Source apportionment of PM2.5 in the most polluted Central Plains Economic Region in China: Implications for joint prevention and control of atmospheric pollution

Abstract

With continuous strengthening of emission control actions, the air quality in northern China during winter has been improved in recent years. However, the fine particulate matter (PM2.5) concentration remains high in the Central Plains Economic Region (CPER). The Nested Air Quality Prediction Modeling System coupled with an on-line source-tagged model was applied to investigate the source apportionment of primary and secondary PM2.5 in the most polluted area of China from November 2017 to March 2018. On average, local emissions represent the largest contributor to ambient PM2.5 levels, followed by transport from circumjacent cities at five receptors in northern CPER. Under high PM2.5 concentrations (more than 150 μg/m3), 60%–70% of the primary PM2.5 is freshly emitted on the current day, while the contribution of the current day, one day ago, and two or more days ago are comparable to secondary aerosols. The estimation of contributions based on distance shows that the contribution from regions within 200 km reaches more than 80% of the primary PM2.5, while the contribution from long-range transport within 200–500 km still accounts for more than 20% of the secondary PM2.5 at the receptor sites. These results indicate that control measures of primary particle emission should be effective to reduce the primary PM2.5 levels within local and nearby regions, and control measures of gas phase precursors one or more days in advance should be beneficial to surrounding regions within 500 km. The process analysis results of the change in PM2.5 mass over the northern part of the CPER during increased PM2.5 periods illustrate that the existing particle total transport is smaller than the secondary aerosol chemical production and primary aerosol emissions since the westerly and southerly net inputs are mostly offset by the large net outputs at the east boundary in both cases. This finding indicates that the ambient PM2.5 mass in a selected area is strongly affected by the upstream region; meanwhile, the PM2.5 in this area also spreads to the downstream region. Joint prevention and control measures that cooperate with upstream regions for both primary particles and gas phase precursor emissions are crucial for improving the air quality over polluted areas. As the emission control measures would lead to some economic losses, beneficiary downstream regions could reasonably provide certain economic compensation to upstream regions if emergency control measures are taken.