Size-resolved atmospheric ice-nucleating particles during East Asian dust events

Asian dust is an important source of atmospheric ice-nucleating particles (INPs). However, the freezing activity of airborne Asian dust, especially its sensitivity to particle size, is poorly understood. In this study we report the first INP measurement of size-resolved airborne mineral dust collected during East Asian dust events. The measured total INP concentrations in the immersion mode ranged from 10(-2) to 10(2) L-1 in dust events at temperatures between 25 and 5 degrees C. The average contributions of heat-sensitive INPs at three temperatures, -10, 15, and 20 degrees C, were 81 +/- 12 %, 70 +/- 15 %, and 38 +/- 21 %, respectively, suggesting that proteinaceous biological materials have a substantial effect on the ice nucleation properties of Asian airborne mineral dust at high temperatures. The dust particles which originated from China's northwest deserts are more efficient INPs compared to those from northern regions. In general, there was no significant difference in the ice nucleation properties between East Asian dust particles and other regions in the world. An explicit size dependence of both INP concentration and surface ice-active-site density was observed. The nucleation efficiency of dust particles increased with increasing particle size, while the INP concentration first increased rapidly and then leveled, due to the significant decrease in the number concentration of larger particles. A new set of parameterizations for INP activity based on size-resolved nucleation properties of Asian mineral dust particles were developed over an extended temperature range (35 to 6 degrees C). These size-dependent parameterizations require only particle size distribution as input and can be easily applied in models.

Automated summary

Asian dust is an important source of atmospheric ice-nucleating particles (INPs), but the freezing activity and sensitivity to particle size are poorly understood. This study reports the first size-resolved INP measurement of airborne mineral dust during East Asian dust events. The nucleation efficiency of dust particles increases with particle size, while the INP concentration first increases rapidly and then levels off due to a decrease in the number concentration of larger particles. New parameterizations for INP activity based on the size-resolved nucleation properties of Asian mineral dust particles were developed for a wider temperature range and can be easily applied in models.