Variations of Aerosol Particles Hygroscopicity During the Dust and Haze Events from Filed Measurements in Spring 2015 in Urban Beijing, China

Hygroscopicity of atmospheric aerosols has significant impact on the aerosol size distribution, cloud condensation nuclei formation, climate forcing, etc. In the spring of 2015, a Volatility/Hygroscopicity-Tandem Differential Mobility Analyzer (V/H-TDMA) was used to evaluate the hygroscopic properties of aerosol during dust and haze events in urban Beijing. The instrument can also measure the particles number concentration and the volatility with particle size range of 10-400nm. Our preliminary results showed that the diurnal variation of particle number concentration was with double peaks in the morning and in the afternoon of the haze days, which is closely related to vehicle emissions during the traffic jam. The hygroscopicity of particles was enhanced significantly during the haze days. The probability distribution function of hygroscopic growth factor (GF-PDF) appears a bimodal distribution, with the average GF value of 1.38. The particles number concentration of fine particles in dust days decreased dramatically due to the clear up effect of dust particles. In contrast to the situation during haze events, the hygroscopisity of the particles in dust days displayed a significant decrease, with average GF of 1.17.