Outdoor wildfire releases different types of pollutants into the atmosphere including Polycyclic Aromatic Hydrocarbons (PAHs), which pose significant risks to both human health and the environment. PAHs are a broad group of organic compounds of carbon and hydrogen atoms, fused into two or more rings. 16 different types of PAHs have been classified as carcinogenic by the US Environmental Protection Agency (USEPA). The project aims to investigate the effect of PAH ring size on the structure and stability in gas and solvent phases using first-principles density functional theory (DFT) calculations. In our study, we considered the 16 PAHs classified by the USEPA with ring sizes varying from 2-6. DFT functionals namely, _B97x-D, PBE-D2, and B97D3 that include the van der Waals dispersion interactions along with B3LYP and a triple-zeta basis set 6-31G(d,p) were considered to compare the role of DFT functionals in predicting PAHs stability and to ascertain the optimal level of theory for studying such systems. We find that, as the ring size or hydrogen-to-carbon (H:C) ratio of PAH increases, the energy gap decreases, and this affects the overall stability/reactivity of the molecule. The stability of PAHs increases with an increase in ring size and PAHs with smaller rings (e.g., naphthalene with two aromatic rings) are more reactive due to their increased strain energy and the potential for forming strained intermediates during reactions. Detailed analysis of the PAHs' structural properties, energy gap, dipole moment, and optical properties were performed to support our findings. The electron conjugation within the PAHs was further analyzed using frontier molecular orbitals. The results from this study will extend our understanding of the role of PAH ring size on molecular stability and help propose PAHs as promising candidates for sensing applications using graphene-based nanomaterials, which constitute the future direction of research.