Dicarboxylic acids, ω-oxocarboxylic acids, α-dicarbonyls, WSOC, OC, EC, and inorganic ions in wintertime size-segregated aerosols from central India: Sources and formation processes

Gas-particle partitioning of low-molecular-weight organic acids in suburban Shanghai: Insight into measured Henry's law constants dependent on relative humidity

Low-molecular-weight (LMW) organic acids are among the most abundant water-soluble organic compounds, but their gas-particle partitioning mechanism remains unclear. In the present study, LMW organic acids were measured using a URG 9000D Ambient Ion Monitor in suburban Shanghai. The average concentrations of formic acid, acetic acid, oxalic acid, and methanesulfonic acid (MSA) in PM2.5 were 405 ± 116, 413 ± 11, 475 ± 266, and 161 ± 54 ng m-3, respectively. The particle fraction exceeded 30 % for formic acid and acetic acid. Model predictions underestimated the particle-phase monocarboxylic acids (MCAs) from the factor of 102 at the highest RH to 107 at the lowest RH. The average measured intrinsic Henry's law constants (Hmea) for formic acid, acetic acid, oxalic acid, and MSA were 3.8 × 107, 4.5 × 107, 8.7 × 108, and 3.4 × 107 mol L-1 atm-1, respectively, approximately four orders of magnitude higher than their literature-based intrinsic Henry's law constants (Hlit) for MCAs and approximately four orders of magnitude lower than Hlit, MSA. The ratio of Hmea /Hlit for MCAs ranged over three orders of magnitude, depending on relative humidity. The strong deviations at low RHs are attributed to the dominance of absorption by the organic phase. The discrepancy at the highest RH possibly relates to surfactant effects and dimer formation. We used Hmea as a model input for the first time to estimate the phase partitioning of particulate MCAs, finding that >80 % of MCAs resided in the organic phase under dry conditions. We propose parameterizing Hmea as model input to predict the multiphase partitioning of MCAs.

Water-soluble organic aerosols over South Asia - Seasonal changes and source characteristics

Water-soluble organic carbon (WSOC) has been identified as a key component in atmospheric aerosols due to its ability to act as cloud condensation nuclei (CCN) owing to their highly hygroscopic nature. This paper discusses about the spatio-temporal variability in WSOC mass concentration, sources (primary and secondary contributions), the role of long-range air-mass transport in modulating their abundance, at distinct sectors over South Asia. We found from our observations that, photochemical ageing of primary organic aerosols that are derived from biomass emissions, significantly contribute to the total WSOC budget over South Asia. The wide range of water-soluble compounds released by biomass burning can contribute directly to the WSOC fraction or undergo further atmospheric processing, such as oxidation or ageing, leading to the formation of additional WSOC. WSOC/OC (organic carbon) ratio and the correlation between the WSOC and secondary organic carbon (SOC) are used for assessing the contribution from secondary sources. The three different ratios are used to delineate different source processes; OC/EC (elemental carbon) for source identification, WSOC/OC for long-range atmospheric transport (ageing) and WSOC/SOC to understand the primary and secondary contribution of WSOC. The present investigation revealed that, the primary OC that have undergone significant chemical processing as a result of long-range transport have a substantial influence on WSOC formation over South Asia, especially in Indo Gangetic Plain outflow regions such as southern peninsular and adjacent marine regions. Overall, oxidation and ageing of primary organic aerosols emitted from biomass burning was found to serve as an important source of WSOC over South Asia.

Sulfate-associated liquid water amplifies the formation of oxalic acid at a semi-arid tropical location over peninsular India during winter

Aerosol liquid water (ALW) can serve as an aqueous-phase medium for numerous chemical reactions and consequently enhance the formation of secondary aerosols in a highly humid atmosphere. However, the aqueous-phase formation of secondary organic aerosols (SOAs) is not well understood in the Indian regions, particularly in tropical peninsular India. In this study, we collected total suspended particulate samples (n = 30) at a semiarid station (Ballari; 15.15°N, 76.93°E; 495 m asl) in tropical peninsular India during the winter of 2016. Homologous series of dicarboxylic acids (C₂-C₁₂), oxoacids (ωC₂-ωC₉), pyruvic acid (Pyr), and glyoxal (Gly) were determined by employing a water-extraction of aerosol and analyzed using capillary gas chromatography (GC). Results show that oxalic acid (C₂) was the most abundant organic acid, followed by succinic (C₄), malonic (C₃), azelaic (C₉), and glyoxylic (ωC₂) or phthalic (Ph) acids. Total diacids-C accounted for 1.7-5.8 % of water-soluble organic carbon (WSOC) and 0.6-3.6 % of total carbon (TC). ALW, estimated from the ISORROPIA 2.1 model, showed a strong linear relationship with sulfate (SO₄^2-), C₂, C₃, C₄, ωC₂, Pyr, and Gly. Based on molecular distribution, specific mass ratios (C₂/C₃, C₂/C₄, C₂/Gly, and Ph/C₉), linear relationships among the measured organic acids, ALW, organic (levoglucosan and oleic acid), and inorganic (SO₄^2-) marker compounds, we emphasize that diacids and related organic compounds, especially C₂, majorly form via aqueous-phase oxidation of precursor compounds including aromatic hydrocarbons (HCs) and unsaturated fatty acids (FAs) originated from biomass burning and combustion-related sources. The present study demonstrates that sulfate driven ALW largely enhances the formation of SOAs via the aqueous-phase reactions over tropical peninsular India during winter.

Geochemical studies of low molecular weight organic acids in the atmosphere: sources, formation pathways, and gas/particle partitioning

Low molecular weight monocarboxylic acids (LMW monoacids, C₁-C₁₀) are the most abundant gaseous organic compound class in the atmosphere. Formic or acetic acid is the dominant volatile organic compound (VOC) in Earth's atmosphere. They can largely contribute to rainwater acidity, especially in the tropical forest, and react with alkaline metals, ammonia, and amines, contributing to new particle formation and secondary organic aerosol production. Gaseous and particulate LMW monoacids were abundantly reported in China. They can be directly emitted from fossil fuel combustion and biomass burring; however, the secondary formation is more important than primary emissions via the photochemical oxidation of anthropogenic and biogenic VOCs. In this paper, we review the distributions of LMW monoacids from urban, mountain, and marine sites as well as from rainwater and alpine snow samples and discuss their sources and formation mechanisms in the atmosphere. We also discuss their importance as cloud condensation nuclei (CCN) and provide future perspectives of LMW monoacids study in the warming world.

Sulfuric acid-dimethylamine particle formation enhanced by functional organic acids: an integrated experimental and theoretical study

Atmospheric new particle formation (NPF), which has been observed globally in clean and polluted environments, is an important source of boundary-layer aerosol particles and cloud condensation nuclei, but the fundamental mechanisms leading to multi-component aerosol formation have not been well understood. Here, we use experiments and quantum chemical calculations to better understand the involvement of carboxylic acids in initial NPF from gas phase mixtures of carboxylic acid, sulfuric acid (SA), dimethylamine, and water. A turbulent flow tube coupled to an ultrafine condensation particle counter with particle size magnifier has been set up to measure NPF. Experimental results show that pyruvic acid (PA), succinic acid (SUA), and malic acid (MA) can enhance sulfuric acid-dimethylamine nucleation in the order PA < SUA < MA with a greater enhancement observed at lower SA concentrations. Computational results indicate that the carboxylic and hydroxyl groups are related to the enhancement. This experiment-theory study shows the formation of multi-component aerosol particles and the role of the organic functional group, which may aid in understanding the role of organics in aerosol nucleation and growth in polluted areas, and help to choose organic molecules of specific structures for simulation.

Temperature- and pH- Dependent OH Radical Reaction Kinetics of Tartaric and Mucic Acids in the Aqueous Phase

Tartaric acid and mucic acid are dicarboxylic acids (DCAs), a substance class often found in atmospheric aerosols and cloud droplets. The hydroxyl radical (^•OH)-induced oxidation in the aqueous phase is known to be an important loss process of organic compounds such as DCAs. However, the study of ^•OH kinetics of DCAs in the aqueous phase is still incomplete. In the present study, the rate constants of the ^•OH reactions of tartaric acid and mucic acid in the aqueous phase were determined by the thiocyanate competition kinetics method as a function of temperature and pH. The following T-dependent Arrhenius expressions (in units of L mol^-1 s^-1) were first derived for the ^•OH reactions with tartaric acid─k(T, H₂A) = (3.3 ± 0.1) × 10¹⁰ exp[(-1350 ± 110 K)/T], k(T, HA^-) = (3.6 ± 0.1) × 10¹⁰ exp[(-580 ± 110 K)/T], and k(T, A^2-) = (3.3 ± 0.1) × 10¹⁰ exp[(-1190 ± 170 K)/T]─as well as mucic acid─k(T, H₂A) = (2.2 ± 0.1) × 10¹⁰ exp[(-1140 ± 150 K)/T], k(T, HA^-) = (4.8 ± 0.1) × 10¹⁰ exp[(-1280 ± 170 K)/T], and k(T, A^2-) = (2.1 ± 0.1) × 10¹⁰ exp[(-970 ± 70 K)/T]. A general trend of the ^•OH rate constant is found as kA2- > kHA- > kH2A. The pH- and temperature-dependent rate constants of the OH radical reactions allow an accurate description of the source and sink processes in the tropospheric aqueous phase.

Organic aerosol compositions and source estimation by molecular tracers in Dushanbe, Tajikistan

To elucidate the molecular composition and sources of organic aerosols in Central Asia, carbonaceous compounds, major ions, and 15 organic molecular tracers of total suspended particulates (TSP) were analyzed from September 2018 to August 2019 in Dushanbe, Tajikistan. Extremely high TSP concentrations (annual mean ± std: 211 ± 131 μg m^-3) were observed, particularly during summer (seasonal mean ± std: 333 ± 183 μg m^-3). Organic carbon (OC: 11.9 ± 7.0 μg m^-3) and elemental carbon (EC: 5.1 ± 2.2 μg m^-3) exhibited distinct seasonal variations from TSP, with the highest values occurring in winter. A high concentration of Ca²⁺ was observed (11.9 ± 9.2 μg m^-3), accounting for 50.8% of the total ions and reflecting the considerable influence of dust on aerosols. Among the measured organic molecular tracers, levoglucosan was the predominant compound (632 ± 770 ng m^-3), and its concentration correlated significantly with OC and EC during the study period. These findings highlight biomass burning (BB) as an important contributor to the particulate air pollution in Dushanbe. High ratios of levoglucosan to mannosan, and syringic acid to vanillic acid suggest that mixed hardwood and herbaceous plants were the main burning materials in the area, with softwood being a minor one. According to the diagnostic tracer ratio, OC derived from BB constituted a large fraction of the primary OC (POC) in ambient aerosols, accounting for an annual mean of nearly 30% and reaching 63% in winter. The annual contribution of fungal spores to POC was 10%, with a maximum of 16% in spring. Measurements of plant debris, accounting for 3% of POC, divulged that these have the same variation as fungal spores.

Soil dust as a potential bridge from biogenic volatile organic compounds to secondary organic aerosol in a rural environment

The role of coarse particles has recently been proven to be underestimated in the atmosphere and can strongly influence clouds, ecosystems and climate. However, previous studies on atmospheric chemistry of volatile organic compounds (VOCs) have mostly focused on the products in fine particles, it remains less understood how coarse particles promote secondary organic aerosol (SOA) formation. In this study, we investigated water-soluble compounds of size-segregated aerosol samples (0.056 to >18 μm) collected at a coastal rural site in southern China during late summer and found that oxygenated organic matter was abundant in the coarse mode. Comprehensive source apportionment based on mass spectrum and ¹⁴C analysis indicated that different from fossil fuel SOA, biogenic SOA existed more in the coarse mode than in the fine mode. The SOA in the coarse mode showed a unique correlation with biogenic VOCs. ¹³C and elemental composition strongly suggested a pathway of heterogeneous reactions on coarse particles, which had an abundant low-acidic aqueous environment with soil dust to possibly initiate iron-catalytic oxidation reactions to form SOA. This potential pathway might complement understanding of both formation of biogenic SOA and sink of biogenic VOCs in global biogeochemical cycles, warrantying future relevant studies.

Seasonal variations in carbonaceous species of PM2.5 aerosols at an urban location situated in Indo-Gangetic Plain and its relationship with transport pathways, including the potential sources

The study examines the variation in organic carbon (OC) and elemental carbon (EC) in PM_2.5 concentration at an urban location of Indo-Gangetic Plains (IGP) to understand the impact of seasonality and regional crop residue burning activities. Seasonal cluster analysis of backward air masses and concentration-weighted trajectory (CWT) analysis was performed to identify seasonal transport pathways and potential source regions of carbonaceous aerosols. The mean PM_2.5 level during the study period was 57 ± 41.6 μgm^-3 (5.0-187.3 μgm^-3), whereas OC and EC concentration ranges from 2.8 μgm^-3 to 28.2 μgm^-3 and 1.3 μgm^-3 to 15.5 μgm^-3 with a mean value of 8.4 ± 5.5 μgm^-3 and 5.1 ± 3.3 μgm^-3 respectively. The highest mean PM_2.5 concentration was found during the winter season (111.3 ± 25.5 μgm^-3), which rises 3.6 times compared to the monsoon season. OC and EC also follow a similar trend having the highest levels in winter. Total carbonaceous aerosols contribute ∼38% of PM_2.5 composition. The positive linear trend between OC and EC identified the key sources. HYSPLIT cluster analysis of backward air mass trajectories revealed that during the post-monsoon, winters, pre-monsoon, and monsoon, 71%, 81%, 60%, and 43% of air masses originate within the 500 km radius of IGP. CWT analysis and abundance of OC in post-monsoon and winters season establish a linkage between regional solid-biomass fuel use and crop residue burning activities, including meteorology. Moreover, the low annual average OC/EC ratio (1.75) indicates the overall influence of vehicular emissions. The current dataset of carbonaceous aerosols collated with other Indian studies could be used to validate the global aerosol models on a regional scale and aid in evidence-based air pollution reduction strategies.

Seasonal variation of dicarboxylic acids in PM2.5 in Beijing: Implications for the formation and aging processes of secondary organic aerosols

Dicarboxylic acids are a group of highly oxidized components, which can provide insights into the formation mechanism and aging process of secondary organic aerosols (SOA). Based on the 12-h day and night PM_2.5 samples collected in downtown Beijing in January, April, July and October of 2017, dicarboxylic acids and relevant components were measured to investigate their seasonal variation pattern and sources. High concentrations of the identified organic acids were observed, following the decreasing order of July > January > October > April. The high fractions of phthalic acid and maleic acid in January indicated severe aromatic SOA pollution during the sampling period in winter, and the high malonic acid to succinic acid and malic acid to succinic acid ratios in July suggested strong photochemical formation over the sampling period in summer. Based on the calculation of principle component analysis and multiple linear regression, water-soluble organic acids were mainly formed from the aerosol aging process during the sampling periods except for January, while water-soluble organic carbon (WSOC) mostly originated from combustion sources. Correlation analysis was conducted between the CO-normalized concentrations of organic acids and PM_2.5, O₃, as well as the meteorological parameters. The results suggested that gas-phase photooxidation contributed significantly to the formation of these organic acids during the entire sampling period, and the aqueous-phase process played an important role over the severe haze event in January. Our results also suggested that the intensity of photooxidation and the aging degree of SOA were enhanced along with the reduction of PM_2.5 in Beijing in recent years.

Molecular characteristics and stable carbon isotope compositions of dicarboxylic acids and related compounds in the urban atmosphere of the North China Plain: Implications for aqueous phase formation of SOA during the haze periods

In the past five years, Chinese government has promulgated stringent measures to mitigate air pollution. However, PM_2.5 levels in the China North Plain (NCP), which is one of the regions with the heaviest air pollution in the world, are still far beyond the World Health Organization (WHO) standard. To improve our understanding on the sources and formation mechanisms of haze in the NCP, PM_2.5 samples were collected during the winter of 2017 on a day/night basis at the urban site of Liaocheng, which is one of the most polluted cities in the NCP. The samples were determined for molecular distributions and stable carbon isotope compositions of dicarboxylic acids and their precursors (ketocarboxylic acids and α-dicarbonyls), levoglucosan, elemental carbon (EC), organic carbon (OC) and water-soluble organic carbon (WSOC). Our results showed that oxalic acid (C₂) is the dominant dicarboxylic acid, followed by succinic acid (C₄) and malonic acid (C₃), and glyoxylic acid (ωC₂) is the most abundant ketocarboxylic acids. Concentrations of C₂, glyoxal (Gly) and methylglyoxal (mGly) presented robust correlations with levoglucosan, suggesting that biomass burning is a significant source of PM_2.5 in the NCP. Moreover, C₂ and Gly and mGly linearly correlated with SO₄^2-, relative humidity (RH), aerosol liquid water content (LWC) as well as particle in-situ pH (pH_is), indicating that aqueous-phase oxidation is the major formation pathway of these SOA, and is driven by acid-catalyzed oxidation. Concentrations and relative abundances of secondary species including SNA (SO₄^2-, NO₃^- and NH₄⁺), dicarboxylic acids, and aerosol LWC in PM_2.5 are much higher in the haze periods than in the clean periods, suggesting that aqueous reaction is a vital role in the haze formation. In comparison with those in the clean periods, stable carbon isotopic compositions (δ¹³C) of major dicarboxylic acids and related SOA and the mass ratios of C₂/diacids, C₂/Gly and C₂/mGly are higher in the haze periods, indicating that haze particles were more aged and enriched in secondary species.

Characteristics and secondary formation of water-soluble organic acids in PM1, PM2.5 and PM10 in Beijing during haze episodes

Water-soluble organic acids are widely involved in various atmospheric physicochemical processes and appear as an important fraction of atmospheric aerosols. Nineteen water-soluble organic acids in 12-h PM₁, PM_2.5 and PM₁₀ samples collected in urban Beijing during haze episodes in winter and spring of 2017 were identified to investigate their characteristics and secondary formation mechanism. The molecular distributions of water-soluble organic acids as well as the high ratio of phthalic acid (Ph)/azelaic acid (C₉) indicated severe aromatic secondary organic aerosol pollution during the haze episodes, especially in winter. The diurnal patterns, size distributions, and concentration ratios of specific organic acids were investigated to reveal the pollution characteristics and possible sources of major organic acids in particulate matter in Beijing during haze events. Multiple linear regression was used to tentatively quantify the relative contributions of photochemical oxidation and aqueous-phase oxidation to the formation of total water-soluble organic acids in PM₁, PM_2.5 and PM₁₀ during haze episodes. The formation mechanism of sulfate and nitrate was also investigated for comparison. Different from the secondary formation of sulfate, the secondary formation of water-soluble organic acids showed enhanced contribution of gas-phase photochemical oxidation though the aqueous-phase oxidation was the dominant process. CAPSULE: Molecular analyses of organic acids in PM₁, PM_2.5 and PM₁₀ in Beijing during haze periods revealed their pollution characteristics, possible sources and formation mechanism.

Source contributions to water-soluble organic carbon and water-insoluble organic carbon in PM2.5 during Spring Festival, heating and non-heating seasons

To investigate the influences of anthropogenic activities on carbon aerosols, especially on water-soluble organic carbon (WSOC), PM_2.5 samples were collected at an urban site in a northern city of China during Spring Festival (SF), heating season (HS), and non-heating season (NHS). Carbonaceous species and ions (Ca²⁺, SO₄^2-, NO₃^-, etc.) were analyzed. Mass concentrations of WSOC and WSIC exhibited higher levels in SF and HS, and high WSOC/OC ratios (67.4%) on average were found. Stronger correlations between WSOC and K⁺, Cl^- occurred in SF, which might due to contributions of firework emissions. Six major sources of PM_2.5 were quantified by PMF model, which contributed in aerosol mass differently in different periods: biomass & firework burning exhibited higher contribution (11.2%) in SF; crustal dust accounted for 19.4% during NHS; secondary particles contributed most (41.0%) in HS; during SF and HS, coal combustion devoted more to aerosol mass. Contributions to WSOC were in the order of vehicular exhaust (41.0% of WSOC) > coal combustion (29.3%) > secondary formation (17.0%) > biomass & firework burning (12.7%). The 82.0% of WIOC were from coal combustion and the rest were devoted by vehicular exhaust. Obvious peaks of firework burning contributions to WSOC were observed on SF's Eve and Lantern Festival. Coal combustion contributed to organic carbons highly in SF and HS. Results implied that anthropogenic activities contributions, like firework burning and coal combustion, significantly influenced the levels of PM_2.5 and WSOC.

Dicarboxylic acids and levoglucosan in aerosols from Indo-Gangetic Plain: Inferences from day night variability during wintertime

This study assesses daytime and nighttime atmospheric abundance and molecular distribution of dicarboxylic acids (DCA: C₂-C₁₀) and biomass burning tracers (levoglucosan and biomass burning derived potassium: K⁺_BB) in PM₁₀ (particulate matter with aerodynamic diameter≤10μm) from an urban location, Kanpur (in central Indo-Gangetic Plain: IGP) during wintertime (December 2015-February 2016). In this study, PM₁₀ varied from 130 to 242 and 175-388μgm^-3 during daytime and nighttime, respectively. The average ratios of OC/EC (day: 12.3; night: 9.3) and WSOC/OC (day: 0.74; night: 0.48) were relatively high during daytime (OC: organic carbon; EC: elemental carbon; WSOC: water-soluble organic carbon). Strong linear correlations (R²≥0.6; p<0.05) of OC with levoglucosan and K⁺_BB suggest biomass burning emission as predominant source of organic aerosols over the IGP. The measured concentrations of total DCA (ΣC₂-C₁₀) showed pronounced diurnal variability with a higher concentration during nighttime (2510±1025ngm^-3) as compared to that in daytime (1499±562ngm^-3). Concentrations of oxalic acid (C₂), succinic acid (C₄) and malonic acid (C₃) were predominantly high as compared to other congeners of DCA (C₂-C₁₀) over central IGP. Relatively higher mass fraction (73.4%) of C₂ in total DCA during nighttime than that in daytime (61.5%) indicates role of secondary organic aerosols (SOAs) formation involving aqueous-phase chemistry. Strong linear correlations of C₂ with C₃ and C₄ plausibly suggest that C₂ can have predominant formation pathways via decomposition of higher congeners of DCA. Overall, strong linear correlations of C₂ with levoglucosan and sulphate suggest that biomass burning emission and secondary transformations are predominant sources of DCA over IGP during wintertime.

Source profiles and contributions of biofuel combustion for PM2.5, PM10 and their compositions, in a city influenced by biofuel stoves

Source and ambient samples were collected in a city in China that uses considerable biofuel, to assess influence of biofuel combustion and other sources on particulate matter (PM). Profiles and size distribution of biofuel combustion were investigated. Higher levels in source profiles, a significant increase in heavy-biomass ambient and stronger correlations of K⁺, Cl^-, OC and EC suggest that they can be tracers of biofuel combustion. And char-EC/soot-EC (8.5 for PM_2.5 and 15.8 for PM₁₀ of source samples) can also be used to distinguish it. In source samples, water-soluble organic carbon (WSOC) were approximately 28.0%-68.8% (PM_2.5) and 27.2%-43.8% (PM₁₀) of OC. For size distribution, biofuel combustion mainly produces smaller particles. OC1, OC2, EC1 and EC2 abundances showed two peaks with one below 1 μm and one above 2 μm. An advanced three-way factory analysis model was applied to quantify source contributions to ambient PM_2.5 and PM₁₀. Higher contributions of coal combustion, vehicular emission, nitrate and biofuel combustion occurred during the heavy-biomass period, and higher contributions of sulfate and crustal dust were observed during the light-biomass period. Mass and percentage contributions of biofuel combustion were significantly higher in heavy-biomass period. The biofuel combustion attributed above 45% of K⁺ and Cl^-, above 30% of EC and about 20% of OC. In addition, through analysis of source profiles and contributions, they were consistently evident that biofuel combustion and crustal dust contributed more to cation than to anion, while sulfate & SOC and nitrate showed stronger influence on anion than on cation.

Role of ammonium ion and transition metals in the formation of secondary organic aerosol and metallo-organic complex within fog processed ambient deliquescent submicron particles collected in central part of Indo-Gangetic Plain

In this study we observed the role of ammonium ion (NH₄⁺) and transition metals (Fe, Mn, Cr, and Cu) present in ambient submicron particles in stabilizing and enhancing the yield of water soluble organic carbon (WSOC). A good correlation of WSOC with transition metals and NH₄⁺ was found (R² = 0.87 and 0.71), respectively within foggy episode collected ambient PM₁ (particles having aerodynamic diameter ≤1.0 μm) suggesting plausibleness of alternate oxidation (primarily various carbonyls into their respective organic acids, esters and other derivatives.) and aging mechanisms. Molar concentration of ammonium ion was observed to be exceeded over and above to require in neutralizing the sulphate and nitrate which further hints its role in the neutralization, stabilization and enhancement of subset of WSOC such as water soluble organic acids. Transition metals were further apportioned using enrichment factor analysis. The source of Fe, Mn, and Cr was found to be crustal and Cu was tagged to anthropogenic origin. This study also described the plausible role of significant predictors (Fe and Cu) in the secondary organic aerosol (SOA) formation through effect of Fenton chemistry. Mass-to-charge ratio of identified oxalic acid from our published recent field study (carried out from same sampling location) was used for understanding the possible metallo-organic complex with Fe supports the substantial role of Fe in SOA formation in the deliquescent submicron particles facilitated by aqueous-phase chemistry.