Objective To analyze the distribution characteristics and sources of atmospheric fine particulate matters (PM2.5) and the heavy metals and polycyclic aromatic hydrocarbons (PAHs) in PM2.5, and provide evidence for the control of air pollution in Ningbo.
Methods On 10-17 every month from 2015 to 2017, PM2.5 samples were collected from a platform of 15 m height within 500 m from a state-controlled environmental air quality monitoring station in an urban area of Ningbo City and detected for mass concentration. The pollution characteristics of 12 heavy metals and 16 priority PAHs were evaluated. The sources of the heavy metals and PAHs were qualitatively analyzed using enrichment factor and characteristic molecular ratio, respectively.
Results From 2015 to 2017, the daily average concentration of PM2.5 in the urban area was 10-196 μg/m3, and the annual average concentration was 53, 46, and 35 μg/m3, respectively; PM2.5 concentrations showed a statistically significant seasonal variation:winter > spring > autumn > summer (F=25.54, P < 0.01). The leading heavy metals were Pb, Mn, Ni, Sb, and As; all the concentrations of selected heavy metals showed seasonal variations except Ni, Cr, and Be (P < 0.01), with higher concentrations in winter and spring than in summer and autumn; the results of enrichment factor suggested that Cd, Se, Sb, Hg, and Pb pollution were possibly derived from anthropogenic activities. The daily average concentration of PAHs was 1.28-55.22 ng/m3, and showed a seasonal variation similar to PM2.5; the leading three priority PAHs were benzob fluoranthene (BbF), indene1, 2, 3-c, d pyren (IcdP), and anthracene (Ant); the results of characteristic molecular ratio suggested the main source of PAHs was gasoline combustion, followed by coal and biomass combustion.
Conclusion The level of PM2.5 pollution in this urban area of Ningbo is decreasing year by year, but still at a high level. The pollution of heavy metals and PAHs show a distinct seasonal variation, with higher concentrations in winter than in other seasons. Anthropogenic activities are potential main sources of heavy metals, while motor vehicle emission and coal combustion are the potential main sources of PAHs.
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