Environmental Engineering Reference
In-Depth Information
2. Methodology
The Atmospheric Composition and Emergency Modelling System SILAM was
started as emergency model described by Sofiev et al. (2006) and then extended
towards more general atmospheric composition problems. It has two parallel
dynamic cores. The Lagrangian random-walk particle model is based on well-
mixed boundary layer assumption while he other core uses the Eulerian scheme of
M.Galperin (1999, 2000) and the extended resistive analogy for vertical exchange
by Sofiev (2002). A physico-chemical module of SILAM includes basic SOx-
NOx-NHx-VOC-O3 chemistry, the linearized scheme for sulphur oxides, primary
particles of various types, covers up to 496 radioactive nuclides, and probability.
Meteorological information and geophysical data are routinely taken from regional
NWP models, such as the HIRLAM, and from global models, such as the ECMWF
Integrated Forecasting System.
New module for the biogenic VOC is based on the Guenther et al. (1995) model
where the emission flux is computed as a product of several factors reflecting the
type of the vegetation, released species, and the external meteorological forcing.
The module considers the temperature- and light-dependent fluxes of monoterpenes,
hemi-terpenes represented by isoprene, while the list of other compounds includes
formaldehyde and a few hydrocarbons.
The smoke emission fluxes for SILAM are produced by a standalone Fire
Assimilation System (FAS) based on Level 2 MODIS Collection 4 and 5 Active
Fire Products. FAS consists of two parallel branches based on semi-independent
products: the Temperature Anomaly and Fire Radiative Power (Sofiev et al., 2009).
3. Examples of the Model Applications
At present, the transformation modules responsible for the classes of substances
outlined above do not interact with each other. However, even without interaction,
the model-measurement comparison or the estimation of the total aerosol concent-
rations in air requires considerations of all relevant substances groups.
For instance, spring of 2006 in Europe appeared to be tough for allergic people:
during several days at the end of April and the beginning of May high concentrations
of birch pollen were reported in several countries, in particular, in Northern Europe.
Absolute levels of birch pollen concentrations in air (pollen counts) varied from a
few hundred grains per cubic meter (Iceland, 8-11 May) to a few thousands in
Russia, Denmark, Germany, Poland, etc (20 April-10 May) and up to more than
10,000 grains m
−3
in Finland (6-10 May). The weekly number of phone calls to
Finnish Asthma and Allergy Association for advisory service from 24 April to 14
May 2006 was from double to triple, compared to the same period of previous years.
However, the amount of pollen was not record-breaking and the severity of the
episode can hardly be explained by pollen counts alone. An extra complexity to
