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Changes in wintertime visibility across China over 2013-2019 and the drivers: A comprehensive assessment using
Lu Chen1, Fang Zhang2, Jingye Ren3
1Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China; School of Civil and Environmental Engineering, Harbin Institute of Technology (Shenzhen), 518055 Shenzhen, China.
The Science of the Total Environment
|December 22, 2023
Summary
Despite emission reductions, visibility issues persist in China. A new study reveals rising humidity and aerosol effects, not just particulate matter, are driving visibility changes, necessitating region-specific air quality strategies.
Area of Science:
- Atmospheric Science
- Environmental Science
- Air Quality Research
Background:
- Particulate matter reduction has improved visibility in some Chinese regions, but low-visibility events remain frequent.
- Climate change and carbon neutrality goals necessitate understanding evolving visibility mechanisms.
- Existing air quality strategies may not fully address the complex factors influencing visibility trends.
Purpose of the Study:
- To comprehensively assess visibility changes in China from 2013-2019.
- To identify the key drivers of visibility trends, including particulate matter (PM2.5), relative humidity (RH), aerosol hygroscopicity (κ), and boundary layer height (BLH).
- To provide region-specific insights for effective air pollution control strategies.
Main Methods:
- Combined site observations, model-derived datasets, and machine learning techniques for a novel assessment approach.
- Analyzed visibility trends across different regions of China, including North China, South China, the Fenwei Plain, and central and southern China (CSC).
- Quantified the contributions of various factors (PM2.5, RH, κ, BLH, temperature, wind speed) to visibility changes.
Main Results:
- Wintertime visibility improved in North China, South China, and the Fenwei Plain, but deteriorated in CSC (approx. 1 km yr⁻¹).
- In CSC, visibility decline was driven by increased RH (47%), enhanced aerosol hygroscopicity (9%), and reduced BLH (8%), outweighing PM2.5 reduction.
- RH became a dominant factor (40% ± 24% in 2019), while PM2.5's contribution decreased (18% ± 19%). Other factors like temperature, wind speed, BLH, and κ accounted for over 40%.
Conclusions:
- Visibility trends in China are complex and influenced by multiple factors beyond PM2.5.
- Increased relative humidity and aerosol properties play a significant role, especially in regions experiencing visibility deterioration.
- Region-specific air pollution control strategies are crucial for mitigating low-visibility events effectively.
