PAH levels in the air depend on the area—with levels higher in urban areas than in the countryside—and the season—with greater amounts in the winter than in the summer. Because PAHs are always mixtures of different substances, BaP is often used as an indicator of the total amount of PAHs.

BaP and PAHs in tobacco smoke

PAHs, including BaP, also occur in tobacco smoke. They are not present in the tobacco itself but are mostly produced as the tobacco burns. To some extent, the amount of PAKs in tobacco smoke is also affected by the way the tobacco is dried (by smoking or the sun). PAH levels in tobacco smoke also differ between different types and origins of tobacco. 

Adverse health effects

Exposure to PAHs while smoking is one of the most important causes of cancer. This is partially due to the high exposure. In the body, enzymes break down PAHs, enabling them to damage DNA. If this damage is not repaired, this can lead to the development of cancer, especially in the airways. Additionally, PAHs can stimulate the growth of cells with damaged DNA, which in turn can lead to the formation of a cancerous tumour. BaP has been classified by the International Agency for Research on Cancer (IARC) as ‘carcinogenic to humans’ (Group 1). 

Sources
International Agency for Research on Cancer (IARC) 1
International Agency for Research on Cancer (IARC) 2

Agency for Toxic Substances and Disease Registry (ATSDR)

Y.S. Ding, L. Zhang, R.B. Jain, N. Jain, R.Y. Wang, D.L. Ashley, and C.H. Watson, Levels of Tobacco-Specific Nitrosamines and Polycyclic Aromatic Hydrocarbons in Mainstream Smoke from Different Tobacco Varieties Cancer Epidemiol Biomarkers Prev 2008;17(12):3366-71