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Custódia, nestled in the agreste region of Pernambuco, Brazil, occupies a geographically significant position within a transitional landscape. Located at approximately -8.0875° latitude and -37.6431° longitude, the city sits at an elevation of roughly 450 meters above sea level, placing it within a zone characterized by rolling hills and valleys. The surrounding terrain is predominantly dominated by *caatinga* vegetation, a semi-arid biome typical of northeastern Brazil, interspersed with areas of agricultural land, primarily sugarcane and maize cultivation. This proximity to agricultural zones introduces potential sources of particulate matter, particularly during harvest seasons when burning practices, though regulated, can still occur. Custódia’s location is not directly adjacent to major rivers or coastal areas, minimizing the influence of marine aerosols or coastal breezes. However, it lies within a broader watershed, impacting regional water quality and indirectly influencing atmospheric conditions. The urban–rural gradient around Custódia is relatively gradual, with small settlements and agricultural plots blending seamlessly into the *caatinga* landscape. The city itself exhibits a typical Brazilian urban character, with a central commercial area and residential zones radiating outwards. The regional industrial presence is limited, primarily consisting of small-scale agricultural processing facilities, which contributes to a generally lower industrial pollution load compared to larger Brazilian cities. The prevailing winds, often influenced by the seasonal shifts in the Intertropical Convergence Zone (ITCZ), play a crucial role in dispersing or concentrating pollutants within the local atmosphere.

Custódia’s tropical climate dictates a distinct wet and dry season pattern, profoundly influencing its air quality. The dry season, typically spanning from August to November, is characterized by reduced rainfall and increased temperatures. This period often sees a build-up of particulate matter due to reduced precipitation to wash pollutants from the atmosphere and increased dust from agricultural activities and soil erosion exacerbated by drier conditions. Temperature inversions, where cooler air is trapped beneath a layer of warmer air, are more frequent during the dry season, hindering vertical mixing and trapping pollutants closer to ground level. The wet season, from December to July, brings increased rainfall and higher humidity, naturally cleansing the atmosphere and reducing particulate concentrations. However, intense rainfall events can occasionally lead to increased levels of mold spores and allergens. During the transition months (May-June and August-September), wind patterns become more variable, leading to unpredictable air quality fluctuations. The ITCZ’s influence brings periods of intense convective activity, which can temporarily disperse pollutants but also generate dust storms. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during periods of high dust or stagnant air. Outdoor activities are generally more favorable during the wet season, although pollen allergies should be considered. Agricultural burning, if practiced, poses the greatest risk during the dry season, and local authorities should be consulted regarding any burn bans or advisories.