Critical Role of Simultaneous Reduction of Atmospheric Odd Oxygen for Winter Haze Mitigation

Abstract

The lockdown due to COVID-19 created a rare opportunity to examine the nonlinear responses of secondary aerosols, which are formed through atmospheric oxidation of gaseous precursors, to intensive precursor emission reductions. Based on unique observational data sets from six supersites in eastern China during 2019−2021, we found that the lockdown caused considerable decreases (32−61%) in different secondary aerosol components in the study region because of similar-degree precursor reductions. However, due to insufficient combustionrelated volatile organic compound (VOC) reduction, odd oxygen (O x = O 3 + NO 2 ) concentration, an indicator of the extent of photochemical processing, showed little change and did not promote more decreases in secondary aerosols. We also found that the Chinese provinces and international cities that experienced reduced O x during the lockdown usually gained a greater simultaneous PM 2.5 decrease than other provinces and cities with an increased O x . Therefore, we argue that strict VOC control in winter, which has been largely ignored so far, is critical in future policies to mitigate winter haze more efficiently by reducing O x simultaneously.

Attribution of Air Quality Benefits to Clean Winter Heating Policies in China: Combining Machine Learning with Causal Inference

“…38 This is consistent with a recent study demonstrating that strict VOC control in winter is critical to mitigate PM 2.5 more efficiently by reducing O x simultaneously. 39 Future modeling studies are required to further investigate the impacts of heating emissions on O 3 as well as O x during heating periods in northern China.…”

In Situ Construction of Manganese Oxide Photothermocatalysts for the Deep Removal of Toluene by Highly Utilizing Sunlight Energy

“…Volatile organic compounds (VOCs) emitted from anthropogenic and natural sources come into human living space and endanger human health. Moreover, VOCs are major precursors leading to ozone and secondary organic aerosols in the atmosphere. − Human yearning for good living space has driven the development of air pollution elimination technology. For VOCs with low concentration and flow rate, photocatalysis and catalytic oxidation are effective degradation methods. − However, for the degradation of aromatic compounds, such as toluene, they still suffer from low quantum efficiency and high energy consumption, respectively, which make it essential to find a good way that integrates multiple advantages to handle pollutants .…”

Urban–Rural Disparities in Air Quality Responses to Traffic Changes in a Megacity of China Revealed Using Machine Learning

“…Similar phenomena were also observed in other VOC-limited regions around the world. 18,21,29 The deweathered O X -dailyave, O Xnoontime, and O X -nighttime levels during the lockdown compared to prelockdown were 3.38 ± 1.85, 4.60 ± 5.17, and 1.91 ± 2.78 μg/m 3 lower in the urban area, 5.0%, 6.2%, and 3.0% decreases. The reduction in O X -nighttime is the lowest, due to the relative smaller reduction of precursors at night considering the diurnal variation of anthropogenic emissions.…”

“…11 We performed a weather normalization for NO X , O 3 , PM 2.5 and the total gaseous oxidant (i.e., O X = NO 2 + O 3 ), a parameter representing net photochemical productions. 18,29,30 Figure 2 (deweathered) and Figure S6 (observed) show the pollutant concentration changes between the lockdown and pre-COVID period with and without weather normalization. The changes in observed NO 2 , maximum daily 8 h average (MDA8) O 3 , and PM 2.5 concentrations are larger than the deweathered ones, especially for the urban area.…”