## 2 Materials and Methods
### Testing Procedures
#### 2.3.2 Primary and Secondary VOC Emissions  
The primary and secondary VOC emissions from the materials before and after exposure to ozone were analyzed using the following procedure. After putting the material in the chamber, with or without exposure to ozone, the air was extracted after 4 h from the chamber for chemical analysis. Concentrations of the 24 target pollutants were sampled (GilAir Plus, Sensidyne, St. Petersburg, FL, USA) in Tenax TA tubes at 0.1 L-min\({}^{-1}\) for 30 min. The selected pollutants included aromatic (e.g., benzene and toluene), aliphatic (e.g., undecane), and ester compounds (e.g., ethyl acetate). The gas chromatography-mass spectrometer (Finnigan TRACE DSQ, Thermo Electron Corporation, Waltham, MA, USA) method was used to analyze the mass of the targeted compounds in the Tenax TA tubes [40], which were kept at room temperature after sampling. Despite the advantages of using the Chinese 40 L desiccator method to measure the formaldehyde from wooden materials [41], the method outlined in [42] was adopted to measure aldehydes (formaldehyde, acetaldehyde, etc.) and ketones (e.g., acetone) using the same procedure for all seven materials. Aldehydes and ketones were sampled by DNPH cartridges with ozone filters (Sep-Pak, Waters, Milford, MA, USA) at 0.5 L-min\({}^{-1}\) for 30 min. The samples were stored at <4 degC after being eluted from the DNPH cartridges and were analyzed via the ultra-performance liquid chromatography (Acquity UPLC H-Class Plus System, Waters, Milford, MA, USA) method with a tunable UV detector (Waters, Milford, MA, USA). In terms of the possible high concentrations of air pollutants, the DNPH cartridge and Tenax TA tube were connected in series to avoid breakthrough. The background VOC concentrations in the empty chambers exposed to ozone at a designated concentration were also obtained following the procedure before each round of testing. Assuming all the free-run materials were exposed to the indoor environment long enough to reach a quasi-steady state, the emission factor of the \(i\)-th compound from the testing specimen, \(F_{i}\), was determined using Equation (4) [29]:  
\[F_{i}=\frac{NV(y_{i}-y_{i,\text{in}})-NV(y_{i,\text{e}}-y_{i,\text{in}})\Big{(} 1-\frac{A_{\text{d,s}}}{A_{\text{d,w}}}\Big{)}}{A_{\text{d,s}}}, \tag{4}\]  
where \(y_{i}\) is the concentration of the \(i\)-th compound in the chamber containing a material specimen, \(\text{\mu}\text{g}\text{-}\text{m}^{-3}\) and \(y_{i,\text{in}}\) and \(y_{i,\text{e}}\) are the concentrations of the \(i\)-th compound in the supplied air and the empty chamber, respectively, in \(\text{\mu}\text{g}\text{-}\text{m}^{-3}\). Notably, the gas-phase and surface reactions involving the \(i\)-th compound were not independently measured. Therefore, in Equation (4), \(F_{i}\), was grouped together considering the total molecules consumed by reacting with ozone and/or the possible production yield as one of the outcomes of the reactions. Nevertheless, methods to independently measure the gas-phase consumption and area-averaged yield of related compounds by ozone deposition are recommended. A summary of the testing procedure for detecting primary and secondary VOC emissions is given in Table 4. Due to the limited resources and time, one specimen from each material was subjected to testing of the changes in VOC emission rates, while two parallel samplings were conducted, and the averaged concentration data were used to determine the \(F_{i}\) for each compound.