Indoor air pollution

resources, conservation ELSEVIER

Resources, Conservation and Recycling 16 (1996) 77-91

and recycling i

Indoor air pollution Wei-Han Su Environmental Engineering Program, Asian Institute of Technology, Bangkok, Thailand

Keywords: Air quality; Indoor environment; Pollutant; Emission

1. Introduction The quality of the air we breath and the attendant consequences for human health are influenced by a variety of factors. These include hazardous material discharges indoors and outdoors, meteorological and ventilation conditions, and pollutant decay and removal processes. Over 80% of time for most people is generally spent in indoor environments [1] so that the influence of building structures, surfaces, and ventilation are important considerations when evaluating air pollution exposures. Recognition that the indoor air environment is not an exact reflection of outdoor conditions is of relatively recent emergence. The impact of cigarette smoking, store and oven operation, and emanations from certain types of particle board, cement, and other building materials are often the most significant determinants of indoor air quality. The impact of energy conservation on inside environments may be substantial, particularly with respect to decreases in ventilation rates. A variety of indoor-air measurement studies have been carried out [2,1]. On the basis of these studies, typical nonindustrial indoor concentration for some pollutants of concern are listed in Table 1. For calculating indoor pollutant, a pollutant mass balance model for an interior space can be used, it's general form is: Pollutant flow in - pollutant flow out + source emission - sink removals = indoor pollutant accumulation The use of this equation makes possible the comparison of a variety of altematives for control of an indoor pollution problem. In order to protect public health, air quality standards for indoor air have been recommended in some countries, e.g., the United States. A partial list of occupational standards in the US is given in Table 2. However, there is still a lack of definition about the governmental agencies responsible for indoor Elsevier Science B.V.

SSDI 0 9 2 1 - 3 4 4 9 ( 9 5 ) 0 0 0 4 8 - 8

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air quality and there are presently no legally enforceable health-related standards for living and recreational space or transportation modes. W i t h the continued increase in e n e r g y cost, both present and future dwellings, as w e l l as public and office buildings, will be d e s i g n e d o r altered to c o n s e r v e heat and refrigeration. A n d these changes call for the application o f both existing and n o v e l characterization and control techniques w h i c h h a v e b e e n adapted to and e v a l u a t e d for the nonindustrial setting. This paper, h o p e f u l l y , supplies a basis for understanding indoor air pollution problems, and also characterization and control of indoor air pollutants.

Table 1 Typical indoor pollutant concentrations Pollutants of concern

Concentration (sampling time)

Location

Carbon monoxide, CO

2.5-2.8 ppm 3.1-7.8 ppm (seasonal averages of 12-h samples) 0.005-0.317 ppm (1 wk) 0.005-0.11 ppm (24 il) < 0.06 ppm(24 h)

Offices, restaurants, bars, arenas Kitchen of homes with gas stoves

Nitrogen dioxide, NO 2

Respirable particles, RP

Total suspended particles, TSP

Asbestos

Formaldehyde, HCHO

Ozone, 03 Radon, Ra-222

Radon daughters

Benzo( a )pyrene Dimethylnitrosamine Carbon dioxide, CO2

Viable particles

100-700/zg/m 3 (8-50 rain) 20-60/,tg/m 3 (I-42 mill) 10-70 ~ g / m 3 (24 h) 39-66/xg/m 3 (averages of 12-h samples; 26-72% of outdoor concentrations) 2.7-79.4/xg/m 3 (48 h) 0-100 ng/m 3 (0-2X 104 fibers/m 3) (5 min to 10 h) 20X 106 fibers/m 3 60-1673 ppb ( ~ 1 h; 463 ppb average for all measurements) 30-1770 ppb (35-60 rain) < 0.002-0.068 ppm (40 rain to 2 h) < 0.002-0.018 ppm (30 rain) 0.005-0.94 pCi/l (0.01 pCi/I average) < 25-34 pCi/I (averages of 3- to 6-rain samples) 0.003-0.013 WL (average: 0.004 WL) 0.005-0.05 WL (average: 0.01 WL; averages of > 24-h to 1-wk samples) 7.1-21.0 ng/m 3 ( ~ 2-4 h) 0.I 1-0.24 p g / m 3 (90 rain) 0.086% (5 min) 0.06-0.25% 0.9% (continuous measurements for ~ 8 wk) 20-700 CFP/m 3 (averages of 10-rain samples taken every 40 rain)

English homes with gas cookers American homes with gas stoves American homes with electric stoves Restaurants, sport arenas, residences with smoking without smoking Residences Homes, public buildings

Urban hospital Normal activities During maintenance Homes with chipboard walls Mobile homes Photocopying machine room Homes with electrostatic air cleaners House in Boston House on Florida reclaimed phosphate land Houses in New York, Hew Jersey Houses on reclaimed phosphate land in Florida Sports arena Bar Lecture hall School room Nuclear submarines Schools, hospitals, residences

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2. Characterization of principal indoor air pollutants These indoor air pollutants include carbon monoxide, nitrogen oxides, tobacco smoke components, suspended particulate matter - both total suspended particulate matter (TSP) and respirable particles (RP), asbestos, formaldehyde, ozone, radon (Ra-222), carbon dioxide, and organics viable particulate matter.

2.1. Carbon monoxide (CO) It is a chemical asphyxiant gas. Its affinity for hemoglobin in red blood cells is 200-250-times that of oxygen, which can result in significant reduction in oxygen-carrying capacity.

2.2. Nitrogen oxides (NOx) Most health effects associated with NO x have been attributed to nitrogen dioxide NO 2. Levels of NO 2 above 282 m g / m 3 (150 ppm) can be lethal, while concentrations in the range of 94-282 m g / m 3 (50-150 ppm) can produce chronic lung disease.

2.3. Tobacco smoke Tobacco smoke contains both particulate matter (most of which is in the respirable range < 1 ~m) and gaseous components. Some of these are listed in Table 3. Other components include phenols, naphthalenes, trace metals, hydrogen cyanide, ammonia, and radioactive polonium 210 [3]. There is evidence which points out the association between involuntary smoking and adverse health conditions. Parental smoking appears to be a cause of increased respira-

Table 2 Air quality standards promulgated by the United States Environmental Protection Agency Standard concentration p,g/m3 Suspended particulate matter, TSP Sulfur dioxide, SO 2

Carbon monoxide, CO Nitrogen oxides, NO 2 Ozone, 03 Nonmethane hydrocarbons Lead, Pb

ppm

75 (60) b _ 260 (150) b -80 0.03 365 0.14 (1300) b (0.50) b 10000 9 40000 35 100 0.05 235 0.12 160 0.24 1.5

a [9].

b Secondary standards in parentheses.

averaging time Annual geometric mean 24h Annual mean 24h 3h 8 h no more than once per year 1 h no more than once per year Annual mean 1 h dally maximum no more than once per year 6 - 9 a.m. average no more than once per year 3 month average

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Table 3 Emission factors for mainstream and sidestream smoke Properties General characteristics Duration of smoke production Amount of tobacco burnt Number of particles per cigarette Particle number median diameter Particulate phase Total suspended particulate matter Tar (chloroform extract) Nicotine Total phenols Pyrene Benzo( a)pyrene Naphthalene Methylnaphthalene Aniline NNN a NNK u Cadmium Nickel Arsenic 2-Naphthylamine Hydrogen cyanide Polonium-210 Gases and vapors Carbon monoxide Carbon dioxide Acetaldehyde Hydrogen cyanide Methylchloride Acetone Ammonia Pyridine Acrolein Nitric oxide Nitrogen dioxide Formaldehyde DMN e NPy f

Mainstream

Sidestream

Sidestream/ mainstream ratio

20 s 347 mg 1.05 × 10 t2

550 s 411 mg 3.5 × 1012

27 1.2 3.3

0.2/~m

0.15/~m

0.75

p,g/cigarette 36200

/.tg/cigarette 25 800

0.7

< 500-29000 100-2500 228 50-200 20-40 2.8 2.2 0.36 0.1-0.55 0.08-0.22 0.13 0.08 0.012 0.002-0.028 - 4 0.029-0.044 p C i / cigarette /.tg/cigarette 1000-20000 20000-60000 18-1400 430 650 100-600 10-150 9-93 25-140 10-570 0.5-30 20-90 10-65 10-35

44100 2700-6750 603 180-420 68-136 40 60 10.8 0.5-2.5 0.8-2.2 0.45 0.08 -

2.1 2.7 2.6 3.6 3.4 16 28 30 5 10 3.6 39 -

p,g/cigarette 25000-50000 160000-480000 40-3100 110 1300 250-1500 980-150 000 90-930 55-300 2300 d 625 d 1300 520-3380 270-945

2.5 8.1 2.2 c 0.25 2.1 2.5 98 10 2.2 c 4 20 15 52 27

a Nitrosonornicotine (NNN). u 4-(N-methyl-N-nitrosamino)-l-(3-pyridyl)- l-butanone (NNK). c Ratioed from total aldehydes. d Assuming a mixing factor of 1.0. Values will be lower if mixing was less than ideal. e Dimethylnitrosamine (DMN). f Nitrosopyrolidine (NPy).

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tory disease in children in the first year of life. Involuntary smoking by patients with coronary heart disease has been shown to reduce the time at which angina occurs after exercise. Questions on involuntary smoking by workers are still more serious in view of the known synergism between voluntary smoking and occupational carcinogens such asbestos and uranium [4].

2.4. Asbestos Asbestos is a generic term that applies to several naturally occurring, hydrated mineral silicates. Asbestos particles in the ambient air appear as fibers. Most of the asbestos is used in bonded form in the construction industry, another part is friable or in powder forms in insulation and acoustical products, and asbestos cement powders. Significantly increased risk of death from nonmalignant respiratory disease has been reported in the insulation and other asbestos industries [5]. In addition, all commercial forms of asbestos have been shown to be carcinogenic in man.

2.5. Formaldehyde It is an important industrial chemical used to produce synthetic urea- and phenol-formaldehyde resins. Formaldehyde also is one of the reaction products of atmospheric photochemical smog. In addition it is present in tobacco smoke, emissions from combustion processes, and most dangerous for people in their homes, emanation from furniture, building materials, and textiles containing HCHO resins. Burning of the eyes, lacrimation, and general irritation of the upper respiratory passages are the first signs experienced at HCHO concentrations in the 0.1-5 ppm range. The odor of formaldehyde is generally sensed at 1 ppm, but some individuals can detect it at 0.05 ppm [6].

2.6. Suspended particulate matter (TSP) It is generally considered to consist of all airborne solid and low-vapor-pressure liquid particles less than a few hundred micrometers in diameter. In general, the concentration of total suspended particulate matter is significantly lower indoors than outdoors. However, there has been considerable interest in the respirable fraction of suspended particulate matter (RP), where the particle mass is < 2.5 /zm in diameter. Since RP is contained in cigarette smoke, consumer spray products, and other indoor sources, the potential health implications are of concern.

2.7. Radon and radon daughters Radon-222 (Rn-222) is a noble gas decay product of radium-226 (Ra-226) which, in turn, is part of the decay chain of uranium-238 (u-238). Rn-222 has a half-life (tt/2) of 3.8 days, is an ot emitter as are several of its daughters (polonium-218, tt/2 = 3 min; polonium-214, tl/2 = 1.6 × 10 -4 s), and is essentially inert to chemical reaction. Any substance containing uranium or radium is a source of Ra-222. Since the t~/2 for Ra-226

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is over 1600 years, the Ru-222 production rate is essentially a constant. Various types of soil and masonry building materials have been identified as sources [7,8]. The average indoor-to-outdoor radiation close ratio has been estimated at 1.3 for buildings constructed of granites, brick and concrete, in contrast to a ratio of about 0.75 for wooden structures [8]. The presence of Rn-222 and its daughter products have been identified as a major factor in the causation of lung cancer in uranium miners in the United States, Canada, and non-uranium miners in Sweden, Newfoundland, and the United Kingdom [7,8]. The mean induction rate of lung cancer for all ages has been estimated to be in the range of 200-450 x 10 -6 rad -1 of radon-222 type radiation and is likely to be higher for males and females over 35 years of age (the rad, the common unit of absorbed radiation dose, is equal to 100 ergs/g in any medium). 2.8. Ozone

Ozone is a pulmonary irritant that affects the nocuous membranes, other lung tissues, and respiratory function [9]. Indoor sources that may contribute significant amounts of ozone include copying machines and electrostatic air cleaners. 2.9. Carbon dioxide

Carbon dioxide is produced by human metabolism and exhaled through the lungs. The amount of CO 2 produced is a function of food composition and the activity level of an individual. The amount of CO 2 normally exhaled by an adult with an activity level representative of an office worker is about 200 m l / m i n [10]. Exposure of healthy individuals for prolonged periods to 1.5% CO 2 apparently causes mild metabolic stress, while exposure to 7-10% will produce unconsciousness within a f e w minutes [11]. Ventilation standards are normally set to maintain CO 2 indoor concentration < 0.5%, a level with appears not to adversely affect persons with normal health [12]. 2.10. Organic compounds

A great variety of organic materials have been identified in indoor air. These include aliphatic and aromatic hydrocarbons, chlorinated hydrocarbons, and various ketones and aldehydes [13]. While some of these have been suggested as possible carenogens, e.g., benzene and tetrachloroethylene, the actual health implications of most organics found in indoor air are not presently well defined. 2.11. Viable particulate matter

Pollen, bacteria, fungal and plant spores, and viruses are all associated with airborne particles. A common measurement of viable particles is called total viable particles (TVP) or colony-forming particles (CFP). Ordinarily this measure reflects bacterial activity and does not include pollen or viruses and often also excludes fungal spores. In general, TVP concentrations are closely related to living conditions and indoor activity.

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Table 4 Emissions of some pollutants from wood burning stoves and fireplaces Pollutant Emissions, g/kg wood (range) CO NOx as NO2 SOx as SO2 Formaldehyde Acetaldehyde Phenols Total particulate matter Benzo(ot)pyrene

stoves

fireplaces

160 (83-270) 0.5 (0.2-0.8) 0.2 (0.15-0.45) 0.2 (0.1-0.3) 0.1 1.0 (0.1-2.4) 9.2 (1-28) 0.0025

22 (11-40) 1.8 0.4 0.02 9.1 (7.2-12) 0.00073

It has been established, based on measurements in schools, hospitals, and residences, that humans live in air with a 'bioburden' between 20 C F P / m 3 to 70 C F P / m 3 without apparent ill effects. Air conditioners and cool-mist humidifiers have been identified as devices where pathogenic organisms may concentrate and later be released as concentrated viable aerosols [6].

3. I n d o o r sources

3.1. Combustion

The major indoor combustion sources are appliances burning coal, gas, kerosene, wood, and also agricultural waste, even animal waste in some individual places. Typically, range, oven, and pilot light emissions are not rented and can contribute to indoor levels of CO, NO, NO 2, SO 2, HCHO, particulates including soot and some polyaromatic organic compounds, e.g., benzo(a)pyrene. Indoor measurements in kitchens with coal or wood stoves indicated that average indoor TSP and benzo( ct)pyrene levels were, respectively, 3- and 5-times the levels when stoves were not used ([14], see Table 4). 3.2. Smoking

Tobacco smoke contains a great variety of potentially hazardous materials. Actual emission factors per cigarette for a number of these substances are given in Table 3. Mainstream smoke is that which is inhaled by a smoker and the emission factors are representative of pre-inhalation conditions. Many of the pollutants will be filtered out in the smoker's lungs, e.g., 70% of the particulate matter [15]. Sidestream smoke is primarily the unfiltered smoke emitted from an idling cigarette, cigar, or pipe. The emission factors for sidestream smoke are consequently more useful for characterization of indoor environments where smoking is allured (see Table 3). The particle sizes of

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Table 5 Radon emanation rates of various materials [8] Material

Emanation rate of Rn-222 per unit activity concentration of Ra-226 ( p C i / m 2. s per p C i / g )

Comments

By-product gypsum By-product gypsum Concrete Uranium mill tailings Uranium mill tailings Soil Light concrete Heavy concrete

0.01 0.001 0.005 0.2 1.6 0.5 0.02 0.01

Internal walls 76 m m thick Ceilings 13 m m thick 10 cm thick 10 cm thick 'Infinite' thickness 'Infinite' thickness 20 cm thick 8 cm thick

smoke particles shown in Tables 3 and 4 are likely to penetrate and deposit in the alveolar spaces of the lung.

3.3. Building materials 3.3.1. Radon daughters Various types of construction materials have been identified as sources of hazardous materials. Table 5 indicates the Rn-222 emanation rate per unit activity concentration of Ra-226 ( p C i / m 2- s per pCi/g). Table 6 shows the radon concentration in a natural gas in the distribution line. The diffusion of Rn-222 from building materials is influenced by moisture content of the material, density, the presence of sealants, the nature of the substances with which it is mixed. 3.3.2. Formaldehyde Particle board and urea-formaldehyde foam insulation have been identified as HCHO emission sources [16]. HCHO concentration of 60-1673 ppb (°C, 1 atm) with an average

Table 6 Radon concentration in natural gas in the distribution line [8] Radon concentration (pCi/I) Area

average

range

Poland (Warsaw) United States Chicago New York City Denver West coast Colorado Nevada New Mexico Houston

8

4-14

14.4 1.5 50.5 15 25 8 45 8

2.3-31.3 0.5-3.8 1.2-119 1-100 6.5-43 5.8-10.4 10-53 1.4-14.3

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Table 7 Emission factors for several urca-formaldehydefoams Number of Observations Average of data from 3 commercial foams tested at 33°C under 10 and 85% relativehumiditiesover the intervalof 10-30 days after foaming. 85% Relativehumidityonly 10% Relativehumidityonly Commercial foam exposed at 35°C and 90% relativehumidityover the interval of 9-26 days.

Emission factor (/.tg HCHO/g foam. min) mean

standard deviation

42

o. 109

0.050

21 21 2

o. 122 0.095 0.170

0.040 0.056

of 463 ppb were measured in 25 rooms in 23 Danish dwellings where chip board was used in the walls, floors, and ceilings [17]. Urea-formaldehyde foam is produced when the two major constituents are combined with a catalyst and forced from a pressurized nozzle. The reaction is H 2 N C N H 2 + HCHO H2NC - NH - CH2OH The product is cured to a hardened resin; HCHO may be emitted from this resin. Emission factors for urea-formaldehyde foams are shown in Table 7. 3.3.3. A s b e s t o s Asbestos fiber contamination of a building interior by fallout, contact or impact, and reentrainment. The rate of fiber release in fallout is continuous, low-level, and persistent. The range of concentrations is roughly from nearly zero for cementations mixes in good repair to 100 n g / m 3 for deteriorating dry mix applications.

Table 8 Ozone emissionsfrom copying machinesand domestic air cleaners

Electrostatic air cleaners 8 Installedin central air conditioningsystems 'Several well-knownmanufacturers'electronicair cleaners' (on central air conditioningsystems) 1 Portableunit Two-stage, low-voltageindustrialunit ( I pass; 2 passes will double the emissionrate)

Maximum voltage

Ozone emissionfactors (p.g/min)

5000-7900

0-546 303-1212

9900 11,000

84 333 (/zg/copy)

11 Photocopyingmachines a Typical copy rate, 5 copies/rain.

3500-11000

range 2-158; typically 15-45

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Table 9 Emissions of chrysotile asbestos from 21 hand-held hair dryers [19] Emission Rate a Fibers/hr Total mass (ng/h)

Maximum

Median

Minimum

1.9× 106 3305

1.1 × l0 s 220

7X 103 I

a Samples of emissions were analyzed by transmission electron microscopy. Data are derived from 2-h high-heat test runs only. There was no statistical difference between results obtained from 2-h high-heat test runs and those obtained by cycling between high and low heat for 2 h. Data under column headings do not necessarily represent tests on the same hair dryer [20].

3.4. Office and domestic electrostatic machine Tests on p h o t o c o p y i n g machines, and d o m e s t i c and c o m m e r c i a l size electrostatic air cleaners h a v e s h o w n these d e v i c e s to be indoor o z o n e sources. Appropriate e m i s s i o n factors are g i v e n in T a b l e 8.

3.5. Other sources D o m e s t i c activities are one o f the sources o f h a z a r d o u s materials. A s b e s t o s is discharged f r o m hair dryers, and typical data are g i v e n in T a b l e 9. A i r fresheners, furniture waxes, and paints are typical o f h o m e products d e l i v e r e d in aerosol form, as s h o w n in Table 10. H u m a n s t h e m s e l v e s constitute e m i s s i o n sources for various materials. T a b l e 11 lists e m i s s i o n factors for a variety o f organic and inorganic substances.

4. Air quality model T h e mass balance for pollutant f l o w into and out o f an i n d o o r v o l u m e , including recycling and interior sources and sinks, is described in Fig. 1 and e x p r e s s e d by A i r mass balance: q0 + q2 -- q3 + q4

(1)

Table 10 Typical aerosol size distributions for estimating inhalation exposure from pressurized consumer products [21] Product type

Total aerosol concentration (mg/m 3)

Mass median aerodynamic diameter (/zm)

Weight % of aerosol in each aerodynamic diameter range < 1 p.m

1-3/~m

3-6 p.m

Air freshener Antiperspirant Dusting aid Fabric protector Fumiture wax Hair spray Paint Wood panel wax

27 246 86 9 22 30 189 15

5.2-6.3 5.9-7.3 6.4-7.5 2.6-4.0 3.0-4.9 5.8 - 6.4 7.2-8.7 1.4-1.5

5 3 2 13 11 5 2 2

16 17 10 30 29 16 8 5

32 30 30 28 34 29 22 22

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Table I 1 Materials emitted by humans [22]

Organic bioeffluent Acetone Acetaldehyde Acetic acid Allyl alcohol Amyl alcohol Butyric acid Diethylketone Ethyl acetate Ethyl alcohol Methyl alcohol Phenol Toluene Inorganic bioeffluent Carbon monoxide Ammonia Hydrogen sulfide Carbon dioxide

Typical concentrations (ppb) (389 people in lecture class at 9:30 a.m.)

Emission rate ( r a g / d a y per person) lecture class

exam

20.6 = 2.8 4.2 = 2.1 9 . 9 = 1.1 1.7 = 1.7 7.6 = 7.2 15.1 = 7.3 5.7 = 5.0 8.6 = 2.6 22.8 = 10.0 54.8 = 29.3 4.6 = 1.9 1.8 = 1.7

50.7 = 27.3 6.2 = 4.5 19.9 = 2.3 3.6 = 3.6 21.9 = 20.8 44.6 = 21.5 20.8 = 11.4 25.4 = 4.8 44.7 = 21.5 74.4 = 5.0 9.5 = 1.5 7.4 = 4.9

86.6 = 42.1 8.6 = 4.6 26.1 = 25.1 6.1 = 4.4 20.5 = 16.5 59.4 = 52.2 1 1 . 0 = 7.7 12.7 = 15.4 109.0 ~ 31.5 57.8 = 6.3 8.7 = 5.3 8.0

4.84× 103 = 1.2× 103 32.2 = 5.0 2.73 = 1.32 6 4 2 × 103 = 34X 103 0.63 ft 3 CO2 a

2.96 = 0.68 930X 103= 52X 103

met. h. person ' [12l. Pollutant mass balance: dCi

V'-d-Z = kqoCo(1 - Fo) + kqlCi( l - F i ) + kq2Co - k ( qo + ql + q2)Ci + S - R

(2) Where

C~ c o n c e n t r a t i o n o f p o l l u t a n t i n d o o r s C O concentration of pollutant outdoors t

time

qo

volumetric flow rate for make-up air

q~

volumetric flow rate for recirculation

q2

volumetric flow rate for infiltration

q3

volumetric flow rate for exfiltration

q4

volumetric flow rate for exhaust

F 0 filter efficiency for make-up air FI

filter efficiency for recirculation air

V

room volume

S

indoor source emission rate

R k

indoor sink removal rate a f a c t o r w h i c h a c c o u n t s f o r i n e f f i c i e n c y o f m i x i n g , is a f r a c t i o n o f i n c o m i n g air which completely mixes within the room volume

88

W.-H. Su / Resources, Conseruation and Recycling 16 (1996) 77-91 Air Quality Models INFILTRATION FROM OUTDOORS, OUTDOOR CONCENTRATION

MAKEUP AIR OUTDOOR CONCENTRATION

RECIRCULATION, INDOOR CONCENTRATION

a2.c o

ao'C o

al.C i

I FI,rE.

,i Fo I F'L'rE"

I

ROOM VOLUME = V POLLUTANT DECAY = R POLLUTANT GENERATION = S MIXING FACTOR = K

I 1

EXFILATRATiON INDOOR CONC ENTRATION

EXHAAUST. INDOOR CONCENTRATION

a 3. C i

a4.C i

Fig. 1. Ventilation system for time varying indoor-outdoor model.

The solution of Eq. 2 for the change in C i with t, holding all other factors constant and with boundary values C i = C s at t = 0, is Ci=

k[q0(1-F0)+q2]Co+S-R k(qo +qlFi + q 2 )

[ l - - e (k/VXq°+qtFl+q2)t ]

•"~ Cse (k/VXqO+qlFl+q2),

(3)

For the case where R is a first-order function of C~, the solution will have the form

Ci =

k[q0(1 - F0) + q2]C0 + S k ( q o + q l F l + q 2 ) + E [1 -- e [(k/VXq°+q'F'+q2)+Elt ] + Cs e-[(k/vXq°+q~F~+q2)+e]t

(4)

Where E is a proportionality constant of sink removal rate for the particular pollutant of interest, such that R = EC i. Steady-state values of indoor concentrations, C~,ss will result by letting t approach infinitive which, for Eq. 4, result in k[q0(1 - F0) + q2]C0 + S Ci'ss =

k(qo+q,F,

+q2) +E

(5)

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89

Eq. 4, or similar forms, have been applied in analyzing indoor ozone decay, odor control, particulate matter and carbon monoxide, particulate matter from cigarette smoke, CO 2 from respiration, and energy control strategies.

5. Air cleaning approaches The application of air cleaning to indoor environments such as office buildings, schools, and commercial establishments, as well as single- and multi-family residential buildings, has been a more recent occurrence. Its application is in some ways similar to the industrial case, in that development and use of air cleaning technologies has centered on the control of particulate matter, commonly referred to as dust. However, gaseous air pollutants, especially organic gases and odor, have drawn more attention. 5.1. Particulate matter control

Particulate matter is a problem sufficient in most buildings to justify some level of air cleaning. Dust may be generated indoors (tobacco smoke, fabric lint, etc.) or drawn in from outdoors through ventilation systems a n d / o r by infiltration. In large buildings with mechanical heating, ventilation, and air conditioning systems, and in residences with forced-air heating a n d / o r cooling units, a minimal level of air cleaning is engineered into such systems to collect lint and large dust particles to prevent damage to blower fans. Dust stop filters of low efficiency (10-15%) are typically used for this application. Dust and a variety of other particles can be removed from contaminated indoor air by the application of relatively simple techniques adapted from use in industrial gas cleaning. Principal techniques are filtration and electronic air cleaners [18]. 5.2. Removal of gaseous contaminants

In theory, the removal of gaseous contaminants from indoor air, or from outdoor air drawn into ventilation systems, can be achieved by the application of a variety of well-known principles. These include adsorption, direct oxidation catalytic oxidation or reduction, absorption, etc. 5.2.1. Adsorption

Many gases, vapors or liquids coming into contact with a surface will adhere to it to some degree, as a result, adsorption happens. Although adsorption is a chemical/physical phenomenon, no chemical reaction takes place. The more effective and popular sorbent for organic gases and vapors is activated carbons. For adsorbing water-soluble gases in wet air metal oxides and silicaceous- and active-earth type sorbents can be used since they retain water preferentially. 5.2.2. Absorption

In industrial applications, a variety of contaminant gases (including SO 2 and HC1) are removed from waste gas streams by absorbing in water or a reactive liquid reagent or

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slurry. The c o n t a m i n a n t is r e m o v e d b y chemical reaction with the absorbing m e d i u m . T h i s principle can also be applied to the r e m o v a l of water-soluble gases from indoor air. The effect o f absorption on the r e m o v a l of formaldehyde from an air stream has b e e n investigated. 5.2.3. Direct oxidation and catalytic treatment S o m e organic gases can be oxidized in the air by ozone. Small ozone produce is b e i n g tried to clean the air in cars. The p r o b l e m which r e m a i n s is to control the ozone concentration b e l o w a level which is not too high to d a m a g e h u m a n health. T r e a t m e n t of indoor air b y catalytic processes at room temperature theoretically is possible, e.g., the effect of catalysis b y activated carbon o n i n d o o r c o n t a m i n a n t s such as O a and H2S. However, its cost m a y be relatively high.

References [1] Dockery, D.W. and Spengler, J.D., 1981. Personal exposure to respirable particulates and sulfates. J. Air Pollut. Control Assoc., 31: 153-159. [2] Yocum, J.E., Cote, W.A. and Benson, F.B., 1977. Effects of indoor air quality. In: Stem, A.E. (Ed.), Air Pollution, Vol. If, 3rd exln. Academic Press, New York. [3] HEW, 1979. Smoking and Health - A Report of the Surgeon General. Department of Health, Education and Welfare, Publication No. (PHS) 79-50066. [4] Selikoff, lJ., Nicholson, WJ. and Langer, A.M., 1972. Asbestos air pollution. Arch. Environ. Health, 25: 1-3. [5] Lemen, R.A., Dement, J.M. and Wagoner, J.K., 1980. Epidemiology of asbestos-related diseases. Environ. Health Perspect., 34: 1-11. [6] NAS, 1981. Formaldehyde and Other Aldehydes. National Academy of Sciences, Washington, DC. [7] Guimond, R.J., Ellett, W.H., Fitggerald, J.E., Windham, S.T. and Cuny, P.A., 1979. Indoor Radiation Exposure due to Radium-226 in Florida Phosphate Lands. US EPA Report EPA-502/4-T8-013. [8] UN, 1977. Sources and Effects of Zonizing Radiation. United Nations Scientific Committee on the Effects of Atomic Radiation 1977 Report to the General Assembly, with Annexes, United Nations, New York. [9] EPA, 1979. Resisions to the national ambient air quality standards for photochemical oxidant. Fed. Reg., 44: 8201-8233. [10] Woods, J.E., t980. Environmental implications of conservation and solar space heating. Energy Research Institute, lowa State Univ., Ames, IA, BELL 80-3. Meeting of the New York Academy of Sciences, New York, January 16~ [11] ACGIH, 1979. Documentation of the threshold limit values. American Conference of Governmental Industrial Hygienists, Cincinnati, OH, pp. 69-70. [12] ASHRAE, 1980. Standards for ventilation required for minimum acceptable indoor air quality. American Society of Heating, Refrigerating and Air-Conditioning Engineers, ASHRAE 62-73 R, New York. [13] Jarke, F.H., Dravnieks, A. and Gordon, S.M., 1981. Organic contaminants in indoor air and their relation to outdoor contaminants. ASHRAE, Trans., 87 (Part l): 153-166. [14] Zebransky, J., 1981. Proceedings; Conference on Wood Combustion Environmental Assessment, New Orleans. US Environmental Protection Report EPA 600/59-81-029. Jeomet Technologies, Inc. [15] Hoegg, V.R., 1972. Cigarette smoke in closed space. Environ. Health. Perspect., 2: tl7-128, October. '[16] Breysse, P.A., 1981. The health cost of tight homes. J. Am. Med. Assoc., 245: 267-268. [17] Andersen, 1., Lundquist, G.R. and Molhave, L., 1975. Indoor air pollution due to chipboard used as a construction material. Almos. Environ., 9:1121-1127. [18] Godish, T., 1991. Indoor Air Pollution Control, Lewis Publisher, Inc., Michigan.

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[19] Hellenbeck, W.H., 1981. Consumer product safety: Risk assessment of exposure to asbestos emissions from hand-held air dryers. Environ. Manage., 5: 23-32. [20] Geraci, C.L., Baron, P.A., Carter, J.W. and Smith, D.L., 1979. Testing of hair dryers for asbestos emissions. National Institute of Occupational Safety and Health, Cincinnati, OH. [21] Mokler, B.V., Wong, B.A. and Snow, M.J., 1979. Respirable particulates generated by pressurized consumer products. 1. Experimental method and general characteristics. Am. Ind. Hyg. Assoc. J., 40: 330-338. [22] Wang, I.C., 1975. A study of bioeffluents in a college classroom. ASHRAE Trans., 81 (Part 1): 32-44.