MAX-DOAS measurements of tropospheric NO<sub>2</sub> and HCHO in Nanjing and a comparison to ozone monitoring instrument observations
<p>In this paper, we present long-term observations of atmospheric nitrogen dioxide (<span class="inline-formula">NO<sub>2</sub></span>) and formaldehyde (HCHO) in Nanjing using a Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) instrument. G...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/10051/2019/acp-19-10051-2019.pdf |
| Summary: | <p>In this paper, we present long-term observations of atmospheric nitrogen dioxide (<span class="inline-formula">NO<sub>2</sub></span>) and formaldehyde (HCHO) in Nanjing using a
Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) instrument. Ground-based MAX-DOAS measurements were performed from April 2013 to February 2017. The MAX-DOAS measurements of <span class="inline-formula">NO<sub>2</sub></span> and HCHO vertical column densities (VCDs) are used to validate ozone monitoring instrument (OMI) satellite observations over Nanjing. The comparison shows that the OMI observations of <span class="inline-formula">NO<sub>2</sub></span> correlate well with the MAX-DOAS data with Pearson correlation coefficient (<span class="inline-formula"><i>R</i></span>) of 0.91. However, OMI observations are on average a factor of 3 lower than the MAX-DOAS measurements. Replacing the a priori <span class="inline-formula">NO<sub>2</sub></span> profiles by the MAX-DOAS profiles in the OMI <span class="inline-formula">NO<sub>2</sub></span> VCD retrieval would increase the OMI <span class="inline-formula">NO<sub>2</sub></span> VCDs by <span class="inline-formula">∼30</span> % with correlation nearly unchanged. The comparison result of MAX-DOAS and OMI observations of HCHO VCD shows a good agreement with <span class="inline-formula"><i>R</i></span> of 0.75 and the slope of the regression line is 0.99. An age-weighted backward-propagation approach is applied to the MAX-DOAS measurements of <span class="inline-formula">NO<sub>2</sub></span> and HCHO to reconstruct the spatial distribution of <span class="inline-formula">NO<sub>2</sub></span> and HCHO over the Yangtze River Delta during summer and winter time. The reconstructed <span class="inline-formula">NO<sub>2</sub></span> fields show a distinct agreement with OMI satellite observations. However, due to the short atmospheric lifetime of HCHO, the backward-propagated HCHO data do not show a strong spatial correlation with the OMI HCHO observations. The result shows that the MAX-DOAS measurements are sensitive to the air pollution transportation in the Yangtze River Delta, indicating the air quality in Nanjing is significantly influenced by regional transportation of air pollutants. The MAX-DOAS data are also used to evaluate the effectiveness of air pollution control measures implemented during the Youth Olympic Games 2014. The MAX-DOAS data show a significant reduction of ambient aerosol, <span class="inline-formula">NO<sub>2</sub></span> and HCHO (30 %–50 %) during the Youth Olympic Games. Our results provide a better understanding of the transportation and sources of pollutants over the Yangtze River Delta as well as the effect of emission control measures during large international events, which are important for the future design of air pollution control policies.</p> |
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| ISSN: | 1680-7316 1680-7324 |