The cause-effect relationship between synoptic and local wind patterns and PM10 concentrations in the complex-orography urban area of Naples (Italy)

Abstract

This study examines the relationship between the temporal variability of PM₁₀ concentrations and synoptic and local wind patterns in Naples over a four-year period (2018, 2020–2022). PM₁₀ data were collected from three monitoring stations (IT1493, IT1491, and IT1497), representing different atmospheric pollution conditions: suburban traffic, urban traffic, and background, respectively. The mean PM₁₀ concentrations recorded at these stations were 33.3 ± 0.5 µg/m³, 32.1 ± 0.4 µg/m³, and 27.4 ± 0.3 µg/m³, all remaining below the EU annual limit of 40 µg/m³. However, extreme daily peaks during the sampling period reached 203.1 µg/m³ at the suburban site, 128.6 µg/m³ at the urban site, and 129 µg/m³ at the background site, indicating severe pollution episodes. The intradiurnal cycle showed a bimodal pattern in PM₁₀ concentrations at the urban and suburban sites, with peaks occurring in the morning and evening, coinciding with traffic activity. In contrast, the background site showed a flatter profile, suggesting a weaker influence of local sources. The occurrence of high concentrations is mainly registered in winter. A backward trajectory analysis using the HYSPLIT model identified eight dominant synoptic airflow patterns, with nearby, westerly, and northerly flows being the most frequent. Notably, nearby airflows—often associated with sea-land breeze circulations, as it is observed by analyzing surface winds—were responsible for 75 % of the exceedances of the EU daily limit of 50 µg/m³, highlighting their role in pollutant accumulation and restricted dispersion. These findings underscore the critical influence of local wind circulation and large-scale transport mechanisms on air quality in Naples. They emphasize the need for integrated air quality management strategies that address both local emissions and regional transport processes to develop effective mitigation policies for Mediterranean coastal cities.