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Cajari, Maranhão, Brazil, nestled within the Cerrado biome, presents a unique geographic profile significantly influencing its air quality. Located at approximately -3.3208° latitude and -45.0108° longitude, the city sits at a modest elevation of around 170 meters above sea level, contributing to relatively stable atmospheric conditions. The surrounding landscape is dominated by the characteristic savanna vegetation of the Cerrado, interspersed with patches of gallery forests along the Pindaré River, which flows nearby. This riverine influence moderates local temperatures and humidity, but also introduces potential sources of particulate matter from agricultural runoff and occasional flooding. Cajari’s position within Maranhão state places it within a transitional zone between the Amazon rainforest to the north and the drier Northeast region. This creates a complex interplay of climate patterns. The urban character of Cajari is primarily that of a regional service center, with agriculture (particularly soybean and maize cultivation) and livestock farming being significant economic drivers in the surrounding rural areas. This proximity to intensive agricultural practices means that pesticide drift and dust from tilling operations can impact local air quality. The urban–rural gradient is relatively sharp, with agricultural activities becoming dominant within a short distance of the city limits. The Cerrado’s naturally low tree cover, combined with agricultural land use, limits the natural filtration of air pollutants, making Cajari susceptible to localized air quality challenges, particularly during drier periods when windblown dust is prevalent.

Cajari’s tropical climate dictates a distinct wet and dry season cycle, profoundly impacting its air quality. The dry season, typically spanning from August to November, is characterized by reduced rainfall, higher temperatures, and increased wind speeds. This combination often leads to elevated levels of particulate matter, primarily from agricultural activities like harvesting and soil preparation. The lack of rainfall means less atmospheric cleansing, and the drier vegetation is more prone to wildfires, further exacerbating the problem. Temperature inversions, though less frequent than in temperate climates, can occasionally trap pollutants near the ground, especially during cooler nights. The wet season, from December to July, brings frequent rainfall and higher humidity, which generally improves air quality by washing away pollutants and suppressing dust. However, intense rainfall events can lead to flooding, mobilizing sediment and organic matter, which can temporarily degrade air quality. Fog, though not a common occurrence, can form during cooler, calmer periods, trapping pollutants and reducing visibility. During the dry season months of September and October, sensitive groups like children, the elderly, and individuals with respiratory conditions should limit prolonged outdoor activity, particularly during midday when temperatures are highest and wind speeds may be strong. The wet season offers a respite, but caution should still be exercised during periods of heavy rainfall or flooding due to potential waterborne contaminants and increased humidity, which can aggravate respiratory issues. Maintaining indoor air quality through proper ventilation and air filtration is crucial throughout the year.