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Novo Horizonte, nestled within the sprawling municipality of São Paulo, Brazil, occupies a geographically complex position in the southeastern region. Located at approximately -21.4678° latitude and -49.2208° longitude, the city sits on a gently undulating plateau, part of the larger Serra do Mar mountain range foothills. This terrain, characterized by rolling hills and valleys, influences local wind patterns and can contribute to localized air quality challenges. Novo Horizonte’s proximity to the larger urban conurbation of São Paulo, a major industrial and economic hub, is a critical factor. The city exists within a distinct urban–rural gradient, transitioning from dense residential areas to agricultural lands and patches of Atlantic Forest remnants. While not directly bordering a major river, it benefits from the regional rainfall patterns characteristic of the southeastern Brazilian climate. The surrounding landscape is a mix of cultivated fields – often sugarcane and maize – and increasingly fragmented patches of native vegetation. This agricultural activity, combined with the influence of São Paulo’s industrial belt located further east, introduces both particulate matter and gaseous pollutants into the regional atmosphere. The elevation, averaging around 800 meters above sea level, can exacerbate temperature inversions, particularly during the drier months, trapping pollutants closer to the ground. The city’s relatively small population (38,324) means that local emissions are less significant than the broader regional influences, making it susceptible to downwind pollution transport from São Paulo.

Novo Horizonte’s air quality follows a distinct seasonal pattern dictated by the region’s subtropical climate. The wet season, typically from October to March, brings increased rainfall and higher humidity, generally leading to improved air quality as precipitation washes away particulate matter and dilutes gaseous pollutants. Stronger winds associated with convective storms also help disperse pollutants. However, periods of prolonged rainfall can also lead to increased mold and fungal spore concentrations, impacting respiratory health for sensitive individuals. The dry season, from April to September, presents a more challenging scenario. Reduced rainfall, coupled with lower humidity and more stable atmospheric conditions, frequently results in temperature inversions, particularly during the months of July and August. These inversions trap pollutants near the ground, leading to a build-up of emissions from agricultural burning (a common practice for land clearing) and transport from São Paulo. Fog, more prevalent during the dry season mornings, further exacerbates this issue by reducing visibility and trapping pollutants. During these periods, individuals with respiratory conditions like asthma or bronchitis should limit outdoor exertion, especially during peak morning hours. Children and the elderly are also particularly vulnerable. While the wet season offers a respite, the increased humidity can trigger allergic reactions in some. The transitional months of March and October see fluctuating conditions, with unpredictable air quality depending on rainfall patterns and wind direction. Overall, minimizing outdoor activity during the drier months, particularly when visibility is reduced, is advisable for maintaining respiratory health.