Temporal and spatial variation of forest VOC emissions in Germany in the decade 1994–2003

Biogenic emissions are strongly governed by temperature and light. One key issue for air quality modelling is to quantify the emission source strength variation of biogenic volatile organic compounds (BVOC) on different temporal and spatial scales. In Germany, this variation has been investigated for forests (the major source of BVOC) at country, state, and local scales over 10 years. Hourly emission rates for each vegetation period (April to October) from 1994 until 2003 were calculated in 10 km resolution. A database was compiled containing land cover, forest distribution, foliar biomass density, leaf area index (LAI) and plant specific emission potential. Meteorological input parameters were obtained using the non-hydrostatic meteorological mesoscale model MM5. The semi-empirical BVOC model (seBVOC) uses these parameters as input. SeBVOC considers in addition seasonality of the emission potentials, light extinction within the canopy as well as leaf temperature, air humidity, wind speed, and solar angle. The results show an average BVOC emission of 366 Gg, with 40 Gg isoprene, 188 Gg monoterpenes, and 138 Gg other VOC (OVOC), for the period 1994–2003. The dominating emitter type is Norway spruce (Picea abies  ) contributing approximately 40% to the total BVOC. In the years 1994–2003, the annual BVOC emissions varied in the range of ±20%±20%. However, in specific episodes and at specific locations the variation is as high as 150% compared to average emissions. Also the BVOC composition emitted is location specific. Using a sensitivity analysis, the contribution of uncertainties in estimating foliar biomass, emission potential, as well as temperature to the overall uncertainty of calculated potential surface BVOC emission rates is addressed.