Fluxes of ozone and nitrogen dioxide measured by eddy correlation over a harvested wheat field

Flux measurements of O-3 and NO2 were made at Scherzheim in the so-called nested area of the TRACT experiment. The nested area consisted mainly of agricultural terrain with patches of forest. The flux measurements at Scherzheim were made by applying the eddy-correlation technique over a field which had been harvested and then covered with re-grown wheat. The total resistance to deposition was calculated and subdivided into aerodynamic, laminar boundary-layer and surface resistance. The results were related to diffent fetch conditions. A clear diurnal variation was found for fluxes as well as deposition velocities and resistances which indicated stomatal activity as a regulating factor. The fluxes were highest during the early afternoon with maximum fluxes of -0.6 mu g O-3 m(-2) s(-1) and -0.2 mu g NO2 m(-2) s(-1). The average daily maximum deposition velocity of O-3 was 0.5 cm s(-1) and of NO2 0.35 cm s(-1). Surface resistances (r(c)) to O-3 uptake were up to 600 s m(-1) during nighttime and 200 s m(-1) during daytime. r(c)'s to NO2 were even higher; 800-1000 s m(-1) during the night and 200-400 s m(-1) during the day. (C) 1998 Elsevier Science Ltd. All rights reserved.