An assessment of Biomass Burning Aerosol Optical Properties over the
Mediterranean Basin based on Satellite Data
Abstract
The Mediterranean basin is characterized by the coexistence of various
aerosol types such us anthropogenic, desert dust, biomass burning (BB)
and background marine particles, with relatively high aerosol load
affecting the regional radiative budget. This diversity results in
complex aerosol properties with high temporal and spatial variability,
which is enhanced by the sporadic character of dust transport and
wildfire events. The impact of aerosol load on the regional or local
radiative budget is intensified during the summer cloud-free period due
to the intense solar radiation. During the warm period the Mediterranean
experiences the impact of BB emissions when forest and shrubland fires
occur due to favorable meteorological conditions. BB aerosols consisting
of two major components, black carbon which is the most absorbing
aerosol species and organic aerosols that scatters solar radiation, can
have a strong impact on the solar radiation budget, altering atmospheric
temperature lapse rates and dynamics over a region. In this work an
assessment of temporal variability and spatial distribution of biomass
burning aerosol optical properties over the broader Mediterranean basin
for the period 2002-2016 is conducted. To that end satellite databases
are used. At first, wildfire events are identified in terms of ignition
date and geographical location based on MODIS (MODerate resolution
Imaging Spectroradiometer) collection 006 data. For our analysis
wildfires with a burned area of at least 500ha are considered. Then, for
each event aerosol optical properties namely spectral AOD, Ångström
Exponent (AE), Fine Fraction (FF) and Aerosol Index (AI), that describe
the atmospheric load and size of BB aerosols, are assessed. The relevant
data are derived from Collection 006 MODIS - Terra database, except for
AI which is taken from TOMS (Total Ozone Mapping Spectrometer) and
OMI-Aura (Ozone Monitoring Instrument) databases for the periods
2002-2004 and 2005-2016, respectively. The spatial distribution and the
inter-annual variability of BB aerosol optical properties are analyzed.
The AI values are greater than 2 with maxima attaining 4.3. Ångström
Exponent presents a mean value around 1.5 with maxima exceeding 2.5,
whereas mean value of FF is about 0.84. AOD (AOD550) can reach values up
to 3.3. For selected large wildfire events (mega-fires) the spatial
expansion of smoke plume is estimated through forward - trajectories
using the HYSPLIT (Hybrid Single Particle Lagrangian Integrated
Trajectory Model) model and then BB aerosol properties are calculated
over areas affected by the smoke.