Reduction in polycyclic aromatic hydrocarbon exposure in Beijing following China's clean air actions

PAHs are among the most important hazardous compounds present ubiquitously in the environment. As the largest emitter of PAHs, China accounted for over one fifth of the global PAHs emissions in 2007 – most of these emissions occurred in close proximity to general population (e.g., vehicular emissions). Substantial evidence has documented the presence of high levels of PAHs exposure in China, which was associated with a range of adverse health effects such as cancers, cardiovascular diseases and birth defects. While most of these studies were conducted before 2013, China has implemented the toughest-ever national clean air policies (i.e., APPCAP) in 2013-2017, followed by another national clean air plan of BSDW in 2018-2020. These efforts have unprecedentedly changed the anthropogenic emissions of combustion sources in China, but to what extent these actions have changed population exposure to PAHs is unknown.

In this study, a multidisciplinary team consisting of researchers from Peking University, University of California Los Angeles (UCLA), and Duke University has continuously monitored the ambient PAHs levels in Beijing from 2014 to 2021 and apportioned their major sources. The results indicated a remarkable decline of 96.6% in ambient PAH concentrations over 8 years. Greater reduction in PAHs concentrations was observed during the APPCAP phase owing to >80% emission reductions in traffic exhaust, coal combustion, and biomass burning. However, the decrease in ambient PAHs slowed down during the BSDW phase, because the reduction in coal and biomass emission were offset by flattened emissions from traffic sources. Furthermore, the results also supported the effectiveness of the clean heating renovation in 2017 in mitigating PAHs pollution, as evidenced by the drastic decrease in coal-originated PAHs during heating seasons from 2017 to 2018.

The team also bio-monitored PAHs exposure among five panels of UCLA students who traveled from Los Angeles to Beijing for 10 weeks in the summers of 2014-2018. The results indicated that the students’ exposure to PAHs were not changed in Los Angeles from 2014 to 2018, however, the PAHs exposure decreased by 52.3% in Beijing from 2014 to 2018, in associations with ambient concentrations of fine particles (PM_2.5) or nitrogen dioxide (NO₂). These results provide direct evidence demonstrating that air pollution control measures reduced human exposure to airborne toxins such as PAHs.

In this study, the team determines the effectiveness of air pollution control measures in reducing PAHs exposure using a natural experiment among international travelers, which allowed the use a country without such policies as control. Furthermore, the 8-year ambient monitoring also illustrated the changes of emission and ambient concentrations of PAHs, as two intermediate steps linking policy with human exposure. Taken together, this study provides compelling evidence to demonstrate the effectiveness of long-term air pollution control in reducing human exposure to PAHs. The unprecedented reduction in ambient PAH levels (by 97%) from 2014 to 2021 also highlights the need for future studies on the health effects of contemporary low-level PAH pollution in China.

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