A group of organic compounds formed in incomplete combustion are Polycyclic Aromatic Hydrocarbons (PAH). Some PAH are found to be carcinogenic to animals and are thus potentially carcinogenic to humans. The most well-known PAH is benzo(a)pyrene (B(a)P), which is classified by International Agency for Research on Cancer (IARC, 1983; 1989) as 2A i.e. probably carcinogenic to humans. A way to compare individual PAH relative to each other with respect to cancer potency is to use Toxic Equivalence Factors (TEFs) of which the TEF for B(a)P is set to one by definition. Compounds with larger TEFs than one are more carcinogenic than B(a)P and vice versa. Some dibenzopyrenes reported in the scientific literature have TEF values in the range of 1 to 100 (Boström et al., 2002). A new developed analytical method for determination of B(a)P and highly carcinogenic dibenzopyrenes has been validated using Standard Reference Material (SRM) 1649a Urban dust, Washington air particles sampled 1976-1977, (Bergvall and Westerholm, 2005) and applied on Stockholm ambient air particulate material.