Determining the differences in O₃-NO_x-VOCs sensitivity between sauna and roast days

Area of Science:

• Atmospheric Chemistry
• Meteorology
• Environmental Science

Background:

• Tropospheric ozone (O3) pollution is exacerbated by high temperatures, occurring under both humid-heat (sauna) and dry-heat (roast) conditions.
• The distinct mechanisms driving O3 formation and degradation during these two distinct high-temperature weather patterns are not well understood.

Purpose of the Study:

• To investigate the differences in O3 formation and precursor dynamics between sauna and roast days.
• To provide a scientific basis for targeted O3 control strategies under varied high-temperature weather scenarios.

Main Methods:

• Field observations of O3, its precursors, and meteorological factors in Beijing (2019-2021).
• Analysis of 18 O3 exceedance days (10 sauna, 8 roast).
• Box model simulations to assess O3 sensitivity to precursors.

Main Results:

• Roast days exhibited significantly higher sensible heat flux and wind speed gradients, indicating greater thermal and dynamic turbulence.
• Enhanced vertical cycling of nitrogen dioxide (NO2) and O3 was observed on roast days, with increased upward NO2 transport and downward O3 transport.
• O3 sensitivity was primarily driven by NO2-O3 vertical cycling speed.

Conclusions:

• Ozone pollution control strategies must consider distinct meteorological conditions.
• On sauna days, O3 formation is sensitive to both nitrogen oxides (NOx) and volatile organic compounds.
• On roast days, O3 formation is predominantly limited by NOx availability due to enhanced vertical mixing.