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 (SO42-), 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 (SO42-) 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.

Seasonal characteristics of biogenic secondary organic aerosol tracers in a deciduous broadleaf forest in northern Japan.

We collected total suspended particulate (TSP) samples from January 2010 to December 2010 at Sapporo deciduous forest to understand the oxidation processes of biogenic volatile organic compounds (BVOCs). The gas chromatography-mass spectrometric technique was applied to determine biogenic secondary organic aerosols (BSOAs) in the TSP samples. We found the predominance of the isoprene SOA (iSOA) tracers (20.6 ng m-3) followed by α/ß-pinene SOA (pSOA) tracers (8.25 ng m-3) and ß-caryophyllene SOA (cSOA) tracer (1.53 ng m-3) in the forest aerosols. The results showed large isoprene fluxes and relatively high levels of oxidants in the forest atmosphere. The iSOA and pSOA tracers showed a clear seasonal trend with summer and autumn maxima and winter and spring minima. Their seasonal trends were mainly controlled by BVOCs emission from the local broadleaf deciduous forest. Additionally, the regional level of isoprene emissions from the oceanic sources may also be contributed during summertime aerosols. cSOA tracer showed high concentrations in the winter and spring, possibly due to an additional contribution of biomass burning (BB) aerosols from the local or regional BB activities. The biogenic secondary organic carbon (BSOC) was contributed mainly by the oxidation products of isoprene (136 ngC m-3) followed by ß-caryophyllene (63.0 ngC m-3) and α/ß-pinene (35.9 ngC m-3). The mass concentration ratio (0.92) of pinonic acid + pinic acid and 3-methyl-1,2,3-butanetricarboxylic acid ((PNA + PA)/3-MBTCA) indicates the photochemical transformation of first-generation oxidation products to the higher generation oxidation products. The average ratios of isoprene to α/ß-pinene (1.64) and ß-caryophyllene (18.6) oxidation products suggested a large difference in the emissions of isoprene and α/ß-pinene compared to ß-caryophyllene. The cSOA tracers in the forest aerosols are also contributed by BB during the winter and spring. Positive matrix factorization analyses of the BSOA tracers confirmed that organic aerosols of deciduous forests are mostly related to isoprene emissions. This study suggests that isoprene is a more significant precursor for the BSOA than α/ß-pinene and ß-caryophyllene in a broadleaf deciduous forest.

Unraveling the sources of atmospheric organic aerosols over the Arabian Sea: Insights from the stable carbon and nitrogen isotopic composition.

The isotopic composition of stable carbon (δ13C) and nitrogen (δ15N) in marine aerosols influenced by the continental outflows are useful proxies for understanding the aging and secondary formation processes. Every winter, the haze pollutants transported from South Asia significantly affect the chemical composition of marine atmospheric boundary layer of the Arabian Sea. Here, we assessed the δ13C of total carbon (TC) and δ15N of total nitrogen (TN) in marine aerosols collected over the Arabian Sea during a winter cruise (6-24 December 2018). TC (2.1-13.4 µg m-3) is strongly correlated with TN (0.9-5.0 µg m-3), likely because of their common source-emissions, biomass burning and fossil-fuel combustion in the Indo-Gangetic Plain and South Asia (corroborated by backward-air mass trajectories and satellite fire counts). Besides, the linear relationship between the mass ratios of water-soluble organic carbon (WSOC) to TC (0.04-0.65) and δ13CTC (-25.1‰ to -22.9‰) underscores the importance of aging process. This means oxidation of organic aerosols during transport not only influences the WSOC levels but also affects their δ13CTC. Likewise, the prevalent inverse linear relationship between the equivalent mass ratio of (NH4+/non-sea-salt- or nss-SO42-) and δ15NTN (+15.3‰ to +25.1‰) emphasizes the overall significance of neutralization reactions between major acidic ([nss-SO42-] ≫ [NO3-]) and alkaline species (NH4+) in aerosols. Higher δ15NTN values in winter than the spring inter-monsoon clearly emphasizes the significance of the anthropogenic combustion sources (i.e., biomass burning) in the South Asian outflow. A comparison of δ13CTC and δ15NTN with the source emissions revealed that crop-residue burning emissions followed by the coal fired power plants mostly dictate the atmospheric abundance of organic aerosols in the wider South Asian outflow.

Seasonal and temporal variations of ambient aerosols in a deciduous broadleaf forest from northern Japan: Contributions of biomass burning and biological particles.

Total suspended particulate (TSP) samples were collected in a deciduous broadleaf forest in Sapporo, Hokkaido, Japan, from January to December 2010 to understand the molecular composition and abundance of sugar compounds (SCs) in atmospheric aerosols. We analyzed the samples for anhydrosugars, primary sugars, and sugar alcohols using a gas chromatograph-mass spectrometer. The annual mean concentrations of total SCs ranged from 16.1 to 1748 ng m-3 (avg. 311 ng m-3) with maxima in spring (avg. 484 ng m-3) and minima in winter (avg. 28.2 ng m-3). Primary sugars and sugar alcohols followed the seasonal pattern of total SCs. High levels of anhydrosugars in winter (avg. 22.9 ng m-3) suggest a contribution of biomass burning from domestic heating due to lower ambient temperature. The high levels of arabitol and mannitol in spring followed by summer and autumn denote the contribution from multiple sources, i.e., growing vegetation and fungal spores in Sapporo forest. We observed an enhanced contribution of bioaerosols emitted from plant blossoms in spring and leaf decomposition in autumn. The identical seasonal trends of glucose and trehalose implied their similar sources in forest aerosols. Conversely, the highest concentration of sucrose in spring was due to the pollen emissions by blooming plants. Positive matrix factorization (PMF) analyses of the SCs suggested that organic aerosols in the deciduous forest are associated with the emissions from multiple sources, including vegetation, microbes, pollens, and wintertime biomass burning. The PMF analysis also suggested that vegetation is the primary carbon source in the forest atmosphere. The diagnostic mass ratios of levoglucosan to mannosan demonstrated the dominance of softwood burning. We noted that the meteorological parameters substantially affect the emission sources and seasonal concentrations of SCs in the deciduous forest.

Distinctive Sources Govern Organic Aerosol Fractions with Different Degrees of Oxygenation in the Urban Atmosphere.

Understanding how the sources of an atmospheric organic aerosol (OA) govern its burden is crucial for assessing its impact on the environment and adopting proper control strategies. In this study, the sources of OA over Beijing were assessed year-around based on the combination of two separation approaches for OA, one from chemical fractionation into the high-polarity fraction of water-soluble organic matter (HP-WSOM), humic-like substances (HULIS), and water-insoluble organic matter (WISOM), and the other from statistical grouping using positive matrix factorization (PMF) of high-resolution aerosol mass spectra. Among the three OA fractions, HP-WSOM has the highest O/C ratio (1.36), followed by HULIS (0.56) and WISOM (0.17). The major sources of different OA fractions were distinct: HP-WSOM was dominated by more oxidized oxygenated OA (96%); HULIS by cooking-like OA (40%), less oxidized oxygenated OA (27%), and biomass burning OA (21%); and WISOM by fossil fuel OA (77%). In addition, our results provide evidence that mass spectral-based PMF factors are associated with specific substructures in molecules. These structures are further discussed in the context of the FT-IR results. This study presents an overall relationship of OA groups monitored by chemical and statistical approaches for the first time, providing insights for future source apportionment studies.

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.

The size distributions of aerosols can provide evidences for their sources and formation processes in the atmosphere. Size-segregated aerosols (9-sizes) were collected in urban site (Raipur: 21.2°N and 82.3°E) in central India during winter of 2012-2013. The samples were analyzed for dicarboxylic acids (C2-C12), ω-oxocarboxylic acids (ωC2-ωC9), pyruvic acid and α-dicarbonyls (C2-C3) as well as elemental carbon (EC), organic carbon (OC), water-soluble OC (WSOC) and inorganic ions. Diacids showed a predominance of oxalic acid (C2) followed by succinic and azelaic acid whereas ω-oxoacids exhibited a predominance of glyoxylic acid and glyoxal was more abundant than methylglyoxal in all the sizes. Diacids, ω-oxoacids and α-dicarbonyls showed bimodal size distribution with peaks in fine and coarse modes. High correlations of fine mode diacids and related compounds with potassium and levoglucosan suggest that they were presumably due to a substantial contribution of primary emission from biomass burning and secondary production from biomass burning derived precursors. High correlations of C2 with higher carbon number diacids (C3-C9) suggest that they have similar sources and C2 may be produced via the decay of its higher homologous diacids in fine mode. Considerable portions of diacids and related compounds in coarse mode suggest that they were associated with mineral dust particles by their adsorption and photooxidation of anthropogenic and biogenic precursors via heterogeneous reaction on dust surface. This study demonstrates that biomass burning and dust particles are two major factors to control the size distribution of diacids and related compounds in the urban aerosols from central India.

Molecular markers in ambient aerosol in the Mahanadi Riverside Basin of eastern central India during winter.

Organic molecular markers are important atmospheric constituents. Their formation and sources are important aspects of the study of urban and rural air quality. We collected PM10 aerosol samples from the Mahanadi Riverside Basin (MRB), a rural part of eastern central India, during the winter of 2011. PM10 aerosols were characterized for molecular markers using ion chromatography. The concentration of PM10 ranged from 208.8 to 588.3 µg m(-3) with a mean concentration of 388.9 µg m(-3). Total concentration of anhydrosugars, sugar alcohols, primary sugars, and oxalate were found to be 3.25, 5.60, 10.52, and 0.37 µg m(-3), respectively, during the study period. Glucose was the most abundant species followed by levoglucosan and mannitol. Significant positive correlation between the molecular markers, anhydrosugars, sugar alcohols, primary sugars, and oxalic acid confirmed that biomass burning, biogenic activity, and re-suspension of soil particles were the main sources of aerosol in the eastern central India study area.

Removal of phenolic compounds from aqueous phase by adsorption onto polymer supported iron nanoparticles.

The removal of phenolic compounds, i.e., o-cresol, m-cresol, and p-cresol from aqueous solution have been evaluated employing activated carbon (AC) coated with polymer supported iron nanoparticles (FeNPs). The synthesized FeNPs were characterized by scanning electron microscope and X-ray diffraction analysis. High correlation coefficient values indicated that the adsorption of phenolic compounds onto AC coated with polyvinylpyrrolidon (PVP) supported FeNPs obey Freundlich and Langmuir adsorption isotherms. Higher Freundlich and Langmuir constant values for AC coated with PVP supported FeNPs indicated its greater efficiency than AC. The adsorption data are well represented by both the Freundlich and Langmuir isotherms, indicating favourable adsorption of cresols by the adsorbents. Cresols were effectively removed (90 %) by adsorption process from aqueous solution using AC coated with FeNPs. The percentage removal of above phenolic compounds was studied under varying experimental conditions such as pH, temperature, adsorbent dosage, and contact time. The adsorption of phenolic compounds is quite sensitive to pH of the suspension and optimum uptake value was found at pH 7.0. Temperature also has a favorable effect on adsorption when varied from 20 to 50°C. On the contrary, beyond 30°C, a decrease in the adsorption was noticed.

Seasonal air quality profile of size-segregated aerosols in the ambient air of a central Indian region.

Seasonal distribution trends of size-segregated aerosols i.e. submicron (PM1), fine (PM2.5) and coarse (PM2.5-10) and their relationship with meteorological variables employing correlation analysis were studied in the ambient air of central India from July 2009 to June 2010. The annual mean concentrations of PM1, PM2.5 and PM2.5-10 were found to be 65.7, 135.0 and 118.5 µg m(-3), respectively. The annual mean PM2.5 concentration is three times higher than the National Ambient Air Quality Standards of India (NAAQS). Higher concentrations of PM1, PM2.5 and PM2.5-10 were found during winter due to enormous biomass burning especially during night time due to the use of combustible goods like fire wood and dung cake in the open space by the peoples to keep themselves warm and lower concentrations were observed during monsoon when there were high precipitations. PM2.5 showed high positive correlation with PM1 (r = 0.69) and moderate correlation with PM2.5-10 indicating that variation in PM2.5 mass is governed by the variation in PM1 mass or vice versa.

Mass loading of size-segregated atmospheric aerosols in the ambient air during fireworks episodes in eastern Central India.

The effects of combustion of the fire crackers on the air quality in eastern Central India were studied for the first time during Diwali festival. This case study analyzes the size distribution and temporal variation of aerosols collected in the rural area of eastern Central India during pre-diwali, Diwali and post-diwali period for the year of 2011. Fifteen aerosol samples were collected during the special case study of Diwali period using Andersen sampler. The mean concentrations of PM10 (respirable particulate matter) were found to be 212.8 ± 4.2, 555.5 ± 20.2 and 284.4 ± 5.8 during pre-diwali, Diwali and post-diwali period, respectively. During Diwali festival PM10 concentration was about 2.6 and 1.9 times higher than pre-diwali and post-diwali period, respectively. PM2.5 (fine) and PM1 (submicron) concentrations during Diwali festival were more than 2 times higher than pre-diwali and post-diwali.

Aerosol size distribution and seasonal variation in an urban area of an industrial city in central India.

To study the size distribution and seasonal variations of atmospheric aerosols, size-segregated aerosol samples were collected from July 2009 to June 2010 using the nine-stage cascade impactor aerosol sampler in Durg City, India. The aerosol particles exhibited bimodal size distribution on mass concentration with a peak at 2.5-4.4 µm size ranges in the coarse mode and 2.1-2.5 µm size ranges in the fine mode. The aerosol mass and size distribution during monsoon were found unimodal distribution with a peak in the coarse mode, while they showed trimodal distributions during winter with all three peaks appearing in the fine mode. The annual mean concentration of PM(10) aerosol was found to be 253.5 ± 99.4 µg/m(3), which is four times higher as compared to the annual guideline of National Ambient Air Quality Standards (NAAQS) of India prescribed by the Central Pollution Control Board (CPCB), India. The highest aerosol mass concentrations were found during winter due to enormous biomass burning, while the lowest concentrations were observed during monsoon due to heavy rainfall. Air quality index values calculated in this study showed that 35% of the days were unhealthy for sensitive people, 35% were unhealthy or very unhealthy, while 3.3% were found as hazardous in Durg City, India.

Characteristics and sources of water-soluble ionic species associated with PM10 particles in the ambient air of central India.

PM(10) aerosol samples were collected in Durg City, India from July 2009 to June 2010 using an Andersen aerosol sampler and analyzed for eight water-soluble ionic species, namely, Na(+), NH(4) (+), K(+), Mg(2+), Ca(2+), Cl(-), NO(3) (-) and SO(4) (2-) by ion chromatography. The annual average concentration of PM(10) (253.5 ± 99.4 µg/m(3)) was four times higher than the Indian National Ambient Air Quality Standard of 60 µg/m(3) prescribed by the Central Pollution Control Board, India. The three most abundant ions were SO(4) (2-), NO(3) (-), and NH(4) (+), with average concentrations of 8.88 ± 4.81, 5.63 ± 2.22, and 5.18 ± 1.76 µg/m(3), respectively, and in turn accounting for 27.1 %, 16.5 %, and 15.5 % of the total water-soluble ions analyzed. Seasonal variation was similar for all secondary ions i.e., SO(4) (2-), NO(3) (-), and NH(4) (+), with high concentrations during winter and low concentrations during monsoon. Varimax Rotated Component Matrix principal component analysis identified secondary aerosols, crustal resuspension, and coal and biomass burning as common sources of PM(10) in Durg City, India.