“…However, vehicles remain a major source of nitrogen oxides (NO x ), carbon monoxide (CO), hydrocarbons (HC), particulate matter (PM) and polycyclic aromatic hydrocarbon (PAH) emissions, and many researchers have suggested that mobile sources are the major contributor in urban and suburban environments (Lin et al, 2006a, b, c;Tsai et al, 2010a, b;Wu et al, 2010;Hsieh et al, 2011a, b;Karavalakis et al, 2011;Kim et al, 2011;Li et al, 2011;Shen et al, 2011;Srivastava et al, 2011;Yao et al, 2011;Cheng et al, 2012a, b;Lai et al, 2012;Liang et al, 2012;Liu et al, 2012;Pilusa et al, 2012;Tsai et al, 2012;Wang et al, 2012).…”