Abstract: Objective To study the characteristics of ambient PM_2.5 pollution in different seasons and its impact on the daily deaths of residents in a city of North China. Methods Ambient PM_2.5 samples were collected in the central urban area of the city from November 2013 to May 2016. Concentrations of twelve metals （Pb, Mn, Al, Cd, Cr, Sb, As, Be, Hg, Ni, Se, Ti）, four inorganic water-soluble ions （NO₃^-, SO₄^2-, NH₄⁺, Cl^-）, and sixteen polycyclic aromatic hydrocarbons （PAHs） were analyzed. Data of average daily concentration of PM_2.5 in the atmosphere and daily non-accidental deaths of residents in the city were collected from 2013 to 2015. Generalized additive model （GAM） was used to analyze the relationship between average daily concentration of PM_2.5 and the deaths of residents. Results Obvious seasonal changes were observed in the PM_2.5 concentration, the highest of which was [（223.87 ± 176.13） µg/m³] in winter, followed by （137.81 ± 83.26）µg/m³ in spring and （135.41 ± 89.42）µg/m³ in autumn, and the lowest was （112.88 ± 50.46） µg/m³ in summer（P<0.01）. The concentration of inorganic water-soluble ions in PM_2.5 accounted for the largest proportion （41%-49%）, of which the average SO₄^2- concentration （34.60 µg/m³） was the highest. The metals accounted for 0.19%-0.51%, of which the Al concentration （546.03 ng/m³） was the highest. The PAHs accounted for 0.04%-0.23%, of which the benzo（g,h,i） perylene concentration （190.86 ng/m³） was the highest. Time series analysis showed that for every 10 μg/m³ of increased PM_2.5 concentration, the risks of total non-accidental deaths （lag0-5）, deaths from cardiovascular diseases （lag0-5） and deaths from respiratory diseases （lag1） rose by 0.73% （95%CI： 0.42%-1.04%）, 1.04% （95%CI： 0.64%-1.46%） and 0.63% （95%CI： 0.07%-1.19%）, respectively. Conclusion The proportion of inorganic water-soluble ions such as SO₄^2- and NO₃^- in PM_2.5 was relatively high in this city. The increase of ambient PM_2.5 concentrations may significantly associate with increased risks of non-accidental deaths, particularly the deaths from cardiovascular diseases.

Key words: Particulate matter, Air pollution, PM_2.5, Mortality