Winter evidence of green infrastructure co-benefits across an urban burden gradient in Athens, Greece: Implications for air-quality policy and intervention prioritization

Urban air pollution remains a major public-health challenge in Mediterranean cities, where traffic intensity, mixed land use, green-space fragmentation, and heterogeneous urban form produce spatial inequalities in exposure. Although green infrastructure is increasingly promoted as a multifunctional urban strategy, winter field evidence remains limited, particularly in Southern European metropolitan contexts. This study investigated winter air-quality and microclimatic variation across four urban sites in Athens, Greece, arranged along an urban-context gradient from a traffic-dominated low-green corridor to a spatially open urban park. A January 2026 campaign generated 48 observations of PM₂.₅, PM₁₀, NO₂, O₃, VOCs, CO₂, air temperature, and relative humidity at four daily periods: 08:00, 13:00, 18:00, and 22:00. Results showed a consistent spatial burden pattern, with the traffic-dominated corridor recording the highest pollutant concentrations and the park the lowest. From the traffic site to the park, mean concentrations declined by 62% for PM₂.₅, 64% for PM₁₀, 87% for NO₂, 83% for VOCs, and 7% for CO₂. Between-site differences were statistically significant for all monitored pollutants, with significant negative monotonic trends across the ordered gradient. Diurnal analysis revealed morning elevation, midday decline, evening re-accumulation, and partial nighttime decrease, while burden levels remained site-dependent. These findings indicate that greener, more open urban contexts were associated with lower winter pollutant burden. Because green cover co-varied with traffic exposure, land use, source proximity, and urban form, the study is interpreted as evidence of a combined urban-context effect rather than a vegetation-only causal effect. The results support site-sensitive air-quality policy in compact Mediterranean cities.