The effect of anthropogenic aerosols on nucleation within the Arctic boundary layer during winter

Coating of aerosols with sulphuric acid can delay the ice nuclei formation that leads to increasing precipitation. This process will be studied using the remote sensing observations collected at the CANDAC Eureka site. The large-scale transport of pollution related aerosols is possible from the mid-latitudes over the Arctic regions. The recent laboratory experiments have shown that acidic coating on dust particles substantially reduces the ability of these particles to nucleate ice crystals. We refer this process as the sulphate-induced freezing inhibition (SIFI) effect. Based on observations of Arctic clouds and laboratory experiments, it is hypothesized that acidic aerosols can increase the frequency of mixed phase cloud occurrence and their life time, thus increasing the cloud radiative forcing at surface. The LIDAR and MMCR (mm cloud radar) observations at the Pearl station at Eureka, Canada, were used to investigate the relationship between mixed-phase cloud formation and coated aerosols in highly polluted and clean events. For this purpose, an algorithm has been developed to distinguish the aerosol layers from the cloud phase. In this study, the results of case studies are given for polluted and clean cases at cold and relatively warm temperatures. Preliminary results suggest that anthropogenic aerosols coated with sulphuric acids inhibit the formation of ice crystals through the SIFI process and favors the formation of clear sky ice crystal precipitation (at cold temperature) and mixed-phase clouds (for all temperatures).