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Tollcayuca, Hidalgo, Mexico, occupies a geographically significant position within the central Mexican highlands, approximately 110 kilometers north of Mexico City. Situated at an elevation of around 2,100 meters (6,889 feet) above sea level, the city experiences a distinct high-altitude climate. The surrounding landscape is characterized by rolling hills and valleys, part of the broader Hidalgo Plateau, transitioning from semi-arid scrubland to agricultural fields as one approaches the urban area. This agricultural zone, primarily dedicated to maize and wheat cultivation, contributes to seasonal particulate matter through tilling and fertilizer use. Tolcayuca’s location within the Bajío region, a historically important agricultural and industrial corridor, places it within reach of industrial activity emanating from nearby cities like Pachuca and Tula. The urban–rural gradient is relatively sharp, with the city bordered by agricultural land and sparsely populated rural communities. The terrain, while not dramatically mountainous, can influence local wind patterns, sometimes trapping pollutants within the valley. While not directly adjacent to major bodies of water, the nearby Teotihuacan River provides a limited source of moisture and can influence humidity levels. The city’s relatively small size (population 11,746) means that localized industrial emissions, primarily from small-scale manufacturing and vehicle traffic, are the dominant contributors to air quality concerns, exacerbated by the altitude and regional meteorological conditions.

Tollcayuca’s air quality exhibits a distinct seasonal pattern dictated by its high-altitude climate and regional weather systems. The dry season, typically spanning from November to April, often witnesses the most concerning air quality conditions. Reduced precipitation and lower humidity levels contribute to the accumulation of particulate matter, particularly during periods of agricultural activity and increased vehicle usage. Temperature inversions, common during the cooler months, trap pollutants near the ground, intensifying their impact. The months of December and January frequently experience the poorest air quality, with stagnant air conditions hindering pollutant dispersal. Conversely, the wet season, from May to October, brings relief through increased rainfall, which naturally washes pollutants from the atmosphere. However, even during the wet season, agricultural burning practices can temporarily elevate particulate matter levels. The monsoonal influence, though less pronounced than in other parts of Mexico, contributes to increased humidity and occasional periods of fog, which can trap pollutants and reduce visibility. During the summer months, convective thunderstorms can help to disperse pollutants, but these events are often localized. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, limiting outdoor activity during peak pollution periods, particularly in the mornings and evenings. Maintaining indoor air quality through ventilation and air purification can also be beneficial.