AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Investigating Brown Carbon Formation in Ambient Aerosols Undergoing Drying
VIKRAM PRATAP, Michael Battaglia Jr., Annmarie Carlton, Christopher Hennigan, University of Maryland, Baltimore County
Abstract Number: 204 Working Group: Aerosol Chemistry
Abstract A number of recent laboratory studies observed the formation of brown carbon (BrC) in aerosols undergoing drying. Since ambient particles undergo natural cycles of drying and water uptake each day, this process may contribute substantially to the atmospheric BrC budget. However, BrC formation in ambient particles undergoing drying has not been observed. In this work, we investigated drying-induced BrC formation in ambient particles sampled at Baltimore, MD. Our study included observations during both summer and winter: results from these periods are contrasted. During summer, we find no evidence of BrC formation in particles dried to ~ 40% relative humidity (RH). Diurnal variation suggests particulate water-soluble organic carbon (WSOCp) and BrC concentrations were strongly influenced by SOA formed during the daytime. The observations are consistent across several weeks of measurements, which included a wide range of temperatures, RH levels, and aerosol loadings. Results from the wintertime data also suggest no BrC formation occurred during particle drying. The low concentration of BrC precursor compounds in ambient particles likely explains the lack of measurable BrC formation in a single drying cycle induced by our experimental setup. This process may still represent an important source of light-absorbing organic aerosols if multiple humidification-drying cycles contribute minor amounts of BrC leading to gradual buildup, or in evaporating clouds and fog, a regime our study did not investigate.