Significant OH production under surface cleaning and air cleaning conditions: Impact on indoor air quality

We report measurements of hydroxyl (OH) and hydroperoxy (HO₂ ) radicals made by laser-induced fluorescence spectroscopy in a computer classroom (i) in the absence of indoor activities (ii) during desk cleaning with a limonene-containing cleaner (iii) during operation of a commercially available "air cleaning" device. In the unmanipulated environment, the one-minute averaged OH concentration remained close to or below the limit of detection (6.5×10⁵  molecule cm^-3 ), whilst that of HO₂ was 1.3×10⁷  molecule cm^-3 . These concentrations increased to ~4×10⁶ and 4×10⁸  molecule cm^-3 , respectively during desk cleaning. During operation of the air cleaning device, OH and HO₂ concentrations reached ~2×10⁷ and ~6×10⁸  molecule cm^-3 respectively. The potential of these OH concentrations to initiate chemical processing is explored using a detailed chemical model for indoor air (the INDCM). The model can reproduce the measured OH and HO₂ concentrations to within 50% and often within a few % and demonstrates that the resulting secondary chemistry varies with the cleaning activity. Whilst terpene reaction products dominate the product composition following surface cleaning, those from aromatics and other VOCs are much more important during the use of the air cleaning device.