Environmental Engineering Reference
In-Depth Information
m
∑
,
1
C tQ
vk k k
iF
=
i
=
(2)
E
v
where Cv,k = the benzene concentration in microenvironment k due to vehicular
sources (mg/m
3
), tk = the time spent in microenvironment k (h), Qk = the breathing
rate while in microenvironment k (m
3
/h), and Ev = benzene emissions (mg) over the
time evaluated. Thus, each EXPOLIS participant's intake fraction (iFi) is:
C t Q pC t Q pC t Q pC t Q C t Q
+
+
+
+
iF
=
bc l
ohi r
ow l
ooi l
oo m
(3)
i
E
vy
,
where
C
b
=
residual benzene concentration;
C
o
= the concentration measured outside
the participant's home while the participant was at home;
t
c
= time spent commuting
(h);
t
hi
= the time spent indoors at home;
t
w
= the time spent at work;
t
oi
= time spent
in other indoor microenvironments (h);
t
o
= time spent in all outdoor microenviron-
ments;
p
= the infiltration efficiency for benzene from outdoor air into the indoors;
Q
l
=
light activity breathing rate;
Q
r
= resting breathing rate;
Q
m
= moderate activity
breathing rate;
E
v
,
y
= emissions from vehicles in the Helsinki metropolitan area
in
y
= year 1996 or 1997, depending on when the participant was sampled
[15]
.
The terms on the right-hand-side of Eq. 3 represent exposure while commuting;
at home, at work, in other indoor microenvironments and in all outdoor microenvi-
ronments. We assume here that the outdoor contribution is predominantly from vehicular
emissions and that other sources (including long-range transport) are negligible. The
times spent in each microenvironment were taken from participants' time-activity
diaries and breathing rates were from the U.S. EPA's Exposure Factors Handbook
[7]
.
Results and Discussion
The results obtained for 2000 and 2005 show the same spatial distribution pattern,
though a decrease of concentration for the year 2005 was noticed (~factor 0.5). This
might be a result of the European legislation to reduce benzene content in fuel
(Directive 98/70/EC) and setting limit values for benzene ambient air concentrations
(Directive 2000/69/EC).
The modeled traffic contribution to benzene concentrations in the in HMA in 2000
vary between 0 and 2.7 mg/m, as depicted in Fig.
1
. Previous studies in HMA in 2000
[6]
show traffic benzene concentrations varying between 0.2 and 2.2 mg/m
3
.
The higher concentrations are situated closer to the line sources, where the benzene
is emitted, and decreasing for receptors further away from the streets. The centre of
Helsinki, due to a denser and highly trafficked road network, including main high-
ways, has the highest concentrations ranging between 1.5 and 2.5 mg/m
3
. For the
street canyon calculations the differences between the calculated yearly average
