• Nocturnal Processing Of Nitrogen Oxide Pollution At High Latitudes: Off-Axis Cavity Ring-Down Spectroscopy Method Development And Field Measurement Results

      Apodaca, Randy Lee; Simpson, William (2008)
      Nitrogen oxides, or NOx, play a central role in ozone and nitric acid (HNO3) pollution in the troposphere. Reactions of nitrate radical (NO3) and dinitrogen pentoxide (N2O 5) result in the removal of NOx and ozone from the nighttime atmosphere. In this thesis, we describe the configuration, operation, and performance of an off-axis cavity ring-down spectroscopy (oa-CRDS) field instrument designed for measuring NO3 and N2O5. Furthermore, we report results of an N2O5 instrument intercomparison conducted using an atmospheric simulation chamber in Julich, Germany. The results of the intercomparison demonstrate that the oa-CRDS instrument is an excellent tool for measuring NO3 and N2O 5. Also reported in this thesis are the results of two field campaigns aimed at characterizing NOx removal from the nocturnal pollution plume arising from Fairbanks, AK. The results from the field campaigns suggest ice is responsible for catalyzing N2O5 heterogeneous hydrolysis in cold, high-latitude plumes. When air masses are sub-saturated with respect to ice, the data show longer lifetimes (∼20 minutes) and elevated N2O5 levels while ice-saturated air masses show shorter lifetimes (∼6 minutes) and suppressed N2O 5 levels. Lastly, we present vertical profiles of N2O 5 measured above the seasonal snow pack. The results of the profiling studies suggest that N2O5 can be removed by heterogeneous hydrolysis on ice in the snow pack. Our findings indicate that catalysis on ice surfaces is largely responsible for nocturnal processing of N2O 5 leading to nitric acid production and loss of NOx in high latitude plumes.