10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
N2O5 Reactive Uptake and Chlorine Activation during Nocturnal Processing of Authentic Biomass Burning Aerosol
LYDIA JAHL, Lexie Goldberger, Joel A. Thornton, Ryan Sullivan, Carnegie Mellon University
Abstract Number: 944 Working Group: Aerosol Chemistry
Abstract Nitryl chloride (ClNO2) is a nighttime reservoir of NOx that is formed from the uptake of dinitrogen pentoxide (N2O5) into particles containing chloride. ClNO2 was thought to be formed only in the presence of chloride from sea spray aerosol, but its recent detection in areas far from the ocean has raised the possibility that other unrecognized particulate chloride sources make important contributions to chlorine activation chemistry. ClNO2 is photolyzed each morning to produce the chlorine radical and recycle NOx, thereby increasing the atmospheric oxidant budget. We recently demonstrated the production of ClNO2 from heterogeneous reactions with N2O5(g) under realistic conditions in a smog chamber reactor at Carnegie Mellon University. Iodide adduct chemical ionization mass spectrometry was used to measure gas phase ClNO2 and N2O5, while a soot particle aerosol mass spectrometer measured changes in aerosol composition. Upon the addition of ozone to biomass burning smoke, N2O5 was consistently formed and ClNO2 was subsequently detected in the gas phase. During experiments at high relative humidity, we observed decreases in particulate chloride and increases in particulate nitrate which we believe are due to acid displacement of HCl(g) by HNO3 since no additional ClNO2 was produced in the gas phase. The reactive uptake probability of N2O5 on authentic biomass burning aerosol and the yield of ClNO2 were determined for the first time using flow tube experiments on smoke from biomass fuels including wiregrass, black needlerush, saw palmetto, and longleaf pine needles. Despite significant differences in aerosol composition, similar low reactive uptake coefficients were determined, in the range of 0.002-0.006. We investigated the controlling role that the aerosol particles’ morphology and chloride mixing state play in the reactive uptake of N2O5 through single-particle analysis. N2O5 reactive uptake and the yield of ClNO2 vs. HNO3 were parameterized as a function of aerosol composition and mixing state, for incorporation into chemical transport models.