Please cite this article as: Bluyssen PM. Towards an integrative approach of improving indoor air quality, Building and Environment (2009), doi: 10.1016/j.buildenv.2009.01.012 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Accepted Manuscript Title: Towards an integrative approach of improving indoor air quality Authors: Philomena M. Bluyssen PII: S0360-1323(09)00022-5 DOI: 10.1016/j.buildenv.2009.01.012 Reference: BAE 2270 To appear in: Building and Environment Received Date: 7 November 2008 Revised Date: 15 January 2009 Accepted Date: 27 January 2009 T P I R CS U NA M D E T P E C CA ARTICLE IN PRESS 1 Towards an integrative approach of improving indoor air quality Dr Philomena M. Bluyssen TNO Built Environment and geosciences P.O. Box 49, 2600 AA Delft, The Netherlands Tlf +31 6 51806610 philo.bluyssen@tno.nl ABSTRACT There seems to be a discrepancy between current Indoor Air Quality standards and end-users wishes and demands. Indoor air quality can be approached from three points of view: the human, the indoor air of the space and the sources contributing to indoor air pollution. Standards currently in use mainly address the indoor air of the space. “Other or additional” recommendations and guidelines are required to improve indoor air quality. Even though we do not fully understand the mechanisms behind the physical, chemical, physiological and psychological processes, it is still possible to identify the different ways to be taken regulatory, politically-socially (awareness), technically (process and product) and scientifically. Besides the fact that there is an urgent need to involve medicine and neuro- psychology in research to investigate the mechanisms behind dose-response, health effects and interactions between and with the other factors and parameters of the indoor environment and the human body and mind, a holistic approach is required including the sources, the air and last but not least the human beings (occupants) themselves. This paper mainly focuses on the European situation. KEYWORDS Indoor air quality, source control, labelling, exposure and effect, risk assessment T P I R CS U NA M D E T P E C CA ARTICLE IN PRESS 2 INTRODUCTION Defining indoor air quality can be approached from three points of views: the human, the indoor air of the space and the sources contributing to indoor air pollution. From the human point of view, indoor air quality of a space is the physical effect of exposures of people to indoor air of the space they are visiting or occupying, as experienced by those people. Indoor air quality at a certain point in time can for example by expressed in an odorous unit, while indoor air quality over time can for example be related to the number of people developing a certain illness. From the indoor air point view, indoor air quality is often expressed in a certain ventilation rate (in L/s per person and/or L/s per m 2 floor area) or in concentrations for specific compounds. These concentrations are influenced by the sources present in (indoor sources) or outside the space (outdoor sources and sources present in HVAC systems or surrounding spaces). So, also from the source point of view indoor air quality can be approached. Emission rates per source unit for certain pollutants (used for labelling products in some countries) is then often the result. For mainly the second point of view (indoor air), standards and guidelines are in use for evaluating the indoor air quality (based on WHO air quality guidelines [50], ASHRAE [54], in some cases CEN [55] or nationally determined minimum guidelines based on the presence of people only (CO 2 concentration)). Even though those standards and guidelines are met, the quality of the indoor air, as experienced by the occupants, is still not acceptable and even unhealthy, causing health and comfort problems. There seems to be a discrepancy between current standards with end-users wishes and demands [1], [2]. Therefore, “other or additional” recommendations and guidelines are required to improve indoor air quality. T P I R CS U NA M D E T P E C CA ARTICLE IN PRESS 3 At European level, several initiatives are being taking ranging from exposure threshold values of pollutants to labelling of products and even buildings, such as: - The development of harmonized test methods for release or emission of dangerous substances to satisfy the requirements of Essential requirement 3 (ER 3) of the Construction Product Directive (CPD) (see Figure 1) [3]. - A standardised voluntary approach for the delivery of environmental information on construction products, and to assess the environmental performance of buildings [4]. - Harmonisation of several national labelling schemes for construction and furnishing products [5]. - REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) [6]. - Several currently running European funded projects: EnVIE [7], BUMA [8], HealthyAir [9], etc. This paper describes and discusses the problem(s) encountered with indoor air quality and possible ways to get to “other or additional” recommendations, based on examples and initiatives from mainly European origin. FACTS AND PROBLEMS Basically the following process is taking place in the indoor environment. A source (or sources) emits pollutants that come into the indoor air of a space, directly or indirectly. Those pollutants can react with each other or with pollutants from other sources, creating new pollutants (indoor air chemistry). And pollutants from other sources can react with the source. A person entering or occupying that space, is exposed to those pollutants present in the air of the space, which possibly creates a response (immediate or after some time), depending most likely also on previous and future exposures in the same or other spaces. From this latter step T P I R CS U NA M D E T P E C CA ARTICLE IN PRESS 4 can be concluded that relating a response to a pollutant or source is very difficult, unless lab controlled exposures using specific pollutants focused on specific responses is performed. But even then, since people can response differently and do have a history, this is a complex matter. The following facts and problems can be identified. The emission behaviour of sources is complex. This complexity is partly related to the fact that the mechanisms (diffusion, desorption, evaporation [10]) occurring in and on the sources are not well understood. There are sources in the indoor environment that emit compounds which are absorbed on indoor surfaces, for example occurring during cooking, cleaning or other user activities. Those compounds can be desorbed, react with compounds on the new source, and re-emit (secondary emission). This re-emission, but also the primary emission of sources is a complex phenomenon. For example the mass transfer coefficient for a compound in a building material differs for each of the mechanism mentioned but also for each combination compound (caused by polarity, volatility, vapour pressure) and source (caused by porosity, roughness and specific area) and for different conditions (such as temperature, humidity, air velocity). For the determination of these coefficients, for example for the diffusion coefficient of a pair chemical compound – building material, several experimental techniques are available, each having their pros and cons [11]. Another important issue is the emission over time (see Figure 2). Depending on the compound emitted, a different pattern of emission over time can occur. Emission patterns from more compounds emitted from a source can look quit complex. Nevertheless, a better understanding can possibly result in predictions and explanation on the emission behaviour to be expected (level and time frame of emissions). T P I R CS U NA M D E T P E C CA ARTICLE IN PRESS 5 Indoor and source surface chemistry create “new” fairly unknown compounds, not (yet) accounted for in current standards and guidelines. A source can also emit compounds that are caused by coming into contact with other products such as Ozone with organic compounds transforming to more highly oxidized species [14] or water facilitating the disproportionation of NO 2 in aqueous surface films, leading to increased levels of nitrous acid (HONO) in indoor air [15] (see also [16], [17], 18]). And a source can emit compounds that arise/develop during the in use phase of the source itself, such as ageing, cleaning or microbiological growth. Additionally, the mix of pollutants in indoor environments can be transformed due to chemical reactions resulting in a much broader analytical window of organic compounds that the classic window (as defined by the World Health Organisation (WHO)) used to explain the effects [19]. Ozone reactions, hydroxyl radicals reactions, but also other radical reactions (for example nitrate radical NO 3 ·) occur in the indoor environment. Secondary products formed comprise of formaldehyde, aldehydes and NO 2 . The concentrations of free radicals are not well known and are needed to advance indoor chemistry modelling [15]. The material constituents and moisture retention characteristics of a product determine the risk for microbial growth. Secondary emissions can also comprise of emissions of spores, mycotoxins, synergizers and VOCs from microbial growth on the surface of the product. It is known that moulds grow on practically any organic material provided there is enough water (not necessarily liquid). The availability of water in the indoor environment and on or in construction products is influenced by several factors: thermal performance of a building envelope, ventilation, occupant behaviour T P I R CS U NA M D E T P E C CA ARTICLE IN PRESS 6 (cleaning for example) and material characteristics. Studies have shown that the latter is the primary reason for microbial growth [20], [21]. Additionally, if a product comprises of organic materials, the risk for growth is higher than for completely inert materials. The trend towards eco-friendlier products has thus increased the potential growth risks (for example the use of water-based paints instead of oil-based). Organic dirt on inert material can also increase the risk, making the cleanability of a product an important characteristic. At present, an increased resistance against microbial attack, and therefore the prevention of mould growth, requires addition of biocides, with paints being the main application area. Because the actual period of time of biocides activity is short (max. 1-2 year), research is being performed to incapsulate the biocides and when moulds are present, the encapsulation breaks and slow release of the biocide occurs. An additional problem is that most traditional biocides, e.g. mercury compounds, are under prohibitive rules (European Union Biocidal Product Directive (BPD) [22]) or will be. Eco-friendlier, less toxic alternatives are needed. The HVAC systems can be a source of pollution as well, which is not always acknowledged. Research [23] has indicated that main sources and reasons for pollution in a ventilation system may vary considerable depending on the type of construction, use and maintenance of the system. In normal comfort ventilation systems the filters and the ducts seem to be the most common sources of pollution, especially odours. Oil residuals are the dominating source of pollution in new ducts, while growth of microorganisms, dust/debris accumulated in the ducts during the construction at the work site (mostly inorganic substances) and organic dust accumulated during the operation period in the ducts can be sources of pollution as well. If humidifiers and rotating heat exchangers (RHEs) are used, they are also reasonable to be suspected as remarkable pollution sources especially if not constructed and maintained T P I R CS U NA M D E T P E C CA ARTICLE IN PRESS 7 properly. Micro-organisms are the main source of air pollution if the air humidifier is not used in the manufacturer-recommended way and/or if they are not properly maintained. Desalinisation and demineralization devices/agents can also contribute to pollution of the passing air. In general, RHEs are not pollutant sources in themselves, except when the wheels are dirty. RHEs may transport contaminants from the supply to the exhaust in three ways: through air caught by the wheel, by leakage between wheel and gasket, and by adsorption- desorption on the surface area of the wheel. The pollution load caused by the heating and cooling coils seems to be less notable, except for cooling coils with condense water in the pans, which can be microbiological reservoirs and amplification sites that may be a major sources of pollution in the inlet air. What should be mentioned is that a positive effect of HVAC systems (i.e. mostly the filters) is perhaps the removal of ozone, reducing the indoor ozone concentration and levels of potentially harmful oxidation products [24]. To truly evaluate an exposure, all routes of exposure (physiological and psychologocial) should be taken into account jointly. And different humans will react differently to the same exposure. Human exposure to environmental factors (such as indoor air compounds) occurs mainly through the senses. Receptors in our nervous system receive sensory information as sensations via the eyes, ears, nose and skin, enhanced by bodily processes such as inhalation, ingestion and skin contacts. In addition to the stimuli that can be processed by our sensory system, the environment affects us in other ways, which are not recognisable to us. The latter stimuli can cause changes in our psychological state, of which we apparently do not know the cause (no conscious experience), but can also be harmful to our physical state of well-being (for example gases, chemical compounds, radiation etc.) [25]. So it seems that the received T P I R CS U NA M D E T P E C CA ARTICLE IN PRESS 8 information (sensations) can be looked upon from the physiology of the body and/or from the psychological point of view. Interactions may occur between stimuli in complex, real-life mixtures as well as between various body responses to exposure. Some stimuli cause only nuisance, others can give serious health problems. Some have short term effects, others long term. Our senses perceive individually, but interpretation occurs together. The bodily responses (physiologically and/or psychologically) are produced, regulated and sometimes “killed” by several systems in the body: the nervous system, the immune system and the endocrine system. The health effects of our human body to stimuli from the environment are controlled (or better fought against) by the immune system, while our emotions and evaluations are controlled by our limbic system and other parts of the brain (Figure 3). Additionally, the endocrine system provides boundary conditions for “control” of environmental stimuli by our immune as well as our limbic system. So they are pretty much intertwined. External stress factors such as indoor air compounds, influence all three systems of the human body (the nervous system, the immune system and the endocrine system) and can result in both mental and physical effects. Not being able to cope with a certain situation (consciously or unconsciously) can cause a whole range of different diseases and disorders, mostly indirectly related the environmental factors and affected by psycho-social and personal factors as well. Too much stress can cause short-term illness and long-term health problems both physical and mental. Hormones play an important role in the response [26]. Besides the effects of external stress factors, the performance of the human senses (internal stress factor) can also have a major influence on the first category of complaints. Degradation of the eyes, ears, olfactory bulb etc., usually occurring with age, are examples of this. T P I R CS U NA M D E T P E C CA ARTICLE IN PRESS 9 Degradation of the immune system functions also increases with age. Also here genetics can be of influence as well, such as being anosmic (not being able to smell normally). The way we evaluate our environment (perception) and the way we respond to our environment (behaviour) are two different processes. According to Vroon [27] this can be explained by the fact that the part of the brain that evaluates the environment is not the same as the part of the brain that controls the behaviour of a human being. This might explain why there is often a discrepancy between what people tell us what they need or want and what their behaviour tells us, or what they tell us what the cause is of certain complaints and what the real problem is. There are diverse techniques available to indicate the IAQ people are/were exposed to. An indication of the environmental quality the persons were exposed to can be given in the form of prevalence of symptoms, acceptability, measurable pollutants in the body fluids, prevalence of exposure to specific sources, or even investigating the brain. Questionnaires given to occupants of the investigated buildings [28] [29], interviews per telephone [30], medical examination and biological monitoring of body fluids of exposed people [31] [32], and the response of visitors of the investigated buildings, all belong to this group of techniques. There are no absolute tests for lethargy, headache and dry throat available. Objective measurements have been used to validate dry eyes, blocked nose and asthma symptoms. A diagnosis of allergy and hyper-reactivity can be established by several tests [33]. The same can be said of eye irritation [34] [35] [36] and for sensory irritation of the nose [37]. 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Indoor air quality can be approached from three points of view: the human, the indoor air of the space and the sources contributing to indoor. Defining indoor air quality can be approached from three points of views: the human, the indoor air of the space and the sources contributing to indoor air