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Magalhães de Almeida, nestled in the southeastern Maranhão state of Brazil, occupies a geographically significant position within the Cerrado biome. Located at approximately -3.3958° latitude and -42.2039° longitude, the city’s terrain is characterized by undulating plains and gently sloping hills, typical of the transition zone between the Amazon rainforest and the drier Cerrado savanna. The surrounding landscape is dominated by vast expanses of *cerrado* vegetation – a mosaic of grasslands, shrubs, and scattered trees – interspersed with patches of gallery forest along seasonal streams. While not directly bordering a major river, the city’s proximity to the Itapecuru River basin influences local hydrology and microclimates. The urban footprint of Magalhães de Almeida is relatively small, exhibiting a clear urban–rural gradient as it expands outwards. Agriculture, particularly cattle ranching and soybean cultivation, is a dominant land use in the surrounding areas, contributing to potential sources of particulate matter and ammonia emissions. The city itself is a regional hub for agricultural processing and trade, with some small-scale industrial activity. Elevation plays a role; the gently rising terrain can sometimes trap pollutants, particularly during periods of low wind. The regional climate, hot and humid with a distinct wet and dry season, significantly impacts atmospheric stability and dispersion patterns, influencing how pollutants are transported and diluted. The relatively low population density, compared to larger Brazilian cities, initially suggests lower overall pollution levels, but agricultural practices and localized industrial activity remain key factors.

Magalhães de Almeida experiences a tropical climate with a pronounced wet and dry season, dictating the annual air quality narrative. The dry season, typically spanning from July to October, often sees a build-up of pollutants due to reduced rainfall and increased atmospheric stability. Lower humidity and higher temperatures contribute to stagnant air conditions, hindering the dispersion of emissions from agricultural burning, a common practice for land clearing and pasture management. This period frequently witnesses elevated levels of particulate matter, impacting respiratory health. Conversely, the wet season (November to June) brings frequent rainfall, effectively ‘washing’ the atmosphere and significantly reducing pollutant concentrations. The increased cloud cover also reduces solar radiation, which can influence the formation of ozone, a secondary pollutant. During the transition months (April-May and September-October), fluctuating weather patterns can lead to unpredictable air quality episodes. Fog, particularly during the dry season mornings, can trap pollutants near the ground, creating localized pockets of poor air quality. Sensitive groups, including children, the elderly, and individuals with pre-existing respiratory conditions, should exercise caution during the dry season, limiting outdoor activities during peak burning periods and periods of stagnant air. The intensity of agricultural burning is a crucial factor; years with prolonged drought can exacerbate the problem. While the wet season generally provides relief, heavy rainfall can occasionally lead to flooding and the release of mould spores, impacting indoor air quality.