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Pelotas occupies a strategic position in Brazil's southernmost state of Rio Grande do Sul, situated approximately 250 kilometers southwest of Porto Alegre near the border with Uruguay. The city lies within the Pampas biome on the eastern bank of the São Gonçalo Channel, which connects the Lagoa dos Patos and Lagoa Mirim—two of South America's largest coastal lagoons. This low-lying coastal plain location, with an average elevation of just 7 meters above sea level, creates a flat terrain dominated by grasslands and interspersed with wetlands. Pelotas functions as a regional hub for agriculture and food processing, surrounded by extensive cattle ranches, rice paddies, and fruit orchards that create a distinct urban-rural gradient. The city's urban character reflects its 19th-century prosperity from charque (jerked beef) production, with preserved historic architecture alongside modern expansion. Proximity to these substantial water bodies moderates temperatures but also contributes to humidity that can trap pollutants. The surrounding agricultural activities, particularly during planting and harvesting seasons, introduce particulate matter from soil disturbance and occasional agricultural burning, while urban emissions from transportation and residential heating during cooler months combine with the region's frequent temperature inversions to occasionally degrade air quality. The flat landscape offers little topographic relief to disperse pollutants, making meteorological conditions particularly influential on air quality outcomes.

Pelotas experiences distinct seasonal variations in air quality influenced by its temperate climate with four defined seasons. During autumn (March-May), decreasing temperatures and increasing rainfall help cleanse the atmosphere, though agricultural activities including rice harvesting can elevate particulate levels. Winter (June-August) presents the most challenging period for air quality as temperature inversions become frequent in the cool, calm conditions, trapping pollutants from residential wood burning and vehicle emissions near the surface. Sensitive groups should limit prolonged outdoor exposure during winter mornings when inversions are strongest. Spring (September-November) brings improving conditions as increasing winds and precipitation disperse pollutants, though agricultural burning and soil preparation for summer crops can cause temporary spikes. Summer (December-February) offers the cleanest air with frequent sea breezes from the nearby Atlantic Ocean and convective mixing that effectively ventilates the urban area. The warmest months are ideal for outdoor activities, though occasional heat waves can increase ozone formation. Throughout the year, fog is common, particularly in winter, which can combine with pollution to create reduced visibility and respiratory concerns. The city's proximity to large water bodies moderates extreme pollution events but contributes to humidity that can enhance secondary aerosol formation. Visitors with respiratory conditions should be particularly cautious during winter and monitor local air quality advisories.