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Porto da Folha, nestled within the Sergipe state of Brazil, occupies a geographically significant position along the Sergipe River estuary, where it meets the Atlantic Ocean. Located at approximately -9.9169° latitude and -37.2778° longitude, the city’s terrain is predominantly low-lying, characteristic of deltaic regions. The surrounding landscape is a mosaic of mangroves, coastal forests (Mata Atlântica remnants), and agricultural lands, primarily dedicated to sugarcane cultivation and fruit orchards. This proximity to agricultural zones introduces potential sources of particulate matter, particularly during harvest seasons when burning practices, though regulated, can still occur. The urban–rural gradient transitions rapidly, with the city bordered by extensive rural areas, influencing local wind patterns and pollutant dispersion. Elevation is minimal, rarely exceeding 10 meters above sea level, which can exacerbate the trapping of pollutants during periods of atmospheric stability. The Sergipe River itself plays a crucial role, both as a transportation artery and a potential sink for pollutants carried from upstream agricultural activities and urban runoff. The coastal location exposes Porto da Folha to maritime influences, including sea breezes that generally contribute to ventilation, but also the potential for salt spray and episodic marine aerosol events. The region’s climate is tropical, with high humidity and consistent temperatures, impacting the chemical reactions and persistence of airborne pollutants. The city’s relatively small size (population 26,576) means that localized industrial activity, primarily related to fishing and small-scale processing, is the dominant contributor to urban air pollution, alongside vehicle emissions from the limited road network.

Porto da Folha experiences a tropical climate with distinct wet and dry seasons, significantly influencing its air quality profile. The wet season, typically spanning from February to July, brings frequent rainfall and high humidity. This increased precipitation naturally helps to cleanse the atmosphere, washing away particulate matter and reducing overall pollution levels. The consistent rainfall also suppresses dust generation from agricultural fields. However, periods of prolonged rainfall can lead to increased biological volatile organic compounds (BVOCs) emissions from the surrounding forests and mangroves, potentially impacting local air quality, though generally not to a significant degree. The dry season, from August to January, is characterized by lower rainfall and higher temperatures. This often leads to a decrease in atmospheric ventilation, particularly during periods of calm winds, which can trap pollutants near the surface. Temperature inversions, where a layer of warm air sits above cooler air, are more common during the dry season, further hindering pollutant dispersion. Agricultural burning, though regulated, may be more prevalent during this period as farmers prepare fields for the next planting cycle, contributing to particulate matter. Sensitive groups, such as children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly in the mornings when temperature inversions are most likely. Outdoor activities are generally more favorable during the wet season, although pollen levels may be elevated during certain periods. The high humidity throughout the year can also exacerbate respiratory issues for some individuals, regardless of the season.