Environmental Engineering Reference
In-Depth Information
The objective of this work is to test a new method, where the influence of meandering
on the dispersion could be accounted for. The new function described below is
called by CAR-FMI after reading the meteorological time series. Computed receptor-
oriented wind direction, effective distance, and probability are assigned to the
computation of dispersion parameters and concentration. Only NO
x
concentration
is treated in this study.
Emission Computation
The Norwegian emission dataset is calculated using the AirQUIS emission module
[6]
, which consists of an area source module, a point source module, and a line source
module. The latter module needs information such as annual daily traffic, speed limit,
road data and classification of vehicles. The emission is calculated as traffic based
(function of fuel type, vehicle classes, driving speed, etc.) or as fuel based (with
regard to CO
2
, SO
2
the emission is calculated based on mass balance, fuel consump-
tion and the content of carbon, sulphur, and lead in the fuel). In addition, factors
describing the age of the vehicle, road gradient, the share of NO
2
in the total NO
x
emissions are included. The emission factors are based on COPERT III
[7]
.
Receptor-Oriented Mean Wind Direction
In the treatment of lateral fluctuation of wind direction, temporal and hourly mean
values are presented with sub- and superscripts, correspondingly. Normal distribu-
tion is assumed for temporal wind direction wd with mean value WD and standard
deviation s
m
. Chosen critical value for c, c(crit) = 3.21, corresponds to p-value
< 0.001 in two tailed distribution. Standard deviation s
m
of meandering is grouped
as a function of wind speed
[8]
and is applied to all stability regimes, because stability
seems to have a minor influence on crosswise oscillations
[2]
. The range for temporal
wind direction is accordingly
wd = WD ± cs
m
(1)
The range of the view angles (a1, a2), as illustrated in Fig.
1
, is transformed to (HI,
LO) determining the allowed wind sector, where HI = a1 + c s
m
and LO = a2 - c
s
m
. From the mean wind direction WD we calculate the probability P for the
flow to be in the (HI, LO) sector according to Eq.
2
. Standardized values (x
= (x − WD)/ s
m
) and cumulative normal distribution F(x) is applied to determine
the probability P.
P = Ф[HI - WD)/s
m
] - Ф [(LO - WD)/s
m
]
(2)
The probability P is assumed to be independent from short term fluctuations being
outside the integrand and becomes directly proportional to concentration. The
