Hydrolysis of N2O5
Heterogeneous hydrolysis of N2O5 on the surface of deliquescent aerosols provides an efficient removal path for nitrogen oxides at nighttime, and the result can impact both atmospheric photochemistry and the nitrate budget. Laboratory measurements have shown that the values for the reaction probability of N2O5 hydrolysis are dependent on meteorological conditions, such as temperature and relative humidity, and composition of the aerosols. In particular, nitrate and organic contents within the aerosol have been shown to inhibit N2O5 uptake. These findings motivated us to investigate the impact of the hydrolysis of N2O5 on the surface of aerosols on a regional scale, focusing on the relevance for ozone, NO3, volatile organic compounds (VOC), and nitrate. To elucidate the role of atmospheric transport, we employed a 1D-model with only vertical turbulent diffusion acting as transport process. The simulation results showed strong but varying vertical gradients for N2O5 and aerosol concentrations. The deviation in the altitudes where peak concentrations of N2O5 and aerosol were found suggest that the magnitude of the impact N2O5 on tropospheric chemistry is not as straightforward as suggested by pure chemistry calculations in a box-model settings, but heavily meteorologically dependent. Thus, nocturnal boundary layer must be adequately resolved in simulating tropospheric N2O5 dynamics.
Current work
Recent field measurements of surprisingly large quantities of nitryl chloride suggest the importance of halogen activation through N2O5 hydrolysis on particulate chloride. These observations were not limited to coastal regions with abundant sea salt aerosols, but also in continental urban regions such as Boulder, Colorado. Our goal is to develop a meteorology- and composition-based parameterization for heterogeneous N2O5 hydrolysis that accounts for halogen activation suitable for state-of-the-art air quality models. One of the test beds for this modeling development is the Los Angeles Air Basin, where the performance of the newly developed techniques will be evaluated against observations made during the recent CalNex 2010 campaign.Publications
W. Chang, P. Bhave, S. Brown, N. Riemer, J. Stutz, D. Dabdub [2011] Tropospheric N2O5: A review of ambient measurements and model calculations, Aerosol Sci. and Technol., 45, 655-685.
N. Riemer, H. Vogel, B. Vogel, T. Anttila, A. Kiendler-Scharr, Th.F. Mentel [2009] The relative importance of organic coatings for the heterogeneous hydrolysis of N2O5, J. Geophys. Res., 114, D17307, DOI: 10.1029/2008JD011369.
N. Riemer, H. Vogel, B. Vogel, B. Schell, I. Ackermann, Ch. Kessler, H. Hass [2003] The impact of the heterogeneous hydrolysis of N2O5 on tropospheric chemistry and nitrate aerosol formation, Journal of Geophysical Research 108, 4144, DOI: 10.1029/2002JD002436. (pdf)