ИСТИНА

A better understanding of aerosol emissions from Siberian boreal forest fires is crucial, as they exert critical environmental and climate impacts in subarctic regions and the Arctic. The ability of biomass burning aerosol to absorb/scatter incoming radiation as well as act as cloud condensation nuclei strongly depends on microphysical, chemical and hygroscopic particle characteristics, for which a comprehensive regional database does not exist to date. In this work small-scale combustion experiments were performed with the purpose to fill the gaps in available data on particulate emissions from Siberian boreal forest fires. Typical regional biomass species, pine and debris, were burned in a Large Aerosol Chamber (LAC) under controlled combustion conditions representative of wildfires and prescribed burns. Comprehensive physico-chemical characterization of smoke aerosols are performed, including morphology, elemental composition, carbon and ion content, organic/inorganic functionalities, and selected organic compounds. Individual particle analysis of smoke morphology and elemental composition reveals the strong dependence on combustion temperature, indicating the dominant abundance of soot agglomerates at flaming versus roughly spherical organic particles at smoldering phase. Similarly, smoldering emissions are characterized by very low EC content (0.4% of PM mass) and high OC/EC ratios (62-194), while flaming emissions contain around 10% of EC and have OC/EC ratios in the range 0.32-0.57. Calcium and potassium combined with sulfates, chlorides, phosphates, and nitrates compose inorganic salts found dominantly at flaming while the low temperatures during the smoldering phase are not sufficient for salt formation. Both flaming and smoldering smoke aerosols are characterized by high levoglucosan concentration (up to 25% of PM mass), confirming levoglucosan as a good molecular marker for Siberian boreal forest wood burning. The ratio of levoglucosan/mannosan ~ 2-4 is found as an indicator of softwood burning. This study shows the importance of obtaining the chemical characteristics for dominant PM components in order to enable the assessment of contributions from Siberian biomass burning to atmospheric pollution and the aerosol/climate system.