CR 77:77-89 (2019)  -  DOI: https://doi.org/10.3354/cr01546

ABSTRACT: In this study, we analyzed the evolution of the surface ozone concentration in north-western Italy and its relation to weather types (WTs) during the 2003-2014 period, by downloading and processing the ozone data from monitoring stations for the cities of Turin, Asti, Genoa and Savona. The corresponding trends were calculated and the correlation between ozone and the WTs assessed. Specifically, daily surface atmospheric patterns were obtained from sea level pressure data from the NCEP/NCAR reanalysis data set, and the WTs were classified following the Lamb catalogue. Furthermore, the influence of nitrogen dioxide (NO₂), temperature, precipitation and wind speed on ozone values was evaluated on a daily basis. Results showed a cyclical evolution of ozone on a daily, weekly and seasonal scale, with maximum values in daytime and summer, and minimum values at night and during winter. The observed trends were not significant because of strong inter-annual variability. Inland ozone values were generally lower than coastal ones, but fluctuated more. The average ozone concentrations were statistically related to WTs: high ozone values were associated with the eastern type and low values with the cyclonic and western types. Also, temperature and wind speed had a significant influence on the ozone concentration for both inland and coastland cities. More specifically, temperature had a positive correlation with ozone in each city, wind had a positive correlation only in inland areas; the correlation in the coastal zone was negative. Precipitation generally showed a negative and less significant correlation with daily ozone concentrations.

KEY WORDS: Ozone · Weather types · Climatic variables · Northwestern Italy