Investigating the Significance of Water Associated With Organic Matter Towards Atmospheric Aerosol Liquid Water Content in Florida

MEGAN NEUMANN, Marwa El-Sayed, Shannon Capps, Embry-Riddle Aeronautical University

     Abstract Number: 709
     Working Group: Aerosol Chemistry

Abstract
Aerosol liquid water content (ALWC) is ubiquitous in the atmosphere and is influenced by relative humidity, as well as inorganic and organic aerosol concentrations and their composition. However, the contribution of organic versus inorganic aerosol towards ALWC is highly uncertain at present. While some studies report the negligible contribution of organic aerosol to the concentration of ALWC, others provide evidence for a contribution of organic aerosol similar to that of inorganic aerosol. Hence, the aim of this study is to determine the contribution of organic aerosol to the concentrations of ALWC under contrasting environmental conditions in Florida across different seasons. Organic and speciated inorganic concentrations of fine particulate matter (PM2.5) were provided by the Florida Department of Environmental Protection, and assessed through the U.S. Environmental Protection Agency Air Quality Database, at three sites during 2017-2022. Gaseous concentrations of ammonia and nitric acid were acquired from the EPA’s CASTNET network during the same period. Water associated with inorganic aerosol (Winorg) was calculated using the hyperdual version of ISORROPIAv2.1 aerosol thermodynamic equilibrium model. Concentrations of aerosol inorganic composition (Na+, NH4+, K+, SO42-, Mg2+, Ca2+, NO3- and Cl-), temperature, and RH as well as nitric acid and ammonia gaseous concentrations were input to calculate partitioned inorganic concentrations and ALWC as well as sensitivities of each of these concentrations to the sum of the aerosol and gaseous concentrations. The liquid water associated with organics (Worg) was calculated based on organic concentrations, meteorological data, and hygroscopicity assumptions based on the kappa-Kohler theory. The total ALWC was thus calculated as the sum of the liquid water associated with inorganic and organic aerosol constituents. These analyses will provide insight into the significance of organic matter towards ALWC in the atmosphere with implications for the accurate representation of ALWC in models.

Keywords: Aerosol Liquid Water Content, ISORROPIA 2, organic aerosol, inorganic aerosol, air quality monitoring.