Size-resolved measurements of ice nucleating particles at six locations in North America and one in Europe

Abstract

Abstract. Detailed information on the size of ice nucleating particles (INPs) may be useful in source identification, modeling their transport in the atmosphere to improve climate predictions, and determining how effectively or ineffectively instrumentation used for quantifying INPs in the atmosphere captures the full INP population. In this study we report immersion-mode INP number concentrations as a function of size at six ground sites in North America and one in Europe. The lowest INP number concentrations were observed at Arctic and alpine locations and the highest at suburban and agricultural locations, consistent with previous studies of INP concentrations in similar environments. We found that 91, 79, and 63 % of INPs had an aerodynamic diameter > 1 μm at ice activation temperatures of −15, −20, and −25 °C, respectively, when averaging over all sampling locations. In addition, 62, 55, and 42 % of INPs were in the coarse mode (> 2.5 μm) at ice activation temperatures of −15, −20, and −25 °C, respectively, when averaging over all sampling locations. These results are consistent with six out of the seven studies in the literature that have focused on the size distribution of INPs in the atmosphere. Taken together, these findings strongly suggest that supermicron and coarse mode aerosol particles are a significant component of the ice nuclei population in many different ground-level environments. Further size-resolved studies of INPs as a function of altitude are required.