Derivation of aerosol hygroscopicity at SGP from size and composition measurements

 

Authors

Hagen Telg — Cooperative Institute for Research in Environmental Sciences
Elisabeth Andrews — University of Colorado
Graham Feingold — NOAA- Earth System Research Laboratory
Allison C. McComiskey — Brookhaven National Laboratory
Don R. Collins — University of California, Riverside
Thomas B. Watson — Brookhaven National Laboratory

Category

Microphysics (cloud, aerosol and/or precipitation)

Description

Aerosol hygroscopicity--water uptake dictated by particle composition and size--has considerable control on light extinction and aerosol radiative effects. Accurate models of hygroscopicity are required for improving treatment of aerosol processing in climate models and for relating detailed aerosol in situ measurements (often made in ‘dry’ conditions) to column remote sensing, which is frequently used to evaluate models, and always performed at ambient relative humidity. Measurements of aerosol humidification can be approached in various ways: as a scattering enhancement factor (fRH) or a particle growth factor (gRH). The ARM Aerosol Observing Systems has made both measurements. With the recent addition of continuous, high-temporal-resolution composition measurements, fRH can also be derived from these data in combination with a size distribution. For aerosol radiative effect applications, we are ultimately interested in the scattering enhancement: thus we use these measurements to derive fRH from three separate approaches and evaluate them all for consistency. An important aspect of this evaluation is to understand the sensitivity of our results to various aerosol, environmental, and instrumental parameters. These sensitivities are presented in the context of model parameterization improvement and especially in the context of relating in situ measurements at varying humidity to remote-sensing measurements at ambient humidity.