Visible and near‐ultraviolet spectroscopy at McMurdo Station, Antarctica: 5. Observations of the diurnal variations of BrO and OClO

Abstract

Observations of the diurnal variations of OClO and BrO during austral spring, 1987, using long‐path visible and near‐ultraviolet absorption spectroscopy are presented and compared to simplified model calculations. It is shown that care must be taken to compare model calculations and measurements along the line of sight of the instrument. Evening twilight observations of OClO are found to be broadly consistent with current photochemical schemes, assuming ClO and BrO levels near 50 mbar of about 0.5 parts per billion by volume (ppbv) and 7 parts per trillion by volume (pptv), respectively, throughout the observing period from late August to mid‐October. Nighttime observations of OClO obtained using the Moon as a light source display evidence for growth after sunset in late August, but not in late September. Further, the observed morning twilight OClO abundances are in agreement with model calculations in late August, but they generally fall below calculations in late September and October. Observations of BrO in mid‐September show far greater evening than morning twilight abundances. It is shown that the diurnal variations of BrO and OClO in mid‐September and October can be explained by formation of the BrONO2 reservoir species at night, although other reservoir species with comparably long lifetimes could also explain the observations. If formation of BrONO2 is the correct explanation for these data, the observations suggest that NO2 levels in the Antarctic lower stratosphere are of the order of a few pptv or less in late August, a few tens of pptv in mid‐September, and a few hundred pptv in October.

NDACC/SAOZ UV-visible total ozone measurements: improved retrieval and comparison with correlative ground-based and satellite observations

“…For more than two decades, stratospheric ozone and related trace gases such as NO 2 , BrO, and OClO have been monitored at a number of stations belonging to the Network for the Detection of Atmospheric Composition Change (NDACC) using ground-based zenith-sky UV-visible absorption spectrometers (e.g., Pommereau and Goutail, 1988;Solomon et al, 1989;McKenzie, et al, 1991;Kreher et al, 1997;Richter et al, 1999;Van Roozendael et al, 1998;Struthers et al, 2004;Hendrick et al, 2008). The main difference with the Dobson and Brewer instruments of the Global Atmospheric Watch network of the World Meteorological Organization (GAW/WMO), which are measuring ozone by direct sun and by zenith-sky spectrophotometry at low sun in the UV Huggins bands, is the use of the visible Chappuis bands, a wavelength range not applicable to ground-based direct sun or satellite nadir-viewing instruments observing at high sun.…”

Nighttime OClO in the winter Arctic vortex

“…Observations of OClO are used as a measure of chemical loss of polar ozone due to BrO and ClO [e.g., Solomon et al , 1987; Salawitch et al , 1987; Solomon et al , 1989; Wagner et al , 2001, 2002]. As these data are often obtained during twilight, inferences of chlorine activation and bromine levels require accurate knowledge of the twilight chemistry of OClO [ Wahner and Schiller , 1992; Sessler et al , 1995].…”

Climatology of the stratospheric BrO vertical distribution by balloon‐borne UV–visible spectrometry

“…Slant column densities of BrO are now measured continuously by UV–visible zenith‐sky spectroscopy from a number of ground‐based stations [ Carroll et al , 1989; Solomon et al , 1989; Fish et al , 1997; Richter et al , 1999; Otten et al , 1998; Friess et al , 1999; Sinnhuber et al , 2002], and, since 1995, from space by the GOME instrument on board the ESA ERS‐2 satellite [ Wagner and Platt , 1998; Richter et al , 2002; Hegels et al , 1998; Burrows et al , 1999a]. Column measurements have been also performed from aircraft [ Wahner et al , 1990; Grendel et al , 1996].…”