Key questions for guidance of EU policies

To effectively advise the revision of European Union air quality policies, the WHO-led REVIHAAP and HRAPIE projects are addressing a list of 26 key questions, formulated by the European Commission and refined by the project Scientific Advisory Board. They cover four areas:

• Particulate matter (PM) - PM2.5 and PM10 (7 questions)
• Ground-level ozone (4 questions)
• Other air pollutants and their mixtures (10 questions)
• General questions (5 questions)

A. Particulate matter (PM) - PM2.5 and PM10

1. What new evidence on health effects has emerged since the review work done for the WHO Air Quality Guidelines published in 2005, particularly with regards to the strength of the evidence on the health impacts associated with exposure to PM2.5?   Based on this new information, do the scientific conclusions given in 2005 require revision?
2. What new health evidence is available on the role of other fractions/metrics of PM, such as smaller fractions (ultra-fines), black carbon, chemical constituents (metals, organics, in-organics, crustal material and PM of natural origin, primary/secondary) or source types (road traffic including non-tailpipe emissions, industry, waste processing …) or exposure times (e.g. individual or repeated short episodes of very high exposure, 1h, 24h, yearly)?  
3. EU legislation currently has a single limit value for exposure to PM2.5 which is based on an annual averaging period. Based on the currently available health evidence, is there a need for additional limit values (or target values) for the protection of health from exposures over shorter periods of time?
4. What health evidence is available to support an independent limit value for PM10 (in parallel to (i) an annual average limit for PM2.5 and (ii) multiple limits to protect from short term and long term exposures to PM2.5)?
5. EU legislation has a concentration limit value and an exposure reduction target for PM2.5. To decide whether it would be more effective to protect human health through exposure reduction targets rather than limit or target values it is important to understand (amongst other things, such as exposure, cost effectiveness, technical feasibility) the shape of the concentration-response functions.  What is the latest evidence on thresholds and linearity for PM2.5? 
6. Based on currently available health evidence, what PM metrics, health outcomes and concentration-response functions can be used for health impact assessment?
7. Are there critical data gaps to be filled to help answer the above questions more fully in future?

B. Ground-level ozone

The current target value for ozone in Directive 2008/50/EC is 120µg/m3 as the daily maximum 8-hour mean. This is less stringent than the guideline recommended by the WHO in its global update from 2005 (air quality guideline of 100µg/m3).

1. What new evidence on health effects has emerged since the review work done for the WHO Air Quality Guidelines published in 2005, particularly with regards to the strength of the evidence on the health impacts associated with short-term and long-term exposure to ozone?    
2. What new health evidence has been published in relation to the evidence or likeliness of a threshold below which impacts are not expected?
3. Based on currently available health evidence, what ozone metrics, health outcomes and concentration-response functions can be used for health impact assessment?
4. Is there evidence that other photochemical-oxidants (individually or in mixtures) are of public health concern e.g. does the impact of outdoor ozone on reaction products indoors explain the outdoor ozone associations, and links to the secondary organic aerosol?

C. Other air pollutants and their mixtures

1. There is evidence of increased health effects linked to proximity to roads.  What evidence is available that specific air pollutants or mixtures are responsible for such increases, taking into account co-exposures such as noise?
2. Is there any new evidence on the health effects of nitrogen dioxide (NO2) that impact upon the current limit values? Are long-term or short-term limit values justified on the grounds that NO2 affects human health directly, or is it linked to other co-emitted pollutants for which NO2 is an indicator substance?
3. Based on existing health evidence, what would be the most relevant exposure period for a short-term limit value for NO2?
4. Based on currently available health evidence, what NO2 metrics, health outcomes and concentration-response functions can be used for health impact assessment?
5. Is there any new evidence on the health effects of air emissions of arsenic, cadmium, mercury, lead and nickel (and their compounds), that would impact upon current target values?
6. Is there any new evidence on health effects due to air emissions of polycyclic aromatic hydrocarbons (PAHs) that would impact upon current target values?
7. Is there any new evidence on the health effects of short term (less than 1 day) exposures to sulphur dioxide (SO2) that would lead to changes of the WHO air quality guidelines based on 10 minute and daily averaging periods or the EU's air quality limit values based on hourly and daily averaging periods?
8. Are there important interactions amongst air pollutants in the induction of adverse health effects that should be considered in developing air quality policy?
9. Are there critical data gaps to be filled to help answer the above questions more fully in future?
10. What is the contribution of exposure to ambient air pollution to the total exposure of air pollutants covered by the regulations, considering exposures from indoor environments, commuting and work places?

D. General questions

1. What new information from epidemiological, toxicological and other relevant research on health impacts of air pollution has become available that may require a revision of the EU air quality policy and/or WHO air quality guidelines notably for particulate matter, ozone, nitrogen dioxide and sulphur dioxide?
2. What evidence is available directly assessing health benefits from reducing air pollution?
3. Is there evidence of new emerging issues on risks to health from air pollution, either related to specific source categories (e.g. transport, biomass combustion, metals industry, refineries, power production), specific gaseous pollutants or specific components of particulate matter (e.g. size-range like nano-particles and ultra-fines, rare-earth metals, black carbon (EC/OC))?
4. The 6th Environment Action Programme aims to "achieve levels of air quality that do not give rise to significant negative impacts on and risks to human health and the environment" (Article 7 (1) of Decision No. 1600/2002/EC). Is there evidence of a threshold in the concentration-response curves for PM2.5, ozone and NO2?
5. What concentration-response functions for key pollutants should be included in cost-benefit analysis supporting revision of EU air quality policy?