Seasonal Variation of Total Column Formaldehyde, Nitrogen Dioxide, and Ozone Over Various Pandora Spectrometer Sites with a Comparison of OMI and Diurnally Varying DSCOVR-EPIC Satellite Data

Abstract. Both The OMI (Ozone Monitoring Instrument) satellite and the Pandora ground-based instruments operate with spectrometers that have similar characteristics in wavelength range and spectral resolution that enable them to retrieve total column amounts of formaldehyde TCHCHO, and nitrogen dioxide TCNO2, and ozone TCO at 13:30 ± 0:45 local time. At most sites, Pandora shows a strong seasonal dependence for TCO and TCHCHO and little seasonal dependence for TCNO2, while OMI sees little seasonal dependence for TCHCHO and TCNO2 but does see seasonal dependence for TCO. The seasonal behavior of TCHCHO is caused by plant growth and emissions from lakes that peak in the summer suggesting that OMI is not correctly retrieving TCHCHO all the way to the Earth’s boundary layer. Since the OMI retrieval is around 13:30 local equator crossing time ± 0:45 and tends to occur near the frequent minimum of the daily TCNO2 time series, OMI underestimates the amount of air pollution that occurs during each year. Better TCNO2 agreement occurs when the Pandora data is averaged between 13:00 and 14:00 hours local time. Comparisons of OMI total column NO₂ and HCHO with Pandora daily time series show both agreement and disagreement at various sites and days. Similar comparisons of OMI TCO with those retrieved by Pandora show good agreement in most cases. Additional comparisons are shown of Pandora TCO with hourly retrievals during a day from EPIC (Earth Polychromatic Imaging Camera) spacecraft instrument orbiting the Earth-Sun Lagrange point L₁.