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Arroio do Meio, nestled in the heart of Rio Grande do Sul, Brazil, occupies a geographically significant position within the Campanha Plateau. Located approximately 30 kilometers northwest of the state capital, Porto Alegre, the city’s coordinates (-29.4008, -51.9450) place it within a gently undulating terrain characterized by rolling hills and fertile plains. The surrounding landscape is a mosaic of agricultural fields – primarily soybean, wheat, and maize cultivation – interspersed with patches of native grasslands (pampas). This proximity to intensive agricultural activity is a key factor influencing local air quality, particularly concerning particulate matter from soil erosion and pesticide drift. The city sits at an elevation of roughly 150 meters above sea level, which, while not exceptionally high, can contribute to localized temperature inversions, especially during cooler months, trapping pollutants closer to the ground. While not directly adjacent to a major river, Arroio do Meio is within the drainage basin of the Sinos River, influencing regional hydrological patterns and indirectly impacting air quality through humidity levels and precipitation. The urban–rural gradient is relatively sharp; the city transitions quickly into agricultural land, meaning that rural activities have a more immediate impact on the urban air quality than in larger, more sprawling metropolitan areas. The regional position, close to Porto Alegre’s industrial belt, also means that Arroio do Meio can experience occasional transport of pollutants from that larger urban center, particularly during periods of stagnant air.

Arroio do Meio experiences a humid subtropical climate, resulting in distinct seasonal variations that significantly influence air quality. The warmer months (December to March) are characterized by higher temperatures and increased humidity, often accompanied by convective rainfall. While rainfall can help cleanse the air, the increased humidity can exacerbate the effects of pollutants, particularly ozone, which forms readily in warm, sunny conditions. The dry season (April to September) presents a different set of challenges. Cooler temperatures during these months, combined with calmer winds, frequently lead to temperature inversions, trapping pollutants near the surface. Agricultural burning, a common practice for land clearing and residue disposal, is most prevalent during this period, contributing significantly to particulate matter pollution. Fog, common in the mornings during the cooler months, further restricts atmospheric mixing and concentrates pollutants. Spring (September to November) typically sees improved air quality as temperatures rise and winds increase, dispersing pollutants. Autumn (March to May) can be variable, with periods of clear, cool air interspersed with episodes of agricultural burning. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly in the mornings when fog is present, and avoid strenuous outdoor activity during periods of agricultural burning. The increased humidity during the warmer months warrants similar precautions for those susceptible to ozone-related respiratory issues.