A WHO working group srutinized the evidence on air quality and health in Europe as the final stage of its systematic review with special focus on pollution from particulate matter, ozone and nitrogen dioxide. The findings will be provided to the European Commission’s Clean Air for Europe (CAFE) programme as a background for development of the European Union policy on clean air in the next decades.

"All over Europe, people’s health is at risk from air pollution. But governments need the latest robust, expert and objective evidence allowing them to adopt the most efficient ways to reduce the risk to population health” says Michal Krzyzanowski, of the WHO European Centre for Environment and health, Bonn Office, WHO/Europe. “This review will provide such evidence.”

The review covers:

• the type and severity of effects of pollution in the concentration range currently observed in Europe;
• factors determining individual susceptibility to pollution;
• specific characteristics of the pollution mix influencing the effects;
• evidence on health benefits of pollution reduction. 

Based on this review, the experts recommended to update parts of the present WHO air quality guidelines.

The review addressed initial questions from the CAFE steering group which were later refined by the scientific advisory committee of the WHO project, a system of literature review involving several research groups in Europe and the United States, and “consolidated documents” drafted by the scientific advisory committee providing concise answers. These answers were then themselves reviewed by external experts to judge their validity and clarity. The review focused on studies published after the second edition of the WHO air quality guidelines for Europe, 1996 which have been influential in changing views on the substances under consideration.

The WHO working group adopted a recommendation to use fine particulate matter, (PM2.5, particles < 2.5 µm), as indicator for pollution-induced health effects such as mortality, to supplement the commonly used PM10, which includes fine and coarse particles. It also accepted the evidence of short-term ozone effects on mortality and respiratory morbidity, even at low ozone concentrations. Based on these findings it was recommended that WHO should update its exposure-response relationships for the most severe health outcomes induced by PM and ozone. These relationships will subsequently be used to develop most effective strategies to combat air pollution in Europe. The working group also concluded that an update of the current WHO air quality guidelines for nitrogen dioxide, which is also an important precursor for the formation of ozone and particulate matter, was not warranted.