Physicochemical characterization of smoke aerosol during large-scale wildfires: Extreme event of August 2010 in Moscowстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 26 ноября 2014 г.
Аннотация:Enhancement of biomass burning-related research is essential for the assessment of large-scale wildfires
impact on pollution at regional and global scale. Starting since 6 August 2010 Moscow was covered with
thick smoke of unusually high PM10 and BC concentrations, considerably affected by huge forest and
peat fires around megacity. This work presents the first comprehensive physico-chemical characterization
of aerosols during extreme smoke event in Moscow in August 2010. Sampling was performed in the
Moscow center and suburb as well as one year later, in August 2011 during a period when no biomass
burning was observed. Small-scale experimental fires of regional biomass were conducted in the Moscow
region. Carbon content, functionalities of organic/inorganic compounds, tracers of biomass burning
(anhydrosaccharides), ionic composition, and structure of smoke were analyzed by thermal-optical
analysis, FTIR spectroscopy, liquid and ion chromatography, and electron microscopy. Carbonaceous
aerosol in August 2010 was dominated by organic species with elemental carbon (EC) as minor
component. High average OC/EC near 27.4 is found, comparable to smoke of regional biomass smoldering
fire, and exceeded 3 times the value observed in August 2011. Organic functionalities of Moscow smoke
aerosols were hydroxyl, aliphatic, aromatic, acid and non-acid carbonyl, and nitro compound groups,
almost all of them indicate wildfires around city as the source of smoke. The ratio of levoglucosan (LG) to
mannosan near 5 confirms the origin of smoke from coniferous forest fires around megacity. Low ratio of
LG/OC near 0.8% indicates the degradation of major molecular tracer of biomass burning in urban
environment. Total concentration of inorganic ions dominated by sulfates SO4
2 and ammonium NH4
þ
was found about 5 times higher during large-scale wildfires than in August 2011. Together with strong
sulfate and ammonium absorbance in smoke aerosols, these observations prove the formation of secondary
inorganic species associated with wildfire gaseous emissions and their transformation in agedsmoke. Accumulation of carbonyl compounds during extreme smoke event in Moscow resulted from
photochemical aging and secondary organic aerosol (SOA) formation in the urban atmosphere. The
mixture of carbonaceous particles and dust revealed multicomponent structure of Moscow smoke
aerosols, pointing the difference with non-smoke ambient aerosols. The abundance of group containing
soot and tar balls approached at least a half of total aerosol concentration during extreme event, relating
to elevated OC, EC and SOA. Fly ash groups contained calcium sulfates and carbonates from soil
entrainment by hot air convection. Small-scale open fire experiments support the identification of
specific chemical features of regional biomass burning and demonstrate the strong impact of large-scale
wildfires on aerosol chemistry and air quality in highly polluted megacity.