Figure 1. TDLAS HNO₃ spectrum, 1721.98 cm^-1 to 1722.2 cm^-1 acquired at Harvard Forest 8 October 1999. 4 hours worth of 15-second spectra have been co-averaged and ratioed against an averaged background spectrum. The fit corresponds to 345 ppt HNO₃. The sawtooth pattern in the unsmoothed spectrum does not significantly alter the retrieved concentration and is an artifact of the long average.