Weather Makes a Difference: 8-hour
Ozone Trends for 1997-2007
State and Local Information for EPA Region 10
Oregon
Washington
Composite trend for available sites in these states:
EPA Region 10 (selected sites)
80 -
70 i
60
JD
CL
Q.
0
C
o
N
o
oi50
CO
0
> 40
<
30
CO
c
o
(/)
ffi 20
CO
Št
o- -
-8 =
O.
Š Adjusted for Weather
Unadjusted for Weather
1998
2000
2002
Year
2004
2006
U.S. Environmental Protection Agency
Office of Air and Radiation
Office of Air Quality Planning and Standards
April 2008
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Oregon
Ozone
In Portland ozone adjusted for weather conditions declined 10 percent between 1997 and
2007. This improvement in ozone is in response to both state and regional reductions in
NOx and VOC emissions.
Trends for 1997-2007 for a site with complete ozone and meteorology data are presented
below. Ozone season (May 1 - September 30) averages of daily maximum 8-hour ozone
were adjusted to remove the influence of year-to-year variability in weather conditions.
The dotted line shows the trend in observed values at monitoring sites, while the solid
line illustrates the underlying ozone trend after removing the effects of weather. The
solid line serves as a more accurate ozone trend for assessing changes in emissions.
Typical weather conditions are determined by averaging conditions (e.g., temperature,
humidity, etc.) for the time period presented. The information provided is useful for
reviewing the weather influence for a particular ozone season. The solid line represents
ozone levels anticipated under typical weather conditions.
Seasonal Average 8-hour Ozone Trends
Portland, OR 8-hr Ozone Trends
n
Cl
Q.
a) 80
c
o
N
O
0) 60
O)
CO
©
- 40
CD
C
o
(/>
03
0) Of)
CO zu
Srrrr
Adjusted for Weather
Unadjusted for Weather
1998
2000
2002
Year
2004
2006
-------
Washington
Ozone
On average, ozone adjusted for weather conditions increased 15 percent between 1997
and 2007. There have been improvements in Seattle in recent years. These
improvements in ozone are in response to both state and regional reductions in NOx and
VOC emissions. Ozone trends vary from site to site.
Trends for 1997-2007 for rural sites and urban areas with complete ozone and
meteorology data are presented below. Ozone season (May 1 - September 30) averages
of daily maximum 8-hour ozone were adjusted to remove the influence of year-to-year
variability in weather conditions. The dotted line shows the trend in observed values at
monitoring sites, while the solid line illustrates the underlying ozone trend after removing
the effects of weather. The solid line serves as a more accurate ozone trend for assessing
changes in emissions. Typical weather conditions are determined by averaging
conditions (e.g., temperature, humidity, etc.) for the time period presented. The
information provided is useful for reviewing the weather influence for a particular ozone
season. The solid line represents ozone levels anticipated under typical weather
conditions.
Seasonal Average 8-hour Ozone Trends
Seattle, WA 8-hr Ozone Trends
JD
CL
CL
a? 80
c
o
N
o
0) 60
CD
OS
L.
-------
Mount Rainier NP, WA
n
CL
CL
a) 80
c
o
N
o
a) 60
CD
(0
L.
60
O)
CO
L.
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