Investigation of Isoprene Dynamics During the Day-to-Night Transition Period

Details

• Journal Title:
  Journal of Geophysical Research: Atmospheres
• Personal Author:
  Wei, Dandan ; Alwe, Hariprasad D. ; Millet, Dylan B. ; Kavassalis, Sarah C. ; Lew, Michelle ; Bottorff, Brandon ; Stevens, Philip S. ; Steiner, Allison L.
• NOAA Program & Office:
  OAR (Oceanic and Atmospheric Research) ; CPO (Climate Program Office)
• Description:
  At the University of Michigan Biological Station during the 2016 AMOS field campaign, isoprene concentrations typically peak in the early afternoon (around 15:00 local time, LT) under well-mixed conditions. However, an end-of-day peak (around 21:00 LT) occurs on 23% of the campaign days, followed by a rapid removal (from 21:00–22:00 LT) at rate of 0.57 hr−1 during the day-to-night transition period. During the end-of-day peak, in-canopy isoprene concentrations increase by 77% (from 3.5 to 6.2 ppbv) on average. Stratification and weak winds (<3.4 m s−1 at 46 m) significantly suppress turbulent exchanges between in- and above-canopy, leading to accumulation of isoprene emitted at dusk. A critical standard deviation of the vertical velocity (σw) of 0.14, 0.2, and 0.29 m s−1 is identified to detect the end-of-day peak for the height of 13, 21, and 34 m, respectively. In 85% of the end-of-day cases, the wind speed increases above 2.5 m s−1 after the peak along with a shift in wind direction, and turbulence is reestablished. Therefore, the wind speed of 2.5 m s−1 is considered as the threshold point where turbulence switches from being independent of wind speed to dependent on wind speed. The reinstated turbulence accounts for 80% of the subsequent isoprene removal with the remaining 20% explained by chemical reactions with hydroxyl radicals, ozone, and nitrate radicals. Observed isoprene fluxes do not support the argument that the end-of-day peak is reduced by vertical turbulent mixing, and we hypothesize that horizontal advection may play a role.
• Keywords:
  Atmospheric Chemistry Isoprene Atmospheric Chemistry
• Source:
  JGR Atmospheres 125(20): e2020JD032784
• DOI:
  https://doi.org/10.1029/2020JD032784
• Document Type:
  Journal Article
• Funding:
  Grant no. NA18OAR4310116
• Rights Information:
  Other
• Compliance:
  Submitted
• Main Document Checksum:
  urn:sha256:ef9f505050121fd1cc3f7b1e20f8c77fa028c82f0f7147ed95ce6d87f24bc54e
• Download URL:
  https://repository.library.noaa.gov/view/noaa/45536/noaa_45536_DS1.pdf
• File Type:
  [PDF - 2.00 MB ]