Observations of BrO and other trace gases in typical regions of China based on MAX-DOAS network

Bromine oxides (BrO) play a critical role in ozone depletion and boundary layer chemistry. During the spring-summer period of 2024 (May 1 to June 15), Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements were conducted in Hangzhou Bay Area, China, to observe the presence of BrO, aerosols, and other trace gases (NO₂, HCHO, etc.). The average BrO volume mixing ratio (VMR) during the observation period was 2.14 ppt, increasing to 4.24 ppt during pollution episodes. High concentrations of BrO were primarily observed in the boundary layer at altitudes of 1.5–2.5 km, while other trace gases are mainly concentrated between 0-1 km near the surface. BrO concentrations tended to peak during the morning hours (7:00 am–10:00 am local time), showing a clear correlation with aerosol variations, indicating significant photochemical activation. A anti-correlation was observed between BrO and ozone (O₃), revealing a bromine-mediated O₃ depletion mechanism.

Furthermore, the overall pollutant concentration in June was higher than in May, and this change is closely related to seasonal meteorological factors, particularly variations in wind direction and temperature, which are considered the main factors influencing BrO levels.

Validation conducted during the CINDI-3 campaign demonstrated the high reliability of MAX-DOAS measurements, confirming the robustness of the MAX-DOAS technique for monitoring coastal air quality. These findings enhance our understanding of BrO dynamics in coastal regions and their impact on atmospheric chemistry.