Environmental Engineering Reference
In-Depth Information
The continued model development and the introduction of new features in the
models SKIRON/Dust and CAMx (Environ, 2006) form the basis of the study
presented in this paper. Specifically, desert dust production is treated using an
8-size bin distribution scheme (Zender et al., 2003) and the CAMx preprocessing
system has been updated in accordance with the new size sections of dust. The
dust composition, in particular the particle alkalinity, affects the ability of the
particles to take up gases like nitric acid and in turn, the uptake of strong acids
affects the mobility and availability of cations. Information on the mineralogy of
dust sources (Claquin et al., 1999) helps to model the interactions with nitrates at
the surface of dust particles in the chemical transport model CAMx. This
presentation addresses several of the processes that alter the chemical composition
of aerosols due to interactions among different pollutants in a wide region around
the Mediterranean, which is affected by long-range transport during August 2005.
2. Methodology
To address the above mentioned objectives, the modelling systems SKIRON/Dust
modelling system and the Comprehensive Air Quality Model with Extensions-
CAMx (Environ, 2006) were used, both as updated versions with additions and
improvements in the aerosol schemes (Astitha and Kallos, 2008). The most
important improvement in the CAMx model has been the reformulation of the
heterogeneous uptake of HNO 3 on desert dust and the use of a new emission
inventory (Visschedijk and Denier van der Gon, 2005) in the simulations performed.
The heterogeneous reactions on dust particles include the uptake of sulfur dioxide
(production of sulfate), nitrogen dioxide (production of nitrate), ozone (destruction
of ozone) and nitric acid (production of nitrate). The relevant algorithms and
uptake coefficients used can be found in detail in Astitha et al. (2007) and in
Astitha and Kallos (2008). In order to improve the nitric acid uptake on the dust,
changes have been made in the parameterization that describes the chemical reactions
on the particle surface. According to laboratory experiments, the reaction-uptake
of the other gases on the dust particles is limited to the surface. When dust
includes significant amounts of calcite (CaCO 3 ) the nitric acid can react with the
bulk of the particle and is not limited to uptake at the surface (Grassian, 2002).
Based on the mineralogy of the dust sources in the region (North and Central Africa)
(Claquin et al., 1999; Y. Balkanski, personal communication, 2008), we consider a
mean mass fraction of calcite in the dust and then limit the uptake of nitric acid at
the dust surface, accordingly.
The anthropogenic emission data for Europe were developed at the Netherlands
Organization for Applied Scientific Research (TNO). The species included were
CH 4 , NO x , NH 3 , SO 2 , NMVOC, CO, PM10 and PM2.5 both for the area and point
sources. The year of reference was 2000 and the horizontal analysis 0.25° ×
0.125° longitude-latitude. More information on the inventory can be found in
Visschedijk and Denier van der Gon (2005). Shipping emissions are from the
 
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