Formic acid measurements from space: TES retrieval evaluation for
constraining primary and secondary sources
Sreelekha
1
Chaliyakunnel (chali011@umn.edu),
Dylan B.
1
Millet ,
K.C.
1University
of Minnesota; 2AER Inc.; 3Environment Canada; 4NASA JPL; 5Harvard University
Introduction
1
Wells ,
K.E.
2
Cady-Pereira ,
M.W.
3
Shephard ,
Data sources
M.
4
Luo ,
F.
5
Paulot
Data intercomparison
Tropospheric Emission Spectrometer (TES)
Map of flight tracks and TES measurements:
INTEX-B C130
INTEX-B C130
MILAGRO C130
NASA Aura satellite
•  Sun-synchronous
•  Equator crossing at 1:45pm (LST)
•  Orbits repeats every 16 days
•  Global coverage every 2 days
Thermal emission Fourier IR
spectrometer
•  spectral resolution 0.06 cm-1
•  5 × 8 km2 footprint
TES
FF
Photochemical
Terrestrial
Dry
vegetation
deposition
BMB&BF
HCOOH
Wet
Soil
deposition
Agriculture
Dust
Sinks (Tg a-­‐1) Dry deposiGon 25.3 Wet deposiGon 20.3 Photo-­‐Chemical 12.2 Dust 1.1 Jul
HCOOH mixing ratio in surface
air (GEOS-Chem simulation)
0
1
2 3 4 5
HCOOH [ppb]
6
7
TES vertical sensitivity
897.2 mb
825.4 mb
681.3 mb
562.3 mb
510.9 mb
421.7 mb
0
897.2 mb
825.4 mb
681.3 mb
562.3 mb
510.9 mb
421.7 mb
TES retrieved
TES a priori
TES RVMR
200
Pressure (mb)
•  Current global
models
0
TES retrieved
TES a priori
underestimate formic
acid
TES
RVMR
200
levels.
400
•  Global production
of
formic acid600 appears to be
underestimated
by 2-3x
800
( Stavrakou
et
al.,
2012)
1000
Pressure (mb)
Jan
Biomass burning 1.5 Soil 1.0 Anthropogenic 0.6 Example of HCOOH spectral
signature in the TES observations
600
800
0.00 0.05 0.10 0.15 0.20 0.25 0.30
Avg K rows
1
2 3 4 5
HCOOH [ppb]
6
6.8
9.0 [ppb]
0.0
2.7
5.3
Measurements:
Wennberg group
2.2 4.5 6.8 9.0 [ppb]
8.0 [ppb]
0.0
DOFS
(a)  Flight data from 500-900 mb is considered.
(b)  At least 1 TES per grid box and TES data is shaded
by DOFS.
TES and GEOS-Chem vs. ground-based FTS at Bremen:
TES
GEOS-Chem
FTS
GEOS-Chem
Measurements: Univ. Bremen
• Averaging Kernel = vertical •  Aircraft , in-situ and TES data show Geos-Chem
sensitivity of TES retrieval
underestimates atmospheric HCOOH over these regions.
(∂xretrieved/∂xtrue).
400
1000
0
4.5
TES measurements vs. GEOS-Chem:
HCOOH RVMR [ppb]
HCOOH sources and sinks in GEOS-Chem
(a)  Measure
radiation.
(b)  Compare
measurement
with forward
model run using a
priori profile.
(c)Adjust profile
to minimize
residual.
2.2
Aircraft measurements vs. GEOS-Chem:
Retrieving HCOOH abundance from
TES spectra
Photochemical sources Terrestrial biogenic,marine
and anthropogenic precursors
Sources (Tg a-­‐1) Photochemical 53.2 Biogenic 3.5 Ca=le 2.0 0.0
HCOOH column
[1015 molec/cm2]
•  Formic acid is one of the dominant atmospheric
carboxylic acids.
•  Significant contribution to acidity of precipitation in
remote environments.
•  Significantly affects the aqueous-phase chemistry in
the atmosphere.
•  Aqueous reactions in cloud droplets are highly pH
dependent, thus sensitive to HCOOH levels.
7
• Convert the vertical
profiles into a single
representative
volume
0.00 0.05 0.10 0.15 0.20 0.25 0.30
Avg K rows
mixing ratio (RVMR).
• For HCOOH, peak sensitivity at
• DOFS (degrees of freedom
~600-900 hPa.
for signal) = trace(Averaging
•  ~3km vertical resolution
Kernel)
(FWHM AK)
Next steps
•  Evaluation of a full year TES retrievals and GS results.
•  Application to constrain the seasonality and abundance
of HCOOH sources.
Acknowledgments
This work is supported by NSF CAREER (#1148951) and the
University of Minnesota Supercomputing Institute.