Air Pollution in Medium-Sized Mexican Cities

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Medium-sized cities are in the population range of between 500,000 and one million inhabitants. Despite the importance of large cities, the greatest urban growth occurs in medium and small cities. During the last century these cities enjoyed acceptable air quality, however from the last years of the last century and the two decades of this century the atmospheric health has deteriorated, generating problems. The dynamics of population growth faced by these cities represent a serious threat to the environment, as well as to the health and quality of life of its inhabitants, since it generates new economic processes, accompanied by an increase in industrial activities, motorization rates, greater fuel consumption and higher emissions of air pollutants.
 Objective: To carry out an analysis of the air quality condition and to show the trends of the criteria pollutants for 10 medium-sized Mexican cities with the highest population growth.
 Materials and Methods: The data for the analysis of air quality of medium-sized cities were downloaded from the consultation system of Air Quality Indicators-SCICA through the http://scica.inecc.gob.mx/exec/addl website. The downloaded data are hourly concentrations of the six criteria pollutants PM10, PM2.5, O3, SO2, NO2 and CO for the monitoring stations of the cities of Aguascalientes (863 893 h), Mexicali (854 186 h), Ciudad Juárez (1 501 551 h), Chihuahua (925 762 h), León (1 579 803 h), Morelia (743 275 h), Puebla (1 542 232 h), Querétaro (794 789 h)), San Luis Potosí (854 186 h) and Torreón (690 193 h), indicators were calculated of the daily, monthly and annual trend, averages, percentages of days with concentrations above the norm and number of days per year in which any of the norms is exceeded during the period 2000-2020. Compliance with environmental health NOMs (at one hour, 8 h, 24 h and annually) was evaluated depending on the pollutant criterion.
 Results and Discussion: Medium-sized cities have grown between 21 and 55% in the last 20 years, some surpassing the category of medium cities. The concentrations of PM10, PM2.5 and O3 in all medium-sized cities are almost always above the normativity which represents a risk to the health of the population. The concentrations of CO, NO2 and SO2 are below the limits of the regulations, so these pollutants currently do not represent a risk to the population of medium-sized cities. Most cities present less than a third of the year with days out of the norm, only Torreón, Puebla and León present values of one third to two thirds of the year above the norm.
 Conclusions: The pollutants PM10, PM2.5 and O3 represent a risk to the health of the population of medium cities in Mexico, while the concentrations of CO, NO2 and SO2 currently do not represent a risk for the population of medium cities.