Abstract：Nine water-soluble ions of PM2.5 including F^-, Cl^-, NO₃^-, SO₄^2-, Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺ were analyzed during haze and non-haze periods in autumn at Wuda station and Tianhong station in Wuhan City.The results show that NO₃^-, SO₄^2- and NH₄⁺are the most important ions in PM_2.5 and the composition of the ions in PM_2.5is relatively stable. The increase of the proportion of water-soluble ions in PM_2.5 during the haze period is an important feature of the air pollution in autumn in Wuhan.They may be derived from the course of biomass burning, soil dust, combustion of fossil fuels, automobile exhaust emissions. The secondary air pollution in Tianhong station is more serious than that in Wuda station.The relative contribution of stationary sources to NO_x and SO₂ in Wuhan's atmosphere during the haze period is greater than that in the non-haze period. The relative contribution of mobile sources to NO_x and SO₂ in Tianhong station is greater than that in Wuda station.

Keywords：haze; fine particulate matter (PM_2.5) ; water-soluble ions