Exploring the Impact of Wildfire Smoke on Cloud-Aerosol Chemistry at Whiteface Mountain, NY: Organic Acids and Growing Importance of Ammonium

ARCHANA TRIPATHY, Christopher Lawrence, Sara Lombardo, Paul Casson, Rudra Patel, Lily Hammond, Kathleen DeMarle, Richard Brandt, Scott McKim, James Schlemmer, James Schwab, Haider Khwaja, Mirza M. Hussain, Elizabeth Yerger, Phil Snyder, Dan Kelting, William May, Sara Lance, Atmospheric Sciences Research Center, University at Albany

     Abstract Number: 469
     Working Group: Carbonaceous Aerosols

Abstract
Organic compounds are vital to atmospheric chemistry, with clouds playing a key role in their formation and transformation. Di-carboxylic organic anions, such as oxalate, act as tracers for aqueous-phase chemical processes. This study presents summer measurements of three organic acids (formic, acetic, oxalic), inorganic anions, and cations in cloud water, aerosol, and cloud droplet residual samples obtained 2018-2024 from the summit of Whiteface Mountain (WFM), a forested site in the Adirondack Mountains of northern New York State. Contributions of these acids to dissolved organic carbon (DOC), ion balance, and acidity are assessed in both cloud and aerosol samples. The current study builds on prior studies linking oxalate-to-DOC ratios with ozone concentrations, from which inferences have been made about biogenic volatile organic carbon (BVOC) contributions to secondary organic aerosol (SOA) formation, and we present new insights based on comparisons between cloud water and aerosol phases. We further expand upon the findings of Lawrence et al. (2023), which showed that more than half of the cloud water samples at WFM exhibit excess ammonium (i.e. exceeding sulfate plus nitrate concentrations) in recent years, by evaluating the relationship between excess ammonium and organic acids in both the cloud and aerosol phases particularly under conditions influenced by wildfire smoke with elevated black carbon (BC) levels. Additionally, we investigate the temperature and ozone relationship, particularly on clear air days, to assess potential interactions between BC and ozone in less polluted conditions vs smoky conditions. These findings provide new insights into multi-phase chemistry and SOA formation processes at a remote forested site downwind of many natural and anthropogenic sources and frequently influenced by wildfire smoke in summer.