The gun may have a receiver element with a barrel extending forwardly from the receiver element with the barrel having a chamber end and a discharge end. The frame may be of a rectangular configuration, but it is to be understood that more complex configurations may be necessary for achieving a water proof connection to the structure in which the window is mounted or to a surrounding window frame. The method can optionally include forming the nucleic acid adduct. The sensing rod is shaped like the number 1 and has a plurality of sampling pores and two air passages. The keys of the first and second side surfaces are similarly shaped.