Observations Of Aerosol Hygroscopic Properties

Aerosol hygroscopicity influences the aerosol optical properties as well as the atmospheric visibility, and hence affects the aerosol direct and indirect climatic effects. In this study, the hygroscopicity of submicron particles was studied from May to July2012in urban Nanjing and studied from September to October in Mount Huangshan. A Humidity Tandem Differential Mobility Analyser (H-TDMA) instrument was applied to measure the hygroscopic growth factor (GF) for particles with dry diameter between40-200nm.The statistical results show that, the GFs of the aerosol show a distinct bimodal distribution, and classified into less-hygroscopic (LH) group (GF<1.15)and more-hygroscopic (MH) group(GF>1.15). For less-hygroscopic group, the GFLH was1.10-1.14, while the GFMH grew with the diameters for more-hygroscopic group. The spread of GF-PDF (σ) are higher in more-hygroscopic group than in less-hygroscopic group with the same size. It means that the compositions of MH group are more complex. The change of relative humidity has an effect on particle hygroscopic growth which is associated with particle size and chemical compositions. Aitken nuclei and condensation nuclei have different deliquescence point under the same relative humidity. The main moisture absorption components are ammonium nitrate and ammonium sulfate.The result of the measurement under different weather condition shows that GF and NFMH are larger in polluted periods than in clean periods. Obvious diurnal variation characteristics were also observed. The hygroscopicity of particles become stronger mainly caused by photochemical reactions and the evolution of the atmospheric mixing layer. The black carbon from automobile exhausts affects the hygroscopicity of aerosol particles by changing the chemical components of aerosol particle.Mount Huangshan is clean and pollution emission source is unitary. the experiment set relative humidity is85%which is lower than in other places. So the hygroscopicity is less than in the Nanjing area. By comparing the hygroscopic growth factor of aerosol particles under the different height, it is found that with increasing altitude, hygroscopicity of particulate matter is reduced. It meanly because the environment in higher altitude is cleaner than the lower. Aerosol particles contained the hygroscopic material is reduced.