Estimation of black carbon emissions from Siberian fires using satellite observations of absorption and extinction optical depths
Authors: Konovalov Igor B. , Lvova Daria A. , Beekmann Matthias , Jethva Hiren , Mikhailov Eugene F. , Paris Jean-Daniel , Belan Boris D. , Kozlov Valerii S. , Ciais Philippe , Andreae Meinrat O. 
Published: October 2018

Abstract. Black carbon (BC) emissions from open biomass burning (BB) are known to have
a considerable impact on the radiative budget of the atmosphere at both global and
regional scales; however, these emissions are poorly constrained in models by atmospheric
observations, especially in remote regions. Here, we investigate the
feasibility of constraining BC emissions from BB using satellite observations
of the aerosol absorption optical depth (AAOD) and the aerosol extinction
optical depth (AOD) retrieved from OMI (Ozone Monitoring Instrument) and
MODIS (Moderate Resolution Imaging Spectroradiometer) measurements,
respectively. We consider the case of Siberian BB BC emissions, which have
the strong potential to impact the Arctic climate system. Using aerosol remote
sensing data collected at Siberian sites of the AErosol RObotic NETwork
(AERONET) along with the results of the fourth Fire Lab at Missoula
Experiment (FLAME-4), we establish an empirical parameterization relating the
ratio of the elemental carbon (EC) and organic carbon (OC) contents in BB
aerosol to the ratio of AAOD and AOD at the wavelengths of the satellite
observations. Applying this parameterization to the BC and OC column amounts
simulated using the CHIMERE chemistry transport model, we optimize the
parameters of the BB emission model based on MODIS measurements of the fire
radiative power (FRP); we then obtain top-down optimized estimates of the total
monthly BB BC amounts emitted from intense Siberian fires that occurred from
May to September 2012. The top-down estimates are compared to the corresponding
values obtained using the Global Fire Emissions Database (GFED4) and the Fire
Emission Inventory–northern Eurasia (FEI-NE). Our simulations using the
optimized BB aerosol emissions are verified against AAOD and AOD data that
were withheld from the estimation procedure. The simulations are further
evaluated against in situ EC and OC measurements at the Zotino Tall Tower
Observatory (ZOTTO) and also against aircraft aerosol measurement data collected
in the framework of the Airborne Extensive Regional Observations in SIBeria (YAK-AEROSIB) experiments.
We conclude that our BC and OC emission estimates, considered with their confidence intervals, are
consistent with the ensemble of the measurement data analyzed in this study.
Siberian fires are found to emit 0.41±0.14 Tg of BC over the
whole 5-month period considered; this estimate is a factor of 2 larger
and a factor of 1.5 smaller than the corresponding estimates
based on the GFED4 (0.20 Tg) and FEI-NE (0.61 Tg) data,
respectively. Our estimates of monthly BC emissions are also found to be
larger than the BC amounts calculated using the GFED4 data and smaller than
those calculated using the FEI-NE data for any of the 5 months. Particularly
large positive differences of our monthly BC emission estimates with respect
to the GFED4 data are found in May and September. This finding indicates that
the GFED4 database is likely to strongly underestimate BC emissions from
agricultural burns and grass fires in Siberia. All of these differences have
important implications for climate change in the Arctic, as it is found that
about a quarter of the huge BB BC mass emitted in Siberia during the fire
season of 2012 was transported across the polar circle into the Arctic.
Overall, the results of our analysis indicate that a combination of the
available satellite observations of AAOD and AOD can provide the necessary
constraints on BB BC emissions.