Abstract View
Differences in Fine Particle Chemical Composition, Hygroscopicity, and Aerosol Liquid Water on Clear and Cloudy Days
AMY CHRISTIANSEN, Annmarie Carlton, Barron Henderson, University of California, Irvine
Abstract Number: 101
Working Group: Aerosols, Clouds and Climate
Abstract
Clouds are abundant and alter fine particulate matter (PM2.5) mass and chemical composition, yet they are sampled infrequently for chemical composition. This leads to a persistent, yet implicit clear sky bias in the characterization of tropospheric composition. For example, satellite retrievals of aerosol properties impacted by clouds are often screened from final data products to avoid measurement artifacts, hindering quantitative estimates of tropospheric chemical composition during cloudy times. Although previous studies have focused on quantitative differences in PM2.5 mass between cloudy and clear sky times, little attention has been given to differences in PM2.5 chemical composition, especially regarding particle hygroscopicity and water uptake. Aerosol mass concentrations and chemical speciation including aerosol liquid water (ALW) influence aerosol radiative properties, cloud microphysics, and mesoscale convective systems. A quantitative understanding of aerosol-cloud interactions, currently a critical uncertainty in atmospheric models, is necessary to improve model representation of aerosol impacts. Here, we investigate differences in surface particle chemical components, particle hygroscopicity, and associated ALW between cloudy and clear sky time periods in the context of satellite cloud flags. We examine surface data from the Interagency Monitoring of PROtected Visual Environments (IMPROVE) network across the contiguous US (CONUS) during cloudy and clear sky times using satellite cloud flag data from the Moderate Resolution Imaging Spectroradiometer (MODIS). We estimate ALW concentrations from inorganic and organic components using the thermodynamic model ISORROPIA and κ-Kohler theory. We find that ALW concentrations and hygroscopic growth factors are on average 31% and 14% larger during cloudy times, when satellites are unable to remotely sense particle properties and impacts. Further, particle chemical composition is significantly altered between cloudy and clear sky times across the CONUS. This suggests that the clear sky bias may hinder accurate model representation of particle chemical constituents, especially ALW, and associated impacts.