Geoscience Reference
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particles have been taken into account. Secondary components of aerosol were
sulphate, nitrate, ammonium, water, and secondary organic compounds, of natural
and anthropogenic origin. A parameterization of aerosol light extinction in the
visible spectral region has been made with the use of Mie formulae and empirical
relationships veri
ed by observational data. Algorithms have been described by
Binkowski and Roselle (2003) which simulate interactions between aerosol and
cloudiness. The obtained results have been illustrated by calculated data with the
use of the box and 3-D models.
Mebust et al. (2003) performed a preliminary analysis of the adequacy of Model-
3 developed by a group of scientists for a multi-scale assessment of air quality
(CMAQ) by comparing calculated and observed values of visibility indices and
concentration of various components of aerosol. Comparisons with the data of
meteorological visibility observations at 130 airports of the USA for the period 11
-
15 July 1995 have shown that calculated values of CMAQ parameters, on the
whole, reliably re
ect the main laws of the spatial-temporal variability of visibility,
including the spatial gradients and extreme levels of visibility.
However, an application of both calculation techniques used in CMAQ to cal-
culate light extinction (with Mie formulae and empirical methods) has led to an
underestimation of visibility reduction (i.e., to its overestimation). In the case of
calculations with Mie formulae, the normalized mean difference (NMD) and nor-
malized mean error (NME) are
fl
−
21.7 and 25.41 %, respectively, and in case of
empirical method
35.5 and 36.2 %. In most cases the accuracy of the calculated
values agree with the observed ones only with the accuracy of the coefficient 2,
though the correlation coef
−
cient is 0.25 and 0.24.
A special comparison has been made in Mebust et al. (2003) with the use of
observed concentrations of sulphate, nitrate, PM-2.5, PM-10, and organic carbon at
18 stations in June 1995. In this case, comparisons have led to the conclusion that
except good results for sulphate (the mean systematic difference of the mass con-
centration constitutes 0.15
gm
−
3
, and NMD = 3.1 %), the model gave a systematic
underestimation of concentration in aerosol of nitrate (
ʼ
gm
−
3
,
−
0.10
ʼ
−
33.1 %),
gm
−
3
,
gm
−
3
,
PM-2.5 (
−
3.9
ʼ
−
30.1 %), PM-10 (
−
5.66
ʼ
−
29.2 %), and organic
gm
−
3
,
carbon (
33.7 %). The adequacy of simulation on concentrations of
various components is as follows: sulphate (r
2
= 0.63, average error 1.75
−
0.78
ʼ
−
gm
−
3
,
ʼ
gm
−
3
, 38.5 %); organic carbon (0.25,
NME = 36.2 %); PM-2.5 (0.55, 5.00
ʼ
gm
−
3
, 40.6 %); PM-10 (0.13, 9.85
gm
−
3
, 50.8 %), and nitrate (0.01,
0.94
ʼ
ʼ
gm
−
3
, 104.3 %). Except for nitrate, in 75
0.33
80 % of cases the calculated values
of concentration agree with those observed within the coef
ʼ
-
cient 2.
Solar radiation absorption in the atmosphere by BC-containing aerosol can cause
a change of the radiative warming of the atmosphere and surface, which, in turn,
affects the dynamics and hydrological processes responsible for the cloud cover
formation. In this connection, Conant et al. (2002) considered a new microphysical
mechanism of the BC impact on climate, consisting of the fact that the radiative
warming due to solar radiation absorption in the presence of BC-containing CCN
slows down or even prevents CCN from functioning as centers of cloud droplets
formation. The temperature of BC-containing droplets turns out to be higher (as a
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