Chemistry Reference
In-Depth Information
PM
10
µg.m
-3
160
150
140
130
120
110
100
90
80
70
Streets
APEI50
m
.
g.m-3.person
0 - 1000
1000 - 2000
2000 - 5000
5000 - 10000
10000 - 15000
15000 - 20000
20000 - 25000
25000 - 50000
Fig. 5 PM
10
simulated field and exposure results for an urban area in Lisbon [
26
]
the pollutant concentration threshold and weighted by the number of inhabitants
exposed. Therefore, it is calculated as a sum of the positive differences between the
hourly mean PM
10
concentration and a threshold, multiplied by the number of
inhabitants exposed, and then integrated over 24 h. Results of a PM
10
hourly field
predicted by the VADIS local dispersion model and the population exposure
expressed in terms of the accumulated index (APEI50) are presented in Fig.
5
.
This methodology was a first approach to estimate population exposure, calcu-
lated as the total daily values above the thresholds recommended by the European
Commission Directive for long- and short-term health effects. Obtained results
revealed that in Lisbon city centre a large number of persons are exposed to PM
levels exceeding the legislated daily limit value of 50
gm
3
.
McNabola et al. [
34
] also used a CFD to investigate whether pedestrians using
the boardwalk would have a lower air pollution exposure than those using the
adjoining footpath along the road. The results show considerable reductions in
pedestrian exposure to traffic derived PM along the boardwalk as opposed to
footpath.
m
5 New Developments
Aerosol modelling tools registered a fast development along the last years. Nowa-
days, and besides the complexity of the formation mechanism of aerosols and the
great number of individual chemical species involved, it is possible to simulate
them and to estimate population exposure based on chemical transport model
results. Modelling organic aerosol is among the most demanding aspects of air
quality simulations because the formation processes and evolution are poorly
understood and, in spite of the recent improvements in air quality models, organic
aerosols can be underestimated by a large amount [
35
,
36
]. Improvements still have
to be done, regarding the chemical and physical processes, especially in the case of
