[Analysis of Water Soluble Organic Aerosol in Spring PM2.5 with Soot Particle Aerosol Mass Spectrometry (SP-AMS)].

To investigate the chemical composition and pollution characteristics of spring fine particles (PM2.5) in Changzhou, a total of 84 PM2.5 samples were collected from March 1st to May 30th, 2017. We measured and analyzed conventional components, such as water-soluble ions (WSIIs) and carbonaceous components (OC and EC). The water-soluble organic aerosol (WSOA) was also analyzed by an aerodyne soot particle aerosol mass spectrometer (SP-AMS). During the sampling period, the average daily PM2.5 concentration was 101.97 µg·m-3, with more than 73.8% sampling days exceeding the Target-2 standard of the national ambient air quality standard of China. The air quality during the sampling period was dominated by light, moderate, and heavy pollution, accounting for 39.3%, 21.4%, and 13.1% of the total days, respectively. The total WSIIs accounted for 39.86% of PM2.5 mass, of which secondary ions (SO42-, NH4+, and NO3-) accounted for 81.85% of the total WSIIs. The slope of the linear fitted line of the anion and cation charge balance (AE/CE) was greater than 1 (1.09), which indicated that PM2.5 was weakly acidic. The average OC/EC ratio was 2.53, indicating that PM2.5 was influenced by the secondary conversion. WSOA included CxHy+(32.1%), CxHyO+(30.4%), CxHyO2+(25.4%), and HyO+(4.7%) identified by SP-AMS. The average oxygen-to-carbon (O/C), hydrogen-to-carbon (H/C), nitrogen-to-carbon (N/C), and organic matter-to-organic carbon (OM/OC) ratios of the WSOA were 0.72, 1.53, 0.04, and 2.15, respectively. Higher O/C indicated higher contributions from secondary photochemical reaction conversion in spring. Positive matrix factorization (PMF) analysis for AMS mass spectra of WSOA identified three sources, namely hydrocarbon-like (HOA), semi-volatile oxygenated OA (SVOOA)-biomass burning OA (BBOA), and low-volatility oxygenated OA (LVOOA), which on average accounted for 18.4%, 34.1%, and 47.4% of the total WSOA, respectively.

Secondary organic aerosol formation from 3C⁎-initiated oxidation of 4-ethylguaiacol in atmospheric aqueous-phase.

In this study, we investigated aqueous-phase triplet excited states (3C⁎)-induced photo-degradation of 4-ethylguaiacol (EG) under both simulated sunlight and ultraviolet (UV) light irradiations. Through quencher experiments, the relative contributions of reactive oxygen species (ROS, such as 1O2/O2-/·OH) and 3C⁎ were calculated and results showed three reactive species, e.g., 3C⁎, 1O2 and O2-, all seemed to play important roles in the photo-degradation of EG, but contribution from ·OH was relatively minor. High steady-state 1O2 concentration after 1 h irradiation further revealed the major contribution of 1O2 to photo-degradation under Xe light irradiation. The degradation experiment under three saturated gases (air, O2 and N2) showed that the degradation rate in air-saturated condition was the largest owing to synergistic effect of 1O2 and 3C⁎. Oxidative capacity of aqueous secondary organic aerosol (aqSOA) increased with reaction time by monitoring oxygen-to­carbon (O/C) ratio and carbon oxidation state (OSc) via an aerodyne soot particle aerosol mass spectrometer (SP-AMS). Moreover, aqSOA mass yields were calculated via SP-AMS data. The UV-vis spectral change suggested formation of light-absorbing organics at first stage under simulated sunlight irradiation. Based on the identified products and the reactive intermediates, we postulated that 3C⁎-induced oxidation might be attributed to direct reactions by 3C⁎ and 1O2, chemical reaction by ROS, as well as oligomerization via H-abstraction. To the best of our knowledge, this is the first time to explore systematically reaction pathways of 4-ethylguaiacol under 3C∗ radical on the basis of thorough analysis of products and reactive species. Our findings highlight the impacts of aqSOA from biomass burning emissions on air quality and climate change.

Characteristics, sources and health risks of toxic species (PCDD/Fs, PAHs and heavy metals) in PM2.5 during fall and winter in an industrial area.

Particulate toxic species, such as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs), polycyclic aromatic hydrocarbons (PAHs) and heavy metals may have significant health risks. This study investigated characteristics, sources and health risks of all three classes of toxic species in PM2.5 (particles with aerodynamic diameter ≤2.5 µm) samples collected at an industrial area in Changzhou, a big city in the Yangtze Delta region of China. Fourteen heavy metals altogether constituted 2.87% of PM2.5 mass, with Fe, Al and Zn as the major elements. Principal component analysis (PCA) suggested that heavy metals came from four sources: vehicles, industry, crustal dust, mixed coal combustion and industrial process. The daily average concentration of 18 PAHs was 235.29 ng/m3, accounting for 0.21% of PM2.5 mass. The dominant PAHs were high molecular weight ones, contributing 73.5% to the total PAHs. Diagnostic analyses indicated that sources of PAHs included vehicle/coal combustion and petroleum emissions, wherein diesel emission played a more important role than gasoline emission. PCA showed that the largest contributor of PAHs was vehicle exhaust mixed with coal combustion, followed by three industry-related sources. Total concentration of 17 PCDD/Fs varied between 3.14 and 37.07 pg/m3, with an average of 14.58 pg/m3. The 10 PCDFs accounted for 70.5% of total concentration of 17 PCDD/Fs. Health risk assessments showed that the carcinogenic risk of heavy metals was acceptable, while risks from PAHs and PCDD/Fs cannot be ignored. Back trajectory analysis indicated that local/regional transported air masses from northern China was the major source areas of the toxic species.

[Secondary Organic Aerosol Mass Yield and Characteristics from 4-ethylguaiacol Aqueous·OH Oxidation: Effects of Initial Concentration].

Aqueous-phase chemical processing, as an essential formation pathway of secondary organic aerosol (SOA), has attracted widespread attention from within atmospheric chemistry fields. Due to the complicated reaction nature, reaction mechanisms, and product characteristics of aqueous-phase chemical processing, its contribution to the SOA budget is still not fully understood. In this work, we investigate how the initial concentration (0.03-3 mmol·L-1) of 4-ethylguaiacol affects SOA formation of aqueous·OH photochemical oxidation. We use soot-particle aerosol mass spectrometry (SP-AMS) to monitor SOA mass yield and oxidation character, and gas chromatography-mass spectrometry (GC-MS) and ion chromatography (IC) to measure products and organic acids. Additionally, we use ultraviolet visible spectroscopy (UV-vis) and high-performance liquid spectrometry (HPLS) to track the formation of light-absorbing products such as humic-like substances (HULIS). Our research indicated that the range of the O/C ratio of EG-aqSOA measured by the SP-AMS exhibited increasing trends with increased reaction time 0.42-0.61 (0.03 mmol·L-1), 0.49-0.84 (0.3 mmol·L-1), and 0.49-0.63 (3 mmol·L-1). Dimers (C16H18 O2+, m/z 302) via SP-AMS were obviously higher under a higher initial concentration, thereby demonstrating that the oligomerization reaction proceeded more easily. The absorption at 250 nm recorded by UV-vis was distinctly enhanced, which might be attributed to new light-absorbing products with absorbance at 250 nm. Furthermore, the HULIS concentration increased with reaction time, in accordance with enhancement of absorbance in the 300-400 nm region, thus suggesting that aqueous-phase processing formed brown carbon. Small organic acids, including formic acid, malic acid, and oxalic acid, were detected by IC in all reaction solutions, with the highest concentration being for formic acid. GC/MS detected ketone, an OH monomer, and dimers in the aqSOA, which further indicates that functionalization and oligomerization took place.

A comprehensive investigation of aqueous-phase photochemical oxidation of 4-ethylphenol.

Secondary organic aerosol (SOA) species formed in atmospheric aqueous phases is recently recognized as an important contributor to fine aerosols, which is known to be a prominent human health risk factor internationally. This work, for the first time, systematically investigated aqueous-phase photochemical oxidation of 4-ethylphenol (4-EP) - a model compound from biomass burning and a surrogate of intermediate volatility organic compounds, under both ultraviolet (UV) (Hg lamp) and simulated sunlight (Xe lamp). We found that 4-EP could degrade upon hydroxal radical (OH) oxidation under UV light nearly 15 times faster than that under simulated sunlight, but large aqueous SOA (aqSOA) yields (108%-122%) were observed under both situations. AqSOA masses and oxidation states continuously increased under simulated sunlight, yet they increased first then decreased quickly under UV light. We proposed a reaction scheme based on identified products, showing that oligomerization, functionalization and fragmentation all can occur during 4-EP oxidation. Our results demonstrate that OH radical may suppress oligomerization and functionalization, but is favorable for fragmentation. Under UV light with H2O2 (high OH), fragmentation was dominant, producing more volatile and smaller molecules, and less aqSOA in later oxidation; Under simulated sunlight with H2O2 (moderate OH), functionalization that can form hydroxylated monomer was more important. Moreover, 4-EP oxidation by the organic triplet excited state (3C*) could form species with stronger visible light absorptivity than those from OH-mediated oxidation, and the absorptivity showed positive link with contents of humic-like substances.

[Day-night Characteristics of Humic-like Substances in PM2.5 During Winter in Changzhou].

To investigate the characteristics of diurnal variation of humic-like substances (HULIS) in atmospheric aerosols during winter in Changzhou, a total of 64 fine particle (PM2.5) samples were collected from January 1 to February 28, 2017. In this study, the concentration as well as light absorption parameters of humic-like substances of carbon (HULIS-C) were examined. The results showed that the average day PM2.5 and HULIS-C concentrations were 122.60 µg·m-3 and 4.18 µg·m-3, respectively, slightly higher than those (111.72 µg·m-3 and 3.74 µg·m-3) at night. Via UV-vis analysis, we found that the ratios of absorbance at 250 nm (A250) of HULIS and WSOA (day:~77%, night:~75%) were significantly higher than the concentration ratios of HULIS-C and WSOC (day:~51%, night:~50%), indicating that more UV-absorbing substances and poly-conjugated aromatic structures exist in HULIS. The daytime E250/E365 and SUVA280 in HULIS were close to the nighttime ones, indicating that there was no obvious difference between day and night in HULIS with reference to aromaticity and molecular weight. There were no significant differences in MAE365 and AAE300-400 of HULIS between day and night. In addition, to obtain the main influencing factors of HULIS in winter in Changzhou, the correlation analysis of HULIS-C and other chemical components were conducted. The results show that biomass burning, fossil fuel combustion, factory emissions, and especially secondary formation, were the main influencing factors. Moreover, daytime HULIS were mainly influenced by secondary reaction of anthropogenic precursor contaminants, while nighttime HULIS were affected not only by secondary formation by but by also primary combustion emissions.

Chemical characterization of PM2.5 from a southern coastal city of China: applications of modeling and chemical tracers in demonstration of regional transport.

An intensive sampling campaign of airborne fine particles (PM2.5) was conducted at Sanya, a coastal city in Southern China, from January to February 2012. Chemical analyses and mass reconstruction were used identify potential pollution sources and investigate atmospheric reaction mechanisms. A thermodynamic model indicated that low ammonia and high relative humidity caused the aerosols be acidic and that drove heterogeneous reactions which led to the formation of secondary inorganic aerosol. Relationships among neutralization ratios, free acidity, and air-mass trajectories suggest that the atmosphere at Sanya was impacted by both local and regional emissions. Three major transport pathways were identified, and flow from the northeast (from South China) typically brought the most polluted air to Sanya. A case study confirmed strong impact from South China (e.g., Pearl River Delta region) (contributed 76.8% to EC, and then this result can be extended to primary pollutants) when the northeast winds were dominant. The Weather Research Forecasting Black carbon model and trace organic markers were used to apportion local pollution versus regional contributions. Results of the study offer new insights into the atmospheric conditions and air pollution at this coastal city.

Morphologies and elemental compositions of local biomass burning particles at urban and glacier sites in southeastern Tibetan Plateau: Results from an expedition in 2010.

Many studies indicate that the atmospheric environment over the southern part of the Tibetan Plateau is influenced by aged biomass burning particles that are transported over long distances from South Asia. However, our knowledge of the particles emitted locally (within the plateau region) is poor. We collected aerosol particles at four urban sites and one remote glacier site during a scientific expedition to the southeastern Tibetan Plateau in spring 2010. Weather and backward trajectory analyses indicated that the particles we collected were more likely dominated by particles emitted within the plateau. The particles were examined using an electron microscope and identified according to their sizes, shapes and elemental compositions. At three urban sites where the anthropogenic particles were produced mainly by the burning of firewood, soot aggregates were in the majority and made up >40% of the particles by number. At Lhasa, the largest city on the Tibetan Plateau, tar balls and mineral particles were also frequently observed because of the use of coal and natural gas, in addition to biofuel. In contrast, at the glacier site, large numbers of chain-like soot aggregates (~25% by number) were noted. The morphologies of these aggregates were similar to those of freshly emitted ones at the urban sites; moreover, physically or chemically processed ageing was rarely confirmed. These limited observations suggest that the biomass burning particles age slowly in the cold, dry plateau air. Anthropogenic particles emitted locally within the elevated plateau region may thus affect the environment within glaciated areas in Tibet differently than anthropogenic particles transported from South Asia.

Atmospheric levels and cytotoxicity of polycyclic aromatic hydrocarbons and oxygenated-PAHs in PM2.5 in the Beijing-Tianjin-Hebei region.

The chemical composition of PM2.5 and cellular effects from exposure to fine aerosol extracts were studied for samples collected in Beijing, Tianjin, Shijiazhuang, and Hengshui, China in winter 2015. Effects of priority polycyclic aromatic hydrocarbons (PAHs) and their oxygenated derivatives (OPAHs) in PM2.5 on cell cultures were a major focus of the study. Total quantified PAHs and OPAHs at Shijiazhuang and Hengshui were higher than at Beijing and Tianjin, and benz(a)anthracene, chrysene and 1,8-naphthalic anhydride were the most abundant species. Exposure to PM2.5 extracts caused a concentration-dependent decline in cell viability and a dose-dependent increase in nitric oxide production. Two cytokines, tumor necrosis factor α (TNF-α) and interleukin 6 (IL-6), also increased when A549 test cells were exposed to PM2.5 extracts. PAHs and OPAHs in PM2.5 can potentially cause cell damage and induce cytotoxicity and pro-inflammatory responses: benzo(a)anthracene-7,12-dione was highly correlated with NO production, dibenz(a,h)anthracene and 1,4-chrysenequinone were correlated with TNF-α production, and 1-naphthaldehyde was significantly correlated with IL-6 production. The study provides a new approach for evaluating relationships between air-quality and cell toxicity with respect to specific chemicals.

Variation in Day-of-Week and Seasonal Concentrations of Atmospheric PM2.5-Bound Metals and Associated Health Risks in Bangkok, Thailand.

While effective analytical techniques to promote the long-term intensive monitoring campaign of particulate heavy metals have been well established, efforts to interpret these toxic chemical contents into policy are lagging behind. In order to ameliorate the interpretation of evidence into policies, environmental scientists and public health practitioners need innovative methods to emphasize messages concerning adverse health effects to state and local policymakers. In this study, three different types of health risk assessment models categorized by exposure pathways. Namely, ingestion, dermal contact, and inhalation were quantitatively evaluated using intensive monitoring data of 51 PM2.5-bound metals that were collected on three consecutive days, from 17 November 2010 to 30 April 2011 in the heart of Bangkok. Although different exposure pathways possess different magnitudes of risk for each PM2.5-bound metal, it can be concluded that ingestion of dust causes more extensive risk to residents compared with inhalation and dermal contact. The investigation of enrichment factors reveals the overwhelming influences of vehicular exhausts on 44 selected metal concentrations in Bangkok. These findings are in agreement with previous studies that highlight the role of public transportation and urban planning in air pollution control.

Spectral dependence of aerosol light absorption at an urban and a remote site over the Tibetan Plateau.

We present a study of aerosol light absorption by using a 7-wavelength Aethalometer model AE33 at an urban site (Lhasa) and a remote site (Lulang) in the Tibetan Plateau. Approximately 5 times greater aerosol absorption values were observed at Lhasa (53±46Mm-1 at 370nm and 20±18Mm-1 at 950nm, respectively) in comparison to Lulang (15±19Mm-1 at 370nm and 4±5Mm-1 at 950nm, respectively). Black carbon (BC) was the dominant light absorbing aerosol component at all wavelengths. The brown carbon (BrC) absorption at 370nm is 32±15% of the total aerosol absorption at Lulang, whereas it is 8±6% at Lhasa. Higher value of absorption Ångström exponent (AAE, 370-950nm) was obtained for Lulang (1.18) than that for Lhasa (1.04) due to the presence of BrC. The AAEs (370-950nm) of BrC were directly extracted at Lulang (3.8) and Lhasa (3.3). The loading compensation parameters (k) increased with wavelengths for both sites, and lower values were obtained at Lulang than those observed at Lhasa for all wavelengths. This study underlines the relatively high percentage of BrC absorption contribution in remote area compared to urban site over the Tibetan Plateau.

A 10-year observation of PM2.5-bound nickel in Xi'an, China: Effects of source control on its trend and associated health risks.

This study presents the first long term (10-year period, 2004-2013) datasets of PM2.5-bound nickel (Ni) concentration obtained from the daily sample in urban of Xi'an, Northwestern China. The Ni concentration trend, pollution sources, and the potential health risks associated to Ni were investigated. The Ni concentrations increased from 2004 to 2008, but then decreased due to coal consumption reduction, energy structure reconstruction, tighter emission rules and the improvement of the industrial and motor vehicle waste control techniques. With the comparison of distributions between workday and non-workday periods, the effectiveness of local and regional air pollution control policies and contributions of hypothetical Ni sources (industrial and automobile exhausts) were evaluated, demonstrating the health benefits to the populations during the ten years. Mean Ni cancer risk was higher than the threshold value of 10-6, suggesting that carcinogenic Ni still was a concern to the residents. Our findings conclude that there are still needs to establish more strict strategies and guidelines for atmospheric Ni in our living area, assisting to balance the relationship between economic growth and environmental conservation in China.

Characteristics of surface O3 over Qinghai Lake area in Northeast Tibetan Plateau, China.

Surface O3 was monitored continuously during Aug. 12, 2010 to Jul. 21, 2011 at a high elevation site (3,200 m above sea level) in Qinghai Lake area (36°58'37″N, 99°53'56″E) in Northeast Tibetan Plateau, China. Daily average O3 ranged from 21.8 ppbv to 65.3 ppbv with an annual average of 41.0 ppbv. Seasonal average of O3 followed a decreasing order of summer>autumn>spring>winter. Diurnal variations of O3 showed low concentrations during daytime and high concentrations during late night and early morning. An intensive campaign was also conducted during Aug. 13-31, 2010 to investigate correlations between meteorological or chemical conditions and O3. It was found that O3 was poorly correlated with solar radiation due to the insufficient NOx in the ambient air, thus limiting O3 formation under strong solar radiation. In contrast, high O3 levels always coincided with strong winds, suggesting that stratospheric O3 and long range transport might be the main sources of O3 in this rural area. Back-trajectory analysis supported this hypothesis and further indicated the transport of air masses from northwest, northeast and southeast directions.

Day-night differences and seasonal variations of chemical species in PM10 over Xi'an, northwest China.

To investigate day-night differences and seasonal variations of PM10 and its chemical composition in an urban environment in Xi'an, northwest China, day- and nighttime PM10 mass and its chemical components including water-soluble ions (Na(+), NH4 (+), K(+), Mg(2+), Ca(2+), F(-), Cl(-), NO3 (-), and SO4 (2-)), organic carbon (OC), elemental carbon, and water-soluble organic carbon (WSOC) were measured on selected representative days from 20 December 2006 to 12 November 2007. Annual mean PM10 concentration in this city was five times of the China Ambient Air Quality Standard for annual average (70 µg m(-3)). Carbonaceous fractions and water-soluble ions accounted for nearly one third and 12.4 %, respectively, of the annual mean PM10 mass. No dramatic day-night differences were found in the loadings of PM10 or its chemical components. Spring samples were highlighted by abundance of Ca(2+), while the secondary aerosol species (SO4 (2-), NO3 (-), and NH4 (+)) and OC dominated in summer, autumn, and winter samples. Relatively low NO3 (-)/SO4 (2-) ratio suggested that stationary source emissions were more important than vehicle emissions in the source areas in this city. Strong relationships between WSOC and biomass markers (water-soluble K(+), OC1, and OP) were observed in winter and autumn, indicating that WSOC was derived mainly from biomass burning in these seasons. This was also supported by analysis results on the biomass burning events. In contrast, poor correlations between WSOC and biomass markers were demonstrated in summer and spring, implying that WSOC was mainly formed as secondary organic carbon through photochemical activities.

Comparison and implications of PM2.5 carbon fractions in different environments.

The concentrations of PM2.5 carbon fractions in rural, urban, tunnel and remote environments were measured using the IMPROVE thermal optical reflectance (TOR) method. The highest OC1 and EC1 concentrations were found for tunnel samples, while the highest OC2, OC3, and OC4 concentrations were observed for urban winter samples, respectively. The lowest levels of most carbon fractions were found for remote samples. The percentage contributions of carbon fractions to total carbon (TC) were characterized by one peak (at rural and remote sites) and two peaks (at urban and tunnel sites) with different carbon fractions, respectively. The abundance of char in tunnel and urban environments was observed, which might partly be due to traffic-related tire-wear. Various percentages of optically scattering OC and absorbing EC fractions to TC were found in the four different environments. In addition, the contribution of heating carbon fractions (char and soot) indicated various warming effects per unit mass of TC. The ratios of OC/EC and char/soot at the sites were shown to be source indicators. The investigation of carbon fractions at different sites may provide some information for improving model parameters in estimating their radiative effects.

Chemical composition, sources, and deposition fluxes of water-soluble inorganic ions obtained from precipitation chemistry measurements collected at an urban site in northwest China.

Precipitation samples were collected at an urban site in Xi'an, northwest China during March to November in 2009 and were then analyzed to determine the pH and concentrations of water-soluble inorganic ions (Na(+), NH(4)(+), K(+), Mg(2+), Ca(2+), SO(4)(2-), NO(3)(-), Cl(-), and F(-)) in precipitation. The pH of precipitation ranged from 4.1 to 7.6 for all of the samples with an annual volume-weighted mean of 6.4. While a large portion of the precipitation events were weakly acidic or alkaline, around 30% of the precipitation events in the autumn were strongly acidic. Precipitation events with air masses from the northeast and the southeast were weakly acidic while those with air masses from the northwest and the southwest were alkaline. SO(4)(2-), Ca(2+), NH(4)(+), and NO(3)(-) were dominant ions in the precipitation, accounting for 37%, 25%, 18%, and 9%, respectively, of the total analyzed ions. Ca(2+) and NH(4)(+) were found to be the major neutralizers of precipitation acidity; however, the contribution of Mg(2+), although much lower than those of Ca(2+) and NH(4)(+), was important, in many cases, in changing the precipitation from weakly acidic to weakly alkaline. Enrichment factor analysis confirmed that SO(4)(2-) and NO(3)(-) were produced from anthropogenic sources, Ca(2+), K(+), and 80% Mg(2+) were from crustal sources, and Na(+), Cl(-), and ∼20% of Mg(2+) were from marine sources. The annual wet depositions were estimated to be 3.5 t km(-2) per year for sulfur; 2.3 t km(-2) per year for nitrogen, of which 0.8 t km(-2) per year was oxidized nitrogen and 1.5 t km(-2) per year was reduced nitrogen; and 3.0 t km(-2) per year for Ca(2+).

Molecular distribution and stable carbon isotopic composition of dicarboxylic acids, ketocarboxylic acids, and α-dicarbonyls in size-resolved atmospheric particles from Xi'an City, China.

Size-resolved airborne particles (9-stages) in urban Xi'an, China, during summer and winter were measured for molecular distributions and stable carbon isotopic compositions of dicarboxylic acids, ketocarboxylic acids, and α-dicarbonyls. To our best knowledge, we report for the first time the size-resolved differences in stable carbon isotopic compositions of diacids and related compounds in continental organic aerosols. High ambient concentrations of terephthalic (tPh, 379 ± 200 ng m(-3)) and glyoxylic acids (ωC(2), 235 ± 134 ng m(-3)) in Xi'an aerosols during winter compared to those in other Chinese cities suggest significant emissions from plastic waste burning and coal combustions. Most of the target compounds are enriched in the fine mode (<2.1 µm) in both seasons peaking at 0.7-2.1 µm. However, summertime concentrations of malonic (C(3)), succinic (C(4)), azelaic (C(9)), phthalic (Ph), pyruvic (Pyr), 4-oxobutanoic (ωC(4)), and 9-oxononanoic (ωC(9)) acids, and glyoxal (Gly) in the coarse mode (>2.1 µm) are comparable to and even higher than those in the fine mode (<2.1 µm). Stable carbon isotopic compositions of the major organics are higher in winter than in summer, except oxalic acid (C(2)), ωC(4), and Ph. δ(13)C of C(2) showed a clear difference in sizes during summer, with higher values in fine mode (ranging from -22.8‰ to -21.9‰) and lower values in coarse mode (-27.1‰ to -23.6‰). The lower δ(13)C of C(2) in coarse particles indicate that coarse mode of the compound originates from evaporation from fine mode and subsequent condensation/adsorption onto pre-existing coarse particles. Positive linear correlations of C(2), sulfate and ωC(2) and their δ(13)C values suggest that ωC(2) is a key intermediate, which is formed in aqueous-phase via photooxidation of precursors (e.g., Gly and Pyr), followed by a further oxidation to produce C(2).