Changing aerosol chemical and microphysical properties due to drought: analysis of the SGP aerosol data

Description

Drought is a recurring extreme of the climate system. The strong perturbation of drought to the land biosphere and atmospheric water cycle will influence chemical and microphysical properties of atmospheric aerosols, the nature and extent of which are not well understood. Our previous work (Wang et al., 2017) has reported observational evidence that aerosol mass concentration at the surface is significantly correlated with drought severity: severe droughts in the US during the period of 1990-2014 were found associated with growth-season (Mar-Oct) mean enhancements in surface PM2.5 of 1.6 μg m-3 (17%). We hypothesize that such a large perturbation of drought to aerosol mass will manifest significant changes in aerosol microphysical properties (size, hygroscopicity, CCN concentration etc.) which will lead to feedbacks to cloud properties (i.e. aerosol indirect effect). To test the hypothesis, we present an integrated analysis of aerosol and cloud property changes over recurring drought-to-wet cycles at the ARM Southern Great Plains (SGP) site. We show that a recent severe drought (summer 2011) at the SGP site leads to a large increase of particle number in the <100 nm size range and a large decrease in the range of 200 nm to 1 μm. These changes suggest a strong signal of drought perturbation to aqueous processing of aerosols. We argue that analysis of the aerosol response to drought can provide quantitative constraints to evaluate and improve our current understanding of aerosol-water cycle interaction in models. References: Wang, Y., Y. Xie, W. Dong, Y. Ming, J. Wang, L. Shen, Adverse Effects of increasing drought on air quality via natural processes, Atmos. Chem. Phys., 17, 12827–12843, doi:10.5194/acp-2017-234, 2017