Design of a straight inlet diffusion scrubber. Comparison of particle transmission with other collection devices and characterization for the measurement of hydrogen peroxide and formaldehyde

Abstract

Particle deposition characteristics of several diffusion scrubber (DS) designs of annular geometry were studied and a straight inlet geometry was selected for further performance evaluation. At sample flow rates of 1–5 ℓ min −1, 5–17% of Boltzmann charged 0.1–3 μm aerosol is deposited in the device, with 0.5–2.5% deposition on the membrane tube, the central collecting element. Most of the wall deposition appears to be due to electrostatic effects caused by the PTFE wall; this is accentuated by dry air (⩽5% r.h.) test conditions. Significant deposition loss is observed with glass denuders under the same test conditions as well. Extensive performance tests were made with the new geometry DS; Nafion® membrane based DS devices are recommended for the measurement of H 2O 2 and HCHO. For NH 3, reasonably fast response times are difficult to attain with Nafion membrane DS devices, however. Some unexpected new findings regarding the transmission of acid gases through a Nafion membrane and their implications are discussed.