Influence of atmospheric parameters on the interaction between Urban Heat and Pollution Islands in a Mediterranean coastal city

Urban Heat Island (UHI) and Urban Pollution Island (UPI) processes shape urban climate and air quality, yet their interaction remains insufficiently quantified, particularly in Mediterranean coastal cities. Existing research often examines these phenomena separately or over short time spans, leaving uncertainties regarding the meteorological drivers governing the UHI-UPI co-evolution. This study provides a multi-year, observation-based assessment of the coupled dynamics between Urban Heat Island Intensity (UHII) and Urban Pollution Island Intensity (UPII) in Rome (Italy), focusing on the atmospheric conditions that modulate their relationship. Air temperature, humidity, and wind speed, together with major air pollutants (PM10, PM2.5, NO2, NO, and O3), were analysed using an integrated statistical framework. Lag-correlation analysis revealed that the strongest UHII-UPII relationship occurs when nocturnal UHII is shifted backward by one day, reflecting daytime pollutant accumulation and nighttime trapping. Regression results highlighted daily mean air temperature and wind speed as the primary drivers modulating the UHII-UPII association. Spearman correlations showed negative associations between UHII and NO (−0.60), PM10 (−0.45), NO2 (−0.35), and PM2.5 (−0.34), alongside positive correlations with O3 (0.54) and NO2/NO (0.42). These correlations intensified during heatwaves and calm wind conditions, suggesting enhanced interactions under extreme weather and stagnant atmospheric conditions. UHII peaks in summer, while UPII maximizes in winter for all pollutants except for O₃, which exhibits an opposite pattern. These findings reveal a complex interplay between urban warming and pollutant accumulation, highlighting the need for integrated urban planning to address joint UHII-UPII challenges under ongoing urbanization and intensifying severe heat episodes.