**2. Study area and data**

#### **2.1 Study area**

According to the latest census in 2020, Mexico City (19.43°N, 99.13°W) is home to 9,210,000 inhabitants [1]. Greater Mexico City (GMC) includes some municipalities of the State of Mexico that are attached to Mexico City, with a total population of about 22 million inhabitants in 2020 [1]. In terms of weather, the GMC experiences middle-latitude systems during the dry season and is exposed to tropical interactions during the rainy season. The wet season lasts from June to November and the dry season is defined from December to May [13].

In terms of urbanization, the layout of the GMC is heterogeneous, meaning that areas depending on land use or land cover are not well defined and they are rather mixed. In this study, we defined urban areas as areas with many built structures such as buildings and roads, rural areas are those with a few built structures and mostly vegetation cover, and semi-urban areas are defined as large green areas within an urban area, such as a large park near the city center [13].

In terms of mobility, in the morning at around 08:00 h local time (LT), most people travel from the municipalities further away from the city to the city center and the eastern business district. Moreover, from 17:00 h LT the flow population is in the opposite direction, from downtown and business district to the outskirts of Mexico City, as reported in the official 2019 mobility report [14].

**Figure 1** shows a satellite image of the GMC and the location of the air quality monitoring stations used in this study.

#### **2.2 Ground-based data**

The Government of Mexico City, through the Secretary of the Environment, operates the Meteorology and Solar Radiation Monitoring Network (REDMET) [15] and the Automatic Ambient Monitoring Network (RAMA) [16], which are used to monitor the weather and air pollution concentrations, respectively.

#### *2.2.1 Air temperature data*

The REDMET measures surface temperature (2 m), relative humidity (2 m), wind direction, and wind speed (10 m) every hour at 26 locations in GMC [15]. REDMET has been in operation since 1986; in 2015, some stations were decommissioned, while new stations were commissioned to cover the entire metropolitan area. To evaluate the effect of meteorological conditions on PM concentrations, 5 REDMET weather stations that report meteorological and pollution concentration data at the same location were selected. The study period was 2012–2022. In some cases, the selected stations report only one type of pollutant, such as PM10, PM2.5, or O3.

**Figure 1.** *Location of stations used in this study.*
