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Effect of Aerosol Humidification on the Column Aerosol Optical Thickness over the ARM Southern Great Plains Site

Li, Zhanqing University of Maryland
Jeong, Myeong-Jae University of Maryland

Category: Aerosols

This study investigates the aerosol humidification effect (AHE) using seventy profiles of the aerosol scattering and absorption coefficients at high (~85%) and low (~40%) relative humidity (RH) levels obtained over the Southern Great Plains (SGP) site from April 2003 through June 2004. The column aerosol humidification factor (AHF) defined as the ratio of the aerosol optical thickness (AOT) at the ambient (or desired) RH to that at RH=40% throughout the column rarely exceeded 1.3 (mean, 1.09±0.12) over the US South Great Plains (SGP) site. However, for an atmospheric column of a constant RH=85%, the AHF is greater than 1.5 for the majority of cases (mean, 1.57±0.28). The function of column AHF on RH was fitted based on this unique aerosol dataset. Several methods were proposed to estimate the column AHF for use when direct measurements of the AHF are not available. It was found that the relationship between the column AHF and aerosol extinction coefficient weighted column mean RH works best. Performance of other methods depends on measurements available. Sensitivity of the column AHF to a very humid (RH=99%) layer with varying depths (0.1~0.3km) is examined.

This poster will be displayed at the ARM Science Team Meeting.