Polycyclic aromatic hydrocarbons (PAH) are ubiquitous compounds produced through incomplete combustion processes from various sources in different proportions. They are of concern because of their recognized mutagenic and carcinogenic properties. There are a number of receptor modelling (RM) studies that identify sources of urban atmospheric PAH, despite concerns over the application of RM to the relatively reactive PAH. This thesis utilizes Positive Matrix Factorization (PMF) with extensive PAH datasets, and compares the results with local and national emission inventories. An atmospheric chemical reactivity study for PAH is also investigated; highlighting the importance of taking reactivity into consideration when applying source apportionment models. The results demonstrate that traffic sources are significantly responsible for the PAH mass (∑PAH) at UK urban sites throughout the year. A substantial fraction of benzo[a]pyrene emissions was apportioned to solid fossil fuel combustion sources, showing significant seasonal variations. A conceptual simulation of PAH ratios has been investigated using urban and rural data. Results were in good agreement between simulated ratios and empirically obtained values. The results provide a better understanding of PAH reactivity and their atmospheric fate, indicating the potential for long-range transport of high molecular weight PAH.