Chemistry Reference
In-Depth Information
scale of representativeness. Representativeness can be seen as an area surrounding
the measurement site where air pollutant concentrations are reasonably similar to
those measured at the monitoring site.
Based on the objectives and scales of spatial representativeness needed, CFR 40
[
13
] differentiates six site types:
(a) Sites located to determine the highest concentrations expected to occur in the
area covered by the network,
(b) Sites located to measure typical concentrations in areas of high population density,
(c) Sites located to determine the impact of significant sources or source categories
on air quality,
(d) Sites located to determine general background concentration levels,
(e) Sites located to determine the extent of regional pollutant transport among
populated areas; and in support of secondary standards and
(f) Sites located to measure air pollution impacts on visibility, vegetation damage
or other welfare-based impacts.
Each site type matches a certain need of spatial representativeness. For example,
sites located to determine local hot-spots are at places where the highest
concentrations are expected and will mostly be microscale monitoring sites, while
those measuring air pollution impacts on visibility and vegetation damage have to
be representative over regional to national scale.
CFR 40 [
13
] reflects this not only in general form but also with respect to specific
pollutants. Ozone, a typical large-scale secondary pollutant (formed in the gas phase
in polluted air) accordingly has only to be measured at urban and larger scales during
the “ozone season”, as derived from seasonal measurements for each federal state
and listed in CFR 40 [
13
]. In contrast, the main areas required to monitor for CO
and NO
2
are at the micro- and middle-scale where the highest concentrations and
exposure may occur. It is interesting to note that microscale (near road) NO
2
measurements according to CFR 40 [
13
] are required to be conducted “within
50 m of target road segments in order to measure expected peak concentrations”.
Amicroscale site typically represents an area impacted by the plume with dimensions
extending up to approximately 100 m. The distance from a source is a very critical
parameter when compliance to limit values is required.
The current strategy and approach for air quality monitoring networks in the
USA is therefore best described as pursuing the aims of ensuring the achievement
of air quality limit values, air quality control, and allowing rapid intervention to
prevent air quality deterioration.
2.2 Asia
Air quality standards and monitoring strategies across Asia are diverse and exhibit
many differences between the countries. For brevity only the standards and moni-
toring concept for Japan are presented in any detail. For Taiwan, India, China and
