Objective  To analyze temporal and spatial distribution and sources of heavy metals in ambient air particulate matter less than 10 μm in aerodynamic diameter (PM₁₀) and less than 2.5 μm (PM_2.5) in Weifang city and to assess the health risks due to exposure to the heavy metals.

  Methods  We collected ambient air PM₁₀ and PM_2.5 samples at five monitoring sites in different function regions of Weifang city during January, April, July, and October 2014. The concentrations of 6 heavy metals were detected with atomic absorption spectrometry and the sources of 6 heavy metals were analyzed by factor analysis. Health risk assessment on respiratory exposures to these heavy metals was performed using the risk assessment model recommended by United States Environment Protection Agency.

  Results  No significant seasonal variations were observed in concentrations of lead (Pb), copper (Cu), manganese (Mn), nickel (Ni) and chromium (Cr) in PM₁₀ and PM_2.5 samples (P > 0.05 for al), except for in the concentration of cadmium (Cd) (P < 0.05); however, the concentrations of the 6 heavy metals in PM₁₀ and PM_2.5 samples differed significantly by monitoring sites of various functional regions (P < 0.05). Factor analysis indicated that the heavy metals in PM₁₀ samples were mainly from traffic pollution, industrial pollution and road dust, accounting for 44.85%, 22.09% and 18.16% of the total content; the heavy metals in PM_2.5 samples were mainly from industrial pollution, road dust and traffic pollution, accounting for 48.54%, 23.60% and 14.10% of the total content, respectively. Non-carcinogenic risks due to respiratory exposure to the heavy metals in the fine particulate matter are all less than 1; but the carcinogenic risks due to the exposures are close to the threshold levels.

  Conclusion  Non-carcinogenic risk due to respiratory exposure to heavy metals in fine particulate matter is acceptable, but carcinogenic risk due to the exposure close to the threshold level for the residents in Weifang city.