Environmental Impacts Assessment - Stage 5

01  Develop a plan for refining existing tools for specific application in your jurisdiction 

From work conducted in previous stages, identify those geographical areas where impacts are likely to be greatest, and the ecosystems, including agricultural and forested areas, and associated ecosystem services that are at greatest risk and/or of greatest concern. Collaboration with colleagues working on Decision Support, Legal Framework and Policy Design, and Public Engagement and Communication, is essential at this stage. The overall aim of Stage 5 is to showcase impacts on the ecosystem services of greatest concern in your jurisdiction. Examples of approaches that could be used are provided in steps 2 – 8 below; you may wish to add additional air pollution/impact combinations to this list.  

First, identify gaps in knowledge in the analyses conducted so far. These might include a lack of knowledge about impacts of air pollution on: nationally important crops and cultivars not currently considered; tree species and provenances that are different to those used in standardised methodology; and ecosystems that are typical of your area that need protecting but do not currently have associated air quality standards.  

Read the descriptions for steps 2 – 9 below and develop an outline plan for a series of pollutant exposure experiments that will fill the knowledge gaps for your jurisdiction. For greatest benefit, these could be placed near pollutant monitoring sites, especially sites where meteorological parameters are monitored at a range of heights relevant to the ecosystem being studied. This monitoring data will be invaluable in interpretation of results and for showcasing the effects that can occur in the field. Establish the best locations for combined monitoring and experimental sites in collaboration with colleagues responsible for air quality monitoring.

The provision of visible evidence of damage in areas identified as at risk from modelling is a powerful tool for understanding the level of threat of pollution impacts in your region and persuading decision makers, NGOs and the public that action is needed. For example, such evidence can help to frame air pollution impacts on crop yields as a food supply issue. Field evidence can also be useful for showing how the magnitude of effects of air pollution compares with effects of climate change or other stresses of particular concern in your jurisdiction.  

02 Customise dose response relationships for ozone effects on crops and collate field evidence of effects

Plan and implement experiments to provide data needed for dose response relationships that are specific for the crops and cultivars of greatest importance in your jurisdiction. Typical exposure systems used are field-based open-top chambers (e.g. Mashaheet et al., 2025) and solardomes (dome-shaped greenhouses, e,g, Hayes et al., 2020) where controlled amounts of ozone are added to filtered air, and field release systems (e.g. Montes et al., 2021) where ozone is added to ambient air as it blows across crops (see Chapter 4 in WMO, 2023, for an overview). Include at least three ozone treatments and ideally use three or more replicate treatments. Applying additional treatments would provide a more robust dose response relationship if funds permit. The aim is to develop dose response functions from these experiments for both yield quantity (e.g. weight of grains) and quality (e.g. grain protein content).  

When planning your approach, you may wish to look at the case study described in Step 3 below that starts with controlled ozone exposure experiments for crops from Sub-Saharan Africa and ends with a spatial assessment of impacts in several countries and then in more detail for one country.

To modify the parameterisation of the DO3SE model to suit local conditions and cultivars, you will need to take measurements of stomatal conductance (moisture release from the leaf pores) throughout the growing season under a range of weather conditions (see example for African crops in Hayes et al., 2020). You will need to keep a record of the timing of key growth stages such as the timing of anthesis in wheat - see a description of the fphen (pheology) function for crops in Chapter 3 of the LRTAP Convention’s Manual. You can use the online version of DO3SE to calculate hourly PODy values.  

To provide persuasive evidence for policy makers of the need for action, collate field evidence of the damaging effects of ozone using protocols such as those developed by the LRTAP Convention’s ICP Vegetation. Evidence collated by participants in the ICP Vegetation was used in the 2010s in decision making by the LRTAP Convention in the 2010s. This evidence base included surveys for the presence of visible leaf damage specific to ozone, yield improvements when ozone concentrations were reduced by filtration and use of a chemical to protect against ozone damage. The locations where evidence was found in Europe were superimposed on maps of a concentration-based metric (AOT40) and a flux-based metric (PODy) (Mills et al., 2011). It was found that flux-based metrics were a better indicator of damage than concentration-based metrics. Based on this evidence, the LRTAP Convention included vegetation guidelines (critical levels) in the 2012 revision of the Gothenburg Protocol along with health-based guidelines, and recommended the use of flux-based metrics and critical levels, as described in the Modelling and Mapping Manual (Chapter 3). The LRTAP Convention’s flux-based critical levels were later included as optional reporting metrics in the European Commission’s Directive 2016/2284 on the reduction of national emissions of air pollutants, 2016. As described for the study by Mills et al., 2011, overlay your locations of damage to crops resulting from ozone on maps from Stage 4, Step 3 of the Environmental Impact Assessment Guidance, and those to be developed in the next step, to show that damage is occurring in areas predicted to be at risk of yield loss.

03 Assess economic losses due to ozone effects on food supply at farm, sub- national and national scales

Re-parameterise DO3SE with new data from Step 2 and develop country-specific dose response relationships, as described in Chapter 3 of the LRTAP Convention’s Modelling and Mapping Manual. The aim will be to conduct a new national-scale assessment calibrated to local conditions and crops/varieties, using the framework developed in Stage 4, Step 3 of the Environmental Impact Assessment Guidance.

We provide here an example of an assessment made for Sub-Saharan Africa (SSA) that describes an approach that could be followed, where dose response functions derived from ozone exposure experiments are applied in a spatial assessment of impacts on yield quantity. In this study, cultivars of African staple food crops (wheat, finger millet, pearl millet, amaranth, common bean, mung bean, cowpea and sorghum) were exposed in solardomes to episodic ozone treatments, and PODyIAM-based dose-response functions were derived (Hayes et al., 2019, Hayes et al., 2020). These functions were applied in a spatial analysis of yield losses, indicating that 2 - 13% of wheat yield and up to 21% of bean yield were being lost per country of SSA as a result of ozone pollution (Sharps et al., 2021). Thus, the study indicated that ozone pollution could be making a significant contribution to yield gaps in SSA countries. The analysis was expanded for impacts on bean production in Uganda, where food supply is already challenged by other factors, and beans are mainly produced on small-scale farms (Sharps et al., 2024). By following the approach in this case study, you could assess the impacts of ozone pollution on food supply for crops of greatest importance in your jurisdiction.        

You could take the analysis suggested in the case study to the next stage by calculating the economic value of lost yield, identifying geographical areas where this is of greatest concern.    

You could analyse year-on-year fluctuations in impacts at the farm- or local-scale for locations where previous studies have indicated that significant impacts on yield are likely. Ideally, select locations that have a long time series of ozone and meteorological data. Consider how ozone impacts both the yield quantity and the yield quality and what the implications might be for farmers and food supply (see Pandey et al., 2023). Use farm-scale analysis to highlight concerns for impacts on small-holders reliant on home grown food and sales in local markets.  

You can also revisit the critical levels for ozone effects on crops included in Chapter 3 of the LRTAP Convention’s Modelling and Mapping Manual and determine whether these need to be modified for application in your jurisdiction using your new dose-response functions. A method for setting critical levels is described in the same chapter of the manual. You may want to set additional critical levels for crops of importance for your jurisdiction that are not currently included in the LRTAP Convention Manual. In collaboration with those working on Decision Support and Source Attribution modelling, use the new/revised critical levels to predict changes in levels of exceedance and economic consequences for selected policy scenarios. 

04 Customise dose response relationships for ozone effects on trees and collate field evidence of effects

Using your chosen experimental system from Step 2, develop PODy-based dose response relationships for the tree species and provenances that are of greatest relevance to your jurisdiction. These may be important for timber production, carbon sequestration and/or be of conservation value.

Your experiments are likely to need to be conducted with young trees (usually 1 – 5 years old) because of space restrictions in exposure systems, although ozone field release systems can be used for older trees (Herrick et al., 2024). You will need to take measurements of stomatal conductance (moisture release from the leaf pores) throughout the growing season under a range of weather conditions as described for crops in Hayes et al., 2019. You will also need to keep a record of the timing of key growth stages such as bud burst in deciduous trees - see a description of the fphen (phenology) function for trees in Chapter 3 of the LRTAP Convention’s Manual. The end point in your experiments will be measurements of above and below-ground biomass and stem diameter at the final harvest. You may also want to take non-destructive measurements of stem diameter as the young trees are growing, allowing you to show growth effects through growing season(s).

To develop PODy-based response relationships from your experimental data, modify the parameterisation of the DO3SE model to suit local conditions and cultivars as described in Chapter 3 of the LRTAP Convention Manual. You can use the online version of DO3SE to calculate hourly PODy values. A method for upscaling dose response relationships from young trees for application to mature trees is described in Karlsson et al., 2025.

To draw the attention of policy makers and foresters to the negative effects of ozone on trees in your jurisdiction, you could collate one or more of the following types of evidence and overlay the locations of evidence with maps of ozone:  

• An air filtration system that reduces the ozone concentration young trees are growing in compared to an unfiltered treatment. These experiments are likely to show that the trees grow better in cleaner air and demonstrate the benefits of implementing control measures for ozone pollution.  
• An epidemiological approach that collates measurements from a large number of trees from a wide geographical area and uses multivariate statistical analysis to determine the impact of ozone pollution relative to other growth modifying factors (see Braun et al., 2022).  
• Locations of visible injury on leaves, caused by ozone. An example of how these results can be presented is available from the US National Parks Service.

05 Assess economic losses due to effects of ozone on tree growth at local to national scales

Repeat Stage 4, Step 5 of the Environmental Impact Assessment Guidance to quantify economic losses for ozone effects on timber harvests and carbon sequestration using your new parameterisations for DO3SE and the dose-response functions derived in the previous step. Apply the methods of Karlsson et al., 2025, to upscale your results from the young trees used in experiments to mature trees. You may also wish to compare results using an alternative approach for modelling the impacts of ozone on carbon sequestration, such as that described for tropical trees by Cheesman et al., 2024.

Identify locations where your results predict significant impacts of ozone on tree growth that have a long time series of ozone and meteorological data (ideally for 5 - 10 years or more). Use your dose-response relationships to determine annual fluctuations in impacts on growth over the time period and calculate the impacts on timber production and carbon sequestration. Work with colleagues in Air Quality Monitoring to identify such sites as described above in Step 1.  

As explained for crops in Stage 4, Step 3 of the Environmental Impact Assessment Guidance, the critical levels and PODy-based approaches included in the LRTAP Convention’s Modelling and Mapping Manual for trees were developed for use in countries that are signatories to the Convention. They can be applied globally or regionally (e.g. De Marco et al., 2020), but may need modification for local conditions and tree types for national application in non-LRTAP countries. Thus, in this step, we suggest that you revisit the critical levels for ozone effects on trees included in Chapter 3 of the Manual and determine whether these need to be modified for application in your jurisdiction using your new dose-response functions. Set new critical levels if needed. Use these new or validated existing critical levels to predict changes in levels of exceedance and economic consequences for selected policy scenarios, in collaboration with those working on Decision Support and Source Attribution modelling.  

06 Conduct a catchment scale assessment of acidification and eutrophication in freshwater ecosystems

Choose one or more freshwater catchments for detailed study that have been identified as being at risk or shown to be damaged by acidification and/or eutrophication from air pollution (See Stage 4, Step 7 of the Environmental Impact Assessment Guidance). The following resources provide useful background information for your decision making:

Brief overviews of the types of effects likely to be found (US EPA, UK APIS);

• An assessment of critical load exceedances and ecological impacts at unmanaged forested catchments in Europe (Forsius et al., 2021)  
• An example showing how LRTAP Convention methodologies for monitoring critical load exceedances have been adapted for application in East and Southeast Asia (Yamashita et al., 2022);  and 
• A national-scale assessment of changes in fish population and water chemistry (historical paper by Rask et al.,1995). In the first part of this step, you will quantify changes in water chemistry, and in the second part you have the option of extending your analysis to quantifying impacts on fish populations based on dose-response relationships derived from experiments.

To detect the earliest signs of aquatic ecosystem responses to excessive atmospheric inputs of sulfur and nitrogen, monitor the water chemistry of lakes and streams, as this reflects the biogeochemical processes occurring within catchments. If funds permit, additional monitoring of diatoms, invertebrates and fish populations in the locations where water samples are collected will provide important indicators of ecosystem health and resilience. Methods for chemical and biological monitoring can be found in the manuals for the LRTAP Convention’s ICP Waters and ICP Integrated Monitoring, and the Acid Deposition Monitoring Network in East Asia, EANET.

Regular monitoring of the water chemistry of streams and lakes is essential for evaluating the long-term effectiveness of air pollution control measures. For example, in Asia, EANET monitoring and related research activities have detected rapid responses of streams and lakes of forested catchments to changing atmospheric deposition (Sase et al., 2021). In analysing your trends over time, it is important to consider how changes in water chemistry resulting from atmospheric deposition are influenced by other factors such as catchment characteristics, land use and climatic conditions (ICP Waters, 2022, De Wit et al., 2023). For example, in Asia, pronounced seasonality, extreme weather events (Sase et al., 2019), and changing precipitation patterns (Zhigacheva et al., 2022), appear to influence the biogeochemical cycling of atmospherically derived substances during the recovery process as emission controls reduce deposition. Furthermore, given the time lags in the biogeochemical cycles involved, changes in water chemistry may not be immediately evident as atmospheric deposition reduces. Biological recovery in freshwater ecosystems may only be detected years to decades later (ICP Waters report, 2023 and Baldigo et al., 2016).

To understand how the populations of key fish species might have changed in the selected catchment(s), conduct controlled experiments that replicate improvements as well as deteriorations in water quality. These so-called mesocosm experiments, depending on their scope and size, allow impacts on species growth, development, and food chains to be investigated (Macaulay et al., 2025). Historical experiments manipulated whole lake acidity (e.g. Experimental Lakes Area of Canada (IISD-ELA), described in Baud et al., 2023), but more usually experiments are conducted in outdoor tanks of the type used in the EU AQUACOSM network.    

Use the dose-response relationships developed from your experiments and historical monitoring or modelled data for sulfur and nitrogen deposition to predict how fish populations might have changed over time in your catchment. Determine a target for reducing freshwater acidification and liaise with Decision Support and Legal Framework and Policy Design colleagues to determine how and when this could be achieved. You could also assess acidification impacts on aquatic ecosystem services using the Stressor–Ecological Production function–Final Ecosystem Services (STEPS) Framework and the Final Ecosystem Goods and Services Classification System (FEGS-CS) described in O’Dea et al., 2017. 

07 Identify ecosystems in need of protection from air pollution and share results with other agencies involved in their conservation

Rather than calculating economic losses as described in Stage 4, Step 6 of the Environmental Impact Assessment Guidance, in this step the focus is on identifying vulnerable ecosystems that need protecting from further damage and making this information available to other agencies involved in their conservation.  

Consider whether the critical loads and levels in the LRTAP Convention’s Modelling and Mapping Manual need modification for vulnerable ecosystems in your jurisdiction. Approaches for modifying these can be found in Bobbink et al., 2022. Then, using the data collated so far, identify the habitats at risk from exceedance of your bespoke critical loads for acidification and eutrophication (excess nitrogen) and critical levels for ozone and NH3. Where time series of data exist, determine trends in exceedance of these critical loads and levels.

Reporting and sharing of your data with agencies involved in conservation at local to national scale helps to draw attention to the need to reduce damaging air pollutant emissions. Consider how best to report and share your data. As an example, data sharing approaches used within the UK are described, where critical loads and levels mapping and modelling is coordinated by a National Focal Centre (NFC). The NFC submits summary data to the Coordination Centre for Effects (CCE) of the LRTAP Convention, for inclusion each year in the Convention’s CCE Status Reports. It also prepares more detailed annual trends reports that are submitted to the UK Department of Environment, Food and Rural Affairs (e.g. for 2024). The critical loads and levels exceedance data is publicly available from UKCEH’s data portal and together with the findings, is used extensively by other agencies to assess the condition of ecosystems of interest to them. For example, the UK Joint Nature Conservation Committee reports data on biodiversity indicators and includes the areas and habitats affected by exceedance of critical loads for acidity and nutrient nitrogen (e.g. for 2025). For use by conservationists working at the local scale, site-specific critical loads and levels data for different types of protected habitats (e.g. Sites of Special Scientific Interest) are available in mapped format on the UK Air Pollution Information System (APIS).  

Having assessed the state of sensitive ecosystems in your jurisdiction and identified those with exceedance of critical levels and loads (modified as needed for your conditions), extend your analysis to include other aspects of air quality decision making. Collaborate with Source Attribution and Decision Support colleagues to show how the ecological quality of ecosystems in your jurisdiction identified as vulnerable or changed by air pollution could be improved by targeted air pollution controls. Take into account the potential time-lags between reductions in concentrations or deposition and biological recovery in ecosystems (Stevens et al., 2020). 

08 Demonstrate the co-benefits of combined air pollution and climate change mitigation strategies

Assess the maps and trends produced in Steps 2 – 7 above and steps 3, 5 - 8 of Stage 4, and the data sources described here to identify geographical areas where climate change may be contributing to negative environmental impacts, alongside the air pollution impacts identified. The aim of this step is to show the co-benefits of having an integrated approach to controlling emissions of pollutants that are both air pollutants and drivers of climate change. Collaborate with colleagues working on Decision Support and Legal Framework and Policy Design as well as those working on climate policies to decide on pollutant: impact combinations that are of the highest priority. Two approaches are suggested here.

Firstly, you could show the geographical areas where negative air pollution impacts co-occur with impacts of other factors that might be contributing to negative effects such as heat stress, drought or uncontrolled pests and diseases. These can be used to draw the attention of agriculturalists, foresters and/or conservation agencies to the negative effects of air pollution, effects that may be being mis-diagnosed as being caused by a different environmental stress. To do this, you may need to develop a scoring system that allows differing impacts to be compared on the same scale (see global application in Mills et al., 2018, and a national application for regions of Uganda in Sharps et al., 2024).

Secondly, you might wish to show the co-benefits of combined emission controls for both food supply and the climate in your jurisdiction using an approach conducted for China (Li et al., 2025). The study modelled the effects of changing climate on the uptake of ozone by leaf pores (PODy) for 2056-2060 for different Shared Socioeconomic Pathway (SSP) scenarios, compared to a baseline for 2015 - 2019. The combined annual yield for four crops (wheat, maize, soybean, and rice) of 537 million tonnes (Tg) in the baseline years was predicted to increase by 38 million tonnes (Tg) in 2056 - 60 following implementation of the stringent SSP126 scenario. Around 90% of this yield increase was predicted to result from reduced anthropogenic emissions. The additional crop yield gained could reduce the amount of land needed for crop production in China. If the spare land was reverted to forest, an additional absorption of 22 Mt of CO2 per year could potentially be achieved, with benefits for the climate.  

In collaboration with colleagues working on Decision Support and Legal Framework and Policy Design, provide a summary for policy makers that highlights the potential co-benefits for the environment and the climate from control of air pollutant emissions. 

09 Disseminate results, make recommendations for further work and co-design strategies to reduce impacts with stakeholders

Assess your progress. Identify strengths and weaknesses in the environmental impact assessments you have conducted, and produce a synthesis report of the current state of knowledge for your jurisdiction.  

Identify pollutants, impacts, and geographical areas that are of greatest concern and work with others involved in all aspects of air quality management to develop a strategy for reducing future environmental impacts by cutting emissions. Make recommendations for further work, including, for example, identifying areas where greater monitoring coverage is required or additional field experiments.

Prepare outputs that are suitable for communication to people with a range of levels of prior knowledge and different interests, including farmers, conservation agencies, policy makers, and recreational users of the natural environment. Run workshops for these stakeholders to review your findings and co-design strategies to reduce air pollution or adapt to its impacts.  

Finally, contribute your findings and methodology back to the global knowledge base. Submit key results to the LEAP Publications Database, the IIASA GAINS publications archive, or the ABaCAS publications database, and share your data and methodology through the AQMx Resource Exchange Library. The global air quality management community advances through shared learning, and a jurisdiction that has reached Stage 5 has both the capacity and the responsibility to contribute to that shared knowledge base.