Anthropogenic dust is an important constituent of airborne particles in the urban environment but its ice nucleation activity remains uninvestigated. Here, we studied the sources and ice nucleating properties of size-resolved particles in the urban atmosphere under mixed-phase cloud conditions. The heat-resistant ice nucleating particles (INPs) unexpectedly contributed ~70% of the INPs in coarse mode at temperatures below −15 oC. Detailed size-resolved particle chemical composition analysis showed that these INPs were contributed by anthropogenic dust, such as traffic-influenced road dust. A parameterization based on coarse particles was developed to predict the anthropogenic dust INP concentration, due to their correlations on concentration and similarity in chemical compositions. The parameterization can be used for further evaluating the anthropogenic dust contribution to INPs on a global scale. We suggest anthropogenic dust associated with rapid urbanization will become an important factor for urban climate change by altering the cloud microphysics.

Mineral dust alters cloud microphysical properties by acting as ice-nucleating particles (INPs). The effects of anthropogenic pollution aging on the ice nucleation activity (INA) of mineral dust are still controversial. Such effects were investigated by verifying the chemical aging of airborne size-resolved Asian dust particles via particle chemistry and morphology analyses and comparing the immersion mode INP properties of aged and normal Asian dust. The INP concentrations and ice nucleation active site densities of chemically aged supermicron dust particles (1.0-10.0 μm) were nearly equal to or slightly higher than those of normal Asian dust, which were 0.70-2.45 times and 0.64-4.34 times at -18 ℃, respectively. These results reveal that anthropogenic pollution does not notably change the INP concentrations and does not impair the INA of Asian dust. Our work provides direct observational evidence and clarifies the non-suppression effect of anthropogenic pollution on the INA of airborne East Asian dust.

The ice-nucleating particles (INPs) modulate the microphysics and radiative properties of clouds. However, less is known concerning their abundance and sources in the most pristine and climatic sensitive regions, such as the Tibetan Plateau (TP). Here, to our best knowledge, we conduct the first investigation on INPs in rainwater collected in the TP region under mixed-phase cloud conditions. The INP concentrations vary from 0.002 to 0.675 L-1 Air over the temperature range from -7.1 to -27.5 °C, being within the INP spectra derived from precipitation under worldwide geophysical conditions, and are also comparable to those in the Arctic region. The heating-sensitive INPs account for 57%±30% of the observed INPs at -20 °C, and become increasingly important at warmer temperature regime, indicating biogenic particles as major contributors to INPs above -20 °C over the TP, especially, on the day with additional input of biogenic materials carried by dust particles. Chemical analysis demonstrates the rainwater components are mixture of dust particles, marine aerosol, and anthropogenic pollutants. Dust particles transported from the surrounding deserts and originated from ground surface of TP may contribute to the heating-resistant INPs at temperatures below -20 °C.