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Assaré, Ceará, Brazil, occupies a strategic position within the interior of the state, nestled within the agreste region – a transitional zone between the coastal forests and the arid hinterland of the Northeast. Located at approximately -6.8739° latitude and -39.8750° longitude, the city’s elevation averages around 450 meters above sea level, contributing to a slightly cooler climate than the immediate coastline. The surrounding landscape is characterized by a mosaic of caatinga vegetation, a unique dry tropical biome adapted to prolonged drought conditions. This vegetation, while resilient, can contribute to particulate matter during the dry season when leaf litter accumulates and occasional wildfires occur. Assaré’s proximity to the São Francisco River, though not directly on its banks, influences regional humidity and wind patterns. The urban fabric of Assaré is relatively compact, reflecting its smaller population of approximately 21,697. The city’s economy is primarily agricultural, with subsistence farming and the cultivation of fruits and vegetables being significant activities. This agricultural activity, coupled with the prevalence of livestock, can contribute to localized emissions of ammonia and other agricultural pollutants. The urban–rural gradient is gradual, with small settlements and agricultural fields extending outwards from the city center. There are no major industrial belts immediately adjacent to Assaré; however, larger regional centers with industrial activity lie within a day's travel, potentially impacting air quality through long-range transport of pollutants. The terrain is gently undulating, which can sometimes trap pollutants, particularly during periods of low wind speed.

Assaré’s tropical climate dictates a distinct wet and dry season pattern, profoundly influencing air quality. The dry season, typically spanning from August to May, is characterized by intense solar radiation, low humidity, and infrequent rainfall. This period often sees a build-up of particulate matter, primarily from agricultural activities like burning crop residue (though increasingly regulated), dust stirred up by wind erosion of the caatinga soil, and emissions from cooking fires using biomass. Temperature inversions, common during the cooler nights of the dry season, can trap pollutants close to the ground, exacerbating the situation. The wet season, from May to August, brings relief as rainfall washes away accumulated pollutants and increased humidity reduces dust levels. Stronger winds associated with the wet season also help disperse pollutants. During the peak of the wet season, fog is rare, allowing for good air ventilation. The months of September through November often experience a transitional period with increased dust storms as the dry season begins, making this a potentially challenging time for air quality. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should limit prolonged outdoor activity during the dry season, particularly on days with high wind and visible dust. Maintaining indoor air quality through proper ventilation and air filtration can also be beneficial. The caatinga vegetation, while generally drought-resistant, can release volatile organic compounds (VOCs) during periods of stress, which may contribute to ozone formation under specific meteorological conditions.