Source and variability of formaldehyde (HCHO) at northern high latitudes: an integrated satellite, aircraft, and model study

[摘要] Here we use satellite observations of formaldehyde (HCHO)vertical column densities (VCD) from the TROPOspheric Monitoring Instrument(TROPOMI), aircraft measurements, combined with a nested regional chemicaltransport model (GEOS-Chem at 0.5 × 0.625 ∘ resolution), to better understand the variability and sources of summertime HCHOin Alaska. We first evaluate GEOS-Chem with in-situ airborne measurementsduring the Atmospheric Tomography Mission 1 (ATom-1) aircraft campaign. We showreasonable agreement between observed and modeled HCHO, isoprene,monoterpenes and the sum of methyl vinyl ketone and methacrolein(MVK + MACR) in the continental boundary layer. In particular, HCHO profilesshow spatial homogeneity in Alaska, suggesting a minor contribution ofbiogenic emissions to HCHO VCD. We further examine the TROPOMI HCHO productin Alaska in summer, reprocessed by GEOS-Chem model output for a prioriprofiles and shape factors. For years with low wildfire activity (e.g.,2018), we find that HCHO VCDs are largely dominated by background HCHO(58 %–71 %), with minor contributions from wildfires (20 %–32 %) andbiogenic VOC emissions (8 %–10 %). For years with intense wildfires(e.g., 2019), summertime HCHO VCD is dominated by wildfire emissions(50 %–72 %), with minor contributions from background (22 %–41 %) andbiogenic VOCs (6 %–10 %). In particular, the model indicates a majorcontribution of wildfires from direct emissions of HCHO, instead ofsecondary production of HCHO from oxidation of larger VOCs. We find that thecolumn contributed by biogenic VOC is often small and below the TROPOMIdetection limit, in part due to the slow HCHO production from isopreneoxidation under low NO x conditions. This work highlights challenges forquantifying HCHO and its precursors in remote pristine regions.

[学科分类] 医学（综合）