Air Quality Guidelines Global Update 2005 - World Health ...

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AIR QUALITY GUIDELINES
Table 2. Ultrafine particle number concentrations measured in urban and roadside
environments
Location
Barcelona, Spain
Birmingham, England
Brisbane, Australia
Brisbane, Australia
Copenhagen, Denmark
Detroit, USA
Erfurt, Germany
Helsinki, Finland
Los Angeles, USA
Rome, Italy
Source: Morawska et al. (27).
Monitoring period
Not stated
Not stated
14–29 January 2004
1995 – April 1997
3–20 May 1999
July 2002
1991–2001
1999–2001
Aug–Oct 2001
Not stated
Average particle number
concentration per cm 3
1.23 x 10 4
1.8 x 105 (roadside)
~2.7 x 104 (roadside)
7.4 x 103 (urban)
1.2 x 105 – 2.0 x 105 (roadside)
1.9 x 104 (roadside)
1.04 x 104 – 1.4 x 104 (roadside)
1.90 x 104 (urban)
6.00 x 104 (roadside)
1.8 x 105 – 3.5 x 105 (roadside)
Reference
Paatero et al. (28)
Harrison et al. (29)
Holmes et al. (30)
Morawska et al. (31)
Wåhlin et al. 2001 (32)
Young & Keeler (33)
Kreyling et al. (34)
(Hussein et al. (35)
(Zhu et al. (36)
(Paatero et al. (28)
large gradients of ozone can be observed. Near strong emission sources of nitrogen
oxides, where there is an abundance of nitric oxide, ozone is “scavenged”
as it reacts with nitric oxide. As a result, the ozone concentrations are often low
in busy urban centres and higher in suburban and adjacent rural areas. Ozone
and some of its precursors are also transported long distances in the atmosphere
and are therefore considered a transboundary problem. Thus, on a scale of tens
of kilometres, regional observation networks provide the data from which these
patterns of ozone can be examined.
The photochemical formation of tropospheric ozone from increased concentrations
of methane and carbon monoxide may also lead to a higher ozone level
on a global scale (37).
Fig. 5 shows model calculations of mean afternoon surface ozone concentrations
for the month of July. Particularly noteworthy is pollution over industrial
areas in the United States, Europe and Asia. In these areas, ozone is formed as a
secondary pollutant when emitted precursor pollutants such as nitrogen oxides
and VOC react under the action of sunlight.
Recent studies have shown that the hemispherical background concentration
of tropospheric ozone is increasing (37).
Surface ozone concentrations are usually assessed as short-term (1- to 8-hour)
averages. The highest 1-hour average ozone concentrations measured in the most
polluted cities are presented in Fig. 6.