Most of the adverse effects caused by air pollution can be attributed to frequent, moderate exposure to very fine particles, says a study sponsored by the French Agency for Sanitary Security and the Environment (AFSSET). Only a tiny percentage (3%) can be attributed to pollution peaks. The study suggests that in order to reduce exposure, tackling the sources of fine particles - wood combustion, coal and fuel burning - must be prioritised. In urban areas, transport is responsible for most fine pollution particles.