Assessing Measurements of Pollution in the Troposphere (MOPITT) carbon monoxide retrievals over urban versus non-urban regions

• Published in: Atmospheric measurement techniques 2020-03, Vol.13 (3), p.1337-1356
• Main Authors: Tang, Wenfu, Worden, Helen M, Deeter, Merritt N, Edwards, David P, Emmons, Louisa K, Martínez-Alonso, Sara, Gaubert, Benjamin, Buchholz, Rebecca R, Diskin, Glenn S, Dickerson, Russell R, Ren, Xinrong, He, Hao, Kondo, Yutaka
• Format: Article
• Language: English
• Subjects: Agreements; Air; Air pollution; Air quality; Airborne observation; Aircraft; Aircraft noise; Aircraft observations; Algorithms; Atmospheric chemistry; Atmospheric composition; Bias; Carbon monoxide; Chemical research; Clouds (Meteorology); Coefficients; Correlation coefficient; Correlation coefficients; Daytime; Environmental aspects; Errors; Filters; Footprints; Measurement; Military aircraft; Night; Night-time; Nighttime; Pollution; Prejudice; Profiles; Regional climates; Regions; Retrieval; Sensitivity; Sensitivity analysis; Signal to noise ratio; Statistical methods; Surface boundary layer; Surface layers; Surveys; Time; Troposphere; Urban areas; Variability
• ISSN: 1867-8548; 1867-1381; 1867-8548
• DOI: 10.5194/amt-13-1337-2020

The Measurements of Pollution in the Troposphere (MOPITT) retrievals over urban regions have not been validated systematically, even though MOPITT observations are widely used to study CO over urban regions. Here we compare MOPITT products over urban and non-urban regions with aircraft measurements from the Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ – 2011–2014), Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEAC4RS – 2013), Air Chemistry Research In Asia (ARIAs – 2016), A-FORCE (2009, 2013), and Korea United States Air Quality (KORUS-AQ – 2016) campaigns. In general, MOPITT agrees reasonably well with the in situ profiles, over both urban and non-urban regions. Version 8 multispectral product (V8J) biases vary from −0.7 % to 0.0 % and version 8 thermal-infrared product (TIR) biases vary from 2.0 % to 3.5 %. The evaluation statistics of MOPITT V8J and V8T over non-urban regions are better than those over urban regions with smaller biases and higher correlation coefficients. We find that the agreement of MOPITT V8J and V8T with aircraft measurements at high CO concentrations is not as good as that at low CO concentrations, although CO variability may tend to exaggerate retrieval biases in heavily polluted scenes. We test the sensitivities of the agreements between MOPITT and in situ profiles to assumptions and data filters applied during the comparisons of MOPITT retrievals and in situ profiles. The results at the surface layer are insensitive to the model-based profile extension (required due to aircraft altitude limitations), whereas the results at levels with limited aircraft observations (e.g., the 600 hPa layer) are more sensitive to the model-based profile extension. The results are insensitive to the maximum allowed time difference criterion for co-location (12, 6, 3, and 1 h) and are generally insensitive to the radius for co-location, except for the case where the radius is small (25 km), and hence few MOPITT retrievals are included in the comparison. Daytime MOPITT products have smaller overall biases than nighttime MOPITT products when comparing both MOPITT daytime and nighttime retrievals to the daytime aircraft observations. However, it would be premature to draw conclusions on the performance of MOPITT nighttime retrievals without nighttime aircraft observations. Applying signal-to-noise ratio (SNR) filter