Retrieval of stratospheric and tropospheric BrO profiles and columns using ground-based zenith-sky DOAS observations at Harestua, 60° N

Abstract

Abstract.A profiling algorithm based on the optimal estimation method is applied to ground-based zenith-sky UV-visible measurements from Harestua, Southern Norway (60 • N, 11 • E) in order to retrieve BrO vertical profiles. The sensitivity of the zenith-sky observations to the tropospheric BrO detection is increased by using for the spectral analysis a fixed reference spectrum corresponding to clear-sky noon summer conditions. The information content and retrieval errors are characterized and it is shown that the retrieved stratospheric profiles and total columns are consistent with correlative balloon and satellite observations, respectively. Tropospheric BrO columns are derived from profiles retrieved at 80 • solar zenith angle during sunrise and sunset for the 2000-2006 period. They show a marked seasonality with mean column value ranging from 1.52±0.62×10 13 molec/cm 2 in late winter/early spring to 0.92±0.38×10 13 molec/cm 2 in summer, which corresponds to 1.0±0.4 and 0.6±0.2 pptv, respectively, if we assume that BrO is uniformly mixed in the troposphere. These column values are also consistent with previous estimates made from balloon, satellite, and other ground-based observations. Daytime events from the polar region to Harestua. The daytime stratospheric BrO columns are compared to the SLIMCAT stratospheric 3-D-CTM. The model run used in this study, which assumes 21.2 pptv for the Br y loading (15 pptv for long-lived bromine species and additional 6 pptv for very short-lived species (VSLS) added by a scaling of CH 3 Br), significantly underestimates the retrieved BrO columns. A sensitivity study shows that a good agreement can only be obtained if 6 to 8 pptv accounting for VSLS are added directly (and not by a scaling of CH 3 Br) to the SLIMCAT long-lived bromine species profile. This contribution of the VSLS to the total bromine loading is also consistent with recently published studies.

The novel HALO mini-DOAS instrument: inferring trace gas concentrations from airborne UV/visible limb spectroscopy under all skies using the scaling method

“…4.2). These concentrations are on the higher end of comparable BrO measurements in the same altitude range (12-13 km) reported in the literature (Harder et al, 1998;Dorf et al, 2006;Hendrick et al, 2007;Werner et al, 2017), which could be caused by the subsidence of stratospheric air from higher altitudes discussed above. Panel (e) of Fig.…”

Global observations of tropospheric BrO columns using GOME-2 satellite data

“…14, it stated that, except for the results at high latitudes in spring, the seasonal and latitudinal variations of the tropospheric BrO columns are generally rather small, with a magnitude lying within the uncertainties of the retrieved tropospheric BrO columns. Our analysis tends to confirm the findings of other studies (Fitzenberger et al, 2000;Wagner et al, 2001;Richter et al, 2002;Van Roozendael et al, 2002;Hendrick et al, 2007;Theys et al, 2007) that a tropospheric BrO background with vertical columns of 1-3 × 10 13 molec cm −2 , in addition to the polar BrO emissions occurring in spring, must be present at the global scale for all seasons. This is in contrast to three studies using spectral observations of direct-sun geometry, at Lauder (Schofield et al, 2004), Arrival Heights, Antarctica (Schofield et al, 2006) and in the tropics (Dorf et al, 2008) showing tropospheric columns significantly less i.e.…”

Airborne multi-axis DOAS measurements of atmospheric trace gases on CARIBIC long-distance flights

“…However, this might largely be excluded for BrO since typical tropospheric mixing ratios are in the order of 0.6-3 ppt (e.g. Fitzenberger et al, 2000;Hendrick et al, 2007;Theys et al, 2007). The observed mixing ratio of 6 ppt BrO and particularly the high ozone mixing ratio support the assumption that this air mass originated in the stratosphere.…”