Toxicological studies have provided evidence of the toxicity of ultrafine particles, but epidemiological evidence for health effects of ultrafines is limited. No quantitative summary currently exists of concentration-response functions for ultrafine particles, that can be used in health impact assessmentii. The goal was to specify concentration response functions for ultrafine particles in urban air including their uncertainty through an expert panel elicitation.

Background: Exposurei to fine ambient particulate matter (PM) has consistently been associated
with increased morbidity and mortality. The relationship between exposure to ultrafine particles
(UFP) and health effects is less firmly established. If UFP cause health effects independently from
coarser fractions, this could affect health impact assessmentii of air pollution, which would possibly
lead to alternative policy options to be considered to reduce the disease burden of PM. Therefore,
we organized an expert elicitation workshop to assess the evidence for a causal relationship