Both the World Health Organization and the UK Expert Panel on Air Quality Standards (EPAQS) have
considered benzo(a)pyrene (BaP) as a marker of the carcinogenic potency of the polycyclic aromatic
hydrocarbons (PAH) mixture, when recommending their respective guidelines for PAHs in outdoor air. The
aim of this research is to compare the concentrations and relative abundance of individual PAH and their
contribution to the overall carcinogenic potential of the PAH mixture in indoor and outdoor environments to
assess the suitability of the UK air quality standard derived for outdoor air for use as a guideline for indoor
environments. Samples were collected onto filters using active sampling in different indoor and outdoor
microenvironments. The ratio of individual compounds to BaP, the BaP equivalent concentrations and the
percentage contribution of each individual compound to the total carcinogenic potential of the PAH mixture
were calculated. Mean concentrations were generally lower indoors (BaP= 0.10 ng/m3
) than outdoors
(BaP= 0.19 ng/m3
), with the exception of indoor environments with wood burners (BaP= 2.4 ng/m3
) or ETS
(BaP= 0.6 ng/m3
). The ratio of individual PAHs to BaP showed no significant differences between indoors
(e.g. DahA/BaP= 0.27) and outdoors (DahA/BaP= 0.31). The relative contribution of BaP to the PAH overall
carcinogenic potency is similar indoors (49%), outdoors (54%) and in the smelter environment (48%) used by
EPAQS to derive the UK Air Quality Standard for ambient air. These results suggest the suitability of BaP as a
marker for the carcinogenic potential of the PAH mixture irrespective of the environment. Despite small
differences in PAH mixture composition indoors and outdoors, the level of protection afforded by the present
EPAQS standard is likely to be similar whether it is applied to indoor or outdoor air.