Particles indoors

A major source of increased particles indoors is cigarette smoking, (e.g., Spengler et al., 1981 Quacken-boss et al., 1989 Neas et al., 1994). Figure 15.16 shows... 

A number of models have been developed for particles indoors (e.g., Nazaroff and Cass, 1989a Sinclair et al., 1990b Nazaroff et al., 1990a Weschler et al., 1996 Wallace et al., 1996, and references therein). This is a complex problem, given the number of potential sources, different deposition velocities for particles of different sizes (e.g., see Chapter 9.A.3 and Nazaroff and Cass (1989b)), the different particle compositions, and the effects of outdoor concentrations and ventila-... 

Empirical studies have used different methods to describe quantitative indoor-outdoor relationships [11]. Many studies have used the indoor I outdoor ratio (I/O ratio). The I/O ratio of occupied homes is difficult to interpret as it is affected by indoor sources and by infiltration of outdoor particles indoors. I/O ratios from different studies have shown a very wide range from well below 1 to well above 1 [11]. Some studies have attempted to exclude homes with major indoor sources such as smoking and use of gas appliances for cooking to obtain more interpretable values [13, 14, 19]. Because of the variety of indoor sources, this has generally not been successful. In a Swedish study that purposefully selected homes without smokers and gas appliances, indoor PM2.s concentrations were still for 60-90% caused by indoor sources [14]. The authors speculate that... 

Chemical leach tests on the bulk settled dust samples showed that the dusts are quite chemically reactive. Leach solutions have high alkali-nities, due to the rapid partial dissolution of calcium hydroxide from concrete particles. Indoor dust samples produced higher pH levels (11.8-12.4) and alkalinities (—600 mg CaCOa) than outdoor dusts (pH 8.2-10.4 alkalinity —30mgL CaCOa), indicating that outdoor dust samples had reacted with rainfall or other water prior to collection. Thurston et al (2002) found that the leachate pH of the dusts decreased with decreasing particle size. Some metals or metalloids in the dusts (aluminum, chromium, antimony, molybdenum, barium, copper, zinc, cobalt, nickel) are readily leached by deionized water many of these form oxyanion species or carbonate complexes that are most mobile at the alkaline pH s generated by the leachates. 

Jamriska M, et al. Control strategies for sub-micrometer particles indoors model study of air filtration and ventilation. Indoor Air 2003 13(1) 96-105. 

In the absence of a widely accepted test suitable for indoor environments, the test engineer will have to use best judgment in deciding how to carry out coarse particle testing. Fortunately, the effects of coarse particles indoors are usually small. 

Whenever unvented combustion occurs iadoors or when venting systems attached to combustion units malfunction, a variety of combustion products win be released to the iadoor environment. Iadoor combustioa units include nonelectric stoves and ovens, furnaces, hot water heaters, space heaters, and wood-burning fireplaces or stoves. Products of combustion include CO, NO, NO2, fine particles, aldehydes, polynuclear aromatics, and other organic compounds. Especially dangerous sources are unvented gas and kerosene [8008-20-6] space heaters which discharge pollutants directly into the living space. The best way to prevent the accumulation of combustion products indoors is to make sure all units are properly vented and properly maintained. 

The concentration of indoor pollutants is a function of removal processes such as dilution, filtration, and destruction. Dilution is a function of the air exchange rate and the ambient air quality. Gases and particulate matter may also be removed from indoor air by deposition on surfaces. Filtration systems are part of many ventilahon systems. As air is circulated by the air-conditioning system it passes through a filter which can remove some of the particulate matter. The removal efficiency depends on particle size. In addition, some reactive gases like NOj and SOj are readily adsorbed on interior surfaces of a building or home. 

Negative ion generators use static charges to remove particles from the indoor air. When the particles become charged, they are attracted to surfaces such as walls, floors, table tops, draperies, and occupants. Some designs include collectors to... 

The setting of indoor air quality targets is much more complicated and individualized, T his is due to the fact that the chemical process in paper making differs from paper type to paper type. Also, the amount of particles is highly dependent on the speed of the machine, the percentage of recycled mass, and the percentage of stone in the paper. 

Modern measuring techniques, an increased requirement for the indoor environment, and the efficiency of filters in separating particles led to EUROVENT 4/9 1992 Method of Testing Air Filters Used In General Ventilation for the Determination of Fractional Efficiency. This method also provides the basis for the next revision or upgrade of European Standard EN 779 1999. 

S. Murakami, S. Kato, S. Nagano, Y. Tanaka. Diffusion characteristics of airborne particles with gravitational settling in a convective-dominant indoor flow field. ASHRAE Transactions. 98(1), 1992, 82-97. 

Two-stage precipitators consist of separate sections for particle charing and collection. Particle charging is realized with corona wires between grounded metal plates. The collection of particles rakes place in a system of parallel plate electrodes of opposite polarities. Two-stage precipitators are typically used in indoor air cleaning and light industrial applications. 

Particle air cleaning is any process that is used intentionally to remove particles from the indoor air. Eiltradon and electronic air cleaning are the two most... 

Environmental tobacco smoke (ETS) is the diluted mixture of pollutants caused by smoking of tobacco and emitted into the indoor air by a smoker. Constituents of ETS include submicron-size particles composed of a large number of chemicals, plus a large number of gaseous pollutants. Fibers in indoor air include those of asbestos, and man-made mineral fibers such as fiberglass, and glass wool. 

Particles are present in outdoor air and are also generated indoors from a large number of sources including tobacco smoking and other combustion processes. Particle size, generally expressed in microns (10-6 m) is important because it influences the location where particles deposit in the respiratory system (U.S. Environmental Protection Agency 1995), the efficiency of particle removal by air filters, and the rate of particle removal from indoor air by deposition on surfaces. 

Some particles and fibers may be generated by indoor equipment (e.g. copy machines and printers). Mechanical abrasion and air motion may cause particle release from indoor materials. Particles are also produced by people, e.g., skin flakes are shed and droplet nuclei are generated from sneezing and coughing. Some particles may contain toxic chemicals. 

Efficiency of any air cleaner or filter is a function of the particle size present in the indoor air and the velocity and volume ot air flowing through the device. 

There are a series of papers that focus on the behavior of the radon decay products and their interactions with the indoor atmosphere. Previous studies (Goldstein and Hopke, 1983) have elucidated the mechanisms of neutralization of the Po-218 ionic species in air. Wilkening (1987) reviews the physics of small ions in the air. It now appears that the initially formed polonium ion is rapidly neutralized, but can become associated with other ions present. Reports by Jonassen (1984) and Jonassen and McLaughlin (1985) suggest that only 5 to 10% of the decay products are associated with highly mobile ions and that much of the activity is on large particles that have a bipolar charge distribution. 

Particle size is a major factor which determines the alpha dose conversion factor for radon daughters (mGy/WLM). Data on indoor environments are emerging and indicate that a variety of specific conditions exist. For example, a dose factor four times that for a nominal occupational or environmental exposure exists if kerosene heater particles dominate the indoor aerosol and four times smaller if a hygroscopic particle dominates. 

It is important to update the bronchial dosimetry for radon daughters as new information becomes available. It is the purpose of this study to show that there is a potential for either significantly increased bronchial dose in the home per unit exposure if the ambient particle size is artificially reduced due, for example, to open-flame burning or use of kerosene heaters, or a decreased dose if hygroscopic particles dominate the indoor aerosol. 

Table II shows the nominal alpha dose factors for occupational mining exposure. Table III shows the alpha dose factors for the nominal environmental situation. Table IV shows the bronchial dose factors for the smallest sized particles, that dominated by the kerosene heater or 0.03 pm. particles. The radon daughter equilibrium was shifted to a somewhat higher value in this calculation because this source of particles generally elevates the particle concentration markedly with consequent increase in the daughter equilibrium. Table V shows the alpha dose for a 0.12 pm particle, the same as the nominal indoor aerosol particle, but for a particle which is assumed to be hygroscopic and grows by a factor of 4, to 0.5 pm, once in the bronchial tree.

---