Abstract
Ice nuclei of some bacterial origin as ice catalysts can initiate ice nucleation at temperatures as warm as –2°C in certain laboratory experiments. The ice nucleation activities of airborne bacteria in the real atmosphere may be different from those experiments. To estimate the impact of typical atmospheric pollutants including monocarboxylic acids (MCAs), dicarboxylic acids (DCAs) and ammonia sulfate on ice nucleation activity of P.syringae pv lachrymans and P.syringae pv.panici, we have conducted some experiments by means of the modified Vali’s droplet freezing testing method in the immersion freezing mode with the mixture of the pure water and the polluted water. Our results show that the ice nucleation activity of bacterial origins can be regulated by such pollutant compounds even though the onset freezing temperatures of water droplets mainly depend on the concentrations of ice nucleation-active bacteria. Atmospheric acids can decrease ice nucleation activity of P.syringae pv lachrymans and P.syringae pv.panici. However, the onset freezing temperatures of water droplets immersed with ice nucleation-active P.syringae pv lachrymans will be enhanced by the low concentration of such atmospheric pollutants.
Highlights
Clouds may consist of ice particles under supercooled conditions
Our results show that the ice nucleation activity of bacterial origins can be regulated by such pollutant compounds even though the onset freezing temperatures of water droplets mainly depend on the concentrations of ice nucleation-active bacteria
The results show that the high concentrations of the mixed pollutants, such as the cases of M1 and M2 can decrease the ice-nucleation activity (INA) of PS when the concentrations of PS are greater than 104 cells/mL, whereas such high concentrations of the mixed pollutants cannot obviously regulate the freezing temperatures of droplets immersed with PS0 since the mixed pollutants for the case M1 cannot decrease the freezing temperatures of droplets immersed with PS0
Summary
Clouds may consist of ice particles under supercooled conditions. Scientists have recognized their important role in precipitation and the Earth's radiation budget. Ice nuclei (IN) in the atmosphere are required to catalyze cloud ice formation at proper conditions. Recent numerical studies show that ice nucleation-active bioaerosols can trigger the ice multiplication in the warmbased precipitating shallow cumulus clouds (Ariya et al, 2009; Sun et al, 2010; Sun et al, 2012). Ice nucleation-active bioaerosols may play an important role in precipitation and even in climate change
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