311 ± 0.03	0.307 ± 0.02	Ethyl acetate	0.262 ± 0.18	0.334 ± 0.15
	CFC-12	0.594 ± 0.02	0.559 ± 0.00	THF	0.031 ± 0.03	0.052 ± 0.02
	CFC-113	0.112 ± 0.00	0.110 ± 0.00	MMA	0.044 ± 0.03	0.005 ± 0.00
	CFC-114	0.068 ± 0.00	0.057 ± 0.00	p-Dioxane	0.031 ± 0.05	0.027 ± 0.03
	Chloromethane	1.214 ± 0.40	0.939 ± 0.19	MNBK	0.126 ± 0.09	0.173 ± 0.15
	Bromomethane	0.035 ± 0.04	0.059 ± 0.01	MIBK	0.058 ± 0.03	0.060 ± 0.02
	DCE: Dichloroethene; DCp: Dichloropropene; TCE: Trichloroethylene; PCE: Perchloroethylene;

HCBD: Hexachlorobutadiene; TMB: Trimethylbenzene; CFC-11: Trichlorofluoromethane; CFC-12: Dichlorodifluoromethane; CFC-113: Trichlorotrifluoroethane; CFC-114: Dichlorotetrafluoroethane; DCM: Dichloromethane; CTC: Carbon tetrachloride; DCA: Dichloroethane; TCP: Dichloropropane; TCA: Trichloroethane; TeCA: Tetrachloroethane; EDB: Ethylene dibromide; BDCM: Bromodichloromethane; DBCM: Dibromochloromethane; DCB: Dichlorobenzene; TCB: Trichlorobenzene; MTBE: Tert-butyl methyl ether; THF: Tetrahydrofuran; MMA: Methyl methacrylate; MNBK: Methyl n-butyl ketone; MIBK: Methyl isobutyl ketone.

However, there was an exception on July 14 during our sampling campaign. The total concentration of VOCs on July 14, which experienced non-cloud/fog conditions, was 33 ppb, higher than some of the levels found on cloudy/foggy days. The back trajectories of July 14 (red line), as shown in Fig.2(a), may explain this phenomenon.On July 14, mixed air masses arrived at the peak of Mount Tai from some industrial cities in Shanxi and Henan Province, such as Taiyuan, Yangquan, Changzhi and Jiaozuo

ACKNOWLEDGEMENTS

We are grateful to Prof. Collett, J.L. for support of cloud/fog sampling guidance and to Environmental Monitoring Central Station of Shandong Province for support of experimental instruments. Special thanks to the Mount Tai Meteorological Station for providing access to the experimental site. This study was funded by the National Natural Science Foundation of China [grant number 41475115], the Science and Technology Development Project of Shandong Province (2014GSF117037), the Major Technology Project of Independent Innovation of Shandong Province (2014GJJS0501), Ministry of Science and Technology of China (2016YFE0112200). This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 690958. The authors specially thank Elsevier English Language service for editing the manuscript for English.

SUPPLEMENTARY MATERIAL

Supplementary data associated with this article can be found in the online version at http://www.aaqr.org.