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Matamoros, Coahuila, nestled along the Rio Grande/Rio Bravo del Norte, occupies a strategically vital position on the Mexico–United States border. Its coordinates (25.5330, -103.2500) place it within the arid to semi-arid climate zone of northeastern Mexico, characterized by a relatively flat terrain gradually rising towards the surrounding plains. The city’s immediate landscape is dominated by the river, forming a natural boundary and influencing local microclimates. To the west, the terrain gently ascends into the Coahuila plateau, a vast expanse of scrubland and grasslands. Eastward, the landscape transitions into agricultural zones, supporting maize and sorghum cultivation, which can contribute to seasonal dust events. Matamoros’s proximity to Brownsville, Texas, creates a significant urban–rural gradient, with the city acting as a major commercial and industrial hub for the region. The presence of maquiladoras (manufacturing plants) along the border, concentrated in industrial parks, is a key factor shaping the urban character and, critically, influencing air quality. These facilities, often involved in automotive parts and electronics assembly, contribute to industrial emissions. The relatively flat topography and prevailing wind patterns can trap pollutants, particularly during periods of atmospheric stability. The surrounding landscape, while largely undeveloped, provides limited natural air purification mechanisms, making the city’s air quality highly susceptible to local emissions and transboundary pollution from the United States.

Matamoros experiences a distinct wet and dry season pattern, significantly impacting air quality. The dry season, typically spanning from late autumn through spring, is characterized by lower rainfall and increased sunshine hours. This period often sees elevated particulate matter concentrations due to windblown dust from agricultural fields and construction activities. Temperature inversions, common during the cooler months, trap pollutants near the ground, exacerbating the problem. The dry, stable air also promotes the accumulation of emissions from maquiladoras and vehicular traffic. Conversely, the wet season, from late spring to early autumn, brings increased rainfall and higher humidity. These conditions naturally cleanse the atmosphere, washing away particulate matter and diluting gaseous pollutants. However, heavy rainfall can also lead to localized flooding, potentially releasing contaminants from industrial sites or agricultural runoff. Fog, particularly in the cooler months, can further reduce visibility and trap pollutants close to the surface. During the hottest months, stagnant air and high temperatures can contribute to ozone formation, although this is generally less pronounced than particulate matter issues. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during periods of high dust or stagnant air. Outdoor activities are generally more favorable during the wet season, although vigilance regarding potential flood-related hazards remains important.