We present an estimation of the uptake coefficient (&gamma;) and yield of nitryl chloride (ClNO₂) (<i>f</i>) 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&thinsp;&plusmn;&thinsp;0.027) and (1.38&thinsp;&plusmn;&thinsp;0.60) with a campaign average of

more »

... nsp;&plusmn;&thinsp;0.35). The large variability in <i>f</i> reflects the highly variable chloride content of particles at the site. Uptake coefficients were also highly variable with minimum, maximum and average &gamma; values of 0.004, 0.11 and 0.028&thinsp;&plusmn;&thinsp;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 parameterisations based on laboratory datasets and with other values obtained by analysis of field data.