The Fourth Air Quality Daughter Directive: Impacts and Consequences of mandatory limits

A briefing on the European Commission Proposal for a Fourth Daughter Directive to the Air Framework Directive (COM (2003) 423).

The European Commission has presented a proposal for a Directive relating to arsenic, cadmium, mercury, nickel and polycyclic aromatic hydrocarbons (PAHs) in ambient air. Unlike the three previous ‘daughter’ Directives to the Air Quality Framework Directive, this proposal does not contain any mandatory limit values for the concentrations of the pollutants. The European Parliament’s Environment Committee has voted in favour of amendments which would introduce such limit values in the Directive, in accordance with the Framework Directive’s requirements and the recommendations of the Commission’s Working Groups.

The main reason to regulate ambient air concentrations of arsenic, cadmium, nickel and PAHs is their impact on human health (for mercury, ambient air concentrations in Europe are below a level where they have adverse effects on human health). Given the evidence of the carcinogenic effects of these substances, it seems obvious that limit values are called for. These should be based on unit risk factors, reflecting the fact that there is no known threshold below which the substances have no impact on human health. It is likely that such values would also ensure adequate protection as regards other health impacts, as well as to crops and ecosystems.