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Urbano Santos, nestled in the state of Maranhão, Brazil, occupies a relatively flat terrain near the Pindaré River, a major tributary of the Amazon River system. Its coordinates (-3.2078, -43.4039) place it within the Amazon rainforest biome, though the immediate surroundings are transitioning into a landscape of fragmented forests and agricultural land. The city’s elevation is low, contributing to limited atmospheric dispersion of pollutants. Urbano Santos functions as a regional hub for agricultural production, particularly for crops like rice and beans, and experiences associated transport and processing activities. The urban-rural gradient is quite sharp; the city centre quickly gives way to extensive agricultural fields and remaining patches of rainforest. This proximity to agricultural zones introduces potential sources of particulate matter from land preparation, burning of crop residues, and fertilizer application. The riverine environment, while providing a water source, can also contribute to humidity and potentially trap pollutants during periods of calm weather. The city’s location within the equatorial climate zone means consistent high temperatures and humidity, influencing chemical reactions in the atmosphere and pollutant behaviour. Industrial activity is limited, but growing, posing a future risk to air quality. The surrounding landscape offers minimal natural barriers to wind flow, but local topography can create microclimates affecting pollutant concentration.

Urbano Santos experiences a distinct wet and dry season, rather than traditional four seasons. Air quality is generally poorer during the dry season (roughly June to November) due to increased dust from agricultural activities and a greater propensity for wildfires in surrounding areas. Reduced rainfall means less atmospheric cleansing, allowing pollutants to accumulate. The dry season also sees increased use of biomass burning for land clearing, significantly impacting particulate matter levels. Conversely, the wet season (December to May) brings improved air quality as rainfall washes away pollutants and increases humidity, suppressing dust. However, even during the wet season, localised pollution from vehicle emissions and small-scale industries can be problematic. February and March, during peak rainfall, are typically the best months for outdoor activity. Temperature inversions, common during the calmer nights of the dry season, exacerbate pollution by trapping pollutants near ground level. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor exposure during the dry season, particularly on days with visible haze. Monitoring wind patterns is crucial; winds from agricultural areas can bring significant particulate matter into the city.