OMI total bromine monoxide (OMBRO) data product: algorithm, retrieval and measurement comparisons
<p>This paper presents the retrieval algorithm for the operational Ozone Monitoring Instrument (OMI) total bromine monoxide (BrO) data product (OMBRO) developed at the Smithsonian Astrophysical Observatory (SAO) and shows comparisons with correlative measurements and retrieval results. The alg...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-04-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/12/2067/2019/amt-12-2067-2019.pdf |
| Summary: | <p>This paper presents the retrieval algorithm for the
operational Ozone Monitoring Instrument (OMI) total bromine monoxide (BrO)
data product (OMBRO) developed at the Smithsonian Astrophysical Observatory
(SAO) and shows comparisons with correlative measurements and retrieval
results. The algorithm is based on direct nonlinear least squares fitting of
radiances from the spectral range 319.0–347.5 <span class="inline-formula">nm</span>. Radiances are modeled from
the solar irradiance, attenuated by contributions from BrO and interfering
gases, and including rotational Raman scattering, additive and
multiplicative closure polynomials, correction for Nyquist undersampling
and the average fitting residual spectrum. The retrieval uses albedo- and
wavelength-dependent air mass factors (AMFs), which have been pre-computed
using a single mostly stratospheric BrO profile. The BrO cross sections are
multiplied by the wavelength-dependent AMFs before fitting so that the
vertical column densities (VCDs) are retrieved directly. The fitting
uncertainties of BrO VCDs typically vary between 4 and <span class="inline-formula">7×10<sup>12</sup></span> <span class="inline-formula">molecules cm<sup>−2</sup></span>
(<span class="inline-formula">∼10</span> %–20 % of the measured BrO VCDs).
Additional fitting uncertainties can be caused by the interferences from
<span class="inline-formula">O<sub>2</sub></span>-<span class="inline-formula">O<sub>2</sub></span> and <span class="inline-formula">H<sub>2</sub>CO</span> and their correlation with BrO. AMF
uncertainties are estimated to be around 10 % when the single
stratospheric-only BrO profile is used. However, under conditions of high
tropospheric concentrations, AMF errors due to this assumption of profile
can be as high as 50 %.</p>
<p>The retrievals agree well with GOME-2 observations at simultaneous nadir
overpasses and with ground-based zenith-sky measurements at Harestua,
Norway, with mean biases less than <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">0.22</mn><mo>±</mo><mn mathvariant="normal">1.13</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mn mathvariant="normal">13</mn></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="96pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="21e81717dfc4ccb936c22a4ec884a85f"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-12-2067-2019-ie00001.svg" width="96pt" height="14pt" src="amt-12-2067-2019-ie00001.png"/></svg:svg></span></span>
and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">0.12</mn><mo>±</mo><mn mathvariant="normal">0.76</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mn mathvariant="normal">13</mn></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="88pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="b0a934d14212a27333a508589a46f793"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-12-2067-2019-ie00002.svg" width="88pt" height="14pt" src="amt-12-2067-2019-ie00002.png"/></svg:svg></span></span> <span class="inline-formula">molecules cm<sup>−2</sup></span>, respectively. Global distribution and seasonal variation of OMI
BrO are generally consistent with previous satellite observations. Finally,
we confirm the capacity of OMBRO retrievals to observe enhancements of BrO
over the US Great Salt Lake despite the current retrieval setup
considering a stratospheric profile in the AMF calculations. OMBRO
retrievals also show significant BrO enhancements from the eruption of the
Eyjafjallajökull volcano, although the BrO retrievals are affected under
high <span class="inline-formula">SO<sub>2</sub></span> loading conditions by the sub-optimum choice of <span class="inline-formula">SO<sub>2</sub></span> cross
sections.</p> |
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| ISSN: | 1867-1381 1867-8548 |