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San Mateo del Mar, nestled along Oaxaca’s Pacific coast, occupies a unique and geographically sensitive position. Located at approximately 16.2105° latitude and -94.9822° longitude, the town sits within the municipality of Santa María del Mar, a region characterized by a dramatic urban–rural gradient. The terrain is predominantly coastal lowlands, sloping gently towards the expansive Pacific Ocean, a defining feature of the landscape. Elevation is relatively low, rarely exceeding 100 meters above sea level, which influences local weather patterns and air circulation. The surrounding landscape is a mosaic of sandy beaches, mangrove forests, and coastal scrub, gradually transitioning to the foothills of the Sierra Madre del Sur mountains further inland. This proximity to the ocean moderates temperatures but also introduces marine aerosols into the air. Agriculture, particularly corn and bean cultivation, is a significant economic activity in the surrounding areas, and while not a concentrated industrial belt, small-scale processing and fishing activities contribute to localized emissions. The town’s urban character is distinctly rural, with a relatively low population density and a reliance on traditional building materials. The prevailing winds, often influenced by the Intertropical Convergence Zone (ITCZ), play a crucial role in dispersing pollutants, though stagnant air conditions can occasionally occur, particularly during periods of high pressure. The coastal location and surrounding agricultural lands create a complex interplay of factors impacting air quality, making it susceptible to both regional and local pollution sources.

San Mateo del Mar experiences a tropical wet and dry climate, dictating a distinct seasonal narrative for air quality. The dry season, roughly from February to May, typically sees clearer skies and improved air quality due to reduced humidity and increased wind speeds. These winds, often originating from the north, effectively ventilate the area, dispersing any accumulated pollutants. However, agricultural burning, a common practice for land clearing and crop residue disposal, can occasionally lead to localized spikes in particulate matter during this period, particularly in April and May. The wet season, from June to October, brings increased rainfall and higher humidity, which generally helps to scrub the atmosphere of pollutants. However, periods of prolonged rainfall can be followed by stagnant, humid air, creating conditions conducive to the build-up of moisture and potentially trapping pollutants near the ground. Fog, common during the transition months (November and December), can also exacerbate this effect. The ITCZ’s influence is strongest during the wet season, bringing frequent thunderstorms and shifting wind patterns. Sensitive groups, such as children, the elderly, and individuals with respiratory conditions, should be mindful of agricultural burning during the dry season and potential fog events during the transition months. Outdoor activities are generally favored during the drier months, but vigilance regarding potential smoke events is advised. The months of March and April, while generally pleasant, require careful monitoring due to the increased risk of agricultural burning.