Spatiotemporal distributions of ambient SO₂ across China based on satellite retrievals and ground observations:...

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Public Health

Background:

• Accurate spatiotemporal distributions of daily ambient sulfur dioxide (SO2) are crucial for assessing management effectiveness and human health risks.
• Understanding SO2 pollution patterns in China is vital due to its significant impact on a large population.

Purpose of the Study:

• To estimate daily and multiyear SO2 levels across China on a 0.1° grid from 2013 to 2016.
• To analyze the spatiotemporal variations, seasonality, and trends of SO2 concentrations.
• To evaluate the effectiveness of SO2 emission reduction strategies and their impact on public health.

Main Methods:

• Utilized the random-forest spatiotemporal kriging (RF-STK) model to assimilate satellite and ground-based SO2 observations.
• Employed cross-validation to assess model accuracy, achieving R² values of 0.64 for daily and 0.81 for multiyear averages.
• Analyzed population-weighted averages, seasonal variations, and long-term trends in SO2 concentrations.

Main Results:

• The multiyear population-weighted average SO2 concentration in China was 28.1 ± 14.0 μg/m³.
• Northern China experienced the most severe SO2 pollution (45.1 ± 14.7 μg/m³), with concentrations peaking in winter and lowest in summer.
• Annual SO2 levels decreased from 34.4 ± 18.2 to 22.7 ± 11.1 μg/m³ between 2013 and 2016, reducing exposed populations by 86% to 48% for non-attainment days (>20 μg/m³).
• Emission reduction effectiveness varied regionally; Shandong saw a 45% SO2 decrease with a 9% coal consumption increase, while Shanxi had a 15% SO2 decrease with a 3% coal consumption decrease, linked to waste gas disposal facilities.

Conclusions:

• Substantial SO2 reduction in China is attributed to decreased emissions, particularly from coal consumption, though effectiveness varies.
• The seasonality of SO2 is primarily driven by meteorological variations, while emission controls significantly impact overall reduction.
• Stricter regulations are necessary to further reduce SO2 concentrations and protect public health, especially in Northern China.