MAX-DOAS measurements of BrO and NO2 in the marine boundary layer

Abstract

During a cruise of the German research vessel Polarstern from Bremerhaven, Germany to Capetown, South Africa in October 2000 mid latitude tropospheric bromine oxide (BrO) and nitrogen dioxide (NO2) abundances were investigated by ground-based MAXDOAS (scattered light Multi Axis Differential Optical Absorption Spectroscopy . By comparing the slant column densities of absorbers measured at different elevation angles above the horizon (5° to 90°) it is possible to draw conclusions regarding the vertical distribution of the investigated absorbers (i.e., BrO and NO2). During a period of 2 days in the region north of the Canary Islands (around 35°N, 13°W) significant boundary layer BrO in the 1 ppt range was found. For the remaining time all data points ranged below the detection limit. Boundary layer NO2 was found near Europe and the Canary Islands with mixing ratios in the range of several ppb. In the remote marine air south west of Africa upper limits were derived.