Winds of change: tracking air quality patterns across Romania's urban and metropolitan areas

Urban air quality has undergone significant change over the past two decades in Romania, yet the spatial dynamics of this transformation remain poorly understood at the national scale, particularly across the urban core-to-peri-urban gradient. This study tracks the space-time evolution of PM2.5 and NO2, as retrieved from the European Environmental Agency, across the 319 cities in Romania. A multi-step methodology is used, comprising a population-weighted air quality index anchored to residential population and built-up surface density, agglomerative hierarchical clustering, and an interaction regression model. The results document a general decline in both pollutants while revealing fundamentally different spatial regimes. NO2 concentrations are driven by population density in metropolitan centres, and by built-up surface density and commuting pressure in peri-urban environments, whereas PM2.5 follows built-up surface patterns only at the peri-urban scale. The core-periphery predictors point to the need for differentiated, metropolitan-scale governance in air quality planning. Policy recommendations comprise low-emission zones, public transport modernisation, fiscal instruments targeting traffic, and regional air quality planning frameworks where pollution exposure extends well beyond municipal boundaries.