Weather Makes a Difference: 8-hour
Ozone Trends for 1997-2007

State and Local Information for EPA Region 9

Arizona

California

Nevada

Composite trend for available sites in these states:

EPA Region 09 (selected sites)

80

60 -

JD
Gl

-70

0
C

o

N

o

S)50

ca

s_

% 40

<

. o	o --





30

CD
C

o
w

. 20

CO

 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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Arizona
Ozone

On average, ozone adjusted for weather conditions increased 2 percent between 1997 and
2007. 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

Chiricahua NM, AZ

.q

Q.

Q.

a) 80
e

o

N

O

 60

O)

03

I



CO

Adjusted for Weather
Unadjusted for Weather

O-JJ



20

1998

2000

2002
Year

2004

2006


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Grand Canyon NP, AZ

JQ
Q.

Q.

0 80
c
o

N

O

 60

O)

cc

L.

CD

f 40
co
c
o

(J)

cc

0
CO

Adjusted for Weather
Unadjusted for Weather



8^.

20

1998

2000

2002
Year

2004

2006

Phoenix, AZ 8-hr Ozone Trends

n

Cl
Cl

0 80
c
o

N

o

0 60

o>

CO

L.

CD

5 40

CD
C

o

V)

cc

cd on

k/5





*	 Adjusted for Weather

	 Unadjusted for Weather

1998

2000

2002
Year

2004

2006


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California
Ozone

On average, ozone adjusted for weather conditions decreased 2 percent between 1997 and
2007. Several monitoring sites showed improvements in ozone. 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

Yosemite NP, CA

JD
Q.

CL

(D 80
C

o

N

O

0) 60

O)

CO

L.

0

- 40
to
c
o

tf)

(0
0
LO

	 Adjusted for Weather

	 Unadjusted for Weather

20

V



1998

2000

2002
Year

2004

2006


-------
Bakersfield, CA 8-hr Ozone Trends

ja

Q_

Q.


-------
Joshua Tree NM, CA

jQ
CL
CL

0 80
c
o

N

o

0	60

CD
(I!

CD

1	40

03
c
o
w
cu

0
73

 Adjusted for Weather
 * Unadjusted for Weather

O,

20 -



1998

2000

2002
Year

2004

2006

Lassen Volcanic NP, CA

.Q
CL
CL

0 80
c
o

N

O

&60
o>

0


-------
Los Angeles, CA 8-hr Ozone Trends

1

Q_

CL

0 80
c
o

N

o

 60

D)

ro

L.



CSS

L.

0

f 40

CQ

c
o

<0
0

CO

Adjusted for Weather
Unadjusted for Weather





- - O.

- o

_.8

20

1998

2000

2002
Year

2004

2006


-------
Sacramento, CA 8-hr Ozone Trends

3
L
Cl

i

. o.



	 Adjusted for Weather

	 Unadjusted for Weather

1998

2000

2002
Year

2004

2006


-------
San Francisco, CA 8-hr Ozone Trends

n

CL

al

0 80
c
o

N

O

 60

OS
03

(D

^ 40
ro
c
o

tf)

CO
0
C/)







20

	 Adjusted for Weather

	 Unadjusted for Weather

i	i	i

1998 2000 2002

i	i

2004 2006

Year


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Nevada
Ozone

In Las Vegas ozone adjusted for weather conditions has gradually declined since 1998.
Trends for 1997-2007 for a aite with complete ozone and meteorology data are presented
below. Ozone season (May I - 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

Las Vegas, NV 8-hr Ozone Trends

3
Ql
O,

0 80
c
o

N

O

60

CD
CO

CD

- 40

03
C

o

00
CO
0)

cn







B"

20 -

	 Adjusted for Weather

	 Unadjusted for Weather

1998

2000

2002
Year

2004

2006


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