Abstract
Staggered-peak production (SP)-a measure to halt industrial production in the heating season-has been implemented in North China Plain to alleviate air pollution. We compared the variations of PM(1) composition in Beijing during the SP period in the 2016 heating season (SP(hs)) with those in the normal production (NP) periods during the 2015 heating season (NP(hs)) and 2016 non-heating season (NP(nhs)) to investigate the effectiveness of SP. The PM(1) mass concentration decreased from 70.0 ± 54.4 μg m(-3) in NP(hs) to 53.0 ± 56.4 μg m(-3) in SP(hs), with prominent reductions in primary emissions. However, the fraction of nitrate during SP(hs) (20.2%) was roughly twice that during NP(hs) (12.7%) despite a large decrease of NO(x), suggesting an efficient transformation of NO(x) to nitrate during the SP period. This is consistent with the increase of oxygenated organic aerosol (OOA), which almost doubled from NP(hs) (22.5%) to SP(hs) (43.0%) in the total organic aerosol (OA) fraction, highlighting efficient secondary formation during SP. The PM(1) loading was similar between SP(hs) (53.0 ± 56.4 μg m(-3)) and NP(nhs) (50.7 ± 49.4 μg m(-3)), indicating a smaller difference in PM pollution between heating and non-heating seasons after the implementation of the SP measure. In addition, a machine learning technique was used to decouple the impact of meteorology on air pollutants. The deweathered results were comparable with the observed results, indicating that meteorological conditions did not have a large impact on the comparison results. Our study indicates that the SP policy is effective in reducing primary emissions but promotes the formation of secondary species.