AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Impact of Meteorology and Aerosol Composition on Heterogeneous N2O5 Hydrolysis and Chlorine Activation during CalNex 2010
WAYNE CHANG, Steven Brown, Nicole Riemer, University of Illinois at Urbana-Champaign
Abstract Number: 22 Working Group: Aerosol Chemistry
Abstract The heterogeneous hydrolysis of dinitrogen pentoxide (N$_2O$_5) on atmospheric particles is an integral part of nighttime chemistry in the troposphere. In particular, recent measurement campaigns have shown that the activation of chlorine by heterogeneous N$_2O$_5 reactions on chloride-containing aerosol is an important source of chlorine atoms in the troposphere, even in regions away from continental coasts. The reaction rate of the hydrolysis is highly dependent on meteorological conditions and aerosol composition. Based on chamber measurements, several parameterizations suitable for air quality models have been developed for the treatment of N$_2O$_5 uptake probability on available aerosol surfaces. Key governing variables for these parameterized functions include temperature, relative humidity, and particulate nitrates, chloride and organics contents. We implemented these parameterized treatments of heterogeneous N$_2O$_5 hydrolysis in the WRF/Chem modeling system, under both the idealized 1-D and full 3-D framework. In addition, we expanded the gas-phase chemical mechanism with inorganic and organic chlorine species, and corresponding chemical reactions. This newly augmented mechanism is coupled with the parameterization method that accounts for the presence of particulate chloride through the inclusion of the heterogeneous production of nitryl chloride (ClNO$_2) by N$_2O$_5 hydrolysis. Under the idealized 1-D framework, we investigated the response of nighttime vertical gradients of N$_2O$_5 and related products of hydrolysis to seasonal variations and emission compositions. The domain of the full 3-D model is the South Coast Air Basin of California. Through evaluations against measurements made during the CalNex 2010 campaign, the performance of the different uptake parameterization techniques and heterogeneous chlorine activation reactions is assessed, and the resulting impact on the tropospheric pollutant dynamics is quantified in this study.