Abstract
Urban air pollution poses a severe health risk, particularly within school environments that frequently function as exposure hotspots. To address this, we implemented a co-participatory citizen science framework to evaluate air quality across contrasting urban microenvironments and assess its impact on youth environmental literacy. Over a ten-month campaign in São Paulo, Brazil, high school students utilized low-cost sensors to monitor particulate matter (PM2.5, PM10) and microclimate parameters at their public school campus and a nearby urban park (Parque CienTec). This instrumental monitoring was integrated with participatory mapping and co-creation workshops. Results revealed marked environmental disparities across different spatial scales. At the micro-scale, mobile monitoring showed that the school grounds acted as a containment zone for atmospheric pollutants, exhibiting higher mean PM10 concentrations than the immediate surrounding streets (57 μg/m 3 versus 39 μg/m 3). At the macro-scale, continuous monitoring confirmed that the school environment was persistently more polluted and thermally stressed than the nearby urban forest, presenting higher overall pollutant levels and a warmer microclimate (campaign mean 30 °C versus 27 °C). Conversely, the urban park functioned as a clean-air refuge, displaying a clear spatial gradient where PM10 dropped by 12% (from 41 μg/m 3 to 36 μg/m 3) from its traffic-exposed perimeter to its forested interior. The participatory methodology yielded substantial educational gains; post-intervention assessments demonstrated a shift toward evidence-based consensus, with 78% of students recognizing the mitigating role of green infrastructure, ultimately prioritizing human health in their co-developed mitigation proposals. This study demonstrates the dual efficacy of youth-led citizen science: it generates robust hyperlocal data to inform public health policy while empowering adolescents as proactive agents of environmental change.