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

Suresh K R Boreddy; Kimitaka Kawamura; Divyavani Gowda; Dhananjay K Deshmukh; K Narasimhulu; K Ramagopal

doi:10.1016/j.scitotenv.2023.162365

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

Sci Total Environ. 2023 May 20:874:162365. doi: 10.1016/j.scitotenv.2023.162365. Epub 2023 Feb 22.

Authors

Suresh K R Boreddy¹, Kimitaka Kawamura², Divyavani Gowda³, Dhananjay K Deshmukh⁴, K Narasimhulu⁵, K Ramagopal⁶

Affiliations

¹ Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram 695022, India; Institute of Low Temperature Sciences, Hokkaido University, Sapporo 060-0819, Japan. Electronic address: reddy_sk@vssc.gov.in.
² Institute of Low Temperature Sciences, Hokkaido University, Sapporo 060-0819, Japan; Chubu Institute for Advanced Studies, Chubu University, Kasugai 487-8501, Japan.
³ Institute of Low Temperature Sciences, Hokkaido University, Sapporo 060-0819, Japan; Faculty of Health Sciences, Hokkaido University, Sapporo 060-0812, Japan.
⁴ Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram 695022, India.
⁵ Department of Physics, SSA Govt. First Grade College, Ballari 583101, India.
⁶ Department of Physics, Sri Krishnadevaraya University, Anantapur 515003, India.

PMID: 36822414
DOI: 10.1016/j.scitotenv.2023.162365

Abstract

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.

Keywords: Aerosol liquid water; Aqueous-phase formation; Levoglucosan; Secondary organic aerosols; Sulfate; Tropical peninsular India.