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Miahuatlán de Porfirio Díaz nestles within the rugged Sierra Sur mountains of Oaxaca, Mexico, at an elevation of approximately 1,720 meters (5,643 feet). This high-altitude location significantly influences its climate and, consequently, its air quality. The city is situated within a valley, a common topographical feature in this region, which can trap pollutants during periods of atmospheric stability. Surrounding Miahuatlán are steep slopes covered in a mosaic of pine-oak forests and agricultural lands, primarily small-scale corn and coffee cultivation. The landscape is deeply incised by numerous rivers and streams, tributaries of the larger Tehuantepec Isthmus watershed, but large bodies of standing water are not immediately proximate. Unlike more industrialized areas of Mexico, Miahuatlán’s economy is largely agrarian and service-based, meaning industrial pollution sources are limited. However, the prevalence of wood-burning stoves for cooking and heating, particularly in the cooler months, contributes to particulate matter pollution. The urban-rural gradient is quite sharp; the city centre transitions rapidly into agricultural fields and forested hillsides. Dust from unpaved roads and agricultural activities also plays a role in localized air quality concerns. The city’s position within a complex orographic system means wind patterns are highly variable and can either disperse or concentrate pollutants.

Miahuatlán experiences a distinct wet and dry season, rather than traditional four seasons. Air quality is generally better during the wet season (roughly May to October) due to frequent rainfall which effectively washes particulate matter from the atmosphere. However, increased humidity can also promote the formation of mold and allergens, impacting respiratory health. The driest months, November to April, consistently present the poorest air quality. This is largely due to increased dust from agricultural activities, road traffic, and the widespread use of wood and charcoal for heating and cooking. Temperature inversions, common during the cooler, drier mornings, trap pollutants near ground level, exacerbating the problem. February and March are typically the months with the most persistent poor air quality. Sensitive groups – children, the elderly, and those with pre-existing respiratory conditions – should limit strenuous outdoor activity during these periods. Strong northerly winds, occasionally occurring during the dry season, can temporarily improve conditions by dispersing pollutants, but can also bring dust from distant sources. Monitoring local conditions and adjusting activity levels accordingly is crucial. The transition periods, April/May and October/November, see fluctuating conditions, requiring vigilance.