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


-------
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.


-------

-------