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We examine upcoming geostationary satellite observations of formaldehyde(HCHO) vertical column densities (VCDs) in East Asia and the retrievalsensitivity to the temporal variation of air mass factors (AMFs) consideringthe presence of aerosols. Observation system simulation experiments (OSSE)were conducted using a combination of a global 3-D chemical transport model(GEOS-Chem), a radiative transfer model (VLIDORT), and a HCHO retrievalalgorithm developed for the Geostationary Environment Monitoring Spectrometer(GEMS), which will be launched in 2019. Application of the retrievalalgorithm to simulated hourly radiances yields the retrieved HCHO VCDs, whichare then compared with the GEOS-Chem HCHO VCDs as true values for theevaluation of the retrieval algorithm. In order to examine the retrievalsensitivity to the temporal variation of AMF, we examine three AMFspecifications, AMFm, AMFh, and AMFmh,using monthly, hourly, and monthly mean hourly input data for theircalculation, respectively. We compare the retrieved HCHO VCDs using thosethree AMFs and find that the HCHO VCDs with AMFh are in betteragreement with the true values than the results using AMFmh andAMFm. AMFmh reflects diurnal variation of planetaryboundary layer and other meteorological parameters, so that the results withAMFmh show a better performance than those with AMFm.The differences between AMFh and AMFm range from−0.76 to 0.74 in absolute value and are mainly caused by temporal changesin aerosol chemical compositions and aerosol vertical distributions, whichresult in −27 to 58 and −34 to 43 % changes in HCHO VCDs over China,respectively, compared to HCHO VCDs using AMFm. We apply ourcalculated AMF table together with OMI aerosol optical properties to OMI HCHOproducts in March 2006, when Asian dust storms occurred, and find−32 to 47 % changes in the retrieved HCHO columns due to temporal changesin aerosol optical properties in East Asia. The impact of aerosol temporalvariability cannot be neglected for future geostationary observations

Sensitivity of formaldehyde (HCHO) column measurements from a geostationary satellite to temporal variation of the air mass factor in East Asia