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The main composition of PM2.5 and masspercentage at the schoolroom sites are organic carbon(26–50%), nitrate (20%), trace elements (22%), elementalcarbon (6–7%), and sulfate (6–7%). From the results above, it can be found that organic carbon is the largest contributor toPM2.5, and has largest impact on the characteristics of PM2.5.PM2.5 containing much organic carbon not only contribute tothe propagation of bacteria, but help bacterial spread. PM2.5endanger occupants’ health directly or indirectly.Furthermore, the dust accumulating on hot surfaces (e.g.,heaters and light fixtures) is likely to emit chemicals whenheated. Pedersen et al. (2001, 2003) compared the emissioncharacteristics of VOCs during heating of different dustsamples relevant to the indoor environment. Emissions ofVOCs from heated dust from different sources were surpris-ingly similar. For most of the samples studied, the emissionswere considerable already at 150 C. Inorganic gases such asCO, CO2,NOX and NH3 have been identified among theemissions from indoor dust heated at 150–600 C.Particle pollutants endanger human body through threeapproaches, namely respiration canal, skin, and alimentarycanal. It is the most dangerous approach that particle pollut-ants enter human body through respiration canal (Kavourasand Stephanou, 2002). The harm degree of particle pollutantsto human body is related to the chemical characteristic,diametermagnitude, and quantity. The chemical characteris-tic of particle pollutants is the main factor because thechemical characteristic determines the degree and speed ofbiochemistry processes which particle pollutants participatein and disturb in human body. Most of the particle pollutantsin air are quite small. They have difficulty in settling and beingcaptured. Conversely, it is easy for them to enter respirationcanal deeply together with inhaled air. Moreover, the surfaceof particle pollutants can adsorb harmful gases, liquid andmicrobe, which increases the harm to human body (Thamand Zuraimi, 2005; Morawska, 2006).Most of indoor particle pollutants are ultra-fine particles(smaller than 100 nm, nanoscale particles called by toxicolo-gist) in terms of particle counts. Ultra-fine particles possessnew physical, chemical and biologic characteristics (Kagonet al., 2005). Therefore future research could explore thebehavior of indoor ultra-fine particles, distribution and effectson indoor environment, and the aggradation of ultra-fineparticles in human body, movement and effects on health.2.2. Gaseous pollutants2.2.1. Primary gaseous pollutantsPrimary gaseous pollutantsmainly include CO, CO2,SO2,NOX,O3, radon and VOCs. Chemical materials have widely beenused indoors recently. The chemical materials can releasemany kinds of chemical pollutants at room temperature,and VOCs are the main composition of these chemical pollut-ants. VOCs can causemany symptoms, such as headache; eye,nose, and throat irritations; dry cough; dizziness and nausea;tiredness. VOCs also have bad effects on respiration systems,blood vessel systems, and nerve systems. Moreover, VOCsmay be carcinogenic (Huang and Haghighat, 2002). Thephysical and chemical characteristics of VOCs attract manyresearchers, and become a research topic.Indoor pollution sources of VOCs mainly include buildingmaterials, decorating materials, and articles used indoors.Among them building materials and decorating materialsare the main pollution sources of VOCs (Cox et al., 2002).They mainly include carpet, man-made board, fine board,agglutination board, composite floor, cork, paint, adiabaticlayer, and heat pipeline. Many numerical models have beendeveloped for simulating the surface emission of VOCs frombuilding materials and decorating materials, and VOCssorption (Won et al., 2001; Yang et al., 2001; Hodgson et al.,2002; Haghighat and Huang, 2003; Huang and Haghighat,2003; Murakami et al., 2003; Zhang and Xu, 2003; Wilke et al.,2004; Xu and Zhang, 2004; Zhang and Niu, 2004; Kim andKim, 2005; Lee et al., 2005; Li and Niu, 2005). Some experimentshave also been performed to investigate VOCs diffusion insidethe materials (Meininghaus and Uhde, 2002; Onwandee et al.,2005; Huang et al., 2006; Zhang et al., 2007). The mainconclusions are as follows: The dimensionless emission rate of VOCs is only a functionof the ratio ofmass transfer Biot number to the partition co-efficient and of mass transfer Fourier number. For the multi-layer materials, the top layer materialsstrongly delay VOCs emission from the bottom layermaterials. The multi-layer materials have a much longerVOCs emission time and a slower VOCs decay rate thanthe single-layer materials. Polar VOCs are more easily adsorbed and quickly desorbedfrom building materials and decorating materials, whichcan reduce VOCs concentrations in the room air initiallyand elevate them as the time progresses.Plenty of paint is usually used to protect or beautifydecoratingmaterials and furniture, but VOCs emitted by paintaffect IAQ more seriously. Many experimental and numericalinvestigations on the emission of VOCs from paint have beenconducted (Chang et al., 2002; Fja ¨ llstro ¨m et al., 2003; Zhangand Niu, 2003a,b; Li et al., 2006). The main conclusions areas follows: 23 inpidual VOCs were detected, and the 7 major VOCswere 1-ethyl-3-methylbenzene, 1,2,4-trimethylbenzene, n-hexane, 1,3,5-trimethylbenzene, propylbenzene, o-xylene,and toluene. The sum of the amount of these 7 VOCs was85% of that of the total VOCs detected. About 65.2% of the VOCs were emitted within the first 4 h,and the emission then slows down and persists for a longperiod.