Daytime and nighttime chemical and optical properties of fine and coarse particles at a central Mediterranean coastal site

The characterization of the day-to-night changes of the atmospheric particle chemical and optical properties in autumn-winter (AW) and spring-summer (SS) is the main goal of this study to contribute to the characterization and understanding of the particulate matter (PM) impact on the environment and climate at one of the most vulnerable areas of the planet to climate change. To this end, PM10 and PM2.5 samples from 14 January 2016 to 5 January 2017 have been collected in Lecce, a coastal site of South-Eastern Italy (40.33°N, 18.11°E), and day-to-night changes of mass concentrations of both fine (PM2.5) and coarse (PM10-PM2.5) particles and corresponding chemical species have been assessed both in AW and in SS. The statistical analysis of local meteorological parameters and their correlations with PM2.5 and chemical species mass concentrations have indicated that the day-to-night changes of temperature (T) and wind speed (WS) likely affected the day-to-night changes of mass concentrations, because of the T and WS impact on the atmospheric turbulence and air particle dispersion. The daily evolution of the anthropogenic activities and the planetary-boundary-layer height likely contributed to the day-to-night changes of the particle chemical composition. The stagnant atmospheric conditions prevailing in SS all over the Mediterranean basin, which favoured the mixing and the accumulation of atmospheric particles from different pollution sources, likely contributed to the changes of the relationships between chemical species and meteorological parameters from AW to SS at daytime and nighttime. The analysis of the aerosol scattering coefficient, scattering Ångström exponent, and scattering Ångström exponent difference, retrieved from nephelometer measurements co-located in space and time with the PM samplings, has allowed characterizing the day-to-night change of the aerosol optical properties. The relationships between the particle chemical and optical properties allowed a good understanding of their changes both in AW and in SS.