Composition and regional characteristics of atmosphere aerosol and its water soluble ions over the Yangtze River Delta Region in a Winter Haze Period

To investigate the pollution characteristics of water soluble ions in fine atmospheric particles in Yangtze River Delta during the haze period from 18^th to 24^th Jan 2013, a joint sampling campaign using Andersen sampler was conducted at five cities (including Nanjing, Suzhou, Hangzhou, Lin'an and Ningbo). The analysis of size distribution of these ionic species coupled with the local meteorological conditions may shed some insightful light on the haze formation mechanism in this region. The result has shown: firstly, during the observation period, when Yangtze River Delta located at high pressure or in the front of high pressure, and has a large pressure gradient, the lower atmosphere has a significant airflow divergence in favor of pollutant dispersion; while located in weak low pressure and weak high pressure, the equalizing pressure field is not favorable for pollutant dispersion, especially accompanied with lower atmosphere convergence airflow. Secondly, during the hazy period, the concentration of fine particles and total water-soluble inorganic ions (TWSS) has increased dramatically; the increasing proportions of TWSS in fine particles are: Hangzhou 0.9%, Lin'an 4.2%, Nanjing 8.1%. The particle size of secondary ions of SO₄^2-, NO₃^-, NH₄⁺ complies fine mode (particle size<2.1 μm), whose peaks migrates from 0.43-0.65 μm to 0.65-1.1 μm during the observation period, the peak of particle size of Ca²⁺, Mg²⁺ appears at 4.7-5.8 μm, while the ions of Na⁺, Cl^-, K⁺ show a bimodal distribution. Moreover, secondary inorganic ions play a significant role in the formation of haze pollution, where the concentrations of secondary inorganic ions of NH₄⁺, SO₄^2- and NO₃^- have higher increasing rates; their relative proportions of increasing from each monitoring points are: Hangzhou 3%, Lin'an 55% and Nanjing 64.9%. Finally, SO₄^2- has the highest mass contribution to SNA, up to 45%; also, the NO₃^-/SO₄^2- ratios in each monitoring points are always higher than a fair 0.5, which could indicate the significant contribution of mobile source towards this particle pollution.