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Daytime and nighttime PM2.5 samples were collected at the summit of Mount Tai (1534 m) located in North China Plain during a week in 2006 summer. Size-segregated aerosol particles were also collected using an eight-stage impactor during the same period. Samples were analyzed for various water-soluble organic compounds using GC/FID and GC/MS techniq...
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... Five organic compound classes were determined in the PM 2.5 samples (Table 2), among which DCAs were found as the most abundant compound class (756 ± 139 ng m À3 in daytime versus 263 ± 123 ng m À3 in nighttime), followed by ketocarboxylic acids (107 ± 29 versus 33 ± 21 ng m À3 ), saccharides (72 ± 36 versus 46 ± 58 ng m À3 ), polyols and polyacids (64 ± 9 versus 32 ± 17 ng m À3 ), and dicarbonyls (33 ± 15 versus 10 ± 9 ng m À3 ). Interestingly, daytime concentrations are 2 -3 times higher than nighttime concen- trations for most of the compound classes determined. ...
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... Homologous dicarboxylic acids (DCAs, C 2 -C 11 ), together with several ketocarboxylic acids and dicarbonyls, were detected in the PM 2.5 samples with oxalic acid being the dominant species, followed by malonic, succinic, and phthalic acids (Table 2 and Figure 3a). Similar distribution has been reported in East Asian aerosols from the lower troposphere within the boundary layer [Wang et al., 2006b] to the middle troposphere . ...
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... Homologous ketocarboxylic acids (wC 2 -wC 4 , wC 9 and Pyr) and a-dicarbonyls (mGly and Gly) were detected in the samples with total concentrations of 13-163 ng m À3 (average 70 ng m À3 ) and 1-65 ng m À3 (average 22 ng m À3 ), respectively (Table 2 and Figure 3b). These ketoacids and carbonyls are secondarily produced via atmospheric photo- oxidation of organic precursors and/or primarily formed by fossil fuel combustion and biomass burning, and further oxidized into saturated DCAs [Chebbi and Carlier, 1996;Kawamura et al., 1996;Volkamer et al., 2006]. ...
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... contrast is consistent with the enhanced concentrations Figure 4. Differences in the mass concentration ratios of selected dicarboxylic acids between the daytime and nighttime samples (PM 2.5 ) collected at Mount Tai. For abbreviations C 2 , C 3 , C 4 , C 6 , C 9 , M, F, Ph, i-Ph, and t-Ph, see Table 2. Bars represent the standard deviations. ...
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... Concentrations of saccharides including levogluco- san and several primary sugars in PM 2.5 samples were 7 -160 ng m À3 (average 59 ng m À3 ) ( Table 2 and Figure 3c), accounting for 66% of those (90 ± 32 ng m À3 ) in total suspended particles (TSP) collected at the same site during the same period [Fu et al., 2008]. Levoglucosan, a tracer for biomass burning, was found as a dominant sugar (43 ± 36 and 36 ± 58 ng m À3 at day and night, respectively) ( Table 2), followed by glucose, sucrose and/or mannitol. ...
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... Concentrations of saccharides including levogluco- san and several primary sugars in PM 2.5 samples were 7 -160 ng m À3 (average 59 ng m À3 ) ( Table 2 and Figure 3c), accounting for 66% of those (90 ± 32 ng m À3 ) in total suspended particles (TSP) collected at the same site during the same period [Fu et al., 2008]. Levoglucosan, a tracer for biomass burning, was found as a dominant sugar (43 ± 36 and 36 ± 58 ng m À3 at day and night, respectively) ( Table 2), followed by glucose, sucrose and/or mannitol. The predom- inance of levoglucosan in the aerosols is consistent with the ground surface samples from Chinese megacities [Wang et al., 2006a]. ...
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... a minor species in this group, is a metabolism product of bacteria in soil. Its higher concentrations in nighttime (2.2 ± 2.1 ng m À3 ) than in daytime (1.7 ± 0.7 ng m À3 ) ( Table 2) were probably caused by an enhanced bacteria activity under higher humid conditions at night. ...
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... Polyols and polyacids, including glycerol and glyc- eric, malic, tartaric and citric acids, were detected in the PM 2.5 aerosols (Table 2 and Figure 3d) with glycerol and glyceric and malic acids being the major species in this group. Concentrations of these compounds in the mountain aerosols (9.6 ± 10.7 ng m À3 ) are less than those (38 ± 35 ng m À3 ) reported in the lowland aerosols from Chinese megacities [Wang et al., 2006a], but are very close to those (7.0 ± 8.1 ng m À3 ) in the summertime tropospheric aerosols collected by aircraft (0.5 -3.0 km altitude) over inland China [G. ...
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... and malic acids are secondary photooxidation products in the atmosphere [Kawamura and Ikushima, 1993;Simoneit et al., 2004c]. The sum of glyceric and malic acids (average 27 ng m À3 ) (Table 2) in the fine particles over Mount Tai is 3 times higher than that (average 7.5 ng m À3 ) reported in the aircraft samples over the North Pacific [Simoneit et al., 2004b]. This may suggest that the mountain aerosols are photo- chemically aged, to some extent, like marine aerosols, although the aircraft samples are more aged but may be more diluted and/or further subjected to photochemical decomposition during the transport over the Pacific. ...
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... Glycerol is a reduced sugar primarily produced by fungal metabolism in soils and is emitted to the atmosphere as wind-blown dusts [Simoneit et al., 2004c]. Its concen- tration (average 15 ng m À3 , Table 2) in the mountain aerosols is much less than that (average 38 ng m À3 ) of the aircraft aerosols over the North Pacific [Simoneit et al., 2004b]. Such a difference may be associated with the fact that Mount Tai samples are PM 2.5 whereas the North Pacific samples are total suspended particles (TSP), and thus soil fungus-derived glycerol that is enriched in coarse particles is less abundant in the PM 2.5 samples from Mount Tai. ...
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Fine-particle pollution associated with winter haze threatens the health of more than 400 million people in the North China Plain. The Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain (McFAN) investigated the physicochemical mechanisms leading to haze formation with a focus on the contributions of multiphase processes i...
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... Both the acids that represent anthropogenic secondary organic aerosols (AnthSOA; SA and PHA) and the biogenic secondary organic aerosol tracers (i.e., SOA tracers of α-pinene oxidation; CPA, 3HGA and MBTCA, and SOA tracers of isoprene oxidation; 2MGA, 2MT1 and 2MT2) showed significantly higher concentrations during the daytime indicating higher biogenic and anthropogenic emissions from gas phase precursors and enhanced transformation into secondary products combined with atmospheric transport mechanisms, such as upslope winds. The mean concentrations of AnthSOA (SA: 9.22, PHA: 1.34 ng/m 3 ) were similar to those reported in a rural background site in the north-east Spain in summer (SA: 15.5, PHA: 2.5 ng/m 3 ; (Jaén et al., 2021)) and in remote sites in Tenerife (SA: 6.5, PHA: 3.2 ng/m 3 ; (García et al., 2017)) and Sanabria Lake (SA: 5.4, PHA: 3.0 ng/m 3 ; (Pérez-Pastor et al., 2023)) but lower than those observed in Mount Tai (China; SA: 57, PHA: 20 ng/m 3 ; (Wang et al., 2009)). The dominant SOA compounds (Table 1) originated from isoprene oxidation (2MGA, 2MT1 and 2MT2). ...
... The dominant SOA compounds (Table 1) originated from isoprene oxidation (2MGA, 2MT1 and 2MT2). They were found in concentrations slightly higher than in these remote sites and in the Tibetan Plateau (Pérez-Pastor et al., 2023;Ren et al., 2018;Wang et al., 2009) but lower than in the rural background sites. The α-pinene SOA also showed similar concentrations than in these studies. ...
... Our previous studies also showed a substantial amount of ON in the TSP aerosols from Cape Hedo, Okinawa [32] and in the alpine snow samples collected from Mt. Tateyama, central Japan [36]. Significant amounts of ON have been reported in Chinese aerosols [37]. However, we cannot exclude the possible evaporative loss of NO 3 − from the filters during sampling, which may cause a potential underestimate of NO 3 − IC . ...
Inorganic components were measured in the aged ambient aerosols from Cape Hedo, Okinawa, an outflow region of East Asia, using online quadrupole Aerodyne aerosol mass spectrometer (Q-AMS) and offline ion chromatography (IC) and Sunset Lab carbon analyzer. Here, we performed an inter-comparison study on nitrate (NO3−), ammonium (NH4+) and sulfate (SO42−) that were measured by IC and AMS. Sulfate and ammonium showed a good agreement between two instruments. However, abundances of NO3− by AMS are on average twice overestimated compared to nitrate obtained by IC. We also found that a significant amount of organic nitrogen (ON) was detected in the filter samples from Okinawa. The online measurement (Q-AMS) data and offline filter based-NO3− data need to be carefully evaluated when ON is abundantly present in aerosols. The OM/OC ratios derived from AMS are consistent with the bulk OMAMS/OCSunset ratios (2.1). This study demonstrates that the OM/OC of 2.1 is the reasonable criteria for more aged aerosols.
... Malonic acid is thermally less stable than succinic acid in vehicular exhaust emissions. Lower C 3 /C 4 ratios were reported in the polluted area where the primary source is significant (Kawamura and Ikushima, 1993;Deshmukh et al., 2018;Jung et al., 2010), while higher ratios were reported for aerosols collected from remote marine and remote Island (Wang et al., 2009;Fu et al., 2013;Kunwar et al., 2017). Higher C 3 /C 4 ratios (0.6-5.8) has been reported from marine aerosols during round the world cruise due to the severe photochemical aging of air masses (Fu et al., 2013). ...
Snowpit samples (n = 10) were collected (19 April 2008) from the snowpit sequences (depth 6.60 m) at the Murodo-Daira site (36.58°N, 137.60°E, elevation of 2450 m a.s.l.) of Mt. Tateyama (3015 m a.s.l.), central Japan. The first time, low molecular weight diacids, ω-oxoacids, pyruvic acid, and α-dicarbonyls were measured for this snowpit sequence. Higher concentrations of short-chain diacids (C2–C5) are observed in dusty snow than non-dusty snow samples. Longer chain diacids (C7–C12) are significant in granular and dusty snow samples. Aromatic and aliphatic unsaturated diacids showed higher concentrations in the slightly dusty layer deposited in winter. Except for a clean layer, molecular distributions of diacids are characterized by the predominance of oxalic acid (C2, ave, 20 ± 22 ng/g-snow) followed by succinic (C4, 7.2 ± 5.9 ng/g -snow), and malonic acids (C3, 3.3 ± 2.9 ng/g -snow) for all the snow layers. Lower C3/C4 ratios (0.46) suggest that organic aerosols are rather fresh without serious photochemical aging during the long-range transport over central Japan. The higher concentrations of the secondary species in dusty snow than non-dusty samples were mainly attributed to the heterogeneous reaction. The strong correlations of incloud oxidation products of isoprene, aromatic acids, and fatty acids suggest that condensation, oxidation, and photolysis are important reaction mechanisms for the formation of diacids. Chinese Loess (Kosa particles) and Mongolian Gobi desert's dust provided the surface area for polar organic compounds, traveled to several thousand kilometers in the lower troposphere, and snow metamorphism altered the chemical composition of diacids and related compounds.
... 25,26,33 Since the diameter of ambient particle-phase levoglucosan is smaller than 0.44 μm when BB tracers originate directly from the source emissions, while typically ranging from 0.44 to 1.0 μm when it is aged and sampled away from combustion sources. 34,35 It is also reported that the concentrations of levoglucosan in PM 1 and PM 2.5 were comparable, either of them accounting for at least 50% of PM 10 in the PRD region. 36 Therefore, the application of PUF−PAS should be feasible for collecting both gas-and particle-phase monosaccharides. ...
... For the Shanghai-samples, besides C 8 H 6 O 4 , C 7 H 6 O 3 and C 7 H 6 O 2 , formulas of C 6 H 8 O 7 and C 9 H 8 O 4 with DBE values of 3 and 6 were observed with high peak abundances. C 6 H 8 O 7 was identified as citric acid in the pollen sample and mountain particle sample in previous studies (Fu et al., 2008;Wang et al., 2009;Jung and Kawamura, 2011), and C 9 H 8 O 4 is probably homophthalic acid derived from estragole (Pereira et al., 2014). For the Guangzhou-samples, besides the formulas of C 8 H 6 O 4 and C 6 H 8 O 7 discussed above, C 4 H 6 O 4 and C 4 H 6 O 5 with low DBE values of 2 were detected with high abundances and are suggested to be succinic acid and malic acid, respectively (Claeys et al., 2004;Wang et al., 2017). ...
Air pollution by particulate matter in China affects human health, the
ecosystem and the climate. However, the chemical composition of particulate
aerosol, especially of the organic fraction, is still not well understood.
In this study, particulate aerosol samples with a diameter of ≤2.5 µm (PM2.5) were collected in January 2014 in three cities located
in northeast, east and southeast China, namely Changchun, Shanghai and
Guangzhou. Organic aerosol (OA) in the PM2.5 samples was analyzed by an
ultrahigh-performance liquid chromatograph (UHPLC) coupled to
a high-resolution Orbitrap mass spectrometer in both negative mode (ESI-)
and positive mode electrospray ionization (ESI+). After non-target
screening including the assignment of molecular formulas, the compounds were
classified into five groups based on their elemental composition, i.e., CHO,
CHON, CHN, CHOS and CHONS. The CHO, CHON and CHN groups present the dominant
signal abundances of 81 %–99.7 % in the mass spectra and the majority of
these compounds were assigned to mono- and polyaromatics, suggesting that
anthropogenic emissions are a major source of urban OA in all three cities.
However, the chemical characteristics of these compounds varied between the
different cities. The degree of aromaticity and the number of polyaromatic
compounds were substantially higher in samples from Changchun, which could
be attributed to the large emissions from residential heating (i.e., coal
combustion) during wintertime in northeast China. Moreover, the ESI-
analysis showed higher H/C and O/C ratios for organic compounds in Shanghai
and Guangzhou compared to samples from Changchun, indicating that OA
undergoes more intense photochemical oxidation processes in lower-latitude
regions of China and/or is affected to a larger degree by biogenic sources.
The majority of sulfur-containing compounds (CHOS and CHONS) in all cities
were assigned to aliphatic compounds with low degrees of unsaturation and
aromaticity. Here again, samples from Shanghai and Guangzhou show a greater
chemical similarity but differ largely from those from Changchun. It should
be noted that the conclusions drawn in this study are mainly based on
comparison of molecular formulas weighted by peak abundance and thus are
associated with inherent uncertainties due to different ionization
efficiencies for different organic species.
... Wang et al. (2013) attributed the increase in OC during dust storms to the input of biogenic organics (e.g., bacteria, fungal spores, plant pollen and debris) carried by sand and dust particles from desert regions. Water-soluble organic compounds such as glucose (Wang et al., 2009b), trehalose (Simoneit et al., 2004), and humic acid (Alexander et al., 2015) are enriched in natural dust particles, and may be associated with peaks in WSOC during dust periods. In contrast, EC decreased substantially to below the detection limit of the carbon analyzer (0.07 ± 0.12 μg m −3 ), indicating that dust samples collected at Erenhot were unaffected by anthropogenic pollution, and rather represent natural dust of the Gobi Desert. ...
As an important type of light-absorbing aerosol, brown carbon (BrC) has the potential to affect the atmospheric photochemistry and Earth’s energy budget. A comprehensive field campaign was carried out along the transport pathway of Asian dust during the spring of 2016, including a desert site (Erenhot), a rural site (Zhangbei), and an urban site (Jinan), in northern China. Optical properties, bulk chemical compositions, and potential sources of water-soluble brown carbon (WS-BrC) were investigated in atmospheric total suspended particulate (TSP) samples. Samples from Zhangbei had higher mass absorption efficiency at 365 nm (MAE365, 1.32 ± 0.34 m² g⁻¹) than those from Jinan (1.00 ± 0.23 m² g⁻¹) and Erenhot (0.84 ± 0.30 m² g⁻¹). Elevated water-soluble organic carbon (WSOC) concentrations and MAE365 values of dust samples from Erenhot are related to the input of high molecular weight organic compounds and biogenic matter from the Gobi Desert, while lower values from Zhangbei and Jinan are attributed to the dilution effect caused by strong northwesterly winds. Based on fluorescence excitation–emission matrix spectra and parallel factor analysis, two humic-like (C1 and C2) and two protein-like (C3 and C4) substances were identified. Together, C1 and C2 accounted for ~64% of total fluorescence intensity at the highly polluted urban Jinan site; C3 represented ~45% at the rural Zhangbei site where local biomass burning affects; and C4 contributed ~24% in the desert region (Erenhot) due to dust-sourced biogenic substances. The relative absorptive forcing of WS-BrC compared to black carbon at 300–400 nm was about 31.3%, 13.9%, and 9.2% during non-dust periods at Erenhot, Zhangbei, and Jinan, respectively, highlighting that WS-BrC may significantly affect the radiative balance of Earth’s climate system and should be included in radiative forcing models.
... Mt. Tai is the highest peak in the central part of the NCP (Supplementary Fig. 1) 22 . Since the relative height difference between the foot and top of the mountain is 1400 meters 23 , it is an ideal place to study aerosols in the free troposphere and their interaction with the planetary boundary layer (PBL) 24 . ...
Nitrogen-containing species are major components in atmospheric aerosols. However, little is known about the sources of N-containing aerosols over high mountainous regions, especially for organic nitrogen (ON). This study aims to reveal the emission sources of both inorganic and organic nitrogen in tropospheric aerosols atop Mt. Tai, China, and to improve our understanding of the N cycle imbalance in the North China Plain (NCP). Total suspended particle (TSP) samples were collected on a daytime/nighttime basis in spring 2017 and were investigated for the concentrations and stable N isotopic compositions of total nitrogen, NH 4 ⁺ , NO 3 ⁻ and ON. Our results show that the concentrations of N-containing compounds were higher in daytime than nighttime, mainly resulting from mountain–valley breezes and the changes of planetary boundary layer height. However, no significant day/nighttime changes were found for their corresponding δ ¹⁵ N values, indicating similar contributions from different N sources between day and night. The MixSIAR Bayesian stable isotope mixing model results suggest that the most important emission source of NH 3 for aerosol NH 4 ⁺ was agriculture, followed by fossil fuel-related sources, human waste and biomass burning. Aerosol NO 3 ⁻ was mainly formed from combustion and mobile emitted NO x . Interestingly, the isotopes of ON suggest that ON were very likely firstly of primary origin. Our study reveals the characteristics of reactive N emission sources and helps understand the regional transport of tropospheric N-containing aerosols in the NCP.
... However, vertical aerosol profile measurements in mountainous areas are limited, and the related studies are subject to specific uncertainties caused by the mountain size, shape, geographical location, and local climate (Kleissl et al., 2007). Aerosol studies in mountainous areas in China have been performed mostly on the tops of mountains in eastern China, e.g., the Taishan, Huashan, and Lushan Mountains (Li, 1988;Zhang and Qin, 1998;Wang et al., 2009;Yin et al., 2010;Li et al., 2014;Liu et al., 2018;Cao et al., 2018). Vertical aerosol profiles related to the topoclimatology of China are quite few, and only two-day measurements at a 100-m height resolution in Lushan Mountain were reported by Chen et al. (1987). ...
In-situ field observations of vertical aerosol profiles for one month in complex terrain (Lushan Mountain, China) were carried out using a cable car, which resolved detailed vertical distributions of mountain aerosols with low-cost operation. Cable-car observations were conducted during the early morning and late afternoon, when mountain and valley winds dominated, respectively. The diurnal aerosol variations at the top and foot of Lushan Mountain were analyzed based on environmental and meteorological stations. The observations indicated that the mountain-valley breezes notably impacted the mountain-area aerosol distribution under weak weather conditions. More uniform aerosol profiles for the afternoon than the morning, with their decreasing rates of PM2.5 (particles with diameters less than 2.5 μm) were 2.28 and 1.64 μg m⁻³/100 m, respectively. The PM2.5/PM10 ratio at the mountain top increased from 0.69 to 0.81, and that at the mountain base decreased from 0.75 to 0.70 from morning to afternoon. The PM2.5 concentration decreased in and around Lushan Mountain from daytime to nighttime, with the impacted diameter of the 300-m topography line being smaller than ~5 km, while the concentration increased in Jiujiang City. The relative decreasing rate of PM2.5 was higher at the mountain top site (~20%) than at the base site (~2%) from daytime to nighttime. Moreover, uniform aerosol profiles could have been caused by regional transport through a relatively strong low-level synoptic flow (~5 m s⁻¹) and the mountain's dynamic lifting effect.
... Malonic acid is thermally less stable than succinic acid in vehicular exhaust emissions. Lower C 3 /C 4 ratios were reported in the polluted area where the primary source is significant (Kawamura and Ikushima, 1993;Deshmukh et al., 2018;Jung et al., 2010), while higher ratios were reported for aerosols collected from remote marine and remote Island (Wang et al., 2009;Fu et al., 2013;Kunwar et al., 2017). Higher C 3 /C 4 ratios (0.6-5.8) has been reported from marine aerosols during round the world cruise due to the severe photochemical aging of air masses (Fu et al., 2013). ...
Snowpit samples (n = 10) were collected (19 April 2008) from the snowpit sequences (depth 6.60 m) at the Murodo-Daira site (36.58°N, 137.60°E, elevation of 2450 m a.s.l.) of Mt. Tateyama (3015 m a.s.l.), central Japan. The first time, low molecular weight diacids, ω-oxoacids, pyruvic acid, and α-dicarbonyls were measured for this snowpit sequence. Higher concentrations of short-chain diacids (C2–C5) are observed in dusty snow than non-dusty snow samples. Longer chain diacids (C7–C12) are significant in granular and dusty snow samples. Aromatic and aliphatic unsaturated diacids showed higher concentrations in the slightly dusty layer deposited in winter. Except for a clean layer, molecular distributions of diacids are characterized by the predominance of oxalic acid (C2, ave, 20 ± 22 ng/g-snow) followed by succinic (C4, 7.2 ± 5.9 ng/g -snow), and malonic acids (C3, 3.3 ± 2.9 ng/g -snow) for all the snow layers. Lower C3/C4 ratios (0.46) suggest that organic aerosols are rather fresh without serious photochemical aging during the long-range transport over central Japan. The higher concentrations of the secondary species in dusty snow than non-dusty samples were mainly attributed to the heterogeneous reaction. The strong correlations of incloud oxidation products of isoprene, aromatic acids, and fatty acids suggest that condensation, oxidation, and photolysis are important reaction mechanisms for the formation of diacids. Chinese Loess (Kosa particles) and Mongolian Gobi desert's dust provided the surface area for polar organic compounds, traveled to several thousand kilometers in the lower troposphere, and snow metamorphism altered the chemical composition of diacids and related compounds.
... Malonic acid is thermally less stable than succinic acid in vehicular exhaust emissions. Lower C 3 /C 4 ratios were reported in the polluted area where the primary source is significant (Kawamura and Ikushima, 1993;Deshmukh et al., 2018;Jung et al., 2010), while higher ratios were reported for aerosols collected from remote marine and remote Island (Wang et al., 2009;Fu et al., 2013;Kunwar et al., 2017). Higher C 3 /C 4 ratios (0.6-5.8) has been reported from marine aerosols during round the world cruise due to the severe photochemical aging of air masses (Fu et al., 2013). ...
Abstract
Snowpit samples (n = 10) were collected (19 April 2008) from the snowpit sequences (depth 6.60 m) at the Murodo-Daira site (36.58°N, 137.60°E, elevation of 2450 m a.s.l.) of Mt. Tateyama (3015 m a.s.l.), central Japan. The first time, low molecular weight diacids, ω-oxoacids, pyruvic acid, and α-dicarbonyls were measured for this snowpit sequence. Higher concentrations of short-chain diacids (C2–C5) are observed in dusty snow than non-dusty snow samples. Longer chain diacids (C7–C12) are significant in granular and dusty snow samples. Aromatic and aliphatic unsaturated diacids showed higher concentrations in the slightly dusty layer deposited in winter. Except for a clean layer, molecular distributions of diacids are characterized by the predominance of oxalic acid (C2, ave, 20 ± 22 ng/g-snow) followed by succinic (C4, 7.2 ± 5.9 ng/g -snow), and malonic acids (C3, 3.3 ± 2.9 ng/g -snow) for all the snow layers. Lower C3/C4 ratios (0.46) suggest that organic aerosols are rather fresh without serious photochemical aging during the long-range transport over central Japan. The higher concentrations of the secondary species in dusty snow than non-dusty samples were mainly attributed to the heterogeneous reaction. The strong correlations of incloud oxidation products of isoprene, aromatic acids, and fatty acids suggest that condensation, oxidation, and photolysis are important reaction mechanisms for the formation of diacids. Chinese Loess (Kosa particles) and Mongolian Gobi desert's dust provided the surface area for polar organic compounds, traveled to several thousand kilometers in the lower troposphere, and snow metamorphism altered the chemical composition of diacids and related compounds.
