Complex Interplay Between Organic and Secondary Inorganic Aerosols With Ambient Relative Humidity Implicates the Aerosol Liquid Water Content Over India During Wintertime. Issue 13 (29th June 2022)

• Record Type: Journal Article
• Authors: Gopinath, Amar Krishna; Raj, Subha S.; Kommula, Snehitha M.; Jose, Christi; Panda, Upasana; Bishambu, Yukti; Ojha, Narendra; Ravikrishna, R.; Liu, Pengfei; Gunthe, Sachin S.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 13(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-06-29
• Subjects: Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2021JD036430
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: Aerosol Liquid Water Content (ALWC), a ubiquitous component of atmospheric aerosols, modulates atmospheric chemistry through aerosol surface reactions and reduces the 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 over the Indian continental region. The factors 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 significantly reduces with decreasing RH. ALWC is observed to display a sharp non‐linear rise, beyond a critical value of ambient RH dependent on the particle hygroscopicity. Further analysis by coupling Weather Research Forecasting‐Chem simulation with ISORROPIA2.1 revealed significant spatial heterogeneity in ALWC over India, strongly associating with regions of high aerosol mass 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 this region. Our findings re‐emphasize that high aerosol mass resulting from intense pollution is vital in modulating aerosol–climate interaction under favorable meteorological conditions. Observations suggest the need for localized pollution control strategies, directed at the reduction in aerosol emissions of specific chemical composition observed to contribute to the enhancement in PM through an increase in ALWC during wintertime in the region. Plain Language Summary: Water vapor condenses on particulates in the air (known as atmospheric aerosols) due to the presence of chemical species with high water affinity. The condensed water, referred to as Aerosol Liquid Water Content (ALWC), is primarily responsible for weather conditions of low visibility like haze and smog, which have impacts on human health, and economy. This study has calculated ALWC using existing measurement data of the chemical composition of fine sized aerosols from literature, for contrasting and diverse environments in India. The study has focused on the winter season marked by spike in pollution levels and haze. Relative humidity, total particle concentration, and chemical composition were identified to play a significant role in influencing ALWC. The Indo‐Gangetic Plain has been identified to be a hotspot of high ALWC due to high pollution levels and relative humidity, particularly during winter season. The study emphasizes on the extensive study of local aerosol chemistry for targeted reduction of the emission of specific chemical species, which would enable the improvement of air pollution and visibility reduction in the region. Key Points: Aerosol Liquid Water Content (ALWC) is ubiquitous in atmospheric aerosols in the Indian region during winter ALWC is enhanced drastically at high aerosol loading with high relative humidity NH3 and NOx emissions are observed to be the drivers of extreme ALWC in the Indo‐Gangetic Plain