Environmental Engineering Reference
In-Depth Information
for sulphur oxides, primary particles of various types, with flexible definition of
the particle size spectrum, and about 500 radioactive nuclides.
2.2. Basic-chemistry scheme and sea salt emission parameterization
The current SILAM basic-chemistry scheme covers 21 transported and 5 short-
lived substances, which are inter-related via ~60 chemical reactions. This mechanism
covers the most important transformation chains for the photochemical smog
formation (except for some of the VOC oxidation pathways that have been para-
meterized in a simplified manner) and takes into account the main reservoir
substances. To reach a sufficient numerical efficiency of the scheme, all reactions
are segregated in accordance with their actual rates (in relation to the model time
step), split to day- and night-time processes and treated via forced-equilibrium,
first-order explicit or third-order implicit numerical algorithms. Other matters such
as: emission of biogenic ozone precursors, boundary conditions for long-living
substances, and proper representation of the solar radiation are addressed.
Within this study, the “classical” parameterization of Monahan et al. (1986)
was applied as the reference formulation and extrapolated towards fine particles
following the laboratory results from Mårtensson et al. (2003). This resulted in a
unified function for particle sizes from 20 nm to 10 μm, for a reference water
temperature of 23°C and salinity 3.3%, and two correction functions for temperature/
salinity with particle size dependency (Sofiev et al., 2010).
The chemical scheme development and evaluation was based on year 2000,
with source emission provided by EMEP and TNO. Sea salt parameterization was
evaluated based on the year 2000 for European and Northern Atlantic region, and
2001 for the globe. The water temperature was set constant for both regional and
global run, 12°C, and salinity of the Ocean was set constant, 33‰. For the sea salt
evaluation, five size bins were described with the following ranges: 20 nm to 0.1
µm, f 0.1 to 1 µm, 1-2.5 µm, 2.5-10 µm, and 10-30 µm.
Depending on the particle
size, mechanisms for dry deposition vary from primarily diffusion-driven removal
characteristic (fine aerosols) to primarily gravitational settling (coarse particles).
Wet deposition distinguished sub- and in-cloud scavenging by both rain and snow
(Sofiev et al., 2006).
3. Results and Discussion
The evaluation of the basic chemistry scheme was based on information from
the database of the European Monitoring and Evaluation Programme, EMEP
(www.emep.int). The basic chemistry and transport mechanisms allow the system
to follow fairly accurately the evolution of primary emitted and secondary
pollutant concentrations throughout the year
(Fig. 1
).
