RELATIONSHIPS BETWEEN ORGANIC NITRATES AND SURFACE OZONE DESTRUCTION DURING POLAR SUNRISE EXPERIMENT 1992

Concurrent measurements of total reactive odd nitrogen species (i.e., NOy) and its major components, including organic nitrates, were carrie d out during 1992 Polar Sunrise Experiment (PSE92) at Alert, Northwest Territories, Canada, to investigate the episodic depletion of surface level ozone following polar sunrise. A series of C-3-C-7 alkyl nitrat es formed from the atmospheric oxidation of hydrocarbons was measured daily during the 13-week study period (January 22 to April 22). In add ition, a large number of gas chromatography/electron capture detector (GC/ECD) peaks with retention times greater than those of the hexyl ni trates were also identified as species containing -ONO2 group(s), usin g a nitrogen specific detector. The total concentrations of these orga nic nitrates ranged from 34 to 128 parts per trillion by volume and th e distribution in the dark period was found to be similar to that foun d for rural lower-latitude air masses. In contrast to observations mad e at lower latitudes where alkyl nitrates make a relatively small cont ribution to NOy, the organic nitrates at Alert were found to contribut e between 7 and 20% of the total odd nitrogen species. After polar sun rise the total concentrations of these organic nitrates decreased stea dily, due primarily to the consumption of larger (>C-4) alkyl nitrates . The C-3 alkyl nitrate concentrations showed little variation during this study. During ozone depletion episodes in April there was a posit ive correlation between the concentration of the larger organic nitrat es and ozone. Most surprisingly, the ratio of concentrations of isomer ic alkyl nitrates with carbon numbers greater than or equal to 5, and in particular those involving the C-5 isomers, was found to show subst antial variations coinciding with the O-3 depletion events. This chang e in the isomeric alkyl nitrate ratios implies a substantial chemical processing of the air masses exhibiting ozone depletion. The possible mechanisms, which must involve consumption of the organic nitrates by either OH radicals or Cl atoms, are discussed in the context of the ch emical and meteorological observations conducted at Alert during these ozone depletion events.