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Brasnorte, nestled in the heart of Mato Grosso, Brazil, occupies a geographically significant position within the Cerrado biome, a vast tropical savanna ecoregion. Located at approximately -12.1550° latitude and -57.9789° longitude, the city’s elevation of around 280 meters above sea level contributes to a relatively stable atmospheric layer, which can, at times, exacerbate pollution events. The surrounding landscape is characterized by undulating plains punctuated by gallery forests along the Paraguay River, a major waterway that forms a partial boundary to the east. This proximity to the river introduces a degree of humidity and potential for localized fog formation, particularly during the wetter months. Brasnorte’s regional position places it within a crucial agricultural belt, with extensive soybean, corn, and cattle farming dominating the landscape. This agricultural activity, coupled with the increasing presence of mechanized farming practices, contributes to particulate matter emissions, particularly from soil erosion and agricultural burning. The urban–rural gradient is relatively sharp; the city transitions quickly into agricultural land, meaning that rural pollution sources can readily impact air quality within Brasnorte itself. The city’s relatively small size (population 17,004) means that localized industrial activity, primarily related to agricultural processing and small-scale manufacturing, is the primary urban source of pollutants. The prevailing winds, generally from the southeast, can transport pollutants from neighboring agricultural areas and influence the city’s air quality profile.

Brasnorte’s tropical climate dictates a distinct wet and dry season pattern, profoundly influencing its air quality. The dry season, typically from April to September, is characterized by lower rainfall and increased temperatures. This period often sees a rise in particulate matter concentrations due to agricultural burning practices, a common method for land clearing and crop residue disposal. The drier air and reduced precipitation limit the natural cleansing effect of rainfall, allowing pollutants to persist for longer durations. Temperature inversions, where a layer of warm air traps cooler air near the ground, are also more frequent during the dry season, further hindering pollutant dispersion. Conversely, the wet season (October to March) brings increased rainfall and higher humidity, which naturally washes away particulate matter and helps to dilute gaseous pollutants. However, periods of intense rainfall can also lead to increased mold and fungal spore concentrations, impacting indoor air quality. During the transition months (March/April and September/October), fluctuating weather patterns can lead to unpredictable air quality events. Outdoor activities are generally more favorable during the wet season, particularly from November to February. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, minimizing prolonged outdoor exposure and avoiding areas with visible smoke. The increased humidity during the wet season can exacerbate allergies for some individuals, requiring appropriate management strategies.