2.1 Air pollution
Daily ground level mass concentrations of PM10 and PM2.5 and gaseous pollutants (NO2, C6H6), as routinely measured by the air quality monitoring program of the Agency for Prevention, Environmental and Energy (Arpae) network, are considered. Measurements cover the time period from January 1st, 2015 to December 31st, 2020 and were recorded at the urban background site and the urban traffic site. The choice of the urban background site is aimed at maximizing the representativeness of population exposure at the urban scale. On the contrary, the traffic site is useful to better highlight changes in emission rates of local traffic-related sources.
Two independent additional measurements, not available for routine air quality monitoring are used as ancillary data to highlight specific chemical features of PM composition, tracing the contribution of combustion PM sources and TRAP, associated with asthma disease in other studies13,15. The first one is f57, deriving from data analysis of the mass spectra of non-refractory submicron particle and representing the relative abundance of the mass fragment at m/z 57 over the total organic PM1 particles (PM less than 1 micron: fine and ultrafine particles) mass spectrum. f57 is commonly used as a spectral tracer for the contribution of PM emitted from fossil fuel combustion and it is mostly attributed to traffic-related sources in urban environment17,18. For this reason it is indicated from hereafter as the TRAP contribution tracer. Data were obtained online by a High-Resolution Time-of-Flight Aerosol Mass Spectrometer19 and refer to measurements during the lockdown period in 2020 and from eight intensive observation periods carried out from November 2011 to May 2014, representative of a wide spectrum of seasonal conditions20. The second additional measurement is the black carbon (BC) fraction of PM, sometimes defined as soot, a major component of PM, emitted through incomplete combustion of fossil fuels and biomass, representing a known tracer of the main anthropogenic sources concentrated in urban areas, including heating and transport. Hourly concentrations are used as quantified from a MetOne (single-wavelength at 880nm) run during the time period January-May in 2019 and 2020.