[Case Analysis of Heavy Air Pollution Process in Xi'an Using Multi-source Data].

Area of Science:

• Atmospheric Science
• Environmental Science
• Chemistry

Context:

• Xi'an faces persistent air pollution challenges.
• A severe pollution event occurred in January 2019.
• Investigated using multi-source data and methods like material balance and sulfur/nitrogen oxidation rate (SOR/NOR).

Purpose:

• To investigate the formation mechanism of a heavy pollution episode in Xi'an.
• To analyze the interaction between meteorological conditions and air pollution.
• To identify the primary chemical components contributing to PM2.5 and visibility reduction.

Summary:

• The pollution event had three phases: accumulation, maintenance, and dispersion.
• Adverse weather conditions (stable atmosphere, limited diffusion) and feedback effects were primary causes.
• Pollutant accumulation led to temperature inversions, decreased mixing layer height, and increased humidity, promoting secondary aerosol formation and growth.

Impact:

• Secondary inorganic ions (SNA) and other components dominated PM2.5 during peak pollution.
• Secondary formation significantly impacted both heavy pollution events and visibility.
• Strong cold air facilitated pollutant dispersion during the final phase.