Diurnal variations of NO<sub>2</sub> tropospheric vertical column density over the Seoul metropolitan area from the Geostationary Environment Monitoring Spectrometer (GEMS): seasonal differences and the influence of the a priori NO<sub>2</sub> profile
<p><span id="page116"/>The Geostationary Environment Monitoring Spectrometer (GEMS), launched in 2020, provides both temporally and spatially continuous air quality data from geostationary Earth orbit (GEO). This study first investigates the seasonal variations and diurnal beha...
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| Main Authors: | , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-01-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/18/115/2025/amt-18-115-2025.pdf |
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| Summary: | <p><span id="page116"/>The Geostationary Environment Monitoring Spectrometer (GEMS), launched in 2020, provides both temporally and spatially continuous air quality data from geostationary Earth orbit (GEO). This study first investigates the seasonal variations and diurnal behavior of nitrogen dioxide (<span class="inline-formula">NO<sub>2</sub></span>) tropospheric vertical column densities (TropVCDs) over the Seoul metropolitan area (SMA) using GEMS data, retrieved by the IUP-UB algorithm. We find that the magnitude of the <span class="inline-formula">NO<sub>2</sub></span> TropVCDs and their diurnal behavior have significant seasonal dependences. In January, the highest <span class="inline-formula">NO<sub>2</sub></span> TropVCD values in the range 27.5–<span class="inline-formula">28.9×10<sup>15</sup></span> <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">molec</mi><mo>.</mo><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">cm</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="60pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="326fae219ada504ce6e38a4700ad9e74"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-18-115-2025-ie00001.svg" width="60pt" height="13pt" src="amt-18-115-2025-ie00001.png"/></svg:svg></span></span> during the four seasons were observed at 15:00 local time (LT) and <span class="inline-formula">NO<sub>2</sub></span> TropVCD increases from the first retrieved values at 10:00 LT. On the other hand, we find the lowest values (7.4–<span class="inline-formula">8.8×10<sup>15</sup></span> <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">molec</mi><mo>.</mo><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">cm</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="60pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="321f0654a1dbc06a9dc99dc1771b5ee4"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-18-115-2025-ie00002.svg" width="60pt" height="13pt" src="amt-18-115-2025-ie00002.png"/></svg:svg></span></span>) are at <span class="inline-formula">∼14</span>:00 LT in July. The VCD values in July increased up to 10:00 LT and then decreased until 14:00 LT but then began to increase again. These different diurnal behaviors of the TropVCDs in the different seasons reflect the differences in photochemical and meteorological conditions as well as the emissions of <span class="inline-formula">NO<sub><i>x</i></sub></span>. Photochemical transformations are typically more rapid in July and slower in January. The absolute values and diurnal behavior of <span class="inline-formula">NO<sub>2</sub></span> TropVCDs are significantly influenced by the wind speed, except in July. Moderate (wind speed <span class="inline-formula">≥3</span> <span class="inline-formula">m s<sup>−1</sup></span>) or strong wind (wind speed <span class="inline-formula">>5</span> <span class="inline-formula">m s<sup>−1</sup></span>) reduced the magnitude of the diurnal behavior in January, implying that the <span class="inline-formula">NO<sub>2</sub></span> plumes were transported downwind. Finally, we compared the retrieved <span class="inline-formula">NO<sub>2</sub></span> TropVCDs by using different a priori <span class="inline-formula">NO<sub>2</sub></span> data simulated by TM5 and WRF-Chem, calculated using the most recent emission inventories. Although simulated VCDs from WRF-Chem and TM5 show differences of up to a factor 2.75, retrieved <span class="inline-formula">NO<sub>2</sub></span> TropVCDs using each a priori data have almost identical values and diurnal behaviors, except in July. Notably, the diurnal behavior of the retrieved <span class="inline-formula">NO<sub>2</sub></span> TropVCDs is independent of that from the two chemical transport models, indicating that observations of slant column densities are the dominant factor in determining the diurnal behavior of <span class="inline-formula">NO<sub>2</sub></span> TropVCDs. Changes in the model horizontal resolution and volatile organic compound (VOC) emission inventory do not significantly affect the retrieved <span class="inline-formula">NO<sub>2</sub></span> TropVCDs in this study. However, when the a priori <span class="inline-formula">NO<sub>2</sub></span> vertical profile was fixed as the values at 13:45 LT, the diurnal patterns of <span class="inline-formula">NO<sub>2</sub></span> TropVCDs showed significant changes, with differences of up to <span class="inline-formula">−</span>18.3 %.</p> |
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| ISSN: | 1867-1381 1867-8548 |