The pollution characteristics and light extinction contribution of water-soluble ions of PM_2.5 in Hangzhou were investigated by sampling and laboratory analysis of aerosol samplers in 2013. The water-soluble ions were dominant in PM_2.5 and the total mass concentration was 37.5 μg·m^-3, accounting for 44.4% of the PM_2.5 mass concentration. Water-soluble ions were mainly composed of secondary ions(SO₄^2-,NO₃^- and NH₄⁺), which accounted for 83.4% of total ions. The highest mass concentrations of PM_2.5 and major ions were observed in winter and the lowest in summer. The proportions of water-soluble ions in PM_2.5 in summer and autumn were obviously higher than those in winter and spring and proportions of secondary ions in water-soluble ions were very close in each season. The contribution was the greatest to PM_2.5 from secondary ions generation caused by fuel combustion and automobile exhaust. The annual average values of SOR and NOR were 0.27 and 0.15 respectively, the conversion rate of SO₂ in atmosphere was greater than that of NO_x. There was obvious positive correlation between SOR or NOR and humidity which indicated the important contribution of heterogeneous oxidation process to the generation of SO₄^2- and NO₃^-. The annual average of[NO₃^-]/[SO₄^2-] was 0.63, and the aerosol pollution was primarily affected by emissions from coal burning. In haze days, with the increase of haze pollution level, the mass concentrations of PM_2.5, water-soluble ions, secondary ions as well as SOR and NOR all increased gradually, and the stable weather condition in haze days could efficiently promote the accumulation and secondary conversion of pollutants. There were obvious positive correlations between mass concentrations of PM_2.5 and SNA and the atmospheric light extinction coefficient. The IMPROVE formula which was used to calculate the light extinction coefficients of different chemical components could efficiently indicate the tendency of aerosol scattering. The extinction contribution of SNA could reach 60.8%. The extinction coefficient of SNA was the highest in winter and lowest in summer, and its value and contribution proportion both increased gradually as the haze pollution level rose.

#	Concept	H-Index	Publications	Citations
1	Air Pollution	1	1	133
2	Air Quality	1	1	133
3	Covid-19	1	1	133

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