A Simple Tiered Methodology for the Determination of Ambient Air Quality Guidelines

Within the scope of the renewal of industrial operating permits in Belgium, the Walloon Agency for Air and Climate needed air quality criteria for a wide range of toxics. Due to the plethora of different existing values for some compounds or the total lack for others, the development of a simple methodology was required to provide both quality and intervention criteria, corresponding respectively to a chemical concentration for which no adverse health effects are expected for a lifetime exposure, and the chemical concentration in air associated with a risk for human health deemed significant. The tiered methodology developed here allows the selection of air guidelines from available databases, and proposes, if needed, approaches based on well-proven procedures to derive air quality guidelines from occupational exposure limits, drinking water guidelines, tolerable daily intakes, or as a last resort acute lethal toxicity data if nothing else is available. If this method has been successfully applied to more than 550 compounds, all values produced should be validated according to the purpose of the guidelines, the technical feasibility of achieving the threshold produced, and the specificity of the environment conditions and the targeted population. Moreover, the criteria obtained from non-air-related data should be critically examined and handled with caution.