## 2 Materials  
### Dataset  
In Figure 1, the monitoring network is shown; it consists of 34 remote stations located MCMA and driven by the Automatic Environmental Monitoring Network program (Red Automatica de Monitoreo Ambiental (RAMA)).  
Our study examines the temporal dynamics of CO and \(O_{3}\) concentrations, measured at seven monitoring stations (currently in operation and measuring the desired parameters, see Figure 1) located in the southwestern zone of MCMA, which is characterized by the highest levels of \(CO\) and \(O_{3}\). The selection of this zone as the focus of analysis is based on its high vulnerability to the accumulation of atmospheric pollutants, resulting from a combination of meteorological, geographic, and urban factors. According to the Mexico City Secretariat of the Environment [8], in 2022, a predominant north-to-south wind pattern was observed--consistent with previous years--especially from April to November, which facilitates the transport of pollutants toward the southwest. In the remaining months, wind behavior was more variable, with east-northeast and southeastly flows converging toward the center, creating zones of confluence that further exacerbate pollutant accumulation. These circulation patterns are compounded by local atmospheric conditions, such as intense solar radiation, high afternoon temperatures, and low cloud cover, which enhance the photochemical formation of ozone. Additionally, the basin's topography--surrounded by mountain ranges--acts as a natural barrier, limiting the dispersion of pollutants and promoting their concentration in this sector. According to the National Air Quality Report [32], the southwestern zone consistently records the highest concentrations of ozone in Mexico City, particularly during the spring months. These conditions, combined with the continuous influx of emissions from vehicular and domestic sources, justify the selection of this region as a critical area to evaluate the spatiotemporal behavior of \(CO\) and \(O_{3}\) in the present study.  
The sampling time is 1 h. Figure 2 shows the time variation of the two pollutants studied. Each hourly value is the spatial average among the stations (See section \"Data Availability Statement\"). Outliers caused by instrument failures or human errors are eliminated; the single gaps are filled by the mean of the nonzero neighboring values, while longer gaps are filled by using the procedure developed by [34]. The percentage of data missing is less than 0.1%.  
At the end of 2020, an increase in air pollutant emissions in MCMA was observed associated with a gradual return to mobility after lifting some of the preventive measures implemented during the COVID-19 pandemic. This increase was related to the reactivation of economic activities, according to the Local Mobility Reports [35], the increase in vehicular traffic, and the more significant influx of people into public spaces, highlighting the impact of urban mobility on air quality in the region. According to the Environmental Monitoring Office (Direccion de Monitoreo Atmosferico in Mexico City, DMA-CDMX), the highest levels \(O_{3}\) are associated with the so-called ozone season, which occurs from February to June. When meteorological conditions favor warm weather and intense solar radiation, the atmosphere's photochemical activity increases, favoring the formation of ozone. In addition, when a high pressure system is present, the pollutant stagnates, and, as a result, its concentrations increase ([[https://www.google.com/covid19/mobility/](https://www.google.com/covid19/mobility/)]([https://www.google.com/covid19/mobility/](https://www.google.com/covid19/mobility/)), accessed on 5 August 2025).  
Figure 1: Spatial distribution of all monitoring stations within the MCMA. The bold contour indicates the boundary of Mexico City. The southwest zone is conformed by the stations highlighted with red stars [33].