Emission characterisation of interior architectural coatings by the use of dynamic environmental chambers

Abstract

Emission characterisation is determine to find the emission rates, changes in emissions over time and the potential indoor pollutant concentrations. The purpose of emission characterisation is to evaluate the sampling and analysis methods for identifying and quantitating chemical species in air samples. Indoor architectural coatings are well recognised as sources for volatile organic compounds (VOCs) and hydrocarbons. The resulting build-up of emissions poses a serious threat to the health and comfort of building occupants. Emissions from indoor architectural coatings depend on a variety of factors. They include those related to the materials themselves (emitting source factors) and those related to the environment within which they are tested (environmental factors). Investigation on the effects of these factors on emissions is, therefore, one appropriate measure for understanding the corresponding impact on the indoor air quality. The amount of VOC and NMHC emissions from two types of interior architectural coatings together with the factors affecting the emission rate measurement are investigated. The correlations between the emission rates and those factors are developed. Environmental chamber testing is proposed to evaluate the emissions from a finishing varnish and an alkyd paint. The major VOCs emitted from the interior architectural coatings were mainly aromatics, namely toluene, chlorobenzene, ethylbenzene, styrene, xylene isomers, and trimethylbenzene isomers. The results showed that the general profiles of the emissions were quite similar and showed rapid changes in the initial emission characteristics. The results indicate that the emission rates become higher when the wet film is thicker and the size of specimen is smaller. Emission rates from painted inert substrate were higher than those from painted real substrate. The results also indicate that increased air exchange rate, temperature and RH level increase the emission rate, which are consistent with theoretical predication far gas-phase, mass transfer-controlled emissions. The emitting source factors (e.g. thickness and material loading) influence significantly on the VOC and NMHC concentration, while the environmental factors (e.g. temperature and relative humidity) influence significantly on the initial VOC and NMHC emissions. The present work confirmed that both the emitting source and environmental factors influenced noticeably the VOC and NMHC emissions. Emission source empirical models, first-order decay and double-exponential models, are proposed in the present study, to be intended to describe the time dependence of VOC and NMHC emission in the environmental test chambers with relatively few parameters, and to evaluate the effectiveness of emission reduction options. The models consider the effect of air exchange rate, source strength and material loading on the emission. The non-linear squared correlation coefficients (R2) and the sum of the squared error (SSE) showed that the models had closely described the measured values. With these emission source models, the concentrations and emissions in indoor air under specific conditions can be predicted.