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Daily PM2.5 (aerosol particles with an aerodynamic diameter of less than2.5 μm) samples were collected at an urban site in Chengdu, aninland megacity in southwest China, during four 1-month periods in 2011,with each period in a different season. Samples were subject to chemicalanalysis for various chemical components ranging from major water-solubleions, organic carbon (OC), element carbon (EC), trace elements to biomassburning tracers, anhydrosugar levoglucosan (LG), and mannosan (MN). Twomodels, the ISORROPIA II thermodynamic equilibrium model and the positive matrixfactorization (PMF) model, were applied to explore the likely chemical formsof ionic constituents and to apportion sources for PM2.5. Distinctiveseasonal patterns of PM2.5 and associated main chemical components wereidentified and could be explained by varying emission sources andmeteorological conditions. PM2.5 showed a typical seasonality of waxingin winter and waning in summer, with an annual mean of119 μg m−3. Mineral soil concentrations increased in spring,whereas biomass burning species elevated in autumn and winter. Six major source factors were identified to have contributed to PM2.5using the PMF model. These were secondary inorganic aerosols, coalcombustion, biomass burning, iron and steel manufacturing, Mo-relatedindustries, and soil dust, and they contributed 37 ± 18,20 ± 12, 11 ± 10, 11 ± 9,11 ± 9, and 10 ± 12%, respectively, to PM2.5masses on annual average, while exhibiting large seasonal variability. Onannual average, the unknown emission sources that were not identified by thePMF model contributed 1 ± 11% to the measured PM2.5 mass.Various chemical tracers were used for validating PMF performance. Antimony(Sb) was suggested to be a suitable tracer of coal combustion in Chengdu.Results of LG and MN helped constrain the biomass burning sources, with woodburning dominating in winter and agricultural waste burning dominating inautumn. Excessive Fe (Ex-Fe), defined as the excessive portion in measured Fethat cannot be sustained by mineral dust, is corroborated to be astraightforward useful tracer of iron and steel manufacturing pollution. InChengdu, Mo / Ni mass ratios were persistently higher than unity, andconsiderably distinct from those usually observed in ambient airs. V / Niratios averaged only 0.7. Results revealed that heavy oil fuel combustionshould not be a vital anthropogenic source, and additional anthropogenicsources for Mo are yet to be identified. Overall, the emission sourcesidentified in Chengdu could be dominated by local sources located in thevicinity of Sichuan, a result different from those found in Beijing andShanghai, wherein cross-boundary transport is significant in contributingpronounced PM2.5. These results provided implications for PM2.5control strategies

PM&lt;sub&gt;2.5&lt;/sub&gt; pollution in a megacity of southwest China: source apportionment and implication

PM<sub>2.5</sub> pollution in a megacity of southwest China: source apportionment and implication