Light absorption potential of water-soluble organic aerosols in the two polluted urban locations in the central Indo-Gangetic Plain

Pradhi Rajeev; Vikram Choudhary; Abhishek Chakraborty; Gyanesh Kumar Singh; Tarun Gupta

doi:10.1016/j.envpol.2022.120228

Light absorption potential of water-soluble organic aerosols in the two polluted urban locations in the central Indo-Gangetic Plain

Environ Pollut. 2022 Dec 1:314:120228. doi: 10.1016/j.envpol.2022.120228. Epub 2022 Sep 23.

Authors

Pradhi Rajeev¹, Vikram Choudhary², Abhishek Chakraborty³, Gyanesh Kumar Singh², Tarun Gupta²

Affiliations

¹ Department of Civil Engineering and APTL at Center for Environmental Science and Engineering (CESE), Indian Institute of Technology Kanpur, Kanpur, 208 016, India; Faculty of Natural Sciences, University of Silesia in Katowice, Sosnowiec, 41-200, Poland. Electronic address: pradhi.rajeev@us.edu.pl.
² Department of Civil Engineering and APTL at Center for Environmental Science and Engineering (CESE), Indian Institute of Technology Kanpur, Kanpur, 208 016, India.
³ Environmental Science and Engineering Department (ESED), Indian Institute of Technology Bombay, Mumbai, 400076, India.

PMID: 36162556
DOI: 10.1016/j.envpol.2022.120228

Abstract

PM_2.5 (particulate matter having aerodynamic diameter ≤2.5 μm) samples were collected during wintertime from two polluted urban sites (Allahabad and Kanpur) in the central Indo-Gangetic Plain (IGP) to comprehend the sources and atmospheric transformations of light-absorbing water-soluble organic aerosol (WSOA). The aqueous extract of each filter was atomized and analyzed in a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Water-soluble organic carbon (WSOC) and WSOA concentrations at Kanpur were ∼1.2 and ∼1.5 times higher than that at Allahabad. The fractions of WSOC and secondary organic carbon (SOC) to total organic carbon (OC) were also significantly higher ∼53% and 38%, respectively at Kanpur compared to Allahabad. This indicates a higher abundance of oxidized WSOA at Kanpur. The absorption coefficient (b_abs-365) of light-absorbing WSOA measured at 365 nm was 46.5 ± 15.5 Mm^-1 and 73.2 ± 21.6 Mm^-1 in Allahabad and Kanpur, respectively, indicating the dominance of more light-absorbing fractions in WSOC at Kanpur. The absorption properties such as mass absorption efficiency (MAE₃₆₅) and imaginary component of refractive index (k_abs-365) at 365 nm at Kanpur were also comparatively higher than Allahabad. The absorption forcing efficiency (Abs SFE; indicates warming effect) of WSOA at Kanpur was ∼1.4 times higher than Allahabad. Enhancement in light absorption capacity was observed with the increase in f44/f43 (fraction of m/z 44 (f44) to 43 (f43) in organic mass spectra) and O/C (oxygen to carbon) ratio of WSOA at Kanpur while no such trend was observed for the Allahabad site. Moreover, the correlation between carbon fractions and light absorption properties suggested the influence of low-volatile organic compounds (OC3 + OC4 fraction obtained from thermal/optical carbon analyzer) in increasing the light absorption capacity of WSOA in Kanpur.

Keywords: Aqueous oxidation; Indo-Gangetic plain; Light absorption capacity; Oxidized organic aerosol; Water-soluble organic aerosol.

MeSH terms

Aerosols / analysis
Air Pollutants* / analysis
Carbon / analysis
Environmental Monitoring
Oxygen
Particulate Matter / analysis
Volatile Organic Compounds*
Water

Substances

Air Pollutants
Water
Volatile Organic Compounds
Aerosols
Particulate Matter
Carbon
Oxygen