Until 1967, about 106 PAH were identified in pit coal tar (K. F. Lang, 1967) , 280 PAH in cigarette smoke (R.L. Snook et. al., 1976) and later, 146 PAH in automobile exhaust (G. Grimmer, 1977), 108 in exhaust from fuel oil , 150 PAH in mineral oil samples on the basis of their characteristic mass and U.V. spectra. Lao et al, 1973 and Lee at et al, 1976 identified 124 and 122 peaks in gas chromatogram of PAH content of airborne particulate matter. Sawaicki et al, 1960 examined BaP content of air in 137 urban and non urban areas of the U.S. in large cities, the highest levels of BaP occurred during summer. Concentration of BaP in the air of non urban areas ranged from 0.01 to 1.9 ng/m³, while concentration in Urban areas ranged from 0.1 to 61.0 ng/m³.Gorden et.al.,1976, reported the annual geometric mean concentration of 15 PAH in air samples collected from 13 areas in Los Angeles, to be 10 g ng/m³, BaP accounted for only 4.2% of the total PAH.

In USA in the 1970s the annual figure of BaP in urban areas without coke-oven was less than 1 ng/m3, In several European cities in the 1960s the annual average concentration of BaP was higher than 100 ng/m³. However the concentration of BaP in large cities of UK such as London have fallen to only few percent of former value over past 30 years as a result of controls on smoke emission and the virtual disappearance of the open coal fire for domestic heating purposes.

Kuniko,1988, measured the BaP and PAH in air borne particulates near a high way in Tokyo, Japan during Dec. 22-21, 1984 within 60m radium from a crossing point of two high ways. The SPM concentration was 15 to 396 m g/m³. The concentration of BaP and B(ghi)P were 3.46-15.0g and 3.83-15.21 ng/m³. The BaP concentration in precipitated dust was 149-130 ng/g. Takada et al, 1991, have identified 63 PAH in street dust in Tokyo, Japan. The sum of these PAH was in the range of 3.20 m g/g (residential street to 8.16 µg/g Heavily trafficked street).

A. Molecular Weight B. Human Carcinogenicity according to IARC. Group 2A: Possibly carcinogenic Group 3 : not classifiable C. Yearly geometic mean of quarterly geometric means for all areas. D. Mean value in Summer (left column) and Winter. E. Minimum – Maximum value f seven Season means.. Range of means at five sites. G. Median value in summer (left column) and winter. H. Annual average I. Mean. J. CHR reported but should include TR (GC peaks can not be resolved).K. Isomer not specified L. Minimum – Maximum value of two years seasonal means combined at five sites (Min. during Monsoon and Max. during Winter season)

(Source: Tyagi, S.K. (1994). Methodological aspects of measuring polycyclic aromatic hydrocarbons (PAHs) in the urban atmosphere, Int. Chem. Environ Res. Vol. 3 & 4 : 165-176)