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TVC
f
NO
2
½
¼
TVC NO
2
½
TVC
b
NO
2
½
fires (in
molecules cm
−
2
) as obtained from the subtraction of TVC
b
NO
2
(y-intercepts or
background NO
2
) from TVC NO
2
. The y-intercepts have been obtained from a
linear regression analysis of the gridded monthly means of TVC NO
2
and FRP.
Here, TVC
f
NO
2
is the number density of NO
2
molecules produced by
A
p
NO
NO
2
TVC
f
½
NO
2
M 1
þ
P
f
¼
N
A
s
The term 1 + NO/NO
2
accounts for the above stated ratio (without units), M is
the molar mass of NO (in g mol
−
1
) and A
p
is the respective pixel area (in cm
2
). N
A
denotes Avogadro
is number (in molecules mol
−
1
) and
is the assumed lifetime of
NO
x
(in seconds). According to the described conversion of TVC NO
2
, the FRP
values have also been multiplied by A
p
. Further details about the conversion are
given in Schreier et al. (
2014a
,
b
).
'
τ
2.5 Estimation of NO
x
Emission Factors
In a next step, a linear regression model is used for the computation of gradients
between P
f
and FRP, here referred to as
fire emission rates (FERs) of NO
x
, for all
pixels with a correlation coef
cient between TVC NO
2
and FRP higher than 0.3.
final step, the FERs are translated into emission factors (EFs) of NO
x
by
applying a conversion factor of 0.41 kg MJ
−
1
In the
as suggested by Vermote et al.
(
2009
), following the
findings of Wooster et al. (
2005
).
3 Results and Discussion
The correlation coef
cients as obtained from the linear regression between TVC
NO
2
and FRP are shown in Fig.
1
. The global map is quite revealing in several
ways. First, a very strong relationship between the two time series is found for the
major biomass burning regions. Hence, the seasonal variation of TVC NO
2
is
explained by the seasonal cycle of FRP to a large degree. Second, the empirical
relationship forms the basis of the approach to estimate FERs of NO
x
as it is a
reasonable tool to separate between different NO
x
sources. In order to assess NO
x
from vegetation
fires, the y-intercepts (background NO
2
) of the linear regression
model (not shown here) have been used for the conversion of TVC NO
2
into Pf
f
as
described earlier.
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