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| An observational study of the hygroscopic properties of aerosols in north suburb of Nanjing |
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Abstract 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 in urban Nanjing was studied from May to July 2012. A Humidity Tandem Differential Mobility Analyser (H-TDMA) instrument was applied to measure the hygroscopic growth factor (GF) at 90% relative humidity (RH) for particles with dry diameter between 40~200nm. The statistical results show that, the GFs of the aerosol show a distinct bimodal distribution, and classified into less-hydrophobic (LH) group (GF1.15). For less-hydrophobic group, the GFLH was 1.10~1.14, while the GFMH varied between 1.47~1.58for more-hygroscopic group. The spread of GF-PDF (σ) are higher in more-hygroscopic group than in less-hydrophobic 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 bigger in polluted periods than in clean periods. Obvious diurnal variation characteristics were also observed. The hygroscopicity of particles become stronger mainly caused by photochemical reaction and the evolution of the atmospheric mixing layer. The black carbon from automobile exhausts effect the hygroscopicity of aerosol particles by changing the chemical components of aerosol particle.
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Received: 02 November 2013
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