Development of the broadband cavity-enhanced absorption spectrometer for in situ measurements of BrO

Correspondence: Pinhua Xie (phxie@aiofm.ac.cn)

Atmospheric halogens, including fluorine (F), chlorine (Cl), bromine (Br), and iodine(I), significantly impact atmospheric chemistry and climate change. Especially BrO plays an important role in the processes of ozone destruction, disturbance of NO_x and HO_x chemistry, oxidation of dimethyl sulfide (DMS), and the deposition of elementary mercury. BrO can be measured using the Differential Optical Absorption Spectroscopy (DOAS) method owing to their structured absorption cross sections in the UV and visible parts of the spectrum. In the troposphere, BrO has been detected in polar regions, at salt lakes, in volcanic plumes, and in the marine boundary layer using optical remote sensing approaches including MAX-DOAS, LP-DOAS, and satellite observations. This study presents an in-situ measurement instrument for atmospheric BrO detection based on broadband cavity-enhanced absorption spectroscopy (BBCEAS). The instrument utilizes a 340 nm UV LED light source operating within the 333-347 nm spectral range, which encompasses three characteristic BrO absorption bands. Allan deviation analysis for BrO reveals a detection sensitivity of about 1 pptV and a custom-built BrO generation system was developed to characterize sampling losses. The system's field deployment at the salt lake successfully conducted ground-based direct observations of atmospheric reactive halogen species. This field validation demonstrates the instrument's capability for field applications in complex environmental conditions.

Acknowledgements:  This research was funded by the National Natural Science Foundation of China (No. 42175155, 42475141) , the Anhui Provincial Key R&D Program, China (No. 2023t07020016), the Youth Innovation Promotion Association of Chinese Academy of Sciences (No. 2023464), and the CASHIPS Director’s Fund (BJPY2024B10).