AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Trends in PM2.5 Strong Acidity Across Canada between 1990 and 2010
JENNIFER MURPHY, Alex Tevlin, University of Toronto
Abstract Number: 545 Working Group: Aerosol Chemistry
Abstract Particle acidity plays a role in the gas-particle partitioning of ionisable constituents, and may influence SOA production and particle health impacts. There is no robust technique to directly measure the acidity or pH of ambient particles. In this analysis, we calculate strong acidity based on the difference in equivalents (eq m$^(-3)) between the dominant anions and cations (2*SO$_4$^(2-) + NO$_3$^(-) + Cl$^(-) - NH$_4$^+ + Na$^+) measured in 24-h integrated PM$_2.5 samples collected daily between 1990 and 2010. At the majority of sites, especially those in central Ontario and Quebec, we find significant decreases in the inferred strong acidity over the time period. Significant seasonal and geographic differences in strong acidity trends exist among the sites. By combining inferred strong acidities with liquid water content calculated by the Extended Aerosol Inorganics Model (E-AIM), we can estimate particle pH for deliquesced particles. However, as acidity values decrease, the propagated uncertainties in the measurement of each analyte lead to strong acidities that are less frequently statistically distinguishable from zero.