Experimental study of reactions between ozone and building products

The purpose of this paper is to present an experimental setup developed to characterize reactions between ozone and building products and document their potential impact on indoor air quality. Preliminary experiments were conducted on four building products: two carpets, a gypsum board and a pine wood board. These preliminary experiments clearly indicate that ozone is significantly removed in contact with the four selected products. Measured ozone removal were around 65% for the two carpets, 70% for the gypsum board and 75% for the pine wood board. In case of exposure to ozone, emissions of building products were modified and reaction products (mainly carbonyl compounds) have been identified. For instance, when exposed to ozone, the carpet with PVC backing shows higher emissions of formaldehyde, the carpet with textile backing emits nonanal and decanal and the pine wood board exhibits increased emissions of hexanal. INDEX TERMS Ozone; Indoor chemistry; Aldehydes; Test chambers; Building products emissions INTRODUCTION The impact of ozone on indoor air chemistry is receiving special attention of late. Without specific indoor sources (such as laser printers), the indoor/outdoor ozone concentration ratio generally ranges from 0.2 to 0.7 indicating indoor sinks (Weschler, 2000; Kirchner et al., 2002). Ozone removal on surfaces of building products has been demonstrated (Morrison and Nazaroff, 2000, 2002; Kleno et al., 2001). Ozone can also react with NOx and with some specific volatile organic compounds (VOC), such as terpenes, which are frequently found indoors (Weschler, 2000). Therefore, ozone-induced reactions have a negative impact on indoor air quality since they produce secondary pollutants, mainly aldehydes, which are known irritants (Weschler, 2000; Wolkoff et al., 2000; Morrison and Nazaroff, 2002), odorous compounds (Knudsen et al., 2000; 2002), and also sub-micron particles (Weschler and Shields, 1999; Wainman et al., 2000; Rohr et al., 2003). In order to document interactions between ozone and building products, an experimental setup based on emission test chamber methods (CEN, 2001) was developed. Its purpose is to document the removal of ozone on the surface of different materials, the influence of ozone on the primary VOC emissions of building products and the identification of secondary emissions. This experimental setup has been tested during preliminary experiments on four building products. METHODS The experimental setup has been adapted from emission test chamber methods described in the ENV 13419-1 pre-standard (CEN, 2001). Inert materials (glass and Teflon PFA) have been selected. The setup is composed of two parallel lines containing a mixing chamber and a test chamber where building products are placed (Figure 1). The two lines are supplied with clean air (particles, silica gel, charcoal filtered). The conditions were kept constant during the test (Table 1). * Corresponding author. E-mail: [email protected] 344 Proceedings: Healthy Buildings 2003 Figure 1 The experimental setup. The first line (hereafter referred to as ‘reference line’), where building products are not exposed to ozone, is used for the measurements of primary VOC emissions from the products. In the second line (hereafter referred to as ‘ozone line’), ozone is introduced in the mixing chamber and transferred in the test chamber. Secondary emissions of the building products exposed to ozone are measured at the outlet of the ‘ozone line’. A 105 ± 5 ppb concentration of ozone is generated using pure oxygen (Air Liquide, O2: 99.999%) through UV light generator (Pen Ray, model SOG 1). Ozone is monitored at the inlet and outlet of the test chamber using a photometric analyser (Environnement SA, model O3 41M). Table 1 Emission test parameters selected for the experimental setup Test parameters Experimental setup Temperature 23 ± 2°C Relative humidity 50 ± 5% Mixing chamber Glass, 0.003 m Test chamber (Vc) Glass, 0.017 m Air flow rate 0.204 m h Air exchange rate (AER) 12 h Test duration 90–120 h Aldehyde compounds were measured according to the ISO 16000-3 standard (ISO, 2001). Sampling was performed using DNPH coated cartridges (Waters) and potassium iodide (KI) ozone scrubbers (Waters) in order to prevent interferences of ozone and sampled compounds during sampling. Fifteen aldehyde compounds (including formaldehyde) were analysed using HPLC (Waters, model Alliance). VOCs were measured during the carpet with textile backing experiment according to the ISO/DIS 16000-6.2 draft standard (ISO, 2002). Sampling was performed using TENAX TA adsorbent tubes (Perkin Elmer). VOC analyses were then performed by thermal desorption and gas chromatography (GC) using mass spectrometry detector (MSD) for identification and flame ionization detector (FID) for quantification (Perkin Elmer ATD 400, Varian 3800/Saturn 2000). VOC were semi-quantified using the toluene response factor. VOC results have to be examined with caution since no ozone scrubbers were used during sampling. Chemical Pollutants 345 Four building products were selected for preliminary experiments: carpet with PVC backing, carpet with textile backing, gypsum board and pine wood board. Carpets and gypsum board have been chosen since they are already known as ozone removing products (Morrison and Nazaroff, 2000, 2002; Kleno et al., 2001) and the pine wood board because of the emissions of terpene compounds. RESULTS Mean ozone concentrations in the test chamber inlet and outlet during preliminary experiments are illustrated in Figure 2 for the empty glass chamber and for all selected building products. 0 20 40 60 80 100 120 Glass chamber Carpet / PVC Carpet / textile Gypsum board Pine wood M ea n oz on e co nc en tr at io n (p pb )