Long Path Tropospheric Absorption Measurements using the NOAA Fritz Peak FTS

In 1993, a high resolution (.0034 cm-1) FTS was developed at Fritz Peak Observatory (18 km west of Boulder, CO) to provide CO abundance measurements for an OH intercomparison campaign. These measurements made use of a 121-element retroreflector array situated near Caribou Mine 10.3 km away, giving a total optical path of 20.6 km at a mean height of about 2.8 km above sea level (see Figure). Recently, the instrument has been used for a general survey of tropospheric absorbance in this mountain airmass, which is relatively clean during times of westerly airflow but may show significant pollution during times of easterly upslope flow from the Front Range urban corridor. These measurements were primarily in the 4000-6700 cm-1 region. The new principles involved in the design of this instrument have already been published1, and more details will appear later; here we will discuss some preliminary results.