AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Particle Water and pH in the Southeastern US
HONGYU GUO, Lu Xu, Kate Cerully, Aikaterini Bougiatioti, Shannon Capps, Annmarie Carlton, Shanhu Lee, Nga Lee Ng, Michael Bergin, Athanasios Nenes, Rodney Weber, Georgia Institute of Technology
Abstract Number: 469 Working Group: Air Quality and Climate in the Southeast US: Insights from Recent Measurement Campaigns
Abstract Particle pH is an important aerosol property that is difficult to directly measure and so often determined from thermodynamic calculations. pH can influence the solubility of metals, partitioning of acidic species, and the formation of secondary organic aerosols. An accurate measurement or prediction of particle water is needed to determine pH. As part of the Southern Oxidant and Aerosol Study (SOAS), Georgia Tech made detailed measurements at Centreville of particle organic and inorganic composition, aerosol hygroscopicity, and indirect measurements of particle liquid water content using nephelometers. Fine particle water was predicted by the sum of water associated with ions and organic species, the former water predicted by ISORROPIA using PILS-measured ions (ionic-water) and the latter water predicted from κorg (organic-water) determined from cloud condensation nuclei (CCN) activity. Predicted liquid water was in good agreement with measured liquid water determined from a measure of f(RH); ambient (RH and T) PM2.5 light scattering coefficient(σsp) and dry σsp. The sum up of ionic-water and organic-water agreed well with the measured water (regression slope of 0.96, intercept of 0.7µg/m3, R=0.86). Organic-water is found to be significant, accounting for 37% of total water based on a study average. At night organics accounted for 63% of total water. Using total predicted water, the study average fine particle pH was predicted at 0.98±0.61, and pH diurnal trends followed liquid water, with nighttime pH near 2 and during day near 0. ISORROPIA predictions were verified by agreement between predicted and measured ammonia. pH of the fine aerosol throughout the southeastern US was assessed based on measurements of inorganic compounds at various sites and during various seasons as part of the Southeastern Center for Aerosol Pollution and Epidemiology (SCAPE). pH generally ranged between 0 and 2. Winter pH was higher than summer, although water content was lower in winter.