AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Spatial Differences in Summertime Enhancement of Aerosol Optical Thickness: Organic Carbon Fractionation and Particle Size
AMY CHRISTIANSEN, Annmarie Carlton, University of California, Irvine
Abstract Number: 150 Working Group: Aerosol Chemistry
Abstract Summertime aerosol optical thickness (AOT) over the United States is strongly enhanced in the Southeast, and not elsewhere. Proposed explanations for this phenomenon in the literature include seasonal patterns in aerosol liquid water (ALW), height of the planetary boundary layer, and formation of biogenic secondary organic aerosol (SOA). Although geospatial patterns and seasonality in total particle organic mass measurements at the surface are inconsistent with satellite AOT, aloft formation of biogenic SOA and seasonal differences in particle organic chemical speciation remain plausible explanations. Here we explore: 1.) seasonal differences in organic mass speciation, specifically organic carbon (OC) fractions OC1, OC2, OC3, and OC4 as defined and reported at Interagency Monitoring of PROtected Visual Environments (IMPROVE) monitoring locations across the continental US, and 2.) seasonal estimates of particle size that include ALW. This is done in the context of spatial and temporal differences in Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO)-measured AOT. In the area of strongest CALIPSO AOT summertime enhancement, OC2 and OC3 fractions show summer/winter differences of several percent by mass concentration. This is contrasted to OC1 and OC4 fractions, in which there is little seasonal difference in mass concentration. Additionally, there is seasonality in particle size and, through Mie scattering calculations, we explore the potential to explain the seasonality in satellite AOT measurements. The chemical composition for individual species or functional groups responsible for differences in OC categories is a topic for future study.