Environmental Advances (Dec 2021)
Diagnosis of ozone formation sensitivity in the Mexico City Metropolitan Area using HCHO/NO2 column ratios from the ozone monitoring instrument
Abstract
The formation of tropospheric ozone is influenced by emissions of volatile organic compounds (VOCs) and nitrogen oxides (NOx), and different regimes of sensitivity to the ozone formation have been identified depending on the concentrations of both groups of compounds. We studied the ozone formation sensitivity in the Mexico City Metropolitan Area (MCMA) using the formaldehyde to nitrogen dioxide ratio (FNR) as a proxy for the VOCs and NOx concentrations, with data retrieved from the Ozone Monitoring Instrument (OMI). To determine the different sensitivity regimes, we compared two previously established threshold values of FNR, which differ from each other in the range of ratios on which the regime transition occurs. The evaluation from 2006 to 2016 showed that the FNR gradually changed, causing variations in the ozone formation sensitivity. While in 2006, more regions were under NOx-limited/transitional regimes, in 2016, the VOC-limited conditions prevailed in most of the city. The analysis disclosed that this change is due to increasing NOx emissions in some regions of MCMA and decreasing VOC emissions in other areas. The observed trend is different from that in major cities in other parts of the world, such as the United States, where ozone formation sensitivity has moved towards NOx-limited conditions. Therefore, reducing VOC emissions would be a suitable approach for decreasing tropospheric ozone concentrations in the MCMA.
