Regime-dependent sensitivity of the atmospheric potential gradient to anthropogenic air pollution in São Paulo, Brazil

Romero R.M.; Tacza J.; Vara-Vela A.; Szpigel S.; Raulin J.-P. · Atmospheric Research (2026) · DOI: 10.1016/j.atmosres.2026.109002

Resumen

Ground-based measurements of the atmospheric potential gradient (PG) are sensitive to near-surface electrical conductivity and can reflect anthropogenic perturbations under carefully defined fair-weather (FW) conditions. This study investigates the coupling between PG and major air pollutants in São Paulo, Brazil, using a long-term dataset (2018–2024) combining rooftop electric field measurements with hourly concentrations of CO, SO₂, NO, NO₂, NOₓ, and PM₁₀. FW periods were identified using surface meteorological screening and satellite-based cloud masking.The analysis reveals a reproducible hierarchy in PG–pollutant coupling controlled by the dynamical regime of the atmospheric boundary layer. During nocturnal stable conditions, primary combustion-related gases (NOₓ, NO, CO) exhibit the strongest associations with PG, with median Pearson correlation coefficients (r) on the order of r ≈ 0.6, representing the central tendency of a regime-dependent distribution. In contrast, PM₁₀ shows weaker and more variable coupling. Across all seasons, PG–pollutant correlations strengthen at night and weaken markedly during the afternoon mixing maximum, with enhanced wind ventilation further suppressing coupling strength.Large-scale emission perturbations support the anthropogenic origin of these relationships. During the 2020 COVID-19 lockdown, FW PG exhibits a persistent shift toward lower values relative to the multi-year baseline while preserving the diurnal phase structure. In contrast, a short (11-day) truck drivers' strike in 2018 produces no statistically distinguishable PG response.These results indicate that PG does not behave as a universal proxy for urban air pollutant concentrations in this megacity environment, but rather as a regime-dependent electrical indicator whose sensitivity to anthropogenic emissions emerges preferentially under stable boundary-layer conditions.