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Giruá, nestled in the heart of Rio Grande do Sul, Brazil, occupies a geographically significant position within the state's Gaucho pampa region. Located at approximately -28.0278° latitude and -54.3500° longitude, the city’s terrain is characterized by gently undulating plains, typical of the pampa biome, with elevations rarely exceeding 300 meters above sea level. This relatively flat landscape, while facilitating urban expansion, can also contribute to localized air quality challenges. Giruá sits within a predominantly agricultural zone, surrounded by extensive grasslands used for cattle ranching and crop cultivation, particularly soybeans and wheat. The proximity to these agricultural activities introduces potential sources of particulate matter, especially during planting and harvesting seasons, and from livestock operations. While not directly adjacent to a major river, Giruá benefits from the presence of smaller streams and tributaries that contribute to the region’s water resources. The urban–rural gradient is gradual, with agricultural land seamlessly blending into the city’s periphery. The city’s regional position, situated approximately 400 kilometers west of Porto Alegre, the state capital, places it within a moderate distance of industrial activity concentrated in the metropolitan area, potentially exposing Giruá to transported pollutants. The prevailing winds, generally from the east, can carry pollutants from more industrialized areas, impacting local air quality. The lack of significant topographic barriers further exacerbates this potential for long-range transport of pollutants, making Giruá’s air quality susceptible to regional influences.

Giruá’s subtropical climate dictates a distinct seasonal pattern influencing air quality. The summer months (December to February) are typically hot and humid, often accompanied by stagnant air conditions. High temperatures and humidity can trap pollutants near the ground, particularly those emitted from agricultural practices like fertilizer application and livestock. The lack of consistent wind during these periods can lead to a build-up of these emissions. Conversely, the autumn months (March to May) often bring more frequent and stronger winds, which help disperse pollutants, generally improving air quality. Winter (June to August) presents a unique challenge. While temperatures drop, the occurrence of temperature inversions – where a layer of warm air sits above cooler air – becomes more common. This inversion traps pollutants close to the ground, leading to periods of reduced visibility and potentially elevated concentrations of particulate matter. Fog, frequently occurring during winter mornings, further exacerbates this issue by limiting atmospheric mixing. Spring (September to November) sees a gradual improvement in air quality as temperatures rise and wind patterns become more consistent. Agricultural activity increases during spring, which can temporarily impact air quality. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during winter mornings and during periods of stagnant air in summer, limiting prolonged outdoor exposure. Avoiding strenuous activity during these times is also advisable. The agricultural cycle significantly influences air quality, with increased emissions during planting and harvesting periods across all seasons.