One indicator of the impact of human activity on the environment is the increase in atmospheric concentrations of nitrogen oxides.  NO₂ is a pollutant that contributes to the formation of smog and can be hazardous to human health.  The nitrate radical (NO₃) also is an important nocturnal oxidizing agent.  Both are present at low concentrations in the atmosphere, and therefore, require fast yet sensitive detection apparatus for accurate NO_x measurement.  This poster identifies a sensitive and portable apparatus suitable for detection of trace amounts of NO_x in the field.

     Very few sensitive spectroscopic techniques are as sensitive and portable as cavity ring-down spectroscopy (CRDS).  This absorption technique is a simple but powerful optical technique.  The key to the sensitivity of this method is the use of highly reflective (R > 99.999%) cavity mirrors, which allow for effective pathlengths on the order of 10-50 km.

      In this poster, Nitrogen dioxide is experimentally detected at 70 ppbv at 670 nm with detection limit of 20 ppbv.  Preliminary work on NO₃ at 660 nm is presented.  Using CRDS, the potential to detect at least 1 pptv of NO₃ is discussed.