2010 Progress Report - International Joint Commission

Progress Report 2010
Figure 22. Ozone Concentrations along the Canada–U.S. Border
(Three-Year Average of the Fourth-highest Daily Maximum 8-hour Average),
2006–2008
Note: Data contoured are the 2006–2008 averages of annual fourth-highest daily values, where the daily value is the highest running 8-hour average for the day. Sites used
had at least 75% of possible daily values for the period.
Sources: Environment Canada National Air Pollution Surveillance (NAPS) Network Canada-wide Database, 2008 (http://www.ec.gc.ca/rnspa-naps/Default.
asp?lang=En&n=5C0D33CF-1)); EPA Aerometric Information Retrieval System (AIRS) Database (www.epa.gov/air/data/index.html)
Ambient Concentrations of Ozone,
NO x
, and VOCs
Annual ozone levels over the 1995–2008 time period
are presented in Figure 23, based on information from
longer-term eastern monitoring sites within 500 km
(310 miles) of the Canada–U.S. border. Ozone levels
have decreased over the period with a notable decline
in ozone levels since 2002. The lower ozone levels
shown for 2004 were due, in part, to the cool, rainy
summer in eastern North America. There is also a
complex regional pattern in ozone level variations,
which is not evident from the graph shown in
Figure 23. Figures 24 and 25 depict the average
ozone season levels of ozone precursors NO x
and
VOCs in the eastern United States and Canada. These
measurements represent information from a more
limited network of monitoring sites than is available
for ozone. Figure 26 shows the network of monitoring
sites actually used to create the trend graphs in
Figures 23 through 25.
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