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San Juan Evangelista, nestled within the state of Veracruz, Mexico, occupies a geographically significant position within the Huasteca Potosina region. Located at approximately 17.88° N, 95.13° W, the city’s terrain is characterized by rolling hills and valleys, typical of the eastern slopes of the Sierra Madre Oriental mountain range. Its elevation, around 450 meters above sea level, influences local climate patterns and, consequently, air quality. The surrounding landscape is a mosaic of tropical deciduous forest and agricultural land, primarily dedicated to maize and bean cultivation, interspersed with smaller plots of citrus and coffee. This agricultural activity contributes to localized particulate matter, particularly during harvest seasons. San Juan Evangelista sits relatively close to the Gulf of Mexico, approximately 150 kilometers east, which moderates temperatures and introduces maritime influences, though prevailing winds often originate from the mountains. The urban–rural gradient is gradual; the city blends seamlessly into the agricultural hinterland, with small villages and rural communities dotting the surrounding hills. While not directly adjacent to major industrial belts, the region experiences transportation-related pollution from the highway connecting to larger urban centers like Tuxpan and Tampico. The topography, with its enclosed valleys, can exacerbate air stagnation, particularly during periods of calm weather, trapping pollutants and reducing dispersion. The presence of smaller-scale artisanal workshops within the city also contributes to localized emissions.

San Juan Evangelista experiences a tropical savanna climate, exhibiting distinct wet and dry seasons rather than the four traditional seasons. The dry season, typically spanning from March to May, often sees a noticeable increase in particulate matter concentrations. This is largely attributable to reduced rainfall, which limits the natural cleansing effect of precipitation, and increased agricultural burning practices as farmers prepare fields for planting. Calm wind conditions are also more frequent during this period, leading to pollutant accumulation within the valleys. The wet season, from June to October, brings frequent rainfall and higher humidity, generally resulting in improved air quality as pollutants are washed from the atmosphere. However, periods of intense rainfall can sometimes lead to flooding and the release of mold spores, impacting indoor air quality. November to February represents a transitional period, with fluctuating rainfall and wind patterns. Fog, particularly in the mornings, can trap pollutants close to the ground, creating localized episodes of reduced visibility and potentially elevated exposure. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during agricultural burning periods. Limiting outdoor exertion during foggy mornings is also advisable. While the wet season generally offers respite, maintaining good ventilation indoors remains crucial to minimize exposure to potential mold and mildew. The regional climate’s inherent variability means air quality can change rapidly, emphasizing the importance of staying informed about local conditions.