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Rio Negrinho, nestled in the heart of Santa Catarina state, Brazil, occupies a geographically significant position within the Serra Catarinense mountain range. Located at approximately -26.2539 latitude and -49.5178 longitude, the city’s elevation, averaging around 950 meters (3,117 feet) above sea level, contributes to a cooler climate compared to coastal regions of Santa Catarina. The surrounding landscape is dominated by rolling hills, dense Atlantic Forest remnants, and agricultural lands, primarily dedicated to dairy farming and poultry production – key economic drivers for the region. This proximity to intensive agriculture introduces potential sources of ammonia and particulate matter, particularly during harvesting and manure management periods. The urban fabric of Rio Negrinho is characterized by a gradual urban–rural gradient; the city center exhibits a more concentrated commercial and residential area, while the outskirts transition seamlessly into agricultural fields and forested areas. While not directly adjacent to a major river, the city benefits from several smaller streams and tributaries that feed into larger river systems, influencing local humidity and potentially affecting the dispersion of pollutants. The Serra Catarinense’s topography creates localized wind patterns, often resulting in stagnant air conditions during certain times of the year, which can trap pollutants and exacerbate air quality issues. The regional position, inland and elevated, shields Rio Negrinho from direct coastal influences but exposes it to pollutants originating from industrial belts further north in Santa Catarina and Paraná states.

Rio Negrinho’s subtropical climate dictates a distinct seasonal pattern influencing air quality. The wet season, typically spanning from November to March, brings frequent rainfall, generally leading to improved air quality as precipitation washes away particulate matter and dilutes gaseous pollutants. However, periods of prolonged fog, common during this season, can trap pollutants near the ground, creating localized air quality concerns. The dry season, from April to October, is characterized by lower rainfall and increased sunshine, often accompanied by temperature inversions, particularly during the months of June, July, and August. These inversions trap cooler air near the surface, preventing the vertical dispersion of pollutants released from agricultural activities (ammonia from livestock) and any localized industrial sources. Agricultural burning, though regulated, can still occur during land clearing in the dry season, contributing to particulate matter pollution. Spring (September-November) often sees a gradual improvement in air quality as temperatures rise and rainfall increases. Autumn (March-May) can be variable, with periods of stagnant air and potential for localized pollution episodes. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during periods of temperature inversions and agricultural burning, limiting outdoor exertion and monitoring for respiratory irritation. While the wet season generally offers respite, fog events warrant similar precautions. Overall, the months of July and August present the greatest potential for poorer air quality due to the prevalence of temperature inversions.