The Group recognised the difficulties involved in setting limit values for particles when the epidemiological studies had not demonstrated a no-effects threshold. However, the Group felt that limit values could be recommended at levels at which public health effects at the population level were likely to be small. On this basis the Group initially considered ranges of daily values of 30-100µgm-3 and 15- 40µgm-3 as an annual average. Drawing on studies in Europe and the US, and considering the WHO summary of exposure-response relationships the majority of the Group recommended a daily limit value of 50µgm-3 as a level at which public health.
