Abstract
Abstract. The Rann of Kutch (India and Pakistan) is one of the largest salt deserts in the world. Being a so-called "seasonal salt marsh", it is regularly flooded during the Indian summer monsoon. We present 10 years of bromine monoxide (BrO) satellite observations by the Ozone Monitoring Instrument (OMI) over the Great and Little Rann of Kutch. OMI spectra were analysed using Differential Optical Absorption Spectroscopy (DOAS) and revealed recurring high BrO vertical column densities (VCDs) of up to 1.4 × 1014 molec cm−2 during April/May, but no significantly enhanced column densities during the monsoon season (June–September). In the following winter months, the BrO VCDs are again slightly enhanced while the salty surface dries up. We investigate a possible correlation of enhanced reactive bromine concentrations with different meteorological parameters and find a strong relationship between incident UV radiation and the total BrO abundance. In contrast, the second Global Ozone Monitoring Instrument (GOME-2) shows about 4 times lower BrO VCDs over the Rann of Kutch than found by OMI and no clear seasonal cycle is observed. One reason for this finding might be the earlier local overpass time of GOME-2 compared to OMI (around 09:30 vs. 13:30 LT), as the ambient conditions significantly differ for both satellite instruments at the time of the measurements. Further possible reasons are discussed and mainly attributed to instrumental issues. OMI additionally confirms the presence of enhanced BrO concentrations over the Dead Sea valley (Israel/Jordan), as suggested by former ground-based observations. The measurements indicate that the Rann of Kutch salt marsh is probably one of the strongest natural point sources of reactive bromine compounds outside the polar regions and is therefore supposed to have a significant impact on local and regional ozone chemistry.
Highlights
Reactive halogen species (RHS) are well known to play an important role in atmospheric chemistry of both the troposphere and stratosphere (e.g. Platt and Janssen, 1995; SaizLopez and von Glasow, 2012, and references therein)
After the monsoon (October–December) the bromine monoxide (BrO) vertical column densities (VCDs) remain at a low level, reaching magnitudes similar to those found at the beginning of the year
We presented the first space-based measurements of BrO originating from a salt marsh/salt lake, emphasizing the capability of satellite instruments to monitor remote areas that are only accessible with difficulty for long-term measurements
Summary
Reactive halogen species (RHS) are well known to play an important role in atmospheric chemistry of both the troposphere and stratosphere (e.g. Platt and Janssen, 1995; SaizLopez and von Glasow, 2012, and references therein). During the last 3 decades, BrO has extensively been measured in the MBL by ground-based DOAS observations, but the observations revealed relatively low BrO mixing ratios of 1–10 ppt Volcanic BrO has been observed by a large number of ground-based DOAS observations at quiescent degassing volcanoes since the early 2000s (e.g. Bobrowski et al, 2003; Oppenheimer et al, 2006; Bobrowski and Platt, 2007; Boichu et al, 2011; Bobrowski and Giuffrida, 2012; Lübcke et al, 2014) and by satellite instruments during minor and major volcanic eruptions (Theys et al, 2009a; Rix et al, 2012; Hörmann et al, 2013)
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