  In this study, we demonstrated the direct use of an inherently narrowband
backward wave in the mid-infrared for CO$_2$ and H$_2$O vapor spectroscopy in
ambient air. This wave is generated in a backward wave optical parametric
oscillator (BWOPO) pumped by a multi longitudinal mode laser at 1030 nm,
eliminating the need for additional spectral narrowing or wavelength
stabilization. A full characterization of the source is presented, revealing a
central output at 2712 nm, showcasing temperature tuning of -1.77 GHz/K, and
achieving an output pulse energy of 2.3 $\mu$J. Novel methods are introduced
for measuring the linewidth and wavelength stability using lab air. These
approaches demonstrate a narrow output of 43 pm and establish an upper limit of
stability at 65 MHz, with no active means of stabilization. These findings
underscore the potential of BWOPOs as a robust platform for future DIAL
systems.
