AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Dinitrogen Pentoxide Reactive Uptake and Chlorine Activation on Authentic Biomass Burning Aerosol: Implications for Reactive Nitrogen and Halogen Budgets
LEXIE GOLDBERGER, Adam Ahern, Lydia Jahl, Ryan Sullivan, Joel A. Thornton, University of Washington, Seattle, WA
Abstract Number: 349 Working Group: Aerosol Chemistry
Abstract Nitryl chloride (ClNO$_2), formed by the heterogeneous reaction of dinitrogen pentoxide (N$_2O$_5) on chloride-containing particles, occurs in polluted marine environments elevating the oxidant budget$^1. Inland observations of ClNO$_2 in moderately polluted regions have motivated efforts to determine the source of particulate chloride, postulated as the limiting ingredient to ClNO$_2 formation$^2. Biomass burning is a major source of both particulate matter and reactive nitrogen oxide radicals, yet the rate and products of N$_2O$_5 reactive uptake onto biomass burning aerosol have not been well studied. Using a smog reactor at Carnegie Mellon University coupled to a biomass combustion chamber with controlled particle and gas injection, we simulated the nocturnal evolution of N$_2O$_5 in biomass burning plumes mixed with ozone. Smoke plumes were generated from a range of authentic fuel types including saw grass and white European birch, mixed into the 12 m$^3 chamber, and exposed to 70-150 ppb of ozone and 0-60% relative humidity in the dark. Gaseous N$_2O$_5, nitric acid (HNO$_3), ClNO$_2, Cl$_2, and HCl were monitored using a high resolution time of flight iodide adduct chemical ionization mass spectrometer. Particle size distributions and composition were monitored continuously with an SMPS and a Soot-Particle Aerosol Mass Spectrometer among other instruments.
We report on N$_2O$_5 uptake coefficients as well as molar yields of ClNO$_2 and correlated changes in Cl$_2 and HCl. We assess the reactivity of N$_2O$_5 on humidified soot particles relative to ammonium bisulfate probed in separate experiments. We report the halogen budget’s dependences on RH and combustion fuel type as well as on the presence of radiation. These results suggest a potentially important impact of chlorine atom initiated oxidation in biomass burning plumes. The gamma(N$_2O$_5) and yields of ClNO$_2, Cl$_2, and HCl determined from this study will allow for more robust parameterizations of these compounds in atmospheric models.
1 Finlayson-Pitts, B. Nature 337,241-244(1989).
2 Thornton, J. Nature 464,271-274(2010).