09 Dec 2022
09 Dec 2022

Ozone–NOx–VOC Sensitivity of the Lake Michigan Region Inferred from TROPOMI Observations and Ground-Based Measurements

Juanito Jerrold Mariano Acdan1, Robert Bradley Pierce1,2, Angela F. Dickens3, Zachariah Adelman3, and Tsengel Nergui3 Juanito Jerrold Mariano Acdan et al.
  • 1Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison, Madison, WI, 53706, United States
  • 2Space Science and Engineering Center, University of Wisconsin-Madison, Madison, WI, 53706, United States
  • 3Lake Michigan Air Directors Consortium (LADCO), Hillside, IL, 60162, United States

Abstract. Surface-level ozone (O3) is a secondary air pollutant that has adverse effects on human health. In the troposphere, O3 is produced in complex cycles of photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs). Determining if O3 production will be decreased by lowering NOx emissions (“NOx-sensitive”), VOC emissions (“VOC-sensitive”), or both (“the transition zone”) can be done by using the formaldehyde (HCHO; a VOC species) to nitrogen dioxide (NO2; a component of NOx) concentration ratio ([HCHO]/[NO2]; “FNR”). Generally, lower FNR values indicate VOC sensitivity while higher values indicate NOx sensitivity. In this study, we use FNRs calculated from 2019–2021 TROPOspheric Monitoring Instrument (TROPOMI) satellite data and 2019 Photochemical Assessment Monitoring Station (PAMS) ground-based data to investigate the ozone–NOx–VOC sensitivity of the Lake Michigan region, an area that regularly exceeds the United States Environmental Protection Agency’s regulatory standards for O3. We find that TROPOMI FNRs are always greater than PAMS FNRs, indicating that they must be interpreted with different threshold values to infer O3 chemistry sensitivities. Further analysis of TROPOMI FNRs reveals that during both typical O3 season days and Chicago, Illinois, O3 exceedance days, the average O3 chemistry sensitivity is: (1) VOC-sensitive in the Chicago metropolitan area (CMA), (2) transitional in the areas surrounding the CMA and up the western Lake Michigan coastline to Milwaukee, Wisconsin, and (3) NOx-sensitive in the rest of the domain. However, the magnitude of FNR values change during exceedance days, indicating that areas that are NOx-sensitive (VOC-sensitive) during typical O3 season days increase in NOx-sensitivity (VOC-sensitivity). Additionally, the transition zone area decreases by 25 % on exceedance days. Comparing weekends to weekdays, O3 chemistry in the Chicago metropolitan area becomes more NOx-sensitive on weekends due lower NOx emissions. Finally, analysed 10-meter wind data shows that the lake breeze circulation, which transports high O3 levels from over Lake Michigan to onshore coastal areas, is stronger during O3 exceedance days compared to typical O3 season days, and there are no major weekday-weekend differences in the properties of the 10-meter wind field.

Juanito Jerrold Mariano Acdan et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1154', Anonymous Referee #1, 01 Jan 2023
  • RC2: 'Comment on egusphere-2022-1154', Anonymous Referee #2, 10 Jan 2023

Juanito Jerrold Mariano Acdan et al.

Juanito Jerrold Mariano Acdan et al.


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Short summary
Ozone is an air pollutant that is harmful to human health. Near the surface of Earth, ozone is created when other pollutants react in the presence of sunlight. This study uses satellite data to investigate how ozone levels can be decreased in the Lake Michigan region of the United States. Our results indicate that ozone levels can be decreased by decreasing volatile organic compound emissions specifically in Chicago, Illinois, and decreasing nitrogen oxide emissions in the region as a whole.