A41K-0216
Particle pH Inferred from Aircraft Data: Validation and Geographical, Vertical and Seasonal Characteristics with Case Studies from the WINTER Campaign
Thursday, 17 December 2015
Poster Hall (Moscone South)
Hongyu Guo, Georgia Institute of Technology Main Campus, Earth and Atmospheric Sciences, Atlanta, GA, United States, Rodney J Weber, Georgia Institute of Technology Main Campus, Atlanta, GA, United States, Athanasios Nenes, Georgia Institute of Technology, Atlanta, GA, United States, Amy Sullivan, Colorado State University, Fort Collins, CO, United States, Joel A Thornton, Univ Washington - Seattle, Seattle, WA, United States, Felipe Lopez-Hilfiker, University of Washington Seattle Campus, Seattle, WA, United States, Jose-Luis Jimenez, Harvard University, Cambridge, MA, United States, Pedro Campuzano Jost, University of Colorado Boulder, Boulder, CO, United States, Jason Clay Schroder, Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States and Jack E Dibb, University of New Hampshire Main Campus, Durham, NH, United States
Abstract:
Particle pH is a critical but poorly understood factor that affects many aerosol processes and properties, including aerosol composition, concentrations, geochemical cycles, and aerosol toxicity. Here we assess the prediction of pH from aircraft data, report pH as a function of geographical location and altitude for different seasons, and investigate causes for variability in pH-dependent aerosol components, such as nitrate. pH is generally predicted with a thermodynamic model since it is difficult to measure directly. We used ISORROPIA-II with particle and selected gas inorganic species, along with RH and T as inputs to calculate aerosol pH. Data are from three aircraft studies: WINTER (2015 Feb-Mar) and NEAQS (2004 July-Aug), both over the northeastern US, and SENEX (2013 Jun-July) over the southeastern US. pH was validated by comparing measured and predicted partitioning of ammonia and nitric acid. The effect of inevitable sample heating associated with aircraft measurements was minimal since partitioning of measured semi-volatile components based on ambient T and RH were accurately predicted. Overall, pH determined from WINTER, NEAQS, and SENEX for altitudes up to 5000 m ranged between -0.4 and 1.9 (10-90% percentiles, mean±SD=0.9±1.0), similar to what we have observed at ground-based sites in the southeastern US. Coupling between water vapor concentrations, temperature, particle composition, liquid water content and particle pH on partitioning of nitric acid-nitrate observed during the WINTER campaign will be investigated.
