Complex interplay between organic and secondary inorganic aerosols with ambient relative humidity implicates the aerosol liquid water content over India during wintertime

Abstract

Aerosol Liquid Water Content (ALWC), a ubiquitous component of atmospheric aerosols, contributes to total aerosol mass burden, modulating atmospheric chemistry through aerosol surface reactions and reducing atmospheric visibility. However, the complex dependency of ALWC on aerosol chemistry and relative humidity (RH) in the Indian region remains poorly characterized. Here, we combine available measurements of aerosol chemical composition with thermodynamic model ISORROPIA2.1 to reveal a comprehensive picture of ALWC in fine mode aerosols during the winter season in the Indian region. The fac-tors modulating ALWC are primarily dependent on the RH, such that the effect of aerosol dry mass and hygroscopicity are significant at high RH while the effect of hygroscopicity loses its significance as RH is lowered. ALWC, depending upon the particle hygroscopicity, displays a sharp non-linear rise beyond a critical value of ambient RH. Further analysis coupling WRF-Chem simulation with ISORROPIA2.1 revealed significant spatial heterogeneity in ALWC over India, strongly associating with regions of high aerosol loading and RH. The Indo-Gangetic Plain is consequently observed to be a hotspot of higher ALWC, which explains the prevalent conditions of haze and smog during winter in the region. Our findings re-emphasize that high aerosol mass resulting from intense pollution is vital in modulating aerosol-climate interaction under favorable meteorological conditions. They suggest the need for pollution control strategies to be directed at the reduction in emissions of specific species like NH3 and NOx, which were observed to contribute to the enhancement of PM and ALWC during wintertime in the region.

Complex Interplay Between Organic and Secondary Inorganic Aerosols With Ambient Relative Humidity Implicates the Aerosol Liquid Water Content Over India During Wintertime

“…The data used in the manuscript has been deposited in an open research depository, accessible at https://doi.org/10.6084/m9.figshare.19703182.v4 (Gopinath et al., 2022). The aerosol chemical composition data (named “Input_data.dat” in the depository) used for Aerosol Liquid Water Content (ALWC) calculations in this manuscript were obtained from various literature, and are also summarised in Table S1 in Supporting Information (references enclosed therein).…”