Hygroscopic Properties Of Aerosol Particles In Nanjing And Mount Huangshan

The hygroscopic properties of submicron aerosol particles have significant effects on specral distribution, CCN activation, climate forcing, human health and so on. Nanjing and Mt.Huang, as two different types of regional background, have distinct characteristics of air pollution. In this study, the hygroscopic data observed at Nanjing 2014.04-05, Mt. Huang 2014.7 was utilized to analyze the hygroscopic properties of aerosol particles in the northern suburb of Nanjing and Mt. Huang, and combined with water-soluble ions sample information, analyzed the chemical composition influence on aerosol hygroscopicity. The average hygroscopicity parameter κ at a wide diameter range was computed by combining the HTDMA data with the size-segregated aerosol chemical composition data. The main conclusions are as follows.(1) At relative humidity(RH) of 90%, for particles with dry diameters 30-230nm, the probability distribution of GF(GF-PDF) observed in Nanjing shows a distinct bimodal pattern, with a dominant more-hygroscopic group and a smaller less-hygroscopic group. The average GF at each diameter was 1.26、1.32、1.29.1.30.1.29.1.28. The hygroscopicity vary little with the growth of the diameter. At relative humidity(RH) of 85%, for particles with dry diameters 70-230nm, the GF-PDF observed at Mt. Huang shows both bimodal and monomodal. Compared with the almost bimodal observation in city, number fractions of less-hygroscopicity aerosol particles are smaller, indicates that the air at Mt.Huang was more clear than that in city. The average GF at each diameter was 1.30、1.30.1.32、1.30、1.36. The hygroscopicity has a tendency to increase slightly with the growth of the diameter. A statistica of the time the biomodal or monomodal appears shows, the monomodals are often appears in the afternoon, while the bimodals appears more in the morning. This declares that the aerosol hygroscopicity was influence by the daily variation of number fractions of the more and less hygroccopic aerosol particles, and the mixing atate of the aerosols during morning is higher. A contrast of the aerosol hygroscopicity between Nanjing and Mt.Huang shows that, the aerosol hygroscopicity at Mt.Huang is higher than that in Nanjing, indicates that aerosol hygroscopicity in clean areas is likely higher than that in pollution areas. The aerosol particles at Mt.Huang tend to have a internally mixed state, and the chemical composition is more onefold. While the aerosol particles in Nanjing have a higher degree of externally mixed state, and the chemical composition may be more complex.(2) A contrast analyses between day and night in Nanjing suggest that, aerosol particles during day time have stronger hygroscopicity and higher number fraction of more-hygroscopic group than that at night overall. Aerosol particles during night have a higher degree of externally mixed state. Statistical analyses of the aerosols hygroscopicity at different weather conditions show that, as photochemical reaction may speed up the aerosol aging process, aerosol hygroscopicity at sunny days is higher and tend to be external mixing state. At polluted days, aerosol hygroscopicity is weaker may be because of more weak hygroscopic organic matter caused by a local emissions. Analysis of aerosol hygroscopicity from different air masses show that, For aitken nuclei, that in northwest continental air masses experienced a longer aging process and have stronger hygroscopicity. For condensation nuclei, that from east air masses have stronger hygroscopicity.(3) Observation at Mt. Huang shows, aerosol hygroscopicity at high Environmental RH is higher than that at low Environmental RH. This indicates that high relative humidity may accelerate the heterogeneous chemical reaction rate and degree of aerosol particles, thereby lead to a higher aerosol hygroscopicity. Analysis of aerosol hygroscopicity from different air masses show that, aerosol particles in local air masses have stronger hygroscopicity, and that from east air masses have the lowest hygroscopicity. Aerosol hygroscopicity from different air masses has a great relevance with sulfate content.(4) The average hygroscopicity parameter κ chem calculated from chemical information and κ HTDMA calculated from HTDMA are nearly equal. (NH4)2SO4 is the major hygroscopic composition in the Atmospheric aerosols. The average hygroscopicity parameter κ and GF at 90% RH at a wide diameter range(0.07-7.28 μm) was calculated by combining the HTDMA data with the size-segregated aerosol chemical composition data, the results shows that aerosol hygroscopicity has two peaks at 0.41μm and 5.54μm.