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Acapetahua, nestled in the southern lowlands of Chiapas, Mexico, occupies a geographically significant position within the Suchiate River basin. Located at approximately 15.23° N, 92.77° W, and with an elevation of just 25 meters above sea level, the city’s topography is remarkably flat, characteristic of the coastal plain. The Suchiate River, a vital waterway, flows nearby, influencing local humidity and microclimates. Acapetahua’s surrounding landscape is dominated by a mosaic of agricultural lands – primarily banana plantations and maize fields – interspersed with patches of tropical forest. This agricultural intensity contributes to potential sources of air pollutants, particularly during harvest and pesticide application. The urban–rural gradient transitions rapidly; the city itself is relatively compact, with a discernible core and expanding peripheral residential areas. It sits within a region experiencing a strong influence from the Pacific Ocean, bringing maritime air masses and seasonal rainfall. While not directly adjacent to major industrial belts, Acapetahua serves as a crucial trading hub for agricultural products destined for larger markets, leading to increased vehicular traffic and associated emissions. The flat terrain and proximity to the river can exacerbate the trapping of pollutants, especially during periods of stagnant air. The surrounding dense vegetation, while generally beneficial for air quality, can also contribute to biogenic volatile organic compound (BVOC) emissions, which react with other pollutants in sunlight to form ozone.

Acapetahua’s tropical climate dictates a distinct wet and dry season pattern, profoundly impacting air quality. The dry season, typically spanning November through April, often sees a slight increase in particulate matter concentrations. This is partly due to reduced rainfall washing pollutants from the atmosphere and increased agricultural burning for land clearing and crop residue disposal, a common practice in the region. The lack of consistent rainfall also allows dust from unpaved roads to become more prevalent. During the wet season (May to October), frequent rainfall effectively ‘scrubs’ the atmosphere, leading to a noticeable improvement in air quality. However, periods of intense rainfall can also mobilize pollutants from agricultural runoff, potentially impacting water quality and indirectly affecting air quality through aerosol formation. Meteorological conditions play a crucial role; periods of calm winds and high humidity, particularly during the transition months, can lead to stagnant air and the accumulation of pollutants. Fog, while infrequent, can trap pollutants close to the ground, creating localized air quality concerns. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during agricultural burning periods. Limiting prolonged outdoor activity during these times and ensuring adequate ventilation indoors is advisable. The increased humidity during the wet season can exacerbate respiratory issues for some, so maintaining indoor air quality remains important year-round.