Air quality in China significantly improved after strict
regulations
were put in place. To assess the efficacy of volatile organic compound
(VOC) control strategies, online measurements of wintertime ambient
VOCs at a Beijing urban location were taken in December and January
from 2014 to 2019. We assessed the changes in mixing ratios of 81
VOC species and cancer risks of 10 hazard species. The impact of meteorology
on VOC mixing ratios was decoupled using a machine-learning approach.
The highest and lowest VOC mixing ratios were observed in wintertime
2017 (December 2016 and January 2017) and 2019 (December 2018 and
January 2019), respectively, with a decrease in 63.5%. Both emission
control policies and meteorological conditions helped reduce VOC mixing
ratios in the winter in Beijing. Alkenes and alkynes decreased significantly
from 2015 to 2019. In contrast, the contribution of aromatics increased
considerably from 2015 to 2017, and many aromatics had higher mixing
ratios in 2019 than in 2015, indicating that aromatics may be a key
group for future air quality improvement. The cancer risks due to
VOC exposure in the wintertime in Beijing in 2019 were lower than
in other years but were still much higher than the safety level.