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

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AIR QUALITY GUIDELINES
Fig. 10. The development of annual average sulfur dioxide concentrations in Chinese
cities from 1990 to 2002
Concentration (μg/m 3 )
120
100
80
60
40
20
0
Source: Hao & Wang (45).
Grade III standard
Northern cities
Average
Southern cities
1990 1992 1994 1996
Year
1998 2000 2002
Fig. 11. Average concentrations of PM10, nitrogen dioxide, sulfur dioxide and ozone
at five Hong Kong monitoring stations
Concentration (μg/m 3 )
80
60
40
20
0
PM10
NO2
SO2
O3
Restriction on sulfur in fuel
1988 1989 1990 1991 1992 1993 1994 1995
Year
Source: reprinted from Hedley et al. (59) with permission from Elsevier.
The introduction of restrictions on sulfur in fuels is one of the reasons for the
decline in sulfur dioxide concentrations. This is clearly seen in Fig. 12 showing
ambient concentrations in Hong Kong, China, where restrictions were imposed
from 1990. Furthermore, cleaner fuels such as natural gas, which contains less
ash and sulfur, have replaced coal and high-sulfur oils. Also, light transport systems,
as mentioned above, have contributed to this improvement in some cities.
A study by the Clean Air Initiative for Asian Cities, summarizing air quality
data from 20 cities in Asia, shows that on average there has been a slight to