资源环境科技发展态势分析平台

In this study, Bigg cloud chamber was used to determine the concentrations of ice nucleating particles (INPs) in the temperature range from −15 to −30 °C in Beijing during the spring of 2017. The concentrations were compared with historical results observed by a similar instrument in Beijing, showing that the INP concentration in 2017 was generally lower than those obtained in 1995 and 1996. Based on air mass trajectory clustering analysis, the high INP concentration in 1995 and 1996 might be attributable mainly to the transport of sand-dust from the northwestern region. Furthermore, the aerosol number size distribution and chemical composition in PM_2.5 were measured simultaneously. The number of aerosols was dominated by particles in Aitken mode and accumulation mode particles during the observation period, but coarse mode particles obviously exhibited stronger correlation with INPs. NO₃⁻, NH₄⁺, and SO₄²⁻ were the major ions and existed mainly in the form of NH₄NO₃ and (NH₄)₂SO₄ in PM_2.5. Ratio analysis indicated that air pollution originated mainly from mobile sources in Beijing and had serious secondary pollution process. The high ratio of organic carbon (OC) to elemental carbon (EC) implies existing severe secondary organic carbon pollution. In addition, we investigated the relationship between INPs and aerosols with different sizes and compositions in spring in Beijing, the results indicated that for aerosols with a diameter above 0.5 μm, the correlation between INPs and aerosols increased clearly with increasing particle size, but for aerosols with sizes below 0.5 μm, the correlation coefficient displayed a clear trend of increasing first and then decreasing with increasing aerosol size. An INP parameterization depending on aerosol particles and the activation temperature was also established. A comparison of the correlations between the INPs and compositions in PM_2.5 shows that NaCl, NH₄NO₃ and (NH₄)₂SO₄ were more correlated with INPs than other ionic compounds, but a strong correlation existed only at −30 °C, there was no correlation at −20 °C and above. Additionally, OC was more relevant to INP than EC, but the correlation was observed only at low temperature region.