Abstract
We use a nested‐grid version of the GEOS‐Chem chemistry transport model, constrained by isoprene emissions from the Model of Emissions of Gases and Aerosols from Nature (MEGAN), and the Lund‐Potsdam‐Jena General Ecosystem Simulator (LPJ‐GUESS) bottom‐up inventories, to evaluate the impact that surface isoprene emissions have on formaldehyde (HCHO) air‐mass factors (AMFs) and vertical column densities (VCDs) over tropical South America during 2006, as observed by the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) and Ozone Monitoring Instrument (OMI). Although the large‐scale seasonal variability of monthly mean HCHO VCDs is typically unaffected by the choice of bottom‐up inventory, large relative differences of up to ±45% in the HCHO VCD can occur for individual regions and months, but typically most VCD differences are of order ±20%. These relative changes are comparable to those produced by other sources of uncertainty in the AMF including aerosols and surface albedo, but less than those from clouds. In a sensitivity test, we find that top‐down annual isoprene emissions inferred from SCIAMACHY and OMI HCHO vertical columns can vary by as much as ±30–50% for each instrument respectively, depending on the region studied and the a priori isoprene emissions used. Our analysis suggests that the influence of the a priori isoprene emissions on HCHO AMFs and VCDs is therefore non‐negligible and must be carefully considered when inferring top‐down isoprene emissions estimates over this, or potentially any other, region.
Highlights
[2] Formaldehyde (HCHO) is a key atmospheric constituent produced from the oxidation of volatile organic compounds (VOCs)
The slant columns are converted to vertical column densities (VCDs) after division by an air-mass factor (AMF = SCD/VCD) which accounts for the satellite viewing geometry, HCHO vertical distribution, surface reflectance, and atmospheric scattering by air-molecules, aerosols, and clouds [Palmer et al, 2001]
We run GEOS-Chem with both inventories using the subsequent HCHO profiles to compute air-mass factors (AMFs) to apply to slant columns retrieved by the SCIAMACHY [Bovensmann et al, 1999] and Ozone Monitoring Instrument (OMI) instruments [Levelt et al, 2006], in order to examine the relative changes in the resulting HCHO VCD distributions
Summary
[2] Formaldehyde (HCHO) is a key atmospheric constituent produced from the oxidation of volatile organic compounds (VOCs). We run GEOS-Chem with both inventories using the subsequent HCHO profiles to compute AMFs to apply to slant columns retrieved by the SCIAMACHY [Bovensmann et al, 1999] and OMI instruments [Levelt et al, 2006], in order to examine the relative changes in the resulting HCHO VCD distributions. [4] In section 2 we provide a brief overview of the GEOSChem model, and describe the SCIAMACHY and OMI HCHO slant column retrievals and the computation of their AMFs. In section 3 we present the results of our sensitivity analysis, and in section 4 we examine the impact of the different a priori isoprene inventories on subsequent top-down isoprene emission estimates.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
