Retrieval of stratospheric and tropospheric BrO columns from multi-axis DOAS measurements at Reunion Island (21° S, 56° E)

Abstract

Abstract. Spectral measurements of BrO using zenithsky and off-axis viewing geometries are combined in a linear multiple regression retrieval algorithm to provide stratospheric and tropospheric BrO vertical columns. One year of measurement data are investigated over • S, 55. profiles shows a good agreement only by considering a contribution from the very short-lived organic bromine substances to the stratospheric inorganic bromine budget, of 6 to 8 pptv. Furthermore, stratospheric BrO profiles retrieved from late twilight zenith-sky observations are consistent with a total inorganic bromine (Br y ) loading of approximately 23 pptv. This represents 6 to 7 pptv more than can be supplied by long-lived organic bromine sources, and therefore supports an added contribution from very shortlived organic bromine substances as recently suggested in several other studies. Moreover strong evidences are presented for the existence of a substantial amount of BrO in the tropical free-troposphere, around 6 km altitude, possibly supplied by the decomposition of short-lived biogenic bromine organic compounds. Tropospheric BrO vertical columns of 1.1±0.45×10 13 molec/cm 2 are derived for the entire observation period. Comparisons between ground-based BrO vertical columns and total BrO columns derived from SCIA-MACHY (onboard the ENVISAT satellite) nadir observations in a latitudinal band centered around 21 • S present a good level of consistency, which further strengthens the conclusions of our study.

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.…”

“…The random slant column error is evaluated for each satellite orbit by the standard deviation of the measured columns around the mean for latitude bands of 5 • width. Based on calculations using the formalism of Rodgers (2000) (see also Theys et al, 2007), sensitivity tests made on GOME-2 spectra and the experience with BrO retrieval from GOME and SCIAMACHY 2004), a typical systematic slant column error of about 20% including the uncertainty on the BrO crosssection and its temperature dependence has been estimated. For the error on the stratospheric slant column, we consider an error equal to 20%, as derived in Theys et al (2009b).…”

“…Observations from space (e.g., Richter et al, 2002;Van Roozendael et al, 2002), ground-based Theys et al, 2007) and balloon-borne (Harder et al, 1998;Fitzenberger et al, 2000) instruments have shown that inorganic bromine may be produced and sustained in the free troposphere at the global scale. Elaborating on these observations, modelling results (von Glasow et al, 2004;Lary, 2005;Yang et al, 2005Yang et al, , 2010 have shown that freetropospheric bromine might have a significant impact on the tropospheric ozone budget (and on tropospheric chemistry in general), leading to a reduction in the O 3 mixing ratio of up to 40% locally.…”

Detection of iodine monoxide in the tropical free troposphere

“…Fig. 3A assumes that the average ozone vertical profile as measured during the Pacific Exploratory Mission (PEM) Tropics field campaign (same area as our flight track during March of 1999) is representative for our case study and further assumes that 0.5 ppt bromine oxide (BrO) is present over the entire tropospheric air column (6,18,(39)(40)(41) (SI Text). Under the rather low ozone concentrations observed during PEM tropics (Table S4), iodine chemistry determines 23%, 26%, and 11% of the overall ozone loss rate in the MBL, TL, and FT, respectively.…”

Determination of aerosol properties from MAX-DOAS observations of the Ring effect

“…Thus, from the measured strength of the Ring effect, information on aerosols and clouds can be obtained (Park et al, 1986;Joiner et al, , 2002Joiner et al, , 2004de Beek et al, 2001;Wagner et al,496 T. Wagner et al: Determination of aerosol properties from MAX-DOAS observations of the Ring effect this study we focus on the potential to retrieve aerosol information from observations of the Ring effect using a ground based Multi-Axis-DOAS (MAX-DOAS) instrument. MAX-DOAS instruments observe scattered sun light under a variety of elevation angles (Hönninger and Platt, 2002;Leser et al, 2003;Bobrowski et al, 2003;van Roozendael et al, 2003;Wittrock et al, 2004;Hönninger et al, 2004;Heckel et al, 2005;Wagner et al, 2004Wagner et al, , 2007bFrieß et al, 2006;Fietkau et al, 2007;Theys et al, 2007). The MAX-DOAS observations used in this study make simultaneous measurements in three different azimuth directions.…”