Circulation patterns influencing the concentration of pollutants in central Mexico

Abstract

In this study, weather patterns producing circulation features that result in poor air quality in the Mexico City basin during the dry season (November–May) were examined. Cluster analysis of the 500-hPa winds for a 30-year period (1990–2019) identifies a set of weather patterns that are then used to explore daily anomalous concentrations of ozone, nitrogen dioxide, and particulate matter. Above-normal levels of pollution occur under the influence of a mid-troposphere high pressure system centered around 20°N that shifts eastward over Mexico. This weather pattern is characterized by below-normal cloudiness, greater solar radiation, weaker surface winds, and a stronger morning temperature inversion that persists later than normal. High pollution events associated with this pattern occur preferentially during the dry season: March–May for O3, and December–February for NO2 and PM2.5. PM10 events occurred evenly throughout the season. At the interannual scale, the El–Niño–Southern Oscillation is related to the frequency of pollution-related weather patterns: La–Niña (El–Niño) years favor the occurrence of patterns associated with more (less) pollution during the dry season. This work reveals the seasonality and predictability of pollution-related atmospheric patterns in the Mexico City basin, which can be used for air quality assessments at both seasonal and intraseasonal scales.