Organic Acids in Cloud Water, Aerosols and Cloud Droplet Residuals at the Summit of Whiteface Mountain

Organic compounds in the atmosphere play a significant role in atmospheric chemistry, and clouds can play an important role in the formation and transformation of organic compounds. Di-carboxylic organic anions like oxalate are considered a tracer of aqueous processing. In this talk, we report summertime measurements of 3 major organic acids (formic acid, acetic acid, oxalic acid), along with inorganic anions (sulfate, chloride, nitrate) in cloud water and aerosol samples collected at the summit of Whiteface Mountain (WFM) in the Adirondack Mountains in northern New York State in 2021-2023. We also assess the contribution of these organic acids to the measured water-soluble organic carbon (WSOC) concentrations. Previous studies have evaluated the relationship between oxalate:WSOC ratio and ozone concentrations, to infer the contribution of biogenic Volatile Organic Compounds (VOCs) to Secondary Organic Aerosol (SOA) formation from the surrounding forest ecosystem. In this talk, we show observations that substantially expand upon the relationship between oxalate:WSOC ratio and ozone concentrations, allowing us to compare very different environments across the globe, and compare the cloud water and aerosol phases. We also report oxalate:sulfate ratios for our dataset, which other researchers have proposed as an important aqueous processing indicator because the ions’ production rates are enhanced by either liquid water content (sulfate ion) or droplet surface area (oxalate ion). The range of oxalate:sulfate ratios observed in our dataset are compared to field campaigns in other regions, and the impact of wildfire smoke is discussed.