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Rio Grande, situated in the southernmost state of Rio Grande do Sul, Brazil, occupies a unique geographic position at the mouth of the Lagoa dos Patos, South America’s largest coastal lagoon. The city’s terrain is largely flat, characteristic of the Pampa biome, with gentle slopes rising inland. This low elevation, combined with its coastal location, significantly influences air quality. The prevailing winds, often originating from the Atlantic Ocean, carry maritime air masses, which can both dilute pollutants and transport them inland. However, the city is also impacted by continental air masses from Argentina and Uruguay, potentially bringing dust and agricultural aerosols. To the north and west lie extensive agricultural lands, primarily dedicated to rice cultivation and livestock farming, contributing to potential ammonia emissions and particulate matter from field activities. The urban-rural gradient is relatively sharp, with the city centre densely populated and transitioning quickly to rural landscapes. A significant industrial presence, focused on port activities, shipbuilding, and related industries, forms a belt along the coastline, acting as a concentrated source of emissions. The Lagoa dos Patos, while a vital ecosystem, can also trap pollutants due to limited water circulation, exacerbating local air quality issues. This interplay of geographical factors creates a complex air quality profile for Rio Grande.

Rio Grande experiences a humid subtropical climate, with distinct seasonal variations impacting air quality. The summer months (December-February) often see higher ozone levels due to increased solar radiation and warmer temperatures, fostering photochemical smog formation. While winds from the Atlantic can provide some relief, stagnant air masses can lead to localized pollution build-up. Autumn (March-May) brings more frequent rainfall, effectively scavenging pollutants from the atmosphere, resulting in generally improved air quality. However, agricultural burning, common during this period for preparing fields for the next planting season, can cause spikes in particulate matter. Winter (June-August) is characterized by cooler temperatures and increased frequency of temperature inversions, trapping pollutants near the ground, particularly from industrial sources and residential heating. This is often the period with the poorest air quality. Spring (September-November) sees a transition, with increasing temperatures and wind speeds gradually dispersing pollutants. Sensitive individuals, such as those with respiratory conditions, should be particularly cautious during winter and summer. Monitoring wind patterns and avoiding outdoor exertion during periods of stagnation is advisable. The wet season generally offers the most favourable conditions for outdoor activities.