Effects of nitrogen oxide (NO and NO₂) concentration levels and meteorological variables on ozone (O₃) formation in the petrochemical industry area in the Monterrey Metropolitan Area, Mexico

The petrochemical industry emits large amounts of nitrogen oxides (NOx). It is the second source of volatile organic compounds (VOCs), which, through photochemical reactions, can form tropospheric ozone (O₃) and, together with geographic and meteorological conditions, determine pollution's spatial and temporal behavior. The objective of this study is to assess the influence of air pollutants NOx, NO₂, and NO, as well as meteorological factors, on O₃ concentration levels in the city of Cadereyta, Nuevo Leon, which is characterized by its petrochemical industry as part of the metropolitan area of ​​Monterrey, Mexico. The data were analyzed using the Spearman correlation coefficient, identifying a weak to moderate negative association between NOx and NO₂ with O₃ in the spring season and a null relationship in the summer. However, the fall and winter seasons observed a moderate to strong negative relationship. Subsequently, a multiple linear regression analysis determined the influence of air pollutants NOx, NO₂, and NO, as well as meteorological factors, on O₃ concentration levels. In this sense, when the concentration levels of NOx and NO₂ decrease, the concentration of O₃ will increase proportionally according to the year's season. The prediction model obtains a coefficient of determination (R²) of 0.61 and a value in the root-mean-square error (RMSE) metric of 0.0107 ppm. In the prediction model, all variables presented a significant effect on the interpretation of the dependent variable, and the independent variables that provided the most significance in the variation in the concentration levels of O₃ were NOx and NO₂.