Modelling ozone fluxes to forests for risk assessment: status and prospects (original) (raw)
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New flux based dose–response relationships for ozone for European forest tree species
Environmental Pollution, 2015
To derive O 3 doseeresponse relationships (DRR) for five European forest trees species and broadleaf deciduous and needleleaf tree plant functional types (PFTs), phytotoxic O 3 doses (PODy) were related to biomass reductions. PODy was calculated using a stomatal flux model with a range of cutoff thresholds (y) indicative of varying detoxification capacities. Linear regression analysis showed that DRR for PFT and individual tree species differed in their robustness. A simplified parameterisation of the flux model was tested and showed that for most non-Mediterranean tree species, this simplified model led to similarly robust DRR as compared to a species-and climate region-specific parameterisation. Experimentally induced soil water stress was not found to substantially reduce PODy, mainly due to the short duration of soil water stress periods. This study validates the stomatal O 3 flux concept and represents a step forward in predicting O 3 damage to forests in a spatially and temporally varying climate.
Comparison of different stomatal conductance algorithms for ozone flux modelling
Environmental Pollution, 2007
The DO 3 SE (Deposition of O 3 for Stomatal Exchange) model is an established tool for estimating ozone (O 3 ) deposition, stomatal flux and impacts to a variety of vegetation types across Europe. It has been embedded within the EMEP (European Monitoring and Evaluation Programme) photochemical model to provide a policy tool capable of relating the flux-based risk of vegetation damage to O 3 precursor emission scenarios for use in policy formulation.
DO3SE modelling of soil moisture to determine ozone flux to forest trees
Atmospheric Chemistry and Physics, 2012
The DO 3 SE (Deposition of O 3 for Stomatal Exchange) model is an established tool for estimating ozone (O 3 ) deposition, stomatal flux and impacts to a variety of vegetation types across Europe. It has been embedded within the EMEP (European Monitoring and Evaluation Programme) photochemical model to provide a policy tool capable of relating the flux-based risk of vegetation damage to O 3 precursor emission scenarios for use in policy formulation.
Tropospheric ozone (O 3) produces harmful effects to forests and crops, leading to a reduction of land carbon assimilation that, consequently, influences the land sink and the crop yield production. To assess the potential negative O 3 impacts to vegetation, the European Union uses the Accumulated Ozone over Threshold of 40 ppb (AOT40). This index has been chosen for its simplicity and flexibility in handling different ecosystems as well as for its linear relationships with yield or biomass loss. However, AOT40 does not give any information on the physiological O 3 uptake into the leaves since it does not include any environmental constraints to O 3 uptake through stomata. Therefore, an index based on stomatal O 3 uptake (i.e. PODY), which describes the amount of O 3 entering into the leaves, would be more appropriate. Specifically, the PODY metric considers the effects of multiple climatic factors, vegetation characteristics and local and phenological inputs rather than the only atmospheric O 3 concentration. For this reason, the use of PODY in the O 3 risk assessment for vegetation is becoming recommended. We compare different potential O 3 risk assessments based on two methodologies (i.e. AOT40 and stomatal O 3 uptake) using a framework of mesoscale models that produces hourly meteorological and O 3 data at high spatial resolution (12 km) over Europe for the time period 2000–2005. Results indicate a remarkable spatial and temporal inconsistency between the two indices, suggesting that a new definition of European legislative standard is needed in the near future. Besides, our risk assessment based on AOT40 shows a good consistency compared to both in-situ data and other model-based datasets. Conversely, risk assessment based on stomatal O 3 uptake shows different spatial patterns compared to other model-based datasets. This strong inconsistency can be likely related to a different vegetation cover and its associated parameterizations.
Tellus A, 2011
The negative impacts of surface ozone (O 3 ) on vegetation are determined by external exposure, leaf gas exchange and plant antioxidant defence capacity, all dependent on climate and CO 2 concentrations. In this study the influence of climate change on simulated stomatal O 3 uptake of a generic crop and a generic deciduous tree at ten European sites was investigated, using the LRTAP Mapping Manual stomatal flux model. O 3 concentrations are calculated by a chemistry transport model (MATCH) for three 30-yr time-windows (1961-1990, 2021-2050, 2071-2100), with constant precursor emissions and meteorology from a regional climate model (RCA3). Despite substantially increased modelled future O 3 concentrations in central and southern Europe, the flux-based risk for O 3 damage to vegetation is predicted to remain unchanged or decrease at most sites, mainly as a result of projected reductions in stomatal conductance under rising CO 2 concentrations. Drier conditions in southern Europe are also important for this result. At northern latitudes, the current parameterisation of the stomatal conductance model suggest O 3 uptake to be mainly limited by temperature. This study demonstrates the importance of accounting for the influences by climate and CO 2 on stomatal O 3 uptake, and of developing their representation in models, for risk assessment involving climate change.
Atmospheric Environment, 2004
The current European critical levels for ozone (O 3) to protect crops, natural and semi-natural vegetation and forest trees (Level I) are based on exposure-response relationships using the AOT40 exposure index. In the context of the revision of the 1999 UNECE multi-pollutant/multi-effect protocol that is expected in 2004 ("... no later than one year after the present Protocol enters into force"; UNECE, 1999, Article 10), a transition to a flux-based limiting value is currently under discussion. In principle, there are three alternatives for replacing the Level I approach based on European literature and scientific discussions. One alternative is a modified AOT40 index. Because of several uncertainties discussed in the literature during the recent years that approach appears questionable. The second alternative is the German VDI's MPOC (Maximum Permissible O 3 Concentration at the canopy top) concept. In contrast to the current European critical AOT40 levels, MPOC values are based on a significantly higher number of experiments, with more than 30 species for crops and wild plants and 9 species for forest trees. In principle, the MPOC concept can be applied from local, up to the European scale and fulfil the demand for the UNECE abatement strategies. The third alternative under discussion is the flux approach. Here, critical levels will have to be replaced by critical cumulative stomatal uptake (critical absorbed dose). The main problems with that approach can be attributed to uncertainties due to, (1) parameterisation of stomatal conductance (e.g. how representative are they of different geographic regions in Europe in up-scaling from leaf estimates to canopy level, (2) parameterisation of non-stomatal deposition, and (3) the representativeness of species used in flux-effect studies. Nevertheless, establishing realistic fluxeffect relationships clearly requires chamber-less experiments, especially for species rich ecosystems, but will have to be based on flux estimates at the canopy level. Compared to Europe, the situation is quite different in North America. Although in general, the flux approach is well accepted by plant effects scientists there, concerted research efforts have not taken place in that direction due to a distinct lack of funding. Furthermore, because of the differences in the approach to setting ambient air quality standards in N. America, it appears very doubtful that policy makers and air quality regulators in the US and Canada will readily accept the overall philosophy.
Estimation of stomatal ozone uptake of deciduous trees in East Asia
Annals of Forest Science, 2011
& Background To assess ozone risks to temperate deciduous forest trees in East Asia, the stomatal ozone uptake was estimated based on a flux-based modeling approach. & Methods In this model, key parameters were obtained from scientific literatures on deciduous tree species in East Asia. In addition, regional characteristics of the leaf duration were estimated using a phenological model. & Results The result showed a difference in spatial pattern between AF st 0 (accumulative stomatal ozone uptake) and AOT40 (accumulative exposure above a threshold concentration of 40 ppb during daylight hours). Although most of the areas of high ozone concentration corresponded to humid climate areas, not only the ozone concentration, but also the length of the leaf duration and the species-specific stomatal response to environmental factors, limited AF st 0 in East Asia. • Conclusion These results suggested that an approach based on stomatal ozone uptake would be a useful tool for ozone risk assessment in East Asia.