Source apportionment of environmentally persistent free radicals (EPFRs) in PM2.5 over Xi'an, China

Environmentally persistent free radicals (EPERs) have recently attracted considerable attention as a new type of environmental risk substance due to their potential health effects. However, the sources and contributions of EPFRs in PM2.5 are not yet clear. Therefore, this study reports the sources of EPERs in PM25 based on chemical analysis and positive matrix factorization (PMF). Daily PM2.5 samples (116) were collected in Xi'an city from April 4 to December 29, 2017, and were quantitatively analyzed for EPERs and other chemical constituents. The PMF model revealed contributions from five main sources of EPFRs in PM-25 (dust sources, coal combustion, secondary nitrates, industrial emissions and motor vehicle emissions). Coal combustion, motor vehicle emissions and dust sources are the top three contributors to EPERs (76.12% in total). Coal combustion is highly important for PM225 (35.10%) and EPERs (16.75%). A high dust source contribution to EPERs in spring may be clue to dust storm events. Motor vehicle emissions are the top contributor to EPERs, with a mean percentage of 32.13%. Secondary nitrates barely contributes to EPFRs (3.42%), indicating an EPFR origin from primary emissions rather than secondary inorganic reactions. Industrial emissions contribute less to PM2.5 (4.31%) than to EPFRs (11.71%), which implies that fossil fuels contains many high-molecular-weight organics that could emit EPERs. Integrating the PMF results with meteorological data revealed that atmospheric pollutants emitted in Xi'an city center could be transported to the sampling site by southern winds. These results suggest the need for further studies on the public health effects of EPFRs and can be used to help formulate source control measures to reduce the potential health risks posed by EPFRs in PM2.5. (C) 2019 Elsevier B.V. All rights reserved.