Diffusion Scrubber-Based Field Measurements of Atmospheric Formaldehyde and Hydrogen Peroxide

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Abstract
Field measurements were conducted to determine atmospheric concentrations of HCHO and H2O2 with automated instrumentation that relies on diffusion-based collection of water-soluble gases by an aqueous absorber flowing through a hydrophobic porous membrane tube. These measurements were made as part of the Carbonaceous Species Methods Comparison Study (CSMCS) at Cirrus College, Azusa, CA, during August 12–20, 1986. Both HCHO and H2O2 showed marked diurnal cycles, decreasing at night (to a minimum of 2–4 ppbv for HCHO, and near the detection limit, ∼ 30 pptv for H2O2) and increasing to a maximum in the late afternoon (15–19 ppbv for HCHO, ∼ 2 ppbv for H2O2). For the most part, the instrumentation performed unattended as designed; however, particle deposition in sampling lines and in the membrane-based diffusion scrubbers suggest that in-line losses can be significant for continued sampling of ambient air containing a relatively high concentration of particulate matter. Periodic (e.g., daily or every 2 days) cleaning of all in-line components should be part of any such measurement program.