New observations of NO<sub>2</sub> in the upper troposphere from TROPOMI
<p>Nitrogen oxides (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"><mrow><mrow class="chem"><msub><m...
| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-03-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/14/2389/2021/amt-14-2389-2021.pdf |
| Summary: | <p>Nitrogen oxides (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"><mrow><mrow class="chem"><msub><mi mathvariant="normal">NO</mi><mi>x</mi></msub></mrow><mo>≡</mo><mrow class="chem"><mi mathvariant="normal">NO</mi></mrow><mo>+</mo><mrow class="chem"><msub><mi mathvariant="normal">NO</mi><mn mathvariant="normal">2</mn></msub></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="85pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="72fae000e07cdf06702a94248543dc74"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-2389-2021-ie00001.svg" width="85pt" height="13pt" src="amt-14-2389-2021-ie00001.png"/></svg:svg></span></span>) in
the <span class="inline-formula">NO<sub><i>x</i></sub></span>-limited upper troposphere (UT) are long-lived and so have a
large influence on the oxidizing capacity of the troposphere and formation
of the greenhouse gas ozone. Models misrepresent <span class="inline-formula">NO<sub><i>x</i></sub></span> in the UT, and observations to address deficiencies in models are sparse. Here we obtain a year of near-global seasonal mean mixing ratios of <span class="inline-formula">NO<sub>2</sub></span> in the UT (450–180 hPa) at <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">1</mn><msup><mi/><mo>∘</mo></msup><mo>×</mo><mn mathvariant="normal">1</mn><msup><mi/><mo>∘</mo></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="34pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="2f0cd8b2e0fda9823788cc41d80ac5a2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-2389-2021-ie00002.svg" width="34pt" height="11pt" src="amt-14-2389-2021-ie00002.png"/></svg:svg></span></span> by applying
cloud-slicing to partial columns of <span class="inline-formula">NO<sub>2</sub></span> from TROPOMI. This follows
refinement of the cloud-slicing algorithm with synthetic partial columns
from the GEOS-Chem chemical transport model. TROPOMI, prior to
cloud-slicing, is corrected for a 13 % underestimate in stratospheric
<span class="inline-formula">NO<sub>2</sub></span> variance and a 50 % overestimate in free-tropospheric <span class="inline-formula">NO<sub>2</sub></span> determined by comparison to Pandora total columns at high-altitude free-tropospheric sites at Mauna Loa, Izaña, and Altzomoni and MAX-DOAS and
Pandora tropospheric columns at Izaña. Two cloud-sliced seasonal mean UT
<span class="inline-formula">NO<sub>2</sub></span> products for June 2019 to May 2020 are retrieved from corrected
TROPOMI total columns using distinct TROPOMI cloud products that assume
clouds are reflective boundaries (FRESCO-S) or water droplet layers
(ROCINN-CAL). TROPOMI UT <span class="inline-formula">NO<sub>2</sub></span> typically ranges from 20–30 pptv over remote oceans to <span class="inline-formula">>80</span> pptv over locations with intense seasonal lightning. Spatial coverage is mostly in the tropics and subtropics with
FRESCO-S and extends to the midlatitudes and polar regions with ROCINN-CAL,
due to its greater abundance of optically thick clouds and wider cloud-top
altitude range. TROPOMI UT <span class="inline-formula">NO<sub>2</sub></span> seasonal means are spatially consistent (<span class="inline-formula"><i>R</i>=0.6</span>–0.8) with an existing coarser spatial resolution (5<span class="inline-formula"><sup>∘</sup></span>
latitude <span class="inline-formula">×</span> 8<span class="inline-formula"><sup>∘</sup></span> longitude) UT <span class="inline-formula">NO<sub>2</sub></span> product from the
Ozone Monitoring Instrument (OMI). UT <span class="inline-formula">NO<sub>2</sub></span> from TROPOMI is 12–26 pptv
more than that from OMI due to increase in <span class="inline-formula">NO<sub>2</sub></span> with altitude from the OMI pressure ceiling (280 hPa) to that for TROPOMI<span id="page2390"/> (180 hPa), but possibly
also due to altitude differences in TROPOMI and OMI cloud products and
<span class="inline-formula">NO<sub>2</sub></span> retrieval algorithms. The TROPOMI UT <span class="inline-formula">NO<sub>2</sub></span> product offers
potential to evaluate and improve representation of UT <span class="inline-formula">NO<sub><i>x</i></sub></span> in models and supplement aircraft observations that are sporadic and susceptible to large biases in the UT.</p> |
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| ISSN: | 1867-1381 1867-8548 |