Water soluble organic aerosols in indo gangetic plain (IGP): Insights from aerosol mass spectrometry

Abhishek Chakraborty; Pradhi Rajeev; Prashant Rajput; Tarun Gupta

doi:10.1016/j.scitotenv.2017.05.142

Water soluble organic aerosols in indo gangetic plain (IGP): Insights from aerosol mass spectrometry

Sci Total Environ. 2017 Dec 1:599-600:1573-1582. doi: 10.1016/j.scitotenv.2017.05.142. Epub 2017 May 19.

Authors

Abhishek Chakraborty¹, Pradhi Rajeev¹, Prashant Rajput¹, Tarun Gupta²

Affiliations

¹ Department of Civil Engineering, Indian Institute of Technology Kanpur, India.
² Department of Civil Engineering, Indian Institute of Technology Kanpur, India; Centre for Environmental Science and Engineering, Indian Institute of Technology Kanpur, India. Electronic address: tarun@iitk.ac.in.

PMID: 28535589
DOI: 10.1016/j.scitotenv.2017.05.142

Abstract

Filter samples collected during winter of 2015-16 from two polluted urban locations (Allahabad and Kanpur) residing within Indo-Gangetic plain (IGP) showed high levels of water-soluble organic aerosols (WSOA). Total organic aerosols (OA) in submicron fraction, measured at Kanpur in real time via Aerosol Mass Spectrometer also showed substantially high concentration levels. WSOA to OA contribution in Kanpur was found to be very high (around 55%) indicating significant contributions from secondary OA (SOA). On average, WSOA oxidation ratio (O/C) was found to be higher (15-20%) in Kanpur than at Allahabad. WSOA from Allahabad was found to be following a much shallower slope (-0.38) in Van Krevelen diagram (H/C vs O/C plot) than Kanpur (-0.58). These differences suggest different composition and chemistry of WSOA at these two different locations. O/C ratios of WSOA were found to be much higher (~40%) than that of OA and independent of WSOA loading. Higher OA loadings were found to be associated with less oxidized primary OAs (POA) and culminated into lower WSOA/OA ratios. The presence of organo sulfate in filter samples from both locations indicate a significant amount of aqueous processing of organics. Concentrations and characteristics of water insoluble OA (WIOA) in Kanpur revealed that although they are present in significant quantity, their oxidation levels are much (almost 3 times) lower than that of WSOA. This finding indicates that less oxidized OAs are less soluble in line with the conventional wisdom. This study provides the first insight into oxidation levels and evolution of WSOA from India and also explores the interplay between WSOA and OA characteristics based on AMS measurements.

Keywords: AMS; Interplay; Oxidation; Water soluble organic carbon.