Role of ammonia in the SO2 flux over a mixed forest

Johan Neirynck1
1 Environment and Climate, Research Institute for Nature and Forest

P 3.16 in Fluxes between the atmosphere and ecosystems

Poster Session 2 on Tuesday, 16:30-18:00

Long-term fluxes of sulphur dioxide (SO2) have been measured over a mixed suburban forest subjected to elevated ammonia (NH3) and SO2 concentrations.  During the measuring period 2000-2013, SO2 concentrations decreased from 14 to 3 µg m-3 whereas NH3 concentrations remained constant (3 µg m-3), leading to a decline in the SO2/NH3 ratio.

The deposition efficiency of SO2 depended both on canopy wetness (dry, dew, rain, frost) and SO2/NH3 ratio. Highest deposition efficiency (υd/υdmax) or lowest canopy resistance (Rc) were observed when canopy was dew- or rain-wetted and a low SO2/NH3 ratio was encountered.  During the summer half-year when surface acidity was low due to lower SO2/NH3 ratios, a higher deposition efficiency and a lower non-stomatal resistance (Rw) were observed compared to winter conditions. The canopy sink strength was further enhanced by high friction velocities (u*), optimizing the mechanical mixing into the canopy.

The measured canopy resistances were compared with the improved parameterizations of codeposition which were provided to EMEP/MSC-W and incorporated in the EMEP Eulerian CTM. An alternative approach to parameterize codeposition including the friction velocity and canopy wetness is suggested.

Letzte Änderung 19.06.2014