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.