Concentrations of particulate and gaseous polycyclic aromatic hydrocarbons in London air following a reduction in the lead content of petrol in the United Kingdom.

The environmental importance of tropospheric polycyclic aromatic hydrocarbons (PAH) is reviewed. The impact of reducing lead on airborne PAH is indicated and the importance of monitoring both particulate and gaseous-phase PAH is demonstrated. A Brief description of a sampling regime performed from 1985 to 1987 is given. Sampling of 18 PAH was performed and particulate lead concentrations at the kerbside were measured concurrently. Measurements indicate that there is a pronounced seasonality in PAH concentrations and in the distribution of PAH between particulate and gaseous phases. On average, 47% of the PAH measured were in the gaseous phase, indicating the importance of measuring the volatile fraction. The dominance of the common variation of each PAH was also investigated using principal components analysis. An uneven spread of data prior to and following the reduction in lead content, hindered a thorough examination of the effect of this change on PAH concentrations. However, they appeared to indicate only a small change in PAH concentration and this was linked to an increase in aromatic content of the petrol, which was much less than expected.