ALKYL NITRATE AND SELECTED HALOCARBON MEASUREMENTS AT MAUNA-LOA-OBSERVATORY, HAWAII

Measurements of greater-than-or-equal-to C3 alkyl nitrates, perchlorethylene, and bromoform were made during the Mauna Loa Observatory Photochemistry Experiment (MLOPEX). The median mixing ratios of these compounds in free tropospheric air (3.4 km) were 2.3, 3.2, and .20 pptv, respectively. A diurnal variation in the concentration of these compound at Mauna Loa was driven by the local upslope/downslope circulation and by differences in the concentration of these species between the boundary layer and the free troposphere. Longer tem variation was closely related to synoptic-scale circulation of the North Pacific and to differences in the sources of air masses reaching Hawaii. Alkyl nitrates and their hydrocarbon precursors were present in nearly constant proportions during the experiment. This suggested the possibility that nitrate:hydrocarbon ratios may be determined near source regions and remain steady during long-range transport. Reasonable correlation was observed also between alkyl nitrates and peroxyacetyl nitrate (PAN), but a more complex relationship was found between methyl and higher alkyl nitrates. In general, greater-than-or-equal-to C3 alkyl nitrates were a significant component of the organic nitrate reservoir at Mauna Loa. However, greater-than-or-equal-to C3 alkyl nitrates only accounted for <2% of total NO(y). This evidence suggests that simple alkyl nitrates are not the source of "missing" odd nitrogen in the remote atmosphere.