Direct observations of N2O5 reactivity on ambient aerosol particles

N2O5 reactivity has been measured directly for the first time on ambient aerosol particles using an entrained aerosol flow reactor coupled to a custom-built chemical ionization mass spectrometer at two urban locations during summer. The observed N2O5 reactivity is a strong function of both relative humidity ( RH) and particle chemical composition. We show that particulate organic mass loadings, together with ambient relative humidity, play a leading role in determining the reaction rate of N2O5 with particles. Our observed reactivity values are both more variable and, at times, as much as a factor of ten lower than currently implemented large-scale model parameterizations would predict. Such discrepancies have likely consequences for predictions of NOx availability and ozone production, and the sensitivity of these quantities to aerosol particle loadings. Citation: Bertram, T. H., J. A. Thornton, T. P. Riedel, A. M. Middlebrook, R. Bahreini, T. S. Bates, P. K. Quinn, and D. J. Coffman ( 2009), Direct observations of N2O5 reactivity on ambient aerosol particles, Geophys. Res. Lett., 36, L19803, doi:10.1029/2009GL040248.