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Question:
Which Month Experienced
the Highest 8-Hour Daily Maximum Ozone Concentration for the
Following Sites?
Answer:
Glacier National Park - May (2008), June (2009),
and May (2010)
Yellowstone National Park - April (2008), Sept* (2009), and April
(2010)
Denali National Park - April (2008), April (2009), and April
(2010)
Trinidad Head - April (2008), April (2009), and March (2010)
*The US EPA notes in its database that September 2009 ozone readings
were affected by a wildfire in Yellowstone National Park. The
second highest 8-hour average ozone concentration at the site
was in May.
The Springtime
Months of April and May Predominated
The highest 8-hour daily maximum concentration
occurred for most of the sites during the spring months. Many
of these sites exhibit no consistent statistical significant
changes in their annual 4th highest daily maximum 8-hour average
concentration over time. In most cases, the changes over the
years are statistically insignificant. Precursor emissions associated
with wildfires result in enhanced ozone levels occurring at times
outside the spring months and are considered as exceptional events
by the EPA and a part of background ozone. Lefohn et al. (2001)
and Oltmans et al. (2008) discuss the variability of background
ozone. The ozone monitoring site at Trinidad Head, CA is a site
that many times meets the criteria for identifying surface ozone
background levels. For more information about background ozone,
please click here. An Internet-based slide presentation is available for purposes
of previewing the Lefohn et al. (2001) paper. For
more information about background ozone and ozone trends, please
visit our publication web page.
References
Lefohn A. S., Oltmans S. J. , Dann
T. , and Singh H. B. (2001) Present-day variability of background
ozone in the lower troposphere. J. Geophys. Res., 106 (D9):9945-9958.
Oltmans S. J., Lefohn A. S., Harris J. M., and Shadwick
D. (2008) Background ozone levels of air entering the west coast
of the U.S. and assessment of longer-term changes. Atmospheric
Environment. 42:6020-6038. |
