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Santa Rosa, nestled in the pampas region of Rio Grande do Sul, Brazil, occupies a geographically significant position within a vast, relatively flat agricultural landscape. Located at approximately -27.87° S, -54.48° W, the city’s terrain is characterized by gently rolling hills and fertile plains, typical of the pampas biome. Its elevation averages around 280 meters (919 feet) above sea level, contributing to a generally stable atmospheric profile, though susceptible to temperature inversions under specific conditions. The city sits near the Ijuí River, a tributary of the Ibicuí River, providing a localized source of moisture and influencing microclimates. Surrounding Santa Rosa is a predominantly rural expanse dominated by extensive cattle ranches and soybean farms, a major agricultural belt impacting regional air quality. The urban–rural gradient is relatively sharp; the city transitions quickly into agricultural land, meaning agricultural practices and livestock emissions are a constant factor. While Santa Rosa isn't directly adjacent to major industrial centers, its proximity to larger regional hubs like Ijuí and Santo Ângelo means it can experience transported pollutants. The prevailing winds generally flow from the northwest, carrying potential contaminants from agricultural areas and distant industrial zones. The pampas climate, with its distinct seasons, also plays a crucial role in air quality dynamics, influencing the dispersion and accumulation of pollutants. The flat topography limits vertical mixing, potentially trapping pollutants near the surface, especially during periods of stable atmospheric conditions.

Santa Rosa’s subtropical climate dictates a distinct seasonal pattern in air quality. The warm, humid summers (December to March) often see increased levels of ground-level ozone, formed through photochemical reactions driven by sunlight and high temperatures. Stagnant air masses during this period, coupled with emissions from agricultural activities (fertilizer application, livestock) exacerbate this. The rainy season, coinciding with summer, can temporarily flush pollutants from the atmosphere, but the increased humidity also promotes ozone formation. Autumn (April to June) brings cooler temperatures and more frequent rainfall, generally improving air quality. However, agricultural burning, a common practice for land clearing and residue disposal, can significantly degrade air quality during this transition period, particularly in late February and March. Winter (July to September) is typically the most challenging season. Cold, stable air masses frequently lead to temperature inversions, trapping pollutants close to the ground. Fog, common during winter mornings, further restricts dispersion. Spring (October to November) sees a gradual improvement as temperatures rise and winds increase, dispersing accumulated pollutants. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should limit prolonged outdoor activity during winter mornings and on days with visible fog or smoke. During summer, avoiding strenuous activity during peak ozone hours (mid-morning to early afternoon) is advisable. Farmers should adhere to regulations regarding agricultural burning to minimize impacts on air quality. Public awareness campaigns promoting responsible agricultural practices and reducing vehicle emissions are crucial for maintaining acceptable air quality throughout the year.