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Itapecuru Mirim, nestled in the eastern reaches of Maranhão state, Brazil, occupies a relatively flat terrain within the Gurupi-Parnaíba plain. Its coordinates (-3.3928, -44.3589) place it inland, approximately 60 kilometers from the Atlantic coastline, influencing its climate but not directly experiencing the moderating effects of sea breezes as strongly as coastal cities. The Itapecuru River, from which the city derives its name, is a crucial geographical feature, providing water resources but also potentially acting as a conduit for agricultural runoff. The surrounding landscape is dominated by transitional zones between *cerrado* (Brazilian savanna) and *caatinga* (thorn scrub forest), with increasing agricultural activity, particularly soybean and cattle ranching, in recent decades. This agricultural expansion, alongside smaller-scale charcoal production for local industries, contributes to particulate matter emissions. The urban-rural gradient is pronounced; the city centre is densely populated, while the periphery quickly transitions into agricultural land. This proximity to agricultural sources, combined with the flat topography which limits dispersion, creates conditions conducive to localised air pollution events. Dust from unpaved roads and seasonal burning for land clearing further exacerbate the situation. The city’s position within a broader regional agricultural belt means it’s susceptible to pollutants transported from wider areas.

Itapecuru Mirim experiences a distinct wet and dry season, rather than traditional four seasons. Air quality is generally better during the wet season (roughly February to June) due to rainfall effectively scavenging particulate matter from the atmosphere. Increased humidity also suppresses dust resuspension. However, the wet season can bring increased fungal spores, potentially impacting respiratory health. The dry season (July to November) presents the most significant air quality challenges. Reduced rainfall allows dust and agricultural burn smoke to accumulate. The Harmattan wind, a dry, dusty trade wind, can occasionally transport Saharan dust across the Atlantic, contributing to particulate matter levels. Temperature inversions, common during the cooler nights of the dry season, trap pollutants near the ground. September and October are typically the months with the poorest air quality. Sensitive groups – children, the elderly, and those with pre-existing respiratory conditions – should limit strenuous outdoor activity during these periods. Monitoring local fire reports is crucial. Even during the wet season, periods of intense agricultural activity can lead to localised pollution spikes. Staying indoors with windows closed during peak pollution times and using air purifiers can offer protection.