Estimating N₂O₅ uptake coefficients using ambient measurements of NO₃, N₂O₅, ClNO₂ and particle-phase nitrate

We present an estimation of the uptake coefficient (γ) and yield of nitryl chloride (ClNO₂) (f) for the heterogeneous processing of dinitrogen pentoxide (N₂O₅) using simultaneous measurements of particle and trace gas composition at a semi-rural, non-coastal, mountain site in the summer of 2011. The yield of ClNO₂ varied between (0.035 ± 0.027) and (1.38 ± 0.60) with a campaign average of (0.49 ± 0.35). The large variability in f reflects the highly variable chloride content of particles at the site. Uptake coefficients were also highly variable with minimum, maximum and average γ values of 0.004, 0.11 and 0.028 ± 0.029, respectively, with no significant correlation with particle composition, but a weak dependence on relative humidity. The uptake coefficients obtained are compared to existing parameterizations based on laboratory datasets and with other values obtained by analysis of field data.