Spatiotemporal distribution of atmospheric polycyclic aromatic hydrocarbon emissions during 2013–2017 in mainland China

Following implementation of the most stringent clean air policy in China, the emissions of NOx, SO2, and fine particles have greatly reduced since 2013. However, the emissions of polycyclic aromatic hydrocarbons (PAHs), which are highly toxic pollutants, and their spatiotemporal changes remain unclear. In this study, a 0.05° × 0.05° gridded PAH emission inventory was developed for mainland China during 2013-2017. The results show that the total PAH emissions have decreased from 112.92 Gg in 2013 to 100.09 Gg in 2017, with the fastest declines in the industrial (17.32%) and residential/commercial (10.58%) sectors. However, the decline in the PAH emissions is smaller than that of the NOX and SO2 emissions. The average emission density of PAHs in mainland China in 2017 was 10.43 kg/km2. North and East China have the largest PAH emissions. The residential/commercial, industrial, and transportation sectors are the major emission sources, accounting for 48.59%, 29.26%, and 17.21%, respectively. Carcinogenic PAH emissions accounted for 7.49% in mainland China, higher than those of developed countries (5.73%) and the global average (6.19%). Differences in the energy structures lead to significant differences in the spatial distribution of PAH emissions in various sectors. From 2013 to 2017, the emissions declined in most Chinese regions. The emission density in East China decreased the most, reaching 3.39 kg/km2, followed by North China (2.91 kg/km2). The magnitude of the decline in the PAH emissions and reasons for the decline significantly differ in different regions. Particular attention must be paid to the limited decline (5.22%) in Northwest China over the study period. Although China's emission density has been declining, it is still significantly higher than the global average. Therefore, China must further reduce the PAH emissions through technological innovation and reductions of energy consumption and, thus, reduce the regional lung cancer risk.