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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 SEAC4RS (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 (r  =  0.4–0.8 on a 0.5°  ×  0.5°  grid) and in their day-to-day variability (r  =  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 SEAC4RS 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.


Lei Zhu1, Daniel J. Jacob1,2, Patrick S. Kim2, Jenny A. Fisher3,4, Karen Yu1, Katherine R. Travis1, Loretta J. Mickley1, Robert M. Yantosca1, Melissa P. Sulprizio1, Isabelle De Smedt5, Gonzalo González Abad6, Kelly Chance6, Can Li7,8, Richard Ferrare9, Alan Fried10, Johnathan W. Hair9, Thomas F. Hanisco8, Dirk Richter10, Amy Jo Scarino11, James Walega10, Petter Weibring10, and Glenn M. Wolfe8,12

1John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
2Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
3Centre for Atmospheric Chemistry, School of Chemistry, University of Wollongong, Wollongong, NSW, Australia
4School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW, Australia
5Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
6Harvard–Smithsonian Center for Astrophysics, Cambridge, MA, USA
7Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland, USA
8NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
9NASA Langley Research Center, Hampton, VA 23681, USA
10Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO, USA
11Science Systems and Applications, Inc., Hampton, VA, USA
12Joint Center for Earth Systems Technology, University of Maryland Baltimore County, Baltimore, Maryland, USA