Wintertime ozone fluxes and profiles above a subalpine spruce-fir forest

High rural concentrations of ozone (O-3) are thought to he stratospheric in origin, advected from upwind urban sources, or photochemically generated l ocally by natural trace gas emissions. Ozone is known to be transported ver tically downward from the above-canopy atmospheric surface laver and destro yed within stomata or on other biological and mineral surfaces. However, he re the authors report midwinter eddy correlation measurements of upward ver tical O-3 flux of 0.2 mu g m(-2) s(-1) (5.6 kg km(-2) day(-1)) above a suba lpine canopy of Picea engelmannii and Abies lasiocarpa in the Snowy Range M ountains of Wyoming. Simultaneous below-canopy upward fluxes reached 0.1 mu g m(-2) s(-1). These results corroborate similar late winter (presnowmelt) upward O-3 fluxes of 0.5 mu g m(-2) s(-1) (19 kg km(-2) day(-1)) taken at the same site in 1992. Profile results show sustained "countergradient" flu xes below the canopy and sustained "with gradient" fluxes above the canopy. Ozone concentrations that decrease for several hours to several days corre spond to simultaneously increasing positive (upward) O-3 fluxes and vice ve rsa. These phenomena. in addition to above- and below-canopy reversed gradi ent patterns, suggest that O-3 may be stored temporarily in either the snow base or the tree stand itself.