A Cavity-Enhanced Differential Optical Absorption Spectroscopy instrument for measurement of BrO, HCHO, HONO and O₃

Abstract. The chemistry of the troposphere and specifically the global tropospheric ozone budget is affected by reactive halogen compounds like BrO or ClO. Bromine monoxide (BrO) plays an important role in the processes of ozone destruction, disturbance of NO_x and HO_x chemistry, oxidation of DMS, and the deposition of elementary mercury. In the troposphere BrO has been detected in polar regions, at salt lakes, in volcanic plumes, and in the marine boundary layer. For a better understanding of these processes instruments with high spatial resolution and high sensitivity are necessary. A Cavity Enhanced Differential Optical Absorption Spectroscopy (CE-DOAS) instrument was designed and applied. For the first time, such an instrument uses an UV-LED in the UV-wavelength range (325–365 nm) to identify BrO. In laboratory studies at the Atmospheric Chemistry Research Laboratory, University of Bayreuth, Germany, BrO, as well as HONO, HCHO, O₃, and O₄, could be reliable determined at detection limits (for five minutes integration time) of 20 ppt for BrO, 9.1 ppb for HCHO, 970 ppt for HONO, and 91 ppb for O₃, respectively. The best detection limits for BrO (11 ppt), HCHO (5.1 ppb), HONO (490 ppt), and O₃ (59 ppb) were achieved for integration times of 81 min or less.