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.
Citation
ID:
107196
Ref Key:
hormann2016seasonalatmospheric