Measurement and investigation of chamber radical sources in the European Photoreactor (EUPHORE)

Judit Zádor, Tamás Turányi, Klaus Wirtz, Michael J. Pilling

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It is essential to quantify the background reactivity of smog-chambers, since this might be the major limitation of experiments carried out at low pollutant concentrations typical of the polluted atmosphere. Detailed investigation of three chamber experiments at zero-NOx in the European Photoreactor (EUPHORE) were carried out by means of rate-of-production analysis and two uncertainty analysis tools: local uncertainty analysis and Monte Carlo simulations with Latin hypercube sampling. The chemical mechanism employed was that for methane plus the inorganic subset of the Master Chemical Mechanism (MCMv3.1). Newly installed instruments in EUPHORE allowed the measurement of nitrous acid and formaldehyde at sub-ppb concentrations with high sensitivity. The presence of HONO and HCHO during the experiments could be explained only by processes taking place on the FEP Teflon walls. The HONO production rate can be described by the empirical equation W (HONO)EUPHORE dry = a × jNO2 × exp(-T′0/T) in the low relative humidity region (RH < 2%, a = 7.3 × 1021 cm-3, T0 = 8945K), and by the equation W(HONO)humidEUPHORE = W(HONO)dryEUPHORE + jNO2 × b × RHq in the higher relative humidity region (2% < RH < 15%, b = 5.8 × 108 cm3 and q = 0.36, and RH is the relative humidity in percentages). For HCHO the expression W (HCHO)EUPHORE = c × jNO2 exp (-T′0/T) is applicable (c = 3.1 × 1017 cm-3 and T′0 = 5686 K). In the -15% relative humidity range OH production from HONO generated at the wall is about a factor of two higher than that from the photolysis of 100 ppb ozone. Effect of added NO2 was found to be consistent with the dark HONO formation rate coefficient of MCMv3.1.

Original languageEnglish
Pages (from-to)147-166
Number of pages20
JournalJournal of Atmospheric Chemistry
Issue number2
Publication statusPublished - Oct 1 2006



  • European Photoreactor
  • Formaldehyde
  • Master Chemical Mechanism
  • Nitrous acid
  • Radical sources
  • Smog chamber
  • Uncertainty analysis

ASJC Scopus subject areas

  • Environmental Chemistry
  • Atmospheric Science

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