Concentrations of carbon monoxide and methane at two heights above a grassfield and their deposition onto the field

To investigate whether wind is a significant driving force in the diffusion of CO and CH4 from the atmosphere into soil, we measured the concentration s of these two gases at two heights above a temperate grass field in Japan and estimated their deposition velocities using micrometeorological techniq ues. The concentrations were inversely correlated with wind speed, indicati ng that the local concentrations were influenced by ground sources. The CO and CH4 concentrations at 0.33 m were usually lower than those at 1.3 m. Al though nocturnal data are suspected to be non-stationary, by selecting seve ral periods when the changes of the concentrations were small but larger th an analytical precision, we obtained a CO velocity of 2.9 and 3.9 x 10(-2) cm s(-1), agreeing with a CO deposition velocity, 3.4 x 10(-2) cm s(-1), ob tained by applying a method using CO2 as a tracer. The CH4 influx obtained by the method using CO2 as a tracer was 13 ng m(-2) s(-1). The ranges of th e CO deposition velocity and CH4 influx were similar to those obtained in p revious studies in grassfields and in a nearby arable field using a closed- chamber technique. This shows that light winds do not greatly accelerate CO and CHS uptake by soil. (C) 2000 Elsevier Science Ltd. All rights reserved .