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Absorption Spectroscopy (DOAS) method, based on Beer-Lambert
s law. Here, we
use SCDs from an improved NO
2
retrieval for GOME-2 (Richter et al.
2011
).
In the second step, the reference sector method (Richter and Burrows
2002
) and
simulated stratospheric pro
'
les (Hilboll et al.
2013
) are used for removing the
stratospheric part from the NO
2
SCDs over tropical/subtropical regions and over
boreal regions, respectively.
Thirdly, measurements with cloud fraction greater than 0.2 are removed via
cloud screening by using the improved version of the Fast REtrieval Scheme for
Clouds from the Oxygen A-band (FRESCO+) algorithm (Wang et al.
2008
).
Finally, the tropospheric SCDs are converted into TVC NO
2
by applying airmass
factors (AMFs), which are derived using the radiative transfer model SCIATRAN
(Rozanov et al.
2005
) by taking into account the viewing geometry and scattering,
absorption, and re
s surface. Monthly
means of TVC NO
2
between 2007 and 2011 (tropical and subtropical regions) and for
the period 2007
fl
ection within the atmosphere and the Earth
'
2012 (boreal regions) are binned to a horizontal resolution of 1
×
1
°
.
-
2.2 Satellite Measurements of FRP
Accordingly, monthly data of FRP (Kaufman et al.
1998
) from the MODIS
instrument on board Terra have been downloaded at a horizontal resolution of
1
×
1
°
and for the given time period from
ftp://neespi.gsfc.nasa.gov/data/s4pa/Fire/
.
2.3 Land Cover Type Product
The Collection 5 MODIS Global Land Cover Type product (Friedl et al.
2010
),
which has been spatially aggregated to a 1
°×
1
°
resolution applying a majority
filter, is used for the de
nition of biomes evaluated in this study.
2.4 Production Rate of NO
x
from Fire
The retrieved TVC NO
2
is converted into the production rate of NO
x
from
re (P
f
)
by assuming that the background level of TVC NO
2
has no seasonal variation. A
further assumption made in the approach is the constant value for the NO
x
lifetime
(6 h) following the
findings of Beirle et al. (
2011
). While the NO
2
/NO
x
ratio is held
constant (0.75) for the tropical and subtropical regions (Alvarado and Prinn
2009
),
it is derived from the MACC reanalysis data set of atmospheric composition (Inness
et al.
2013
) for the boreal regions. As the scienti
c community is interested in the
production rate of NO
x
rather than the number density of NO
2
molecules in the
vertical column, we compute Pf
f
as shown in the following equations:
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