Seasonal Assessment of Secondary Organic Aerosol Formed through Aqueous Pathways in the Eastern United States

Ahsan Ali, Christopher Hennigan, Havala Pye, Benjamin Murphy, Prashant Shekhar, MARWA EL-SAYED, Embry-Riddle Aeronautical University

     Abstract Number: 168
     Working Group: Aerosol Chemistry

Abstract
The uptake of water-soluble organic gases (WSOC_g) formed from the oxidation of VOCs into atmospheric aerosol liquid water is an important pathway for the formation of aqueous secondary organic aerosol (aqSOA). Despite its significance, numerous uncertainties persist in our understanding of aqSOA formation, including the contribution of aqSOA mass to total SOA across seasons and the relative split between reversible and irreversible aqSOA mass. In this study, we use seasonal WSOC measurements in the particle and gaseous phases (i.e., WSOC_p and WSOC_g, respectively) in Baltimore, Maryland to quantify the total aqSOA as well as the reversible and irreversible aqSOA across seasons. Total aqSOA mass is determined using a polynomial differentiation method based on the increase in the partitioning coefficient, [F_p= WSOC_p/(WSOC_g+WSOC_p)], as a function of relative humidity (RH). Reversible aqSOA concentrations are calculated based on the difference between the ambient and dried WSOC_p measurements. On the other hand, the irreversible aqSOA is estimated based on the dry partitioning coefficient, [F_p’= WSOC_p,dry/(WSOC_g+WSOC_p,dry)], and RH. Further, comparisons between the seasonally measured aqSOA concentrations and their counterpart Community Multiscale Air Quality Modeling System (CMAQ) modeled mass are conducted. In addition to improving our understanding of aerosol multiphase formation, this work holds several implications for atmospheric chemistry and modeling aiming to bridge the current gap between model predictions and field measurements.