formation and aerosol growth

Details

• Journal Title:
  Atmospheric Chemistry and Physics
• Personal Author:
  González Palacios, Laura ; Corral Arroyo, Pablo ; Aregahegn, Kifle Z. ; Steimer, Sarah S. ; Bartels-Rausch, Thorsten ; Nozière, Barbara ; George, Christian ; Ammann, Markus ; Volkamer, Rainer
• NOAA Program & Office:
  CIRES (Cooperative Institute for Research in Environmental Sciences)
• Description:
  The multiphase chemistry of glyoxal is a source of secondary organic aerosol (SOA), including its light-absorbing product imidazole-2-carboxaldehyde (IC). IC is a photosensitizer that can contribute to additional aerosol ageing and growth when its excited triplet state oxidizes hydrocarbons (reactive uptake) via H-transfer chemistry. We have conducted a series of photochemical coated-wall flow tube (CWFT) experiments using films of IC and citric acid (CA), an organic proxy and H donor in the condensed phase. The formation rate of gas-phase HO2 radicals (PHO2) was measured indirectly by converting gas-phase NO into NO2. We report on experiments that relied on measurements of NO2 formation, NO loss and HONO formation. PHO2 was found to be a linear function of (1) the [IC] × [CA] concentration product and (2) the photon actinic flux. Additionally, (3) a more complex function of relative humidity (25 % < RH < 63 %) and of (4) the O2 ∕ N2 ratio (15 % < O2 ∕ N2 < 56 %) was observed, most likely indicating competing effects of dilution, HO2 mobility and losses in the film. The maximum PHO2 was observed at 25–55 % RH and at ambient O2 ∕ N2. The HO2 radicals form in the condensed phase when excited IC triplet states are reduced by H transfer from a donor, CA in our system, and subsequently react with O2 to regenerate IC, leading to a catalytic cycle. OH does not appear to be formed as a primary product but is produced from the reaction of NO with HO2 in the gas phase. Further, seed aerosols containing IC and ammonium sulfate were exposed to gas-phase limonene and NOx in aerosol flow tube experiments, confirming significant PHO2 from aerosol surfaces. Our results indicate a potentially relevant contribution of triplet state photochemistry for gas-phase HO2 production, aerosol growth and ageing in the atmosphere.
• Keywords:
  Aerosols Atmospheric Chemistry Atmospheric Chemistry
• Source:
  Atmospheric Chemistry and Physics, 16(18), 11823-11836
• DOI:
  https://doi.org/10.5194/acp-16-11823-2016
• Document Type:
  Journal Article
• License:
  https://creativecommons.org/licenses/by/3.0/
• Rights Information:
  CC BY
• Compliance:
  Library
• Main Document Checksum:
  urn:sha256:00d72b29d0b3f90781755eb786d601915c38ad104b3bf35b61fb5c4332032be6
• Download URL:
  https://repository.library.noaa.gov/view/noaa/51336/noaa_51336_DS1.pdf
• File Type:
  [PDF - 1.44 MB ]