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Brejo Santo, nestled in the interior of Ceará state, Brazil, occupies a geographically significant position within the Northeast region. Located at approximately -7.4928° latitude and -38.9850° longitude, the city sits within the Agreste region, a transitional zone between the humid coastal forests and the arid hinterland of the Sertão. This location dictates a semi-arid climate and influences the city’s urban character. The terrain is gently undulating, characterized by rolling hills and valleys, a legacy of ancient erosion. Elevation averages around 450 meters above sea level, contributing to a relatively stable atmospheric layer, though susceptible to temperature inversions under specific conditions. The surrounding landscape is predominantly characterized by *caatinga* vegetation, a thorny scrubland adapted to drought conditions, interspersed with agricultural plots – primarily sugarcane and fruit orchards, reflecting the region’s agricultural economy. Brejo Santo’s proximity to the São Francisco River, though not directly adjacent, is crucial; the river’s influence moderates temperatures and provides irrigation for agriculture. The urban–rural gradient is gradual, with small agricultural communities blending seamlessly into the city’s periphery. Industrial activity is limited, primarily focused on sugar processing and related industries, which represent a localized source of potential air pollutants. The prevailing winds, generally from the northeast, carry dust and particulate matter from the Sertão, impacting air quality, particularly during drier periods. The city’s growth has been driven by agriculture and, more recently, by small-scale manufacturing, leading to a dispersed urban form with pockets of denser residential areas.

Brejo Santo experiences a distinct wet and dry season pattern, profoundly impacting its air quality. The dry season, typically spanning from August to November, is characterized by intense heat, low humidity, and infrequent rainfall. This period often witnesses a significant increase in particulate matter concentrations, primarily due to windblown dust from the surrounding *caatinga* and agricultural lands. The lack of rainfall prevents the natural cleansing effect of precipitation, allowing pollutants to accumulate. Temperature inversions, common during these cooler nights, trap pollutants near the ground, exacerbating the situation. Conversely, the wet season (December to July) brings relief. Frequent rainfall effectively washes away particulate matter, and higher humidity reduces dust generation. Stronger winds associated with occasional thunderstorms also disperse pollutants. February and March often see increased agricultural burning, a traditional practice for land clearing and preparing fields, which contributes to localized smoke pollution. During the hottest months (March-May), stagnant air and high temperatures can lead to the build-up of ozone, a secondary pollutant formed from reactions involving sunlight and precursor gases. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, limiting outdoor activities during peak dust events. The transition months (November/December and June/July) are generally favorable for outdoor pursuits, offering a balance of reduced dust and moderate temperatures. Agricultural workers should be particularly vigilant regarding smoke exposure during burning periods, utilizing appropriate respiratory protection.