Environmental and Genetic Differences Agricultural crops Native plants Small variabilityLarge variability
Variables Influencing Plant Response to Ozone Nutrition, primarily nitrogen Species/genotype Moisture: relative humidity and soil moisture Solar radiation, temperature Day length/photoperiod Regional climatic differences Age of plant, phenological state of development Population/ecosystem interactions
Injury and Damage Injury: All physical or biological responses to pollutants, such as changes in metabolism, reduced photosynthesis, leaf necrosis, premature leaf drop, and chlorosis. Damage: Reduction in the intended use or value of the biological or physical resource; for example, economic production, ecological structure and function, aesthetic value, and biological or genetic diversity that may be altered through the impact of pollutants.
Ozone Exposure Definitions Exposure – ozone present in ambient air Dose – ozone taken up into plant tissue Flux – the rate at which plant surfaces absorb ozone Effective flux – flux minus defensive response Defenses –passive and active
Ozone Metrics Related to Vegetation Preferentially weights higher concentrations Cumulative throughout growing season 24 hour exposure
Ozone Metrics Related to Vegetation AOT40: accumulated exposure over a threshold of 40 ppb. (The sum of all hourly concentrations after subtracting 40 ppb from each hourly value.) SUM06: sum of all hourly concentrations 60 ppb (0.06 ppm) N100: number of concentrations 100 ppb W126: sigmoidal weighted function, ppm-hrs W i = 1/[1 + M x e – (A x Ci) ] (where M = 4403 and A = 126 ppm -1 )
Daytime Exposure to Ozone Daylight hours AOT40 in Europe; 50 W/m 2 12 hours SUM06, recommended by EPA 8 am – 7:59 pm 24 hours Some European, U.S. Scientists
Seasonal Exposure to Ozone 3-Month May, June, July (AOT40 - crops) June, July, August (U.S.) Running 3-month (AOT40) Growing Season April through September (AOT40 - forests) April through October (U.S.)
FLAG RECOMMENDATIONS FOR EVALUATING OZONE IMPACTS FLAG has selected the W126 metric as most appropriate to describe ozone exposure for vegetation. The metric is based on a 24-hour, seasonal (April through October) period of measurement. FLAG also recognizes the importance of considering the number of hours in this period of time greater than or equal to 100 ppb (N100) given the importance of peak concentrations in plant response.
W126 (ppm-hrs) and N100 values for injury for selected species. NameW126N100 Table mountain pine Sweetgum Sycamore Winged sumac Black cherry Tall milkweed Black-eyed susan Dwarf dandelion Yellow buckeye Virginia pine Cutleaf coneflower 5.5 3
W126 (ppm-hrs) and N100 values for 10% growth loss for selected species. NameW126N100 Aspen Aspen wild Black Cherry Red Maple Whorled-wood aster Yellow poplar Eastern white pine Sugar maple Sycamore Winged sumac 9.7 4
FLAG RECOMMENDATIONS FOR EVALUATING OZONE IMPACTS NO x and VOC emissions are of concern because they are precursors of ozone. Current information indicates most FLM areas are NO x -limited most or all of the time. Until we determine such is not the case, we will focus on control of NO x emissions.
FLAG RECOMMENDATIONS FOR EVALUATING OZONE IMPACTS FLAG agrees with EPA and others that single source- receptor modeling for ozone is not feasible at this time. FLM actions or specific requests on a permit application will, therefore, be based on the existing air pollution situation at the FLM area(s) that may be affected by the source. FLM response will depend on (1) whether or not ozone phytotoxic effects have been documented in the area, and (2) whether or not ozone exposure levels occurring in the area have been shown to be phytotoxic.
a. The FLM may recommend one or more of the following: - That the proposed source use stricter (than BACT) controls (e.g., Lowest Achievable Emission Rate [LAER]) - That the proposed source obtain NOx emission offsets that will benefit the potentially affected FLM area (as demonstrated by dispersion modeling). - That the permitting authority (i.e.state or EPA) conduct regional modeling to identify sources that are contributing significantly to ozone-associated impacts in the FLM area, and that the permitting authority then undertake actions necessary to reduce emissions from those sources (e.g., SIP revision). b. That the applicant calculate the ozone exposure for vegetation (using the W126 and N100 metrics) for the affected FLM area(s) where such information is not already available. c. That the permitting authority or applicant fund post-construction ambient ozone monitoring in or near the FLM area. d. That the applicant conduct or fund post-construction ozone effects monitoring/research in the FLM area.
Ozone Information Provided in FLAG Report List of plant species sensitive to ozone for foliar necrosis List of ozone sensitive plant species occurring in selected Class I areas List of representative high and low W126 and N100 values for selected NPS and FSW areas Short list of W126 and N100 values causing foliar injury; and causing 10% growth loss for selected plant species
Additional Information Needed Inventory of plant species in FLM areas Identification of ozone sensitive plant species Monitoring of ozone in FLM areas Active monitors – necessary for dynamics of exposure Passive monitors – low cost, indicates ozone loading Source/receptor modeling
Ozone Air Pollution Web Sites U.S. EPA ozone information: gov/oar/oaqps/cleanair.html NPS ozone information: Ozone effects research, USDA ARS, North Carolina: Ozone effects research, England: Ozone effects research, Switzerland: Ozone exposure metrics for vegetation: htm