Aerosol acidity and its neutralization in the eastern Indo-Gangetic Plain: implications for water-soluble organic carbon

2020 ◽  
Author(s):  
Bijay Sharma ◽  
Anuraag J. Polana ◽  
Prashant Rawat ◽  
Sayantan Sarkar
Keyword(s):  
Receptor Site ◽  
Water Soluble ◽  
Dual Function ◽  
Gangetic Plain ◽  
Desert Dust ◽  
Post Monsoon ◽  
Aerosol Acidity ◽  
Water Soluble Organic Carbon ◽  
Soluble Organic Carbon ◽  
Indo Gangetic Plain

<p>Aerosol acidity plays an important role in influencing precipitation pH, which has impacts on the environment as well as human health. It also has significance in shaping aerosol chemistry, including the catalytic formation of water-soluble organic carbon (WSOC), which in turn affects the hygroscopicity of aerosols. Past studies on aerosol acidity in the Indian subcontinent, mostly conducted in biomass burning (BB) source regions in the northwestern and central Indo-Gangetic Plain (IGP) and in western India, have identified Ca<sup>2+</sup> and Mg<sup>2+</sup> sourced from desert dust to be the predominant neutralizing agents. However, the prevalence of desert dust decreases progressively along the IGP corridor and is potentially rendered insignificant in the eastern IGP (eIGP). As such, there exists a critical weakness in our understanding of the processes governing aerosol acidity and its neutralization in the eIGP. To address this, the present study reports the seasonal variability of ionic species, WSOC and associated aerosol acidity in ambient PM<sub>2.5</sub> from a rural receptor site in the eIGP. To this end, a total of 88 PM<sub>2.5</sub> samples collected during the summer, post-monsoon and winter seasons of 2018 were analyzed for SO<sub>4</sub><sup>2-</sup>, NO<sub>3</sub><sup>-</sup>, Cl<sup>-</sup>, Na<sup>+</sup>, NH<sub>4</sub><sup>+</sup>, K<sup>+</sup>, Ca<sup>2+</sup>, Mg<sup>2+</sup>, F<sup>-</sup>, PO<sub>4</sub><sup>3-</sup> and WSOC, followed by estimation of strong acidity. Across all seasons, the aerosol phase was dominated by SO<sub>4</sub><sup>2-</sup>, NH<sub>4</sub><sup>+</sup> and NO<sub>3</sub><sup>-</sup>, with values increasing by factors of 1.8-1.9, 1.4-2.9 and 1.8-11, respectively, for the regional BB-dominated post-monsoon and winter seasons as compared to summer. Significant positive Cl<sup>-</sup> depletion in summer pointed towards the influx of marine air while negative depletion in post-monsoon and winter suggested a BB source, which was further supported by concentration-weighted trajectory analysis. The averaged pH of the aerosol extract decreased progressively from summer (5.5±0.4) to winter (4.5±0.2). NH<sub>4</sub><sup>+</sup> was observed to be the major acid-neutralizing agent across all seasons, with dust-derived Ca<sup>2+</sup> and Mg<sup>2+</sup> playing only minor roles. In general, WSOC formation is known to be catalyzed by the presence of excess acidity; however, during winter, it appeared that the regional transport of organic acids in the BB plume contributed to aerosol acidity at this receptor site (r=0.92; p<0.01 for WSOC and H<sup>+</sup>). BB-derived K<sup>+</sup> appeared to perform a dual function of neutralizing acidity as well as producing it via reactions with WSOC during atmospheric transport. The wintertime acidity was also strongly governed by aerosol NO<sub>3</sub><sup>-</sup> sourced from BB emissions and possibly accentuated via nighttime atmospheric chemistry at lower ambient temperatures, resulting in the formation of haze. These observations of the NO<sub>3</sub><sup>-</sup> and WSOC-driven wintertime acidity, the dual function of K<sup>+</sup> and the dominant role of NH<sub>4</sub><sup>+</sup> in neutralization points to complex atmospheric processing of the IGP outflow during its transport to the eastern end of the corridor, which warrants further investigation.</p>

Variation in carbonaceous and ionic species at a rural receptor location in the eastern Indo-Gangetic Plain

2021 ◽  
Author(s):  
Bijay Sharma ◽  
Anurag J. Polana ◽  
Jingying Mao ◽  
Shiguo Jia ◽  
Sayantan Sarkar
Keyword(s):  
Organic Carbon ◽  
Forest Fires ◽  
Ionic Species ◽  
Water Soluble ◽  
Photochemical Oxidation ◽  
Carbonaceous Aerosol ◽  
Charge Ratio ◽  
Gangetic Plain ◽  
Post Monsoon ◽  
Indo Gangetic Plain

<p>The Indo-Gangetic Plain (IGP) is one of the world’s most populated river basins housing more than 700 million people. Apart from being a major source region of aerosols, the IGP is affected by transported aerosols from the Thar Desert, forest-fires and open burning of crop waste from central India. Studies have been carried out to understand the aerosol chemical composition and optical properties in source regions of IGP but knowledge is severely lacking for receptor locations viz. eastern IGP (eIGP). To address this, the present study reports the seasonal variability of carbonaceous and ionic species in ambient PM<sub>2.5</sub> from a rural receptor location (Mohanpur, West Bengal) along with insights on aerosol acidity, its neutralization and potential source regimes. A total of 88 PM<sub>2.5</sub> samples collected during the summer, post-monsoon and winter seasons of 2018 were analyzed for SO<sub>4</sub><sup>2-</sup>, NO<sub>3</sub><sup>-</sup>, Cl<sup>-</sup>, Na<sup>+</sup>, NH<sub>4</sub><sup>+</sup>, K<sup>+</sup>, Ca<sup>2+</sup>, Mg<sup>2+</sup>, F<sup>-</sup>,<sup></sup>PO<sub>4</sub><sup>3-</sup>, water-soluble organic carbon (WSOC), organic carbon (OC) and elemental carbon (EC) fractions. Sulfate, nitrate and ammonium (SNA) were the dominating ionic species throughout the seasons (67-86% out of the total ionic species measured). Significant positive Cl<sup>-</sup> depletion in summer (49±20%) pointed towards influx of marine air while negative depletion in post-monsoon and winter suggested a biomass burning (BB) source, which was further supported by concentration-weighted trajectory analysis. Strong acidity was found to be highest during post-monsoon (141±76 nmol m<sup>-3</sup>), followed by winter (117±36 nmol m<sup>-3</sup>) and summer (40±14 nmol m<sup>-3</sup>) with significant differences between summer and the other seasons. Neutralization factor (N<sub>f</sub>) and equivalent charge ratio of cation to anion (R<sub>C/A</sub>) revealed that summertime aerosols were neutral in nature while those of post-monsoon and winter were comparatively acidic with NH<sub>4</sub><sup>+</sup> being the major neutralizing agent throughout the seasons. Correlations between WSOC and OC fractions (OC1, OC2, OC3 and OC4) suggested secondary formation of summertime WSOC (WSOC vs OC3: r=0.48, p<0.05) via photochemical oxidation of volatile organic carbons (VOCs) while that of post-monsoon (WSOC vs OC1, OC2, OC3: r=0.45-0.62, <em>p</em><0.05) and winter (WSOC vs OC1, OC2, OC3: r=0.58-0.68, <em>p</em><0.05), both primary and secondary pathways seem important. To elucidate the role of BB, we looked into the two components of EC i.e., char-EC (EC1-PC) and soot-EC (EC2+EC3). The percent contribution of char-EC to EC was 65±17%, 90±10% and 98±1% during summer, post-monsoon and winter, respectively. Along with this, char-EC/soot-EC ratios of 2.3±1.8, 17.6±16.4 and 50.3±18.6 during summer, post-monsoon and winter, respectively, and significant correlations of the same with the BB-tracer K<sup>+</sup> (post-monsoon: r=0.78, <em>p</em><0.001; winter: r=0.64, <em>p</em><0.01) indicated the importance of BB emissions in constraining carbonaceous aerosol profiles during post-monsoon and winter.</p>

scholarly journals Effects of Water-soluble Organic Carbon on Aerosol pH

2019 ◽  
Author(s):  
Michael A. Battaglia Jr. ◽  
Rodney J. Weber ◽  
Athanasios Nenes ◽  
Christopher J. Hennigan
Keyword(s):  
Organic Carbon ◽  
Fine Particulate Matter ◽  
Water Soluble ◽  
Organic Species ◽  
Aerosol Acidity ◽  
Activity Coefficient Model ◽  
Water Soluble Organic Carbon ◽  
Soluble Organic Carbon ◽  
Acidic Conditions ◽  
Beijing China

Abstract. Water soluble organic carbon (WSOC) is a ubiquitous and significant fraction of fine particulate matter. Despite advances in aerosol thermodynamic equilibrium models, there is limited understanding on the comprehensive impacts of WSOC on aerosol acidity (pH). We address this limitation by studying submicron aerosol that represent the two extremes in acidity levels found in the atmosphere: strongly acidic aerosol from Baltimore, MD, and weakly acidic conditions characteristic of Beijing, China. These cases are then used to construct mixed inorganic/organic single-phase aqueous particles, and thermodynamically analyzed by the E-AIM and ISORROPIA models (in combination with activity coefficient model AIOMFAC) to evaluate the effects of WSOC on the H+ ion activity coefficients (γH+) and activity (pH). We find that addition of organic acids and non-acid organic species concurrently increases γH+ and aerosol liquid water. When allowed to modulate pH, these effects mostly offset each other, giving pH changes of

scholarly journals Seasonal variations of water-soluble organic carbon, dicarboxylic acids, ketoacids, and α-dicarbonyls in the central Himalayan aerosols

2012 ◽  
Vol 12 (1) ◽  
pp. 935-982 ◽  
Author(s):  
P. Hegde ◽  
K. Kawamura
Keyword(s):  
Organic Carbon ◽  
Anthropogenic Activities ◽  
Dicarboxylic Acids ◽  
High Elevation ◽  
Water Soluble ◽  
Gangetic Plain ◽  
Water Soluble Organic Carbon ◽  
Soluble Organic Carbon ◽  
Related Compounds ◽  
Himalayan Aerosols

Abstract. Aerosol samples were collected from a high elevation mountain site (Nainital, India; 1958 m a.s.l.) in the central Himalayas, which provide an isolated platform above the planetary boundary layer to better understand the composition of the remote continental troposphere. The samples were analyzed for water-soluble dicarboxylic acids (C2–C12) and related compounds (ketocarboxylic acids and α-dicarbonyls), as well as organic carbon, elemental carbon and water soluble organic carbon. The contributions of total dicarboxylic acids to total aerosol carbon during wintertime were 1.7 and 1.8%, for day and night, respectively whereas they significantly reduced during summer. Molecular distributions of diacids demonstrated that oxalic (C2) acid was the most abundant species followed by C4 and C3 diacids. The average concentrations of total diacids (433 ± 108 ng m−3), ketoacids (48 ± 23 ng m−3), and α-dicarbonyls (9 ± 4 ng m−3) were similar to those from Asian cities such as Tokyo, Beijing and Hong Kong. During summer season most of the organic species were several times more abundant than in winter. Phthalic acid, which originates from oxidation of polycyclic aromatic hydrocarbons such as naphthalene, was found to be 7 times higher in summer than winter. This feature has not been reported in atmospheric aerosols. Based on molecular distributions and air mass backward trajectories, we report that dicarboxylic acids and related compounds in Himalayan aerosols are influenced by the anthropogenic activities from highly populated Indo-Gangetic plain areas.

scholarly journals Seasonal variations of water-soluble organic carbon, dicarboxylic acids, ketocarboxylic acids, and α-dicarbonyls in Central Himalayan aerosols

2012 ◽  
Vol 12 (14) ◽  
pp. 6645-6665 ◽  
Author(s):  
P. Hegde ◽  
K. Kawamura
Keyword(s):  
Organic Carbon ◽  
Anthropogenic Activities ◽  
Dicarboxylic Acids ◽  
High Elevation ◽  
Water Soluble ◽  
Gangetic Plain ◽  
Water Soluble Organic Carbon ◽  
Soluble Organic Carbon ◽  
Related Compounds ◽  
Himalayan Aerosols

Abstract. Aerosol samples were collected from a high elevation mountain site (Nainital, India; 1958 m a.s.l.) in the central Himalayas, a location that provides an isolated platform above the planetary boundary layer to better understand the composition of the remote continental troposphere. The samples were analyzed for water-soluble dicarboxylic acids (C2-C12) and related compounds (ketocarboxylic acids and α-dicarbonyls), as well as organic carbon, elemental carbon and water soluble organic carbon. The contributions of total dicarboxylic acids to total aerosol carbon during wintertime were 1.7% and 1.8%, for day and night, respectively whereas they were significantly smaller during summer. Molecular distributions of diacids revealed that oxalic (C2) acid was the most abundant species followed by succinic (C4) and malonic (C3) acids. The average concentrations of total diacids (433±108 ng m−3), ketoacids (48±23 ng m−3), and α-dicarbonyls (9±4 ng m−3) were similar to those from large Asian cities such as Tokyo, Beijing and Hong Kong. During summer most of the organic species were several times more abundant than in winter. Phthalic acid, which originates from oxidation of polycyclic aromatic hydrocarbons such as naphthalene, was found to be 7 times higher in summer than winter. This feature has not been reported before in atmospheric aerosols. Based on molecular distributions and air mass backward trajectories, we conclude that dicarboxylic acids and related compounds in Himalayan aerosols are derived from anthropogenic activities in the highly populated Indo-Gangetic plain areas.

scholarly journals Desiccation time and rainfall control gaseous carbon fluxes in an intermittent stream

2021 ◽  
Author(s):  
Maria Isabel Arce ◽  
Mia M. Bengtsson ◽  
Daniel von Schiller ◽  
Dominik Zak ◽  
Jana Täumer ◽  
...  
Keyword(s):  
Water Soluble ◽  
Intermittent Flow ◽  
Dry Period ◽  
Intermittent Stream ◽  
Aerobic Activity ◽  
Water Soluble Organic Carbon ◽  
Soluble Organic Carbon ◽  
Microbial C ◽  
Global Biogeochemical Cycles ◽  
The Impact

AbstractDroughts are recognized to impact global biogeochemical cycles. However, the implication of desiccation on in-stream carbon (C) cycling is not well understood yet. We subjected sediments from a lowland, organic rich intermittent stream to experimental desiccation over a 9-week-period to investigate temporal changes in microbial functional traits in relation to their redox requirements, carbon dioxide (CO2) and methane (CH4) fluxes and water-soluble organic carbon (WSOC). Concurrently, the implications of rewetting by simulated short rainfalls (4 and 21 mm) on gaseous C fluxes were tested. Early desiccation triggered dynamic fluxes of CO2 and CH4 with peak values of 383 and 30 mg C m−2 h−1 (mean ± SD), respectively, likely in response to enhanced aerobic mineralization and accelerated evasion. At longer desiccation, CH4 dropped abruptly, likely because of reduced abundance of anaerobic microbial traits. The CO2 fluxes ceased later, suggesting aerobic activity was constrained only by extended desiccation over time. We found that rainfall boosted fluxes of CO2, which were modulated by rainfall size and the preceding desiccation time. Desiccation also reduced the amount of WSOC and the proportion of labile compounds leaching from sediment. It remains questionable to which extent changes of the sediment C pool are influenced by respiration processes, microbial C uptake and cell lysis due to drying-rewetting cycles. We highlight that the severity of the dry period, which is controlled by its duration and the presence of precipitation events, needs detailed consideration to estimate the impact of intermittent flow on global riverine C fluxes.

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