Determination of European methane emissions, using concentration and isotope measurements.

The determination of methane emissions on a regional scale is needed in order to reduce some of the uncertainties in the global methane budget. Our measurements of the concentration and the Carbon-13 isotope composition (δ(13)C) of atmospheric methane are, combined with trajectories, used to get insight in the type and size of the methane emissions of a large area.

Measurement of dry deposition of ammonia on a forest.

Ammonia concentration gradients above a Douglas fir canopy were measured from 16 August to 31 December 1989 by two automated high-precision thermodenuders at the location Speulderbos in The Netherlands. Concentration gradients were used to calculate the dry deposition flux of ammonia via flux-gradient theory. Meteorological data were obtained from a nearby tower. Ammonia concentrations were highly variable with highest values during the night. Concentration gradients were very small during daytime and quite large at night. Median values of the calculated deposition flux and deposition velocity were 0.1 microg m(-2) s(-1) and 3.2 cm s(-1) respectively (N=1624).