Chemical characterization of atmospheric aerosols presents a serious analytical challenge because of the complexity of particulate matter analyte composed of a large number of compounds with a wide range of molecular structures, physico-chemical properties, and reactivity. In this study the chemical composition of the organic constituents of biomass burning aerosol (BBA) samples is characterized by high-resolution electrospray ionization mass spectrometry (ESI/MS). Accurate mass measurement combined with Kendrick analysis allows assignment of the elemental composition for hundreds of compounds in the range of m/z values of 50-1000. ESI/MS spectra of different BBA samples contain a variety of distinct, sample specific, characteristic peaks that can be used as unique markers for different types of biofuels. Our results indicate that a significant number of high-MW organic compounds in BBA samples are highly oxidized polar species that can be efficiently detected using ESI/MS but are difficult to observe using conventional gas-chromatography/mass spectrometry analysis of aerosol samples. More than 70% of the identified species have not been reported in the literature. Detected organic compounds show a clear increase in the degree of saturation as the molecular weight of the analyte molecules increases. The increase is particularly pronounced for the samples containing a large number of the CH(2)-based homologous series.