image increases proportionately with number of sampled pixels (Table 3). 



As seen in Tables 2 and 3, the area of emission (number of non-zero pixels) 

 resulting from 335 rmi excitation was typically 3X lower and 365 nm 2X higher than either 

 the 299 nm or 314 nm bands. Such differences may be related to the optical density of the 

 excitation filters and/or lamp intensity at the particular wavelength. The relatively low 

 number of non-zero pixels is attributed to low PAH signal in comparison to camera and 

 background noise. 



