Chemical characteristics and source apportionment of PM2.5 in a petrochemical city: Implications for primary and secondary carbonaceous component.

• The heavy haze episodes formation in autumn was related with the increase of secondary organic aerosols and NH 4. • The contribution of POC and NH 4 + were significant during the evolution of pollution periods in wintertime. • The local and short-distance air mass transportation have significant impact. To study the pollution features and underlying mechanism of PM 2.5 in Luoyang, a typical developing urban site in the central plain of China, 303 PM 2.5 samples were collected from April 16 to December 29, 2015 to analyze the elements, water soluble inorganic ions, organic carbon and elemental carbon. The annual mean concentration of PM 2.5 was 142.3 μg/m3, and 75% of the daily PM 2.5 concentrations exceeded the 75 μg/m3. The secondary inorganic ions, organic matter and mineral dust were the most abundant species, accounting for 39.6%, 19.2% and 9.3% of the total mass concentration, respectively. But the major chemical components showed clear seasonal dependence. SO 4 2− was most abundant specie in spring and summer, which related to intensive photochemical reaction under high O 3 concentration. In contrast, the secondary organic carbon and ammonium while primary organic carbon and ammonium significantly contributed to haze formation in autumn and winter, respectively. This indicated that the collaboration effect of secondary inorganic aerosols and carbonaceous matters result in heavy haze in autumn and winter. Six main sources were identified by positive matrix factorization model: industrial emission, combustion sources, traffic emission, mineral dust, oil combustion and secondary sulfate, with the annual contribution of 24%, 20%, 24%, 4%, 5% and 23%, respectively. The potential source contribution function analysis pointed that the contribution of the local and short-range regional transportation had significant impact. This result highlighted that local primary carbonaceous and precursor of secondary carbonaceous mitigation would be key to reduce PM 2.5 and O 3 during heavy haze episodes in winter and autumn. [Display omitted] [ABSTRACT FROM AUTHOR]