AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Aerosol Optical Properties Retrieved Using Actinic Flux and Irradiance during DISCOVER-AQ Texas: In-situ Comparisons and Photochemical Impacts
CHELSEA CORR, Jungbin Mok, Nickolay Krotkov, Barry Lefer, Bruce Anderson, John Barrick, Andreas Beyersdorf, Gao Chen, Richard Moore, Michael Shook, Kenneth Thornhill, Edward Winstead, Luke Ziemba, Sasha Madronich, James Crawford, Jack Dibb, ORAU
Abstract Number: 266 Working Group: Urban Aerosols
Abstract Single scattering albedo (SSA) was retrieved using actinic flux (AF SSA) measured with a scanning actinic flux spectrometer (SAFS) and the direct-to-diffuse irradiance ratio (DDR SSA) measured with multifilter shadowband radiometers (MFRSRs). Measurements were made atop the Moody Tower (MT) in Houston, TX during NASA DISCOVER-AQ (Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality) mission in September 2013. Retrievals were performed at four wavelengths (332, 368, 415, and 500 nm) shared by the instruments for three days that met cloudscreening and aerosol optical depth (AOD) criteria: 09/03/13, 09/25/13, and 09/26/13. AF SSAs were consistently lower than DDR SSAs with largest differences when AOD was less than 0.2. However, DDR SSAs were within 0.05 of values retrieved using MT MFRSR irradiance and an independent inversion technique. DDR SSAs also agreed within the uncertainty of SSAs reported by the AErosol RObotic NETwork (AERONET) at 441 nm as well as with column-average values at 450 and 550 nm calculated from aerosol scattering and absorption coefficients measured aboard the NASA P3-B aircraft. Though AF SSAs were lower than both AERONET and column-averaged values, absorption Angstrom exponent (AAE) values calculated from AF SSAs were within 0.4 of AERONET and column-averaged AAEs for all retrieval days suggesting actinic flux retrievals can correctly resolve the spectral dependence of aerosol absorption. These measured and retrieved optical properties were used to assess the impact of aerosols on photochemistry during DISCOVER-AQ TX. Specifically, photolysis rates modeled using a radiative transfer code for an aerosol-free case and using measured and retrieved optical properties were compared to photolysis rates measured at MT and aboard the P3-B. Deviations of measured photolysis rates from either modeled profile type were quantified; relationships between both the magnitude and direction of these deviations and aerosol composition and size are discussed.