BEHAVIOR OF TRACE GAS MIXING RATIOS ON A VERY TALL TOWER IN NORTH-CAROLINA

We present a 15-month record of mixing ratios of CO, CH4, N2O, and eig ht halogenated gases (CCl3F, CCl2F2, CCl2FCClF2, CH3CCl3, CCl4, CHCl3, C2Cl4, and SF6) at a rural site in eastern North Carolina. The data r esult from hourly gas chromatographic analyses of air sampled at three heights on a 610-m-tall telecommunications tower during November 1994 through January 1996. At night, most of these gases were more abundan t near the ground (51 m) than aloft (496 m) because of the buildup of local and regional surface emissions in the shallow nocturnal stable l ayer. The abundance and variability of trace gases at this continental site were generally higher than those at similar latitude remote loca tions. Mixing ratios of most gases were well correlated in polluted ai r masses occasionally advected to the tower. Frequent, strong enhancem ents in CHCl3 at the lower sampling level(s) indicate a local point so urce(s) of this gas that is not associated with combustion. Temporal t rends of regional background mixing ratios at this continental site ar e, for the most part, in good agreement with recent trends of remote b ackground mixing ratios in the northern hemisphere.