Uncertainties in Direct Radiative Forcing of Aerosols
Question
2:
How
to
understand/assess
the
uncertainties
in
the
direct
radiative
forcing
of
aerosols?
Maiheliyaer
Sadeke
(Mac)
Senior
student
in
Environmental
Science
Advised
by
Prof.
Junfeng
Liu
Can
be
constrained
by
measurements
Uncertainty
in
BC
DRF
can
be
attributed
to
variations
in
four
factors:
•
Emission:
6000-18000
Gg/yr
•
Lifetime:
3
.8-11.4
days
•
MAC:
4.4-13.4
m2/g
•
AFE:
90-270
W/m2
per
AAOD
T.C.
Bond
et
al.
2013
Introduction
•
Impact
of
emission
rate
on
RF
varies
regionally
and
globally
.
•
Representation
of
scavenging
affects
the
magnitude
and
seasonality
of
BC
concentration
.
(
Internal
mix
&
External
mix
)
•
In
most
models,
simulated
surface
BC
concentration
is
weak
over-
predicted
in
Europe,
under predicted
in
biomass
burning
regions,
and
large
under
predicted
for
eastern
and
southern
Asia.
[Bond
et
al.
2013]
•
Vertical
profiles
of
BC
show
that
simulated
concentrations
have
large
biases
in
the
free
troposphere. [B.H. Samset et al.
2012]
Emission,
Lifetime,
and
Burden
•
AAOD
provoked
per
gram
of burden,
absorbing
ability
of
pollutant.
•
MAC
depends
on
refractive
index,
water
content,
particle
size,
and
mixing
state
.
•
Mixing
state
:
mixing
with
other
aerosol
components
increases
MAC,
leading
to
an
increase
in
absorption
and
positive
forcing
.
[Haywood
and
Shine
1995]
•
Chung
and
Seinfeld
[
2002]
found
a
forcing
increase
of
36%
for
BC
with
homogeneous
internal
mixing
compared
with
external
mixing.
Mass
Absorption
Cross
Section
(MAC)
•
AAOD
is
the
product
of
emission,
lifetime
and
MAC,
and
it
can
be
scaled
to
observations
to
reduce
uncertainty.
•
Top-down
method
.
•
AAOD
constraining
brings
bias:
BC
AAOD
was
got
from
total
AAOD
subtracting
dust
AAOD
(high
bias).
AAOD
observation
vs.
simulation:
•
Radiation perturbation caused by one
unit of AAOD.
•
Forcing
efficiency
depends
highly
on
environmental
variables,
especially
the
reflectivity
of
the
underlying
surface.
•
Vertical
location
of
BC:
AFE
is
enhanced
when
BC
is
over
clouds.
The
model
with
lowest
AFE
has
14%
of
BC
above
5km
,
while
the
highest
has
37%.
[Textor
et
al.
2006]
•
Horizontal
distribution
of
BC.
Forcing
Efficiency:
•
Bond
et
al.
[
2013]
have
the
final
estimate
of
90%
uncertainty
range
of
+0.08
to
+1.27
W/m2
with
central
estimate
of
+0.71
W/m2 (BC DRF)
.
Uncertainty
comes
from
uncertainties
in
AAOD
and
50%
uncertainty
in
AFE.
•
Bottom-up
method
1.
Emission
2.
Lifetime
3.
AAOD
4.
AFE
•
Top-down
method
1.
Observation
Summary:
Thanks for your listening
The uncertainties in the direct radiative forcing of aerosols can be assessed by considering factors such as emissions, lifetime, Mass Absorption Cross Section (MAC), Aerosol Absorption Optical Depth (AAOD), and forcing efficiency. Variations in these factors contribute to the overall uncertainty in the radiative forcing of aerosols. Bond et al. (2013) reported a 90% uncertainty range of +0.08 to +1.27 W/m2 with a central estimate of +0.71 W/m2 for black carbon (BC) direct radiative forcing. Uncertainties in AAOD and Aerosol Forcing Efficiency (AFE) are key contributors to the overall uncertainty. Methods like top-down observations and bottom-up estimations are used to constrain and evaluate these uncertainties.
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Presentation Transcript
Question 2: How to understand/assess the uncertainties in the direct radiative forcing of aerosols? Maiheliyaer Sadeke (Mac) Senior student in Environmental Science Advised by Prof. Junfeng Liu
Introduction Can be constrained by measurements Uncertainty in BC DRF can be attributed to variations in four factors: Emission: 6000-18000 Gg/yr Lifetime: 3.8-11.4 days MAC: 4.4-13.4 m2/g AFE: 90-270 W/m2 per AAOD T.C. Bond et al. 2013
Emission, Lifetime, and Burden Impact of emission rate on RF varies regionally and globally. Representation of scavenging affects the magnitude and seasonality of BC concentration.(Internal mix & External mix) In most models, simulated surface BC concentration is weak over- predicted in Europe, under predicted in biomass burning regions, and large under predicted for eastern and southern Asia. [Bond et al. 2013] Vertical profiles of BC show that simulated concentrations have large biases in the free troposphere. [B.H. Samset et al. 2012]
Mass Absorption Cross Section (MAC) AAOD provoked per gram of burden, absorbing ability of pollutant. MAC depends on refractive index, water content, particle size, and mixing state. Mixing state: mixing with other aerosol components increases MAC, leading to an increase in absorption and positive forcing. [Haywood and Shine 1995] Chung and Seinfeld [2002] found a forcing increase of 36% for BC with homogeneous internal mixing compared with external mixing.
AAOD observation vs. simulation: AAOD is the product of emission, lifetime and MAC, and it can be scaled to observations to reduce uncertainty. Top-down method. AAOD constraining brings bias: BC AAOD was got from total AAOD subtracting dust AAOD(high bias).
Forcing Efficiency: Radiation perturbation caused by one unit of AAOD. Forcing efficiency depends highly on environmental variables, especially the reflectivity of the underlying surface. Vertical location of BC: AFE is enhanced when BC is over clouds. The model with lowest AFE has 14% of BC above 5km, while the highest has 37%. [Textor et al. 2006] Horizontal distribution of BC.
Summary: Bond et al.[2013] have the final estimate of 90% uncertainty range of +0.08 to +1.27 W/m2 with central estimate of +0.71 W/m2 (BC DRF). Uncertainty comes from uncertainties in AAOD and 50% uncertainty in AFE. 1. 2. 3. 4. Bottom-up method Emission Lifetime AAOD AFE 1. Top-down method Observation
