VEDAIR – an internet tool for air quality calculations in residential areas with small scale woodcombustion.

Typ: Rapport
Författare: Gunnar Omstedt


This report describes a new internet tool for evaluation of air quality in residential areas with small scale wood-combustion. The work has been sponsored by the Swedish Energy Agency and the internet tool is called VEDAIR. The background is a four-year’s research program (2001-2004) called Biomass Combustion Health and Environment. Some conclusions from this program were that emissions from small scale wood-combustion can influence human health manly due to high emitting old wood stoves during cold whether conditions and that the air quality in such areas can improve significantly if old wood stoves were replaced by modern wood boilers attached to a storage tank or with a pellet boiler. The VEDAIR system is based on a combination of pre-calculated concentrations from models of larger (regional and urban) scales and direct model calculations from local scale. It is based on similar methods as SIMAIR [3b], which is an internet tool for air quality calculations from traffic. The main differences are the treatments of emissions and dispersion on local scale. VEDAIR uses two different dispersion models on local scale, one for point sources [17, 18] and one for line sources. They are modern Gaussian plume models, based on boundary layer scaling. Dispersion processes are described in terms of basic boundary-layer scaling parameters such as friction velocity, Monin-Obukhov length and the convective velocity scale. Meteorological data are taken from the routine operated MESAN system [12]. All available measurements from both manual and automatic stations, including radar and satellite information, are analyzed on a 11x11 km grid over Sweden. An emission model for small scale biomass combustion is connected to the local point source model. The following components are included: emission types, emission factors, start and running phases, storage tank and size. Input data are type of boilers and/or stoves, yearly energy consumption divided into share of oil, pellets, wood, wood chips or electricity, storage tank and size. The time variations of the emissions can be dependent on social factors as well as variations due to energy consumption. For the later a method using heating degree hours is used, for each hour the difference between outdoor and indoor temperatures is calculated and related to energy consumption. Urban background concentrations are simulated on a 1x1 km grid using two different model approaches. Emissions are taken from SMED (Database for Swedish Emissions to the Environment). For ground level sources such as small scale wood-combustion and traffic, an urban dispersion model similar to the one developed for Copenhagen [16] is used. For larger point sources a Gaussian plume model [17, 18] is used. Regional background concentrations are simulated by the MATCH model [15]. The contributions from sources outside Sweden and inside Sweden are analysed together with measurements from rural stations using two versions of the model, MATCH Europe and MATCH Sweden. Measurement data from three rural stations in southern, middle and north Sweden are used to support the PM10 model calculations. This is necessary as the model does not include secondary organic aerosol formation and would otherwise sub estimate PM10 levels. Comparison of measured and calculated concentrations of PM10 are done in Lycksele a small town with about 9000 inhabitants situated in the inland of northern Sweden (N64.6 E18.7). Measurements have been done during two winter periods, the first during December 2001 to Mars 2002 and the other during January 2006 to Mars 2006. Both periods shows strong variations of PM10 concentrations due to temperature. During cold conditions (temperatures below -10 ºC) the local contributions were large and during warmer conditions the local contributions were small. VEDAIR describes these variations rather well.