Each local authority in Hertfordshire and Bedfordshire operates
a number of diffusion tube sites to monitor nitrogen
dioxide. While they offer a relatively cheap and easily
operated method of assessing pollution levels, they
are not as accurate as the continuous monitors producing
the data shown in the rest of this web site. Different
analysis laboratories may produce different results,
so care must be taken when comparing pollution levels
between districts that use different laboratories. Further
information on the use and limitations of diffusion
tubes can be found in Chapter 1 of the network's 2003
annual report.
Note: results are now shown in ugm-3 rather than ppb.
