Robert C. Musselman USDA Forest Service Rocky Mountain Research Station Fort Collins, Colorado

Introducing Ozone into Critical Loads Analysis - State of the Science in

Europe and Progress in North America

Robert C. MusselmanUSDA Forest Service

Rocky Mountain Research StationFort Collins, Colorado

Ozone Parameters Related to Vegetation Response

•Cumulative throughout growing season•Preferentially weights higher concentrations

[requires hourly data]•Includes time periods when stomata are open

[requires stomatal conductance data]

Definitions

• Concentration of ozone is the number of moles of ozone per unit volume of air.

Definitions

• Concentration of ozone is the number of moles of ozone per unit volume of air.

• Exposure is the product of the concentration of ozone and the length of time that vegetation is exposed to that pollutant.

Ozone Concentration Metrics “Related” to Vegetation

P1: Maximum daily average

N100: Number of hourly concentration >100 ppb

4thHDM: 4th highest daily maximum concentration

Ozone Exposure Metrics Related to Vegetation

AOT40: accumulated exposure over a threshold of 40 ppbSUM06: sum of all hourly concentrations at or above 60 ppbW126: sigmoidal weighted function, ppm-hrs

[where M = 4403, A = 126 ppm-1]

]e M+1/[1=W )C x (A xi

i-

Definitions

• Stomatal flux is the rate of uptake of ozone through stomata.

Definitions

• Stomatal flux is the rate of uptake of ozone through stomata.

• Dose is the instantaneous stomatal flux of ozone integrated over time, or the total amount of pollutant taken into plant tissue through stomata over time. [cumulative stomatal flux]

Definitions

• Effective flux is the balance between flux and defense, since detoxification mechanisms are present in leaf tissue resulting in not all the ozone taken up being associated with vegetation injury or damage.

Definitions

• Effective flux is the balance between flux and defense, since detoxification mechanisms are present in leaf tissue resulting in not all the ozone taken up being associated with vegetation injury or damage.

• Effective dose is the integral over time of the effective flux.

Critical Loads for Europe

• Critical load: ‘the quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur according to present knowledge’

• (FLAG: the concentration of air pollution above which a specific deleterious effect may occur)

Critical Loads for Europe

• Critical load: ‘the quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur according to present knowledge’

• (FLAG Critical load: ‘the concentration of air pollution above which a specific deleterious effect may occur’)

Critical Levels for Europe

• Critical level: ‘the atmospheric concentrations of pollutants in the atmosphere above which adverse effects on receptors, such as human beings, plants, ecosystems or material, may occur according to present knowledge’ (1996)

• Critical level: ‘the concentration, cumulative exposure or cumulative stomatal flux of atmospheric pollutants above which direct adverse effects on sensitive vegetation may occur according to present knowledge’ (2004)

Critical Levels for Europe

• Critical level: ‘the atmospheric concentrations of pollutants in the atmosphere above which adverse effects on receptors, such as human beings, plants, ecosystems or material, may occur according to present knowledge’ (1996)

• Critical level: ‘the concentration, cumulative exposure or cumulative stomatal flux [dose] of atmospheric pollutants above which direct adverse effects on sensitive vegetation may occur according to present knowledge’ (2004)

“Joint ICP Vegetation/EMEP Ad-hoc Expert Panel Meeting on Modelling and Mapping of Ozone Flux and Deposition to Vegetation”

Harrogate, UK; 16-19 June 2002.

(Massman, Musselman, Panek, Samuelson, Yihau)

Conclusion (1):

‘Although the AOT40 index has provided a useful indicator of the potential for ozone damage to vegetation, it is likely that the current definition for the critical level for ozone, based on AOT40 for a fixed time interval (the level I approach), provides an incorrect assessment of the regional distribution of the risk of damage to vegetation by ozone across Europe.’

Conclusion (2):

‘Flux-based risk assessment methods offer the potential for improved quantitative evaluation of the impacts of ozone on vegetation across European and should be recommended for future application within the Convention.’ (Level II approach)

Conclusion (3):

‘The deposition and flux algorithm now implemented within the EMEP photochemical model provides an adequate basis for first estimation and application of flux-based critical levels.’

gs = gmax * gpot * max {gmin,(glight*gtemp*gvpd*gsmd)}

“Establishing Ozone Criteria Levels II under the UNECE Convention on Long-Range Transboundary Air Pollution”

Goteborg, Sweden; 17-23 Nov 2002

The workshop represented the opportunity to introduce new Ozone Critical Levels II into the revision of the Gothenburg Protocol 2004/2005.

Atmospheric Environment, 38:2211-2437 (May 2004)“New methods of risk assessment for ozone impacts on vegetation”

“The terminology has changed such that ‘Level I’ and ‘Level II’ are no longer used and have been replaced by ‘Concentration-Based’ and ‘Flux-Based’, respectively (UNECE, 2004).”

http://icpvegetation.ceh.ac.uk

Current European Ozone Air Quality Standards

• Exposure-based critical level: cumulative, threshold weighted

• Exposure-based VPD-modified critical level:

cumulative, threshold weighted

• Flux-based critical level: cumulative stomatal flux [dose]

vegetation data

• Not concentration based as in North America • Not effective flux nor effective dose




cumulative, threshold weighted• Flux-based critical level:

cumulative stomatal flux [dose] vegetation data





cumulative, threshold weighted• Flux-based critical level:

cumulative stomatal flux [dose] vegetation data, environmental data


Injury and Damage

• Injury is leaf necrosis, premature leaf senescence, reduced photosynthesis, reduced carbohydrate production and allocation, reduced growth, and/or reduced plant vigor.

• Damage is all effects that reduce the intended value or use of the plant. Included in this definition are reductions in economic, ecologic, or aesthetic value.

Injury and Damage

Damage:•Yield loss is reduction in quality or

quantity of the harvestable portion of a agricultural or forest crop from ozone.

•Crop loss is the reduction in the monetary value of the forest or agricultural crop due to ozone.

European Critical Levelsfor Injury and Damage

• Injury [leaf necrosis]: 8 days, exposure based – AOT30/VPD critical levels for agricultural

crops• Injury [growth loss]: seasonal, exposure

based – AOT40 for forest trees

• Yield loss: seasonal, exposure based – AOT40 critical levels for

agriculture/horticulture crops• Crop loss: seasonal, flux threshold based

– FstY critical levels for wheat and potatoes

Critical Levels for Ozone in North America

Ozone data• Active sampling• Passive samplingVegetation and environmental data• ICP-Forest plots• FHM plots • Stomatal flux/effective flux: models

Critical Levels for Ozone in North America

Ozone data• Active sampling• Passive samplingVegetation and environmental data• ICP-Forest plots• FHM plots • Stomatal flux/effective flux models

The USA has always used a concentration-based secondary standard for ozone.

US EPA Staff in 1996 recommended an exposure-based secondary standard for ozone; but the EPA Administrator decided to stay with a concentration-based standard for ozone.

The Europeans have used an exposure-based critical levels standard (AOT40) for more than a decade, and are now moving toward a flux-based standard.

Current United States ozone primary (and secondary) NAAQS (established Sept 1997):

0.08 parts per million/ 8-hr average, 4th highest daily maximum concentration, 3-year average. [0.084 rounded]

The USA has always used a concentration-based secondary standard for ozone.

US EPA Staff in 1996 recommended an exposure-based secondary standard for ozone; but the EPA Administrator decided to stay with a concentration-based standard for ozone.

The Europeans have used an exposure-based critical levels standard (AOT40) for more than a decade, and are now moving toward a flux-based standard.

Is the US ready for a flux-based critical level NAAQS for ozone?

Is the US ready for an exposure-based ozone critical level NAAQS for ozone?

Latest Ozone Criteria Document (31 Jan 05)http://cfpub.epa.gov/ncea/

[click on ‘ozone’ under ‘risk assessments’]

“ EPAs current practice for setting secondary standards for most criteria pollutants does not appear to be sufficiently protective of sensitive crops and ecosystems.”

from: “Air Quality Management in the Unites States”National Research Council of the National Academy of Sciences, 2004. [www.nap.edu/catalog/10728.html]

“ A major goal of the nation’s AQM system in the coming decades should be to establish an appropriate research and monitoring program that can quantitatively document the links between air pollution and the structure and function of ecosystems and use that information to establish realistic standards and goals for the protection of ecosystems.”

from “Air Quality Management in the Unites States” NRC

Robert C. Musselman USDA Forest Service Rocky Mountain Research Station Fort Collins, Colorado

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