OBSERVATIONS OF PEROXYACETYL NITRATE, PEROXYPROPIONYL NITRATE, METHYL NITRATE AND OZONE DURING THE MAUNA-LOA-OBSERVATORY PHOTOCHEMISTRY EXPERIMENT

Measurements of the title species were made during the Mauna Loa Observatory Photochemistry Experiment (MLOPEX) conducted between May 1 and June 4, 1988, at the Geophysical Monitoring for Climatic Change (GMCC) station at 3.4-km elevation on the Island of Hawaii. Diurnal changes in the organic nitrates primarily resulted from the transition between downslope flow (usually free tropospheric air) and upslope flow (marine boundary layer or a mix of marine boundary layer and free tropospheric air, both influenced by island sources of precursors) characteristic of the site. Longer term trends in the mixing ratios reflected changes in air mass origins from mid-latitudes to more tropical latitudes. The average mixing ratios in free tropospheric samples were peroxyacetyl nitrate (PAN, 17 pptv), peroxypropionyl nitrate (PPN, 0.3 pptv), methyl nitrate (MN, 4 pptv), and O3 (43 ppbv). The organic nitrates (PAN, PPN, MN) represent minor components of the total odd nitrogen budget at the site. In free tropospheric samples, PAN, PPN, and MN constituted average percentages of 7%, <1%, and 2% of total odd nitrogen. In more tropical air masses, MN could constitute as much as 10% of total odd nitrogen. A photochemical model is used to investigate the sensitivity of free tropospheric PAN to local precursor concentrations. The observed mixing ratios of PAN are also contrasted with measurements made at continental surface sites and during aircraft programs.