CATF Comments on Ozone 

NAAQS Revision, 

and Related International and 

Climate Matters

Corrected Version

September 15, 2010
Key points

• Tight new ozone standards are necessary to protect health and the environment but

CATF recognizes they will provide a significant compliance challenge for the states.

• There are multiple levers we can pull to drive ozone down:

– Reducing international ozone precursors will drive down significant 

anthropogenic (15 ppb) global ozone background.

– Methane reductions in the US and globally can provide a portion of those 

background reductions.

• Reducing ozone and methane will also combat global warming and provide nearterm cooling in at-risk areas like the Arctic.

• The US is already making a significant commitment to drive down global methane 

(hence ozone and global warming) via its Global Methane Initiative and this should be 

pointed out to stakeholders.

• Additional actions CATF recommends to enhance likelihood of lower cost US 

compliance:

– Highlight methane ozone impacts and options in the final ozone NAAQS 

preamble, and in future compliance strategy documents.

– Take up climate co-benefits of ozone and ozone precursor reduction in 

future ozone NAAQS.

– Support consideration of ozone for inclusion in the LRTAP protocol revision.

– Support of Global Methane Facility to enhance global methane reductions.

2
Global background ozone is a significant 

portion of total, and has been increasing

Afternoon ozone averages in 

US quadrants: Sources

Long-term trends at 

remote sites worldwide

Source: Oltmans, 2006

Source: Fiore 2003 

(used in 2007 NAAQS Criteria Documents)

Model, Policy Relevant Background

Model, natural emissions only

Model, stratospheric ozone only

Rural (CASTNET) observations

Model, all emissions, CASTNET sites

Model, all emissions, whole quadrant

3
Methane is a significant component of both 

anthropogenic global background and 

regional Midwest-Northeast US ozone (as 

much as 7 ppb)

Difference in Daily Maximum 8-hour 

Average Ozone between base case 

(1.85 ppm methane) and preanthropogenic methane (0.70 ppm 

methane) case for July 13, 2002. 4

Above: change in global ozone 

levels (ppb) from 31% decrease 

in global anthropogenic CH4

emissions 

(Fiore, et. al. JGR, 2008)
The importance of methane-derived 

background ozone increases as 

standards tighten

50%

60%

70%

80%

90%

100%

Estimated Contribution

Ozone from Other Anthropogenic

Ozone from non-CH4 Background

Ozone From CH4 Oxidation

Difference between base case 

(1.85 ppm) and preanthropogenic (0.70 ppm) case 

methane for July W126 O3 

Concentrations (ppm-hours).

Contribution of methane to ozone 

increased from 4% of the 1-hour standard 

to 6% under the 1997 8-hr. standard, and 

would be 8% under a revised 8-hr. 

standard.

0%

10%

20%

30%

40%

1-Hr. Std (125) 8-Hr. Std (85) 8-Hr. Std (60) W126 (7) W126 (15)

Estimated Contribution

5
Global health benefits of ozone reduction 

via methane

Annual avoided 

mortalities in the 

northern 

hemisphere due to 

20% reduction in 

methane = 14,100 

to 40,100

Sources: West

West & Fiore, ES&T, 2005; 

Anenberg et al., ES&T, 

2009

6
Integrated Radiative Forcing for 

year 2000 Global Emissions: 

20-year and 100-year weighting

(gas-phase only)

yr time horizon

Ozone and methane are significant components 

of global climate change, and short term Arctic 

warming; methane and ozone reductions will 

cool much faster than CO2reductions

100-yr time horizon 20-yr time horizon

From IPCC 2007

7
Another way to look at it: methane climate 

forcing from multiple pathways 

Source: Shindell 

et al., Science, 

2009

8
In the current NAAQS reconsideration, 

EPA should:

• Call out methane role more clearly

• Include specific methane reduction strategies for states to consider

• [In messaging, note Administration work in related international forums 

(CLRTAP, GMI, GMF) on both ozone and methane to support states.]

9
In future NAAQS revisions:

• EPA should consider ozone climate effects in setting standard

10
Opportunities to increase international focus 

on ozone and methane

• Include ozone in LRTAP Gothenburg Protocol revision (this could enhance 

international support for Global Methane Initiative)

• Global Methane Initiative

• Global Methane Fund

11
Additional 

material

12
Lower tropospheric ozone = lives saved

Methane reductions of 65 Mt/yr beginning in 2010 would 

prevent 370,000 premature deaths over the next 20 

years

Chart shows avoided 

premature mortalities in 

2030 by world region 

and avoided mortalities 

per million people in 

2030, resulting from 

decreases in surface 

O3 due to a global CH4 

emission reduction of 

65 Mt/yr

West,et.al, PNAS, 2006

13
Elevated tropospheric ozone 

results in crop losses

• Ozone is well documented as the air 

pollutant most damaging to agricultural 

crops and other plants. Most crops are 

grown in summer when ozone 

concentrations are frequently sufficiently 

elevated to reduce yields.

• East Asia, a region Asia, a region that produces produces over 

20% of the world’s grain, could see major 

reductions in agricultural yields due to 

projected increases in surface ozone 

concentrations. 

• Yields could be substantially increased 

through reduction of surface O3

concentrations

14
Double dividend of Methane Controls: Decreased 

greenhouse warming and improved air quality

Methane Ozone Total

W/m2

IIASA- (current 

legislation)

0.099 0.065 0.164

As 

methane

decreases,

ozone and 

methane

Adjusted Radiative Forcing (W/m2) in 2030 Versus 2005 Due to 

Changes in Tropospheric CH4 and O3

legislation)

-75 Tg (18%) 0.033 0.048 0.081

-125 Tg (29%) - 0.029 0.032 0.003

-180 Tg (42%) - 0.097 0.014 - 0.083

Fiore,et.al, JGR, 2008

methane

forcing 

decrease

15