Measuring the Effect of Photocatalytic Purifiers on Indoor Air Hydrocarbons and Carbonyl Pollutants

Abstract

Laboratory tests of photocatalytic air purifiers are usually performed with a single pollutant, in the parts per million by volume domain and at airflow rates [H11349]0.1 m³/hr. Clearly, it is necessary to probe photocatalytic materials and apparatuses under real conditions or conditions closely mimicking reality. Photocatalytic prototypes were placed in an ordinary room. To collect hydrocarbons over a shorter period (15 min) than with adsorbent-containing cartridges, solid-phase microextraction (SPME) was used. Typically, concentrations in substituted benzene hydro-carbons and tetrachloroethene were decreased to 20–35% of initial values; toluene and m- [H11001] p-xylene concentrations dropped to 2–6 parts per billion by volume, and o-xylene and benzene concentrations were still lower. In the absence of appropriate, commercialized SPME fibers, carbonyl compounds (both formed and destroyed by photocatalysis) were extracted using cartridges containing 2,4- dinitrophenylhydrazine-coated silica. The concentration ranges (in parts per billion by volume) were shifted to higher values in treated air: from 9–15.5 to 12.5–18 for methanal, from 1.5–3 to 8–11.5 for ethanal, and from 4.5–19 to 8–26.5 for propanone with the prototype used; these unprecedented results do not exclude using photo-catalysis to treat air, but they illustrate that improvement is needed. Because these tests are time-consuming, preliminary tests are useful; results obtained with a 225-L closed-loop, airtight, photocatalytic reactor with an external turbine enabling the ambient air inside the reactor to be circulated through the purifier device at 15–450 m³/hr flow rates are reported.