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Santa Quitéria do Maranhão, nestled in the northeastern Brazilian state of Maranhão, occupies a geographically significant position within the Lençóis Maranhenses National Park region. Located at approximately -3.5158° latitude and -42.5469° longitude, the city’s terrain is characterized by undulating dunes and seasonally flooded wetlands, a unique landscape shaped by the interplay of windblown sand and the intermittent Gurupitã River. The surrounding landscape is dominated by the vast expanse of the Lençóis Maranhenses, a sprawling system of white sand dunes interspersed with rainwater lagoons. This proximity to the park significantly influences the local climate and, consequently, air quality. The urban character of Santa Quitéria do Maranhão is relatively small-scale, primarily a service center for the surrounding agricultural communities and tourism related to the national park. The urban–rural gradient is sharp, with the city transitioning quickly into the expansive, sparsely populated dune fields. Elevation is generally low, rarely exceeding 30 meters above sea level, which can exacerbate the effects of temperature inversions. While lacking major industrial belts within the city limits, the surrounding region features agricultural zones focused on rice and bean cultivation, and cattle ranching, which can contribute to localized particulate matter emissions. The Gurupitã River, though seasonal, plays a role in humidity levels and potential for fog formation, impacting pollutant dispersion. The prevailing winds, often originating from the Atlantic, can transport pollutants from coastal areas, though the dunes themselves act as a partial barrier.

Santa Quitéria do Maranhão experiences a tropical climate with a distinct wet and dry season, rather than the four traditional seasons. The dry season, typically from July to November, is characterized by intense sunshine, high temperatures, and minimal rainfall. This period often sees a slight increase in particulate matter concentrations due to the increased prevalence of windblown sand from the Lençóis Maranhenses. The lack of rainfall means there's less atmospheric cleansing, and dust particles remain suspended for longer. Conversely, the wet season, from December to June, brings frequent rainfall and significantly higher humidity. The increased precipitation effectively washes pollutants from the atmosphere, leading to a noticeable improvement in air quality. However, periods of prolonged fog, common during the transition months (December/January and May/June), can trap pollutants near the ground, creating localized episodes of reduced visibility and potentially elevated concentrations of certain gases. Temperature inversions, where a layer of warm air sits above cooler air, are less frequent than in more temperate climates, but can occur during the cooler months (July-September), trapping pollutants and reducing dispersion. Sensitive groups, such as children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly on windy days. During the wet season, while overall air quality is better, the humidity can exacerbate respiratory issues for some individuals. Outdoor activities are generally more favorable during the wet season, especially after rainfall, but awareness of potential fog episodes remains important.