Episode-Based Evolution Pattern Analysis of Haze Pollution: Method Development and Results from Beijing, China

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Air Quality Research

Background:

• Beijing faced numerous haze episodes in 2013, leading to 189 polluted days.
• These events varied in sources, formation, and composition, necessitating tailored pollution control policies.

Purpose of the Study:

• To provide an overview of the similarities and differences among Beijing's 2013 haze episodes.
• To link identified haze episode types with prevailing synoptic weather conditions.

Main Methods:

• Conducted one-year of online atmospheric observations in Beijing.
• Developed a program to simultaneously classify haze episodes and identify their characteristics.
• Analyzed particulate matter (PM2.5, PM10) composition, including organic matter (OM), and oxidation ratios (SOR, NOR).

Main Results:

• Identified 73 distinct haze episodes, categorizing them into pure haze (winter), mixed haze-dust (spring), and mixed haze-fog (summer-autumn).
• Organic matter was consistently abundant but typically not the primary driver of pollution; secondary inorganic species production increased with haze severity.
• Haze evolution correlated with rising sulfur and nitrogen oxidation ratios, indicating enhanced secondary aerosol formation.

Conclusions:

• Haze episodes in Beijing exhibit distinct seasonal patterns and compositions.
• Secondary inorganic aerosol formation, rather than organic matter, often drives severe haze events, except during biomass burning.
• Effective air pollution control requires understanding the specific type and drivers of each haze episode.