Enhanced formation of secondary organic aerosol from photochemical oxidation during the COVID-19 lockdown in a background site in Northwest China

Zhong, Haobin; Huang, Ru‐Jin; Chang, Yunhua; Duan, Jing; Lin, Chunshui; Yang, Chen

doi:10.1016/j.scitotenv.2021.144947

Cited by 20 publications

(22 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The formation of nitrate and sulfate was enhanced during the lockdown periods (HE4 and HE5), [33][34][35]45,49,50 which would be related to chemistryfavorable meteorological conditions. Similar to previous studies, 44,51,52 photochemistry played an important role in forming daytime nitrate, as O X explained 10 ± 6, 6 ± 5, 4 ± 4, 6 ± 4, and 3 ± 3 μg m −3 nitrate on average during HE1−HE5, respectively (Figure S5). A number of pieces of evidence prove that the O X -driven daytime nitrate resulted from photochemistry rather than its precursor (NO x , part of the O X composition), particularly during the lockdown period.…”

Section: ■ Results and Discussionsupporting

confidence: 89%

“…The low temperature and high-RH conditions were conducive to nitrate formation because they enhanced the N 2 O 5 heterogeneous hydrolysis reaction and strengthened the partitioning of gas into particles. [45][46][47]52,53 The major pathway of formation of sulfate was different from that of nitrate. The aqueous chemistry was likely the dominant pathway of formation for sulfate because RH accounted for 3 ± 2, 5 ± 4, 6 ± 2, 5 ± 3, and 4 ± 3 μg m −3 sulfate in HE1−HE5, respectively (Figure S6).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…The RH-driven nitrate levels during HE1–HE5 were 2 ± 1, 6 ± 4, 6 ± 3, 5 ± 3, and 4 ± 3 μg m –3 , respectively. The low temperature and high-RH conditions were conducive to nitrate formation because they enhanced the N 2 O 5 heterogeneous hydrolysis reaction and strengthened the partitioning of gas into particles. − ,, …”

Section: Resultsmentioning

confidence: 99%

See 2 more Smart Citations

Revealing Drivers of Haze Pollution by Explainable Machine Learning

Hou

Dai

Song

et al. 2022

Environ. Sci. Technol. Lett.

102

View full text Add to dashboard Cite

Many places on earth still suffer from a high level of atmospheric fine particulate matter (PM2.5) pollution. Formation of a particulate pollution event or haze episode (HE) involves many factors, including meteorology, emissions, and chemistry. Understanding the direct causes of and key drivers behind the HE is thus essential. Traditionally, this is done via chemical transport models. However, substantial uncertainties are introduced into the model estimation when there are significant changes in the emissions inventory due to interventions (e.g., the COVID-19 lockdown). Here we applied a Random Forest model coupled with a Shapley additive explanation algorithm, a post hoc explanation technique, to investigate the roles of major meteorological factors, primary emissions, and chemistry in five severe HEs that occurred before or during the COVID-19 lockdown in China. We discovered that, in addition to the high level of primary emissions, PM2.5 in these haze episodes was largely driven by meteorological effects (with average contributions of 30–65 μg m–3 for the five HEs), followed by chemistry (∼15–30 μg m–3). Photochemistry was likely the major pathway of formation of nitrate, while air humidity was the predominant factor in forming sulfate. Our results highlight that the machine learning driven by data has the potential to be a complementary tool in predicting and interpreting air pollution.

show abstract

Section: ■ Results and Discussionsupporting

confidence: 89%

Section: ■ Results and Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Revealing Drivers of Haze Pollution by Explainable Machine Learning

Hou

Dai

Song

et al. 2022

Environ. Sci. Technol. Lett.

102

View full text Add to dashboard Cite

show abstract

“…The results at the Pudong site clearly show that the enhanced atmospheric oxidation capacity during the COVID-19 pandemic promoted the formation of secondary aerosols and offset the effects of primary emission reductions in the eastern YRD. Such a phenomenon was also observed in many other regions in China during the COVID-19 lockdown (Le et al, 2020;Zheng et al, 2020;Tian et al, 2021;Zhong et al, 2021). These results suggest an important role of atmospheric oxidation capacity in regulating secondary aerosol formation.…”

Section: Nitrate Aerosol Formation During the Covid-19supporting

confidence: 71%

High atmospheric oxidation capacity drives wintertime nitrate pollution in the eastern Yangtze River Delta of China

et al. 2022

View full text Add to dashboard Cite

Abstract. Nitrate aerosol plays an increasingly important role in wintertime haze pollution in China. Despite intensive research on wintertime nitrate chemistry in recent years, quantitative constraints on the formation mechanisms of nitrate aerosol in the Yangtze River Delta (YRD), one of the most developed and densely populated regions in eastern China, remain inadequate. In this study, we identify the major nitrate formation pathways and their key controlling factors during the winter haze pollution period in the eastern YRD using 2-year (2018–2019) field observations and detailed observation-constrained model simulations. We find that the high atmospheric oxidation capacity, coupled with high aerosol liquid water content (ALWC), made both the heterogeneous hydrolysis of dinitrogen pentoxide (N2O5) and the gas-phase OH oxidation of nitrogen dioxide (NO2) important pathways for wintertime nitrate formation in this region, with contribution percentages of 69 % and 29 % in urban areas and 63 % and 35 % in suburban areas during the haze pollution episodes, respectively. We further find that the gas-to-particle partitioning of nitric acid (HNO3) was very efficient so that the rate-determining step in the overall formation process of nitrate aerosol was the oxidation of NOx to HNO3 through both heterogeneous and gas-phase processes. The atmospheric oxidation capacity (i.e., the availability of O3 and OH radicals) was the key factor controlling the production rate of HNO3 from both processes. During the COVID-19 lockdown (January–February 2020), the enhanced atmospheric oxidation capacity greatly promoted the oxidation of NOx to nitrate and hence weakened the response of nitrate aerosol to the emission reductions in urban areas. Our study sheds light on the detailed formation mechanisms of wintertime nitrate aerosol in the eastern YRD and highlights the demand for the synergetic regulation of atmospheric oxidation capacity and NOx emissions to mitigate wintertime nitrate and haze pollution in eastern China.

show abstract

“…The reason was probably that the decrease of NO x since lockdown lead to more photochemical reactions and more generation of O 3 so as to promote the generation of MO-OOA, which was also found in northwest China during lockdown. 70,88 Furthermore, during the period from February 1 to February 5, other gaseous pollutants concentrations were low because of good dispersioncondition while O 3 concentration was still high continuously (Figure 1B). Meanwhile, the generation of MO-OOA was also significant with southerly winds in the morning of February 2 and afternoon of February 3 (Figure 5B and SI Figure S1B).…”

Section: Resultsmentioning

confidence: 99%

Variations and Sources of Organic Aerosol in Winter Beijing under Markedly Reduced Anthropogenic Activities During COVID-2019

Zheng

Zhao

et al. 2021

Environ. Sci. Technol.

View full text Add to dashboard Cite

The COVID-19 outbreak provides a “controlled experiment” to investigate the response of aerosol pollution to the reduction of anthropogenic activities. Here we explore the chemical characteristics, variations, and emission sources of organic aerosol (OA) based on the observation of air pollutants and combination of aerosol mass spectrometer (AMS) and positive matrix factorization (PMF) analysis in Beijing in early 2020. By eliminating the impacts of atmospheric boundary layer and the Spring Festival, we found that the lockdown effectively reduced cooking-related OA (COA) but influenced fossil fuel combustion OA (FFOA) very little. In contrast, both secondary OA (SOA) and O3 formation was enhanced significantly after lockdown: less-oxidized oxygenated OA (LO-OOA, 37% in OA) was probably an aged product from fossil fuel and biomass burning emission with aqueous chemistry being an important formation pathway, while more-oxidized oxygenated OA (MO-OOA, 41% in OA) was affected by regional transport of air pollutants and related with both aqueous and photochemical processes. Combining FFOA and LO-OOA, more than 50% of OA pollution was attributed to combustion activities during the whole observation period. Our findings highlight that fossil fuel/biomass combustion are still the largest sources of OA pollution, and only controlling traffic and cooking emissions cannot efficiently eliminate the heavy air pollution in winter Beijing.

show abstract

Enhanced formation of secondary organic aerosol from photochemical oxidation during the COVID-19 lockdown in a background site in Northwest China

Cited by 20 publications

References 35 publications

Revealing Drivers of Haze Pollution by Explainable Machine Learning

Revealing Drivers of Haze Pollution by Explainable Machine Learning

High atmospheric oxidation capacity drives wintertime nitrate pollution in the eastern Yangtze River Delta of China

Variations and Sources of Organic Aerosol in Winter Beijing under Markedly Reduced Anthropogenic Activities During COVID-2019

Contact Info

Product

Resources

About