AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Aerosol Optical Properties Derived from In Situ Measurements at the DOE ARM Site in Oklahoma
MANASI MAHISH, Don Collins, Texas A&M University
Abstract Number: 608 Working Group: Aerosols, Clouds, and Climate
Abstract Aerosol size and hygroscopic growth factor distributions measured at the rural ARM Southern Great Plains site in Oklahoma were used to estimate ground-level submicron aerosol extinction coefficient (bext), scattering coefficient (bscat), hemispheric backscattering coefficient (bback), and upscatter coefficient (bup) at visible wavelengths. Those optical properties were subsequently used to calculate backscatter fraction (bback/bscat ), upscatter fraction (bup/bscat ) and f(RH) (bscat @ 90% RH/bscat @ 24% RH). The accuracy of the estimated bscat and bback was evaluated through comparison with direct nephelometer measurements. Upscatter fraction (β), a key parameter in assessment of radiative forcing, was determined for 30 selected days on which the boundary layer was deep and well mixed. The hygroscopicity of the aerosol measured at the surface was coupled with estimated height-dependent relative humidity to extend the calculation of β through the boundary layer. The estimated optical properties were also parameterized as functions of RH, scalar quantities derived from the particle size growth factor distributions, and, for β, solar elevation. The average normalized errors between estimated and measured bscat and bback were 16% and 20%, respectively. The calculated β approached a maximum of 0.5 at sunset and at other times was dependent on RH and, within the cases considered, varied seasonally. Parameterizations of the four optical properties, i.e., bext, bscat, bback and β, are promising, with comparison to the original resulting in an r2 above 0.94.