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Vapor Pressure Lowering03:28

Vapor Pressure Lowering

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The equilibrium vapor pressure of a liquid is the pressure exerted by its gaseous phase when vaporization and condensation are occurring at equal rates:
 
Dissolving a nonvolatile substance in volatile liquid results in a lowering of the liquid’s vapor pressure. This phenomenon can be explained by considering the effect of added solute molecules on the liquid's vaporization and condensation processes. To vaporize, solvent molecules must be present at the surface of the solution....
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Decrease in ambient volatile organic compounds during the COVID-19 lockdown period in the Pearl River Delta region,

Chenglei Pei1, Weiqiang Yang2, Yanli Zhang3

  • 1State Key Laboratory of Organic Geochemistry, Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; Guangzhou Sub-branch of Guangdong Ecological and Environmental Monitoring Center, Guangzhou 510060, China; University of Chinese Academy of Sciences, Beijing 100049, China.

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During COVID-19 lockdowns, volatile organic compounds (VOCs) decreased significantly in Guangzhou, with industrial and diesel emissions showing the largest reductions. This highlights the challenge of controlling ozone pollution in megacities.

Keywords:
COVID-19NOxOzonePRDVolatile organic compounds

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Area of Science:

  • Atmospheric Chemistry
  • Environmental Science
  • Air Pollution Studies

Background:

  • COVID-19 lockdowns led to reduced anthropogenic emissions globally.
  • Ozone (O3) pollution in megacities is often VOC-limited, but lockdown impacts on VOCs are understudied.
  • Guangzhou, a megacity in the Pearl River Delta, provided a unique case for studying emission changes.

Purpose of the Study:

  • To investigate the impact of COVID-19 lockdown on ambient volatile organic compounds (VOCs) in Guangzhou.
  • To identify the sources contributing to VOC changes during the lockdown.
  • To assess the implications for ozone (O3) formation and control strategies.

Main Methods:

  • Online monitoring of ambient VOCs in Guangzhou before, during, and after the lockdown.
  • Analysis of changes in total VOCs, alkanes, alkenes, and aromatics.
  • Source apportionment using the positive matrix factorization (PMF) model.
  • Evaluation of ozone (O3) and nitrogen oxides (NOx) levels in conjunction with VOC data.

Main Results:

  • Total VOC mixing ratios decreased by 19.1% during the lockdown.
  • Significant reductions observed in alkanes (19.0%), alkenes (24.8%), and aromatics (38.2%).
  • Higher alkanes (C ≥ 6) decreased by 67.8%, indicating reduced industrial solvent use.
  • Source apportionment attributed 48.9% to industrial emissions, 42.2% to diesel exhaust, and 8.8% to gasoline emissions.
  • Despite VOC and NOx reductions, ozone levels showed complex changes, with a 17% increase in 1-hour O3 and an 11% decrease in daily max 8-hour O3.

Conclusions:

  • COVID-19 lockdown significantly reduced VOCs in Guangzhou, primarily from industrial and diesel sources.
  • The reduction in VOCs and NOx did not lead to a straightforward decrease in ozone, indicating complex atmospheric chemistry.
  • Controlling precursor VOC and NOx emissions remains a critical challenge for mitigating ozone pollution in megacities.