Persistent sulfate formation from London Fog to Chinese haze.

Area of Science:

• Atmospheric Chemistry
• Environmental Science
• Climate Science

Background:

• Sulfate aerosols significantly impact human health, ecosystems, weather, and climate.
• Current atmospheric models underestimate sulfate aerosol concentrations.
• The precise formation mechanisms of sulfate aerosols remain inadequately understood.

Purpose of the Study:

• To elucidate the key mechanism for efficient sulfate aerosol formation.
• To identify the specific atmospheric conditions facilitating this process.
• To provide insights for mitigating severe haze events.

Main Methods:

• Atmospheric measurements conducted in two major Chinese cities.
• Complementary laboratory experiments simulating atmospheric conditions.
• Analysis of sulfur dioxide (SO2) and nitrogen dioxide (NO2) oxidation pathways.

Main Results:

• Aqueous oxidation of SO2 by NO2 is identified as a critical pathway for sulfate formation.
• This process is highly efficient under conditions of high relative humidity with ammonia (NH3) neutralization on fine aerosols, or within clouds.
• In polluted environments, this mechanism significantly enhances sulfate, nitrate, and organic matter formation, contributing to severe haze.

Conclusions:

• The identified sulfate production mechanism explains severe haze episodes, including those in China and the 1952 London Fog.
• Effective haze mitigation strategies can be implemented by controlling ammonia (NH3) and nitrogen dioxide (NO2) emissions.
• This understanding offers a pathway to address air pollution challenges in China and other developing regions.