Characterization of Air and Cloud Water Impacted By Wildfire Emissions during WE-CAN 2018

Clouds play an important role in processing trace gases and atmospheric aerosols due to the abundant water medium for atmospheric aqueous-phase chemical reactions and the possibility of incorporating and depositing scavenged material via precipitation. Relevant reactions include oxidation of volatile compounds to lower volatility compounds, thus contributing to secondary organic aerosol (SOA) production and impacting properties of aerosol released by evaporating clouds. However, direct sampling and measurements of the chemical composition of cloud water impacted by wildfire plumes are scarce. In order to improve understanding of the interaction between wildfire smoke and clouds, cloud water and whole air canister samples were collected aboard the NSF/NCAR C-130 research aircraft during the WE-CAN (Western wildfire Experiment for cloud chemistry, Aerosol absorption and Nitrogen) Study in July and August 2018. Cloud water samples were collected using the CSU/NCAR airborne cloud water collector and analyzed for major inorganic ions, total organic carbon, carboxylic and dicarboxylic acids, levogluocsan and other anhydrosugars, formaldehyde and hydrogen peroxide. Whole air canister samples, meanwhile, were collected using the NCAR Advanced Whole Air Sampler (AWAS). Volatile Organic Compounds (VOCs) were analyzed from these samples using an off-line gas chromatography system.

This presentation will summarize early findings from the cloud water and VOC measurements. Sampled clouds will be characterized in terms of their liquid water content and composition. Particular attention will focus on differences between the composition of clouds influenced more or less strongly by wildfire emissions, including any differences in acidity, concentrations of reactive nitrogen species, and the abundance and composition of organic matter. Measurements of carboxylic and dicarboxylic acids will be examined to provide insight into possible SOA production during cloud aging of fire emissions. Complementary VOC composition measurements will provide insight into the extent of wildfire influence on the cloud-forming air mass and on prior atmospheric aging of fire emissions.