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

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.