Indoor air quality, modelling

Ott, W., P. Switzer, and J. Robinson, Particle Concentrations inside a Tavern before and after Prohibition of Smoking Evaluating the Performance of an Indoor Air Quality Model, J. Air Waste Manage. Assoc., 46, 1120-1134 (1996). 

Ozkaynak, H., P. B. Ryan, G. A. Allen, and W. A. Turner, Indoor Air Quality Modeling Compartmental Approach with Reactive Chemistry, Environ. Int., 8, 461-471 (1982). 

Indoor air quality models that include chemistry and all other important source and loss mechanisms have been developed by a variety of authors (Nazaroff and Cass, 1986 Weschler, Shields and Naik, 1989). These models can be used to determine if a relevant change is likely to occur, by balancing pollutant source rates with removal rates to arrive at a predicted indoor concentration. The key components are shown here for a steady-state, well-mixed mass-conservation model of a building ... 

A mass-balanced air quality model, such as is used in CONSEXPO and MCCEM, is the most widely accepted indoor air quality model. This focuses only on the air in the room environment, assuming that concentration in a room is uniform. Interactions of pollutant gain and loss are most often described through a differential equation that is applied to a defined indoor volume, as follows ... 

Keywords Adsorption Desorption Sink effects Sink models Indoor air quality models... 

In practical terms, an indoor air quality model should provide a reasonable description of the mass balance of the test chamber experiments, trying to address factors such as material emissions, airflows into and out of the chamber and chemical/physical decay or other removal and/or transformation processes of the VOCs. VOC concentrations are increased by emissions within the defined volume of the chamber and by infiltration from external air to the chamber. Similarly, concentrations are decreased by transport via exiting chamber air, by removal to chemical and physical sinks within the chamber air, or by transformation of a VOC to other chemical forms. A general mass balance equation concerning the concentration of a VOC in a test chamber can be written in the form of one or more differential equations representing the rate of accumulation and the VOC gain and loss. This concept for a VOC concentration C (mass units/ m ) in a chamber of volume V (m ) is translated into the following differential equation ... 

R. V. Nielsen. Model experiments for the determination of airflow in large spaces. In Indoor Air 9.. Proceedings of the 6th International Conference on Indoor Air Quality and Climate. Helsinki, Finland, 1993. 

As shown along this chapter, a reliable air quality model is a valuable tool for human exposure studies, once modelled concentrations at different spatial scales and time resolutions allow to better characterising the air quality at the microenvironments visited by a target population, rather than monitoring values that are site and time specific. Moreover, air quality and exposure modelling approach considers the contribution of indoor environments, where people spend most of their time, to the exposure estimation. 

We focus in this chapter on particles from ambient origin. We first illustrate differences in outdoor and personal exposure using data on real-time particle number concentrations (PNC) from a recent study in Augsburg, Germany. We then present a model of indoor PM concentrations, illustrating the factors that affect indoor air quality. We summarize empirical studies that have assessed indoor-outdoor relationships for particle mass, particle number, and specific components of particulate matter. The focus is on European studies, but we included key studies from outside Europe as well. We conclude by comparing the strength of indoor-outdoor relationships of various particle fractions and components. 

Muller, D., Bitter, F., Kasche, J. and Muller, B. (2005) A two step model for the assessment of the indoor air quality. Proceedings of the 10th International Conference on Indoor Air Quality and Climate, Indoor Air 2005, Beijing, China, Vol. I (1), pp. 20-5. 

Clausen, P.A., Laursen, B., Wolkoff, P., Rasmusen, E. and Nielsen, P.A. (1993) Emission of volatile organic compounds from a vinyl floor covering, in Modelling of Indoor Air Quality and Exposure, ASTM STP 1205, American Society for Testing and Materials, Philadelphia, PA, USA, pp. 3-13. 

Guo Z (2002) Development of a Windows-based indoor air quality simulation package. Environ Model Softw, 15 403-410 [models and information available at http // www.epa.gov/appcdwww/iemb/model.htm]. 

Won D, Shaw CY, Biesenthal TA, Lusztyk E, Magee RJ (2002) Applications of chemical mass balance modeling to indoor VOCs. Proceedings of the 9th international conference on indoor air quality and climate. Monterey, CA, USA, p 268... 

Guo Z (1993) In Nagda NL (ed) Modeling of indoor air quality and exposure, American Society for Testing and Materials. Philadelphia, PA, ASTM STP 1205 131 Wolkoff P, Clausen PA, Nielsen PA, Gunnarsen L (1993) Indoor Air 3 291 Wolkoff P (1996) Gefahrst Reinhalt Luft 56 151... 

Abstract Adsorption and desorption of indoor air pollutants to and from indoor surfaces are important phenomena. Often called sink effects, these processes can have a major impact on the concentration of pollutants in indoor environments and on the exposure of human occupants to indoor air pollutants, Basic theories are used to describe the processes using fundamental equations. These equations lead to models describing sink effects in indoor environments. Experimental studies have been performed to determine the important parameters of the sink models. Studies conducted in dynamic, flow-through environmental test chambers have quantified adsorption and desorption rates for many combinations of indoor air pollutants and interior surfaces. Sink effects have been incorporated into indoor air quality (lAQ) models to predict how adsorption and desorption processes affect... 

Dunn JE.Chen T (1993) In Nagda NL (ed) Modeling of indoor air quality and exposure. ASTM, Philadelphia, PA, p 64... 

Fig. 1. Schematic of the role of an air quality model, in the air quality control planning process. Some studies, for example, the prediction of indoor air...

Haley Indoor pollution by tobacco smoke Model studies on the uptake by nonsmokers im Indoor air, radon, passive smoking, particulates, and housing epidemiology Proc. 3rd Internal. Conf. Indoor Air Quality and Climate, Stockholm, Sweden, Vol. 2 (1984) 313-318. 

Several models have been developed in the last decade aimed at describing the emission of volatile organic compounds (VOCs) from indoor materials. These models may be broadly distinguished with respect to their conceptual background (physical-mass transfer models and/or empirical-statistical models) as well as their ability to describe different emission profiles. Physical models are models based on principles of physics and chemistry, whereas the empirical models do not necessarily require fundamental knowledge of the underlying physical, chemical and/or biological mechanisms. Many models used in the indoor air quality field in practice are hybrid models, in which aspects of both physical and empirical approaches are combined. 

However, the two-sink model as well as other existing adsorption (sink) models do not seem to be able to describe the strong asymmetry between the adsorption/desorption of VOCs on/from indoor surface materials (the desorption process is much slower than the adsorption process). Diffusion combined with internal adsorption is assumed to be capable of explaining the observed asymmetry. Diffusion mechanisms have been considered to play a role in interactions of VOCs with indoor sinks. Dunn and Chen (1993) proposed and tested three unified, diffusion-limited mathematical models to account for such interactions. The phrase unified relates to the ability of the model to predict both the ad/absorption and desorption phases. This is a very important aspect of modeling test chamber kinetics because in actual applications of chamber studies to indoor air quality (lAQ), we will never be able to predict when we will be in an accumulation or decay phase, so that the same model must apply to both. Development of such models is underway by different research groups. An excellent reference, in which the theoretical bases of most of the recently developed sorption models are reviewed, is the paper by Axley and Lorenzetti (1993). The authors proposed four generic families of models formulated as mass transport modules that can be combined with existing lAQ models. These models include processes such as equilibrium adsorption, boundary layer diffusion, porous adsorbent diffusion transport, and conveetion-diffusion transport. In their paper, the authors present applications of these models and propose criteria for selection of models that are based on the boundary layer/conduction heat transfer problem. 

Dunn J.E. and Chen T. (1993) Critical evaluation of the diffusion hypothesis in the theory of porous media volatile organic compounds (VOC) sources and sinks. In Nagda N.L.(ed) Proceedings of Modeling of Indoor Air Quality and Exposure, ASTM STP 1205, 64 - 80. 

In modelling of indoor air quality and especially in source characterization of problem buildings, the complete system should, however, be considered. 

The emission process from a flooring material has been characterized by two principal mechanisms a diffusion-controlled mass transfer in the material and an evaporation-controlled emission mechanism from the surface. These mechanisms, together with the air velocity and concentration effects over the evaporative surface, are considered the principal mechanisms governing the physical factors affecting the emissions, and models have been developed to describe the effect on indoor air quality (Gunnarsen, 1991 Matthews et al., 1987 Neretnieks et al., 1993 Sparks, 1996). 

Secondary emissions have the potential to explain continued deterioration of the air quality in many buildings. The small number of studies carried out in real buildings demonstrate that the magnitude of secondary emissions is important for indoor air quality. Future intervention studies involving the diurnal operation of ventilation and heating systems could give more validity to the reported small-chamber experiments and mathematical models giving preliminary credibility to the importance of the processes. 

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