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Heavy Metals modelling study over Italy: effects of grid resolution, lateral
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boundary conditions and foreign emissions on air concentrations
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Water, Air, & Soil Pollution
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An International Journal of Environmental Pollution
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Mario Adani1, Mihaela
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Silibello2
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Development, via Martiri di Monte Sole 4, 40129, Bologna, Italy
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Mircea1, Massimo D'Isidoro1, Matteo Paolo Costa2, Camillo
ENEA-National Agency for New Technologies, Energy and Sustainable Economic
ARIANET Srl, via Gilino, 9 (20128) Milan, Italy
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Corresponding Author: Mario Adani, ENEA, via Martiri di Monte Sole 4, 40129, Bologna,
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Italy, mario.adani@enea.it
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S1. FARM description
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Physical and chemical processes influencing the concentration fields within the modelling domain are described
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by a system of partial differential equations expressing the time variation of the average concentrations. For a
single-phase atmosphere (e.g. gas) this takes the following form:
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¶ci
¶c
¶c
¶c
c
c ¶ æ ¶c ö
= - u i - v i - w i + K xx ¶ 2i + K yy ¶ 2i + ç K zz i ÷ + Si + Ci + Ri
¶t
¶x
¶y
¶z
¶x
¶ y ¶z è
¶z ø
where ci is the i-th chemical species, u, v and w are the components of wind velocity vector, Kxx, Kyy and Kzz the
diagonal components of the diffusivity tensor, Si the source term, Ci the gas-phase reaction term and Ri the
removal term due to deposition processes (dry and wet). The Kinetic Pre-Processor (KPP; Damian et al., 2002)
has been used to configure FARM with the SAPRC99 mechanism (Carter, 2000) that includes the treatment of
gas-phase atmospheric reactions of volatile organic compounds (VOCs) and nitrogen oxides (NOx) and can be
used to simulate photochemical processes that lead to the formation of ozone and secondary organic aerosols in
the lower troposphere.
SAPRC99 mechanism is coupled with the aero3 aerosol module, implemented in CMAQ (Binkowski, 1999),
that considers aerosol particles dynamic and their interactions with gas-phase species. Particles are described by
a superposition of three lognormal distributions, called modes: the Aitken mode (Dg < 0.1 mm, Dg is geometric
mean diameter of the model distribution), the accumulation mode (0.1 mm < Dg < 2.5 mm) and the coarse mode
(Dg > 2.5 mm). Nine aerosol species are considered in the Aitken and accumulation modes: sulphate,
ammonium, nitrate, elemental carbon, primary organics, secondary anthropogenic and biogenic organics,
unspecified anthropogenic compounds and water. The coarse mode includes following species: unspecified
anthropogenic, marine and soil-derived aerosols. All the aerosol particles are assumed to be internally mixed, i.e.
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the chemical composition is the same for the particles of the same size, in a mode. Nucleation and growth of
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S2. Precipitation scavenging module
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The parameterization of wet deposition follows EMEP (2003) approach, including in-cloud and below-cloud
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DCwet = -C
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where P is the precipitation rate (kg/m2/s), z is the scavenging depth (assumed to be 1000 m), w is the water
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DCwet = -C
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where Wsub is the sub-cloud scavenging ratio.
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DCwet = -C
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where A = 5.2 m3/Kg/s is an empirical coefficient (a Marshall-Palmer size distribution is assumed for rain
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drops),
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aerosols by the raindrops. In Table S1 are reported in-cloud ( Win ) and sub-cloud ( Wsub ) scavenging ratios and
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collection efficiencies ( E ) used in precipitation scavenging calculation for PAHs.
existing particles trough condensation are the two pathways for increasing the total aerosol mass. Aerosol growth
by condensation occurs in two steps: the production of condensable material (performed by the gas-phase
chemical module) and the condensation and evaporation of ambient volatile species on aerosols. Particle
collision and coagulation are the main processes that alter the aerosol size distribution. The thermodynamic
equilibrium between gas and aerosol phases of condensable inorganic (ISOROPIA model: Fountoukis et al.,
2007; Nenes et al.,1998) and organic species (SORGAM model: Shell et al. 2001) and the following chemical
reactions within aerosols are responsible for the chemical composition of aerosols. Except for nucleation, where
only inorganic compounds are considered, all aerosol dynamic processes include both inorganic and organic
compounds.
scavenging of gas and particles.
The in-cloud scavenging of a soluble component of concentration C is computed as:
Win × P
Dz × rw
density (1000 kg/m3) and Win is the in-cloud scavenging ratio.
Below-cloud scavenging of gases is computed by means of a similar relationship:
Wsub × P
Dz × rw
In case of particles, below-cloud scavenging is computed by means of Scott (1979) relationship:
Vdr
A×P
E
Vdr
is the raindrop fall speed (assumed to be 5 m/s) and
E is the size-dependent collision efficiency of
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Tables
Win (* 106)
Wsub (* 106)
E
Gaseous phase
0.1
0.03
-
Particulate
1.0
-
0.1
Component
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Table S1: In-cloud (Win) and sub-cloud (Wsub) scavenging ratios and collection efficiencies ( E )
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used in precipitation scavenging calculation for PAHs.
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Figures
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Figure S1: Annual mean differences between NI and IT0 experiments: HMs concentration
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[ng/m3] and emissions from diffuse sources [ng/m2/h] (right column). Panels from top to
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bottom are referred to arsenic, cadmium, nickel and lead.
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References
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Binkowski, F. S,. 1999: The aerosol portion of Models-3 CMAQ. In Science Algorithms of the EPA Models-3
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Carter, W.P.L., 2000. Documentation of the SAPRC-99 Chemical Mechanism for VOC Reactivity Assessment.
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Damian, V., Sandu, A., Damian, M., Potra, F., Carmichael, G.R., 2002. The Kinetic PreProcessor KPP - A
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Fountoukis, C. and Nenes, A.: ISORROPIA II: a computationally efficient thermodynamic equilibrium model
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Schell B., Ackermann I. J., Hass H., Binkowski F. S., Abel A., (2001). Modeling the formation of secondary
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Nenes A., Pandis S.N., Pilinis C., 1998: ISORROPIA: A new thermodynamic equilibrium model for multiphase
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Scott B.C., 1979. Parametrization of sulphate removal by precipitation. J. Appl. Met., 17, 11379-11389.
Community Multiscale Air Quality (CMAQ) Modeling System, edited by D.W. Byun, and J.K.S. Ching, EPA600/R-99/030, 1-23.
Final Report to California Air Resources Board, Contract 92-329 and 95-308, SAPRC, University of California,
Riverside, CA.
Software Environment for Solving Chemical Kinetics. Computers and Chemical Engineering, 26(11), 15671579.
for K+–Ca2+–Mg2+–NH4+–Na+–SO42−–NO3−–Cl−–H2O aerosols, Atmos. Chem. Phys., 7, 4639-4659, 2007
organic aerosol within a comprehensive air quality modeling system. J. Geophys. Res., 106, D22, 28275-28293.
multicomponent inorganic aerosols. Aquat. Geoch., 4, 123-152.
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