An Overview: Experimental Characterization of Biomass Burning Aerosols during EFEU

Vegetation fires are a significant source for atmospheric trace gases and aerosol particles on local, regional, and global scales. Vast fires regularly occur in the tropics as well as in the mid latitudes and boreal regions. Fire emissions and their reaction products are transported by convection into the free troposphere and therefore affect the energy budget of the atmosphere by direct and indirect radiation effects. Up to now there is only limited information on the physical and chemical properties of biomass burning aerosols which are partly responsible for the large uncertainties in quantifying the climatic impact of aerosols generally. Especially, the microphysical properties of the emitted aerosol particles have received little attention to date. This work gives detailed information of the methodology applied to experimentally characterize the physical and chemical properties of fresh (age: <10 minutes) biomass burning aerosols from various biomass fuels. In general, the chemical analysis of the samples show equal results for different fuel types. Submicrometer particles were mainly composed of organic carbon rather than by inorganic ions. Consequently, the hygroscopicity measurements performed at 85 % at various diameters show only slightly hygroscopic behaviour (about 5 to 15 % diameter growth) of the examined smoke particles. Furthermore, our observations show that the humidification growth in scattering properties of the fresh aerosols is relatively low (<15%) compared to ambient aerosols in natural vegetations fires. These results go along with relatively low CCN efficiencies (the ratio of CCN to total particle number concentration). The CCN efficiency from typical wood smoke particles gradually increased with particle size at a given S and particles of 250 nm or larger are normally completely activated at S = 0.2%. It was found that changes in aerosol properties were strongly dependent on the burning conditions. These conditions were characterized by the excess CO and CO2 ratio ((delta)CO/(delta)CO2). This dependence seems to be much stronger as changes due to the type of biofuel used for the different experiments. In particular, for increasing (delta)CO/(delta)CO2, i.e. more smoldering burning conditions, the mass specific absorption coefficient (σabs) decreased monotonically, while the single scattering albedo (ω0) increased.