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More recently 'Air Quality Indexes' were developed to better inform the public about air
quality or the degree of pollution on any given day. These are composite measures of
common air pollutants for which there are demonstrable adverse effects on health and the
environment. At the current time these include CO, NOz, SO2, ground level ozone, suspended
particulate matter (sometimes expressed as a coefficient of haze) and total reduced sulphur
compounds. The Index is reported on a scale of 0 to 100 (or more) with scales of 'very good"
air quality being 0-15 and 'very poor' near the 100 mark (Hilternann, Stolk et al. 1998;
Abelsohn, Stieb et al.2002).
2.2.3 Nitrogen oxides in pollution
NO is a potentially toxic molecule; and both NO and its interrelated forms were discovered as
components in pollution. Space shuttle and jet plane exhaust, lightening and smog are all
known to have a high proportion of NO (Nathan 1992). Nitrogen oxides were detected in the
evaluation of air pollution from the Titan tr firings @iamond and Johnson 1965). NO forms
part of the origin of the shuttle glow which was observed in 1983, and was carefully examined
because of concern that it would interfere with space-based spectroscopy. It was found to be
the reaction between NO and 02 forming an excited form of NO2 which released light as it
desorbed (Viereck, Murad et al. 1991). Increases in air traffic have resulted in increases in
nitrogen oxides in the troposphere, again causing concern about the effects in atmospheric
chemistry (Johnson, Henshaw et al. 1992). There exists an array of compounds that includes
NO, nitrosoium cation (NO +), nitroxyl anion (NO-), peroxynitrite (ONOO-) and hydroxyl
anion (OH-). Most of these are inherently unstable compounds and interact with other
elements particularly ozone and oxygen, so the main compound measurable in pollution from
this class of gases is the stable gas NO2. The ambient NOz levels in London vary between25-
58ppb (24 hour average), European air levels are 78ppb (24 hour average) and the level in the
USA is 53ppb (one year average) (Nicolai 1999).
Many epidemiological studies of outdoor pollution have found associations between NO2
exposure and disease, even at levels below the current WHO guidelines. The 'Air Pollution on
Health: European Approach' studies incorporated data from 15 cities with a total population
of greater than 25 million. A rise in NOz over the one hour safety maximum of 50 pglm3 was
associated with a 2.6Vo increase in asthma admissions and a l.3%o increase in daily all cause
mortality (Touloumi, Katsouyanni et al. 1997). In Toronto, from the total number of
premature deaths related to air pollution, NOz was assessed to be responsible for almost 407o,
and, of the hospital admissions, 60Vo was also thought to be attributable to NOz levels, with
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