Observing atmospheric formaldehyde (HCHO) from space: validation and intercomparison of six retrievals from four satellites (OMI, GOME2A, GOME2B, OMPS) with SEAC4RS aircraft observations over the Southeast US
Other literature type
Jacob, Daniel J.
Kim, Patrick S.
Fisher, Jenny A.
Travis, Katherine R.
Mickley, Loretta J.
Yantosca, Robert M.
Sulprizio, Melissa P.
De Smedt, Isabelle
Abad, Gonzalo Gonzalez
Hair, Johnathan W.
Hanisco, Thomas F.
Scarino, Amy Jo
Wolfe, Glenn M.
(issn: 1680-7324, eissn: 1680-7324)
Formaldehyde (HCHO) column data from satellites are widely used as a proxy
for emissions of volatile organic compounds (VOCs), but validation of the
data has been extremely limited. Here we use highly accurate HCHO aircraft
observations from the NASA SEAC<sup>4</sup>RS (Studies of Emissions, Atmospheric
Composition, Clouds and Climate Coupling by Regional Surveys) campaign over
the southeast US in August–September 2013 to validate and intercompare six
retrievals of HCHO columns from four different satellite instruments (OMI,
GOME2A, GOME2B and OMPS; for clarification of these and other abbreviations
used in the paper, please refer to Appendix A) and three different research
groups. The GEOS-Chem chemical transport model is used as a common
intercomparison platform. All retrievals feature a HCHO maximum over Arkansas
and Louisiana, consistent with the aircraft observations and reflecting high
emissions of biogenic isoprene. The retrievals are also interconsistent in
their spatial variability over the southeast US (<i>r</i> = 0.4–0.8 on a
0.5° × 0.5° grid) and in their day-to-day
variability (<i>r</i> = 0.5–0.8). However, all retrievals are biased low in
the mean by 20–51 %, which would lead to corresponding bias in estimates
of isoprene emissions from the satellite data. The smallest bias is for
OMI-BIRA, which has high corrected slant columns relative to the other
retrievals and low scattering weights in its air mass factor (AMF)
calculation. OMI-BIRA has systematic error in its assumed vertical HCHO shape
profiles for the AMF calculation, and correcting this would eliminate its
bias relative to the SEAC<sup>4</sup>RS data. Our results support the use of
satellite HCHO data as a quantitative proxy for isoprene emission after
correction of the low mean bias. There is no evident pattern in the bias,
suggesting that a uniform correction factor may be applied to the data until
better understanding is achieved.