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Catu, Bahia, nestled in the heart of Brazil’s semi-arid Northeast region, occupies a geographically significant position within the broader metropolitan area of Salvador. Located approximately 60 kilometers west of the state capital, Catu’s coordinates (-12.3531, -38.3789) place it within a transitional zone between the humid coastal plains and the drier interior sertão. The city’s terrain is characterized by rolling hills and valleys, a landscape sculpted by ancient geological processes and further modified by agricultural practices. Elevation varies, but generally ranges between 150 and 300 meters above sea level, influencing local wind patterns and temperature distribution. While not directly adjacent to a major river, Catu benefits from proximity to smaller tributaries and seasonal streams that contribute to the region’s water resources. The surrounding landscape is a mosaic of sugarcane plantations, small-scale farms cultivating beans and maize, and patches of caatinga, a unique thorny scrub forest adapted to arid conditions. This agricultural intensity, particularly the sugarcane industry, represents a key factor impacting local air quality. The urban–rural gradient is relatively sharp, with the city transitioning quickly into agricultural land and then into the more extensive caatinga biome. The prevailing winds, often influenced by the Atlantic coast, can transport pollutants inland, while the topography can create localized areas of stagnant air, particularly during periods of calm weather. The city’s growth, driven by its strategic location along transportation routes, has also contributed to increased vehicular emissions and associated air quality challenges.

Catu’s tropical climate dictates a distinct wet and dry season pattern, profoundly influencing its air quality dynamics. The dry season, typically spanning from September to April, is characterized by reduced rainfall, higher temperatures, and increased atmospheric stability. This often leads to temperature inversions, where a layer of warm air traps cooler air near the ground, hindering the dispersion of pollutants. Agricultural burning, a common practice for land clearing and sugarcane cultivation, intensifies during this period, releasing significant quantities of particulate matter and gases into the atmosphere. Consequently, air quality tends to be poorest during the late dry season, particularly in October and November. The onset of the wet season, from May to August, brings relief as increased rainfall and higher humidity help to cleanse the air. Frequent showers and stronger winds facilitate the removal of pollutants, leading to improved air quality. However, heavy rainfall can also temporarily exacerbate issues by mobilizing dust and soil particles. Fog, though infrequent, can occur during cooler nights, trapping pollutants and reducing visibility. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, limiting outdoor activities during peak pollution periods. During the wet season, while generally cleaner, periods of intense rainfall can still trigger temporary air quality concerns. Maintaining indoor air quality through proper ventilation and air filtration is always advisable, especially for those with pre-existing health vulnerabilities.