1、11.1CHAPTER 11AIR CONTAMINANTSClasses of Air Contaminants 11.1PARTICULATE CONTAMINANTS 11.2Particulate Matter 11.2GASEOUS CONTAMINANTS 11.8Volatile Organic Compounds. 11.12Semivolatile Organic Compounds . 11.14Inorganic Gases . 11.14AIR CONTAMINANTS BY SOURCE . 11.15Outdoor Air Contaminants. 11.15In
2、dustrial Air Contaminants 11.15Nonindustrial Indoor Air Contaminants 11.16Flammable Gases and Vapors 11.18Combustible Dusts 11.18Radioactive Air Contaminants . 11.19Soil Gases. 11.20IR contamination is a concern for ventilation engineers whenA it causes problems for building occupants. Engineers nee
3、d tounderstand the vocabulary used by the air sampling and building aircleaning industry. This chapter focuses on the types and levels of aircontaminants that might enter ventilation systems or be found asindoor contaminants. Industrial contaminants are included only forspecial cases. Because it is
4、not a building air concern, the effects ofrefrigerants on the atmosphere are not included in this chapter; seeChapter 29 for discussion of this topic.Air is composed mainly of gases. The major gaseous componentsof clean, dry air near sea level are approximately 21% oxygen, 78%nitrogen, 1% argon, and
5、 0.04% carbon dioxide. Normal outdoor aircontains varying amounts of other materials (permanent atmosphericimpurities) from natural processes such as wind erosion, sea sprayevaporation, volcanic eruption, and metabolism or decay of organicmatter. The concentration of permanent atmospheric impurities
6、 var-ies, but is usually lower than that of anthropogenic (i.e., caused byhuman activities) air contaminants.Anthropogenic outdoor air contaminants are many and varied,originating from numerous types of human activity. Electric-power-generating plants, various modes of transportation, industrial pro
7、-cesses, mining and smelting, construction, and agriculture generatelarge amounts of contaminants. These outdoor air contaminants canalso be transmitted to the indoor environment. In addition, the indoorenvironment can exhibit a wide variety of local contaminants, bothnatural and anthropogenic.Conta
8、minants that present particular problems in the indoor en-vironment include allergens (e.g., dust mite or cat antigen), tobaccosmoke, radon, and formaldehyde.Air composition may be changed accidentally or deliberately. Insewers, sewage treatment plants, agricultural silos, sealed storagevaults, tunn
9、els, and mines, the oxygen content of air can become solow that people cannot remain conscious or survive. Concentrationsof people in confined spaces (theaters, survival shelters, submarines)require that carbon dioxide given off by normal respiratory functionsbe removed and replaced with oxygen. Pil
10、ots of high-altitude air-craft, breathing at greatly reduced pressure, require systems thatincrease oxygen concentration. Conversely, for divers working atextreme depths, it is common to increase the percentage of helium inthe atmosphere and reduce nitrogen and sometimes oxygen concen-trations.At at
11、mospheric pressure, oxygen concentrations less than 12% orcarbon dioxide concentrations greater than 5% are dangerous, evenfor short periods. Lesser deviations from normal composition can behazardous under prolonged exposures. Chapter 10 further detailsenvironmental health issues.Although lack of ox
12、ygen can be a danger in confined spaces, it isunlikely ever to be a problem in naturally and mechanically venti-lated buildings. Although the amount of oxygen consumed approx-imates the amount of carbon dioxide produced by respiration, thelevel of oxygen in the air is so much greater than that of ca
13、rbon diox-ide to start with that there is effectively no change in oxygen contentbetween air intake and exhaust.CLASSES OF AIR CONTAMINANTSAir contaminants are generally classified as either particles orgases. Particles dispersed in air are also known as aerosols. In com-mon usage, the terms aerosol
14、, airborne particle, and particulatecontaminant are interchangeable. The distinction between particlesand gases is important when determining removal strategies andequipment. Although the motion of particles is described using thesame equations used to describe gas movement, even the smallestparticl
15、es are much larger and more massive than individual gas mol-ecules, and have a much lower diffusion rate. Conversely, particlesare typically present in much fewer numbers than even trace levels ofcontaminant gases.The particulate class covers a vast range of particle sizes, fromdust large enough to
16、be visible to the eye to submicroscopic particlesthat elude most filters. Particles may be liquid, solid, or have a solidcore surrounded by liquid. The following traditional particulate con-taminant classifications arise in various situations, and overlap. Theyare all still in common use. Dusts, fum
17、es, and smokes are mostly solid particulate matter,although smoke often contains liquid particles.Mists, fogs, and smogs are mostly suspended liquid particlessmaller than those in dusts, fumes, and smokes.Bioaerosols include primarily intact and fragmentary viruses,bacteria, fungal spores, and plant
18、 and animal allergens; their pri-mary effect is related to their biological origin. Common indoorparticulate allergens (dust mite allergen, cat dander, house dust,etc.) and endotoxins are included in the bioaerosol class.Particulate contaminants may be defined by their size, such ascoarse, fine, or
19、ultrafine; visible or invisible; or macroscopic,microscopic, or submicroscopic.Particles may be described using terms that relate to their interac-tion with the human respiratory system, such as inhalable andrespirableThe gaseous class covers chemical contaminants that can exist asfree molecules or
20、atoms in air. Molecules and atoms are smaller thanparticles and may behave differently as a result. This class coverstwo important subclasses:The preparation of this chapter is assigned to TC 2.3, Gaseous Air Con-taminants and Gas Contaminant Removal Equipment, in conjunction withTC 2.4, Particulate
21、 Air Contaminants and Particulate Contaminant RemovalEquipment.11.2 2013 ASHRAE HandbookFundamentals (SI)Gases, which are naturally gaseous under ambient indoor or out-door conditions (i.e., their boiling point is less than ambient tem-perature at ambient pressure)Vapors, which are normally solid or
22、 liquid under ambient indooror outdoor conditions (i.e., their boiling point is greater than ambi-ent temperature at ambient pressure), but which evaporate readilyThrough evaporation, liquids change into vapors and mix with thesurrounding atmosphere. Like gases, they are formless fluids thatexpand t
23、o occupy the space or enclosure in which they are confined.Air contaminants can also be classified according to their sources;properties; or the health, safety, and engineering issues faced by peo-ple exposed to them. Any of these can form a convenient classifica-tion system because they allow group
24、ing of applicable standards,guidelines, and control strategies. Most such special classes includeboth particulate and gaseous contaminants.This chapter also covers background information for selectedspecial air contaminant classes (Chapter 10 deals with applicableindoor health and comfort regulation
25、s).Outdoor air contaminantsIndustrial air contaminantsNonindustrial indoor air contaminants and indoor air qualityFlammable gases and vaporsCombustible dustsRadioactive contaminantsSoil gasesIn the 2012 ASHRAE HandbookHVAC Systems and Equip-ment, Chapter 29 discusses particulate air contaminant remo
26、val, andChapter 30 covers industrial air cleaning. Chapter 46 in the 2011ASHRAE HandbookHVAC Applications deals with gaseous con-taminant removal.PARTICULATE CONTAMINANTSPARTICULATE MATTERAirborne particulate contamination ranges from dense clouds ofdesert dust storms to completely invisible and dil
27、ute cleanroomparticles. It may be anthropogenic or completely natural. It is oftena mixture of many different components from several differentsources. A much more extensive discussion of particulate contam-ination by the U.S. Environmental Protection Agency (EPA 2004)is available at http:/cfpub2.ep
28、a.gov/ncea/cfm/recordisplay.cfm?deid=87903.Particles occur in a variety of different shapes, including spheri-cal, irregular, and fibers, which are defined as particles with aspectratio (length-to-width ratio) greater than 3. In describing particlesize ranges, size is the diameter of an assumed sphe
29、rical particle.Solid ParticlesDusts are solid particles projected into the air by natural forcessuch as wind, volcanic eruption, or earthquakes, or by mechanicalprocesses such as crushing, grinding, demolition, blasting, drilling,shoveling, screening, and sweeping. Some of these forces producedusts
30、by reducing larger masses, whereas others disperse materialsthat have already been reduced. Particles are not considered to bedust unless they are smaller than about 100 m. Dusts can be min-eral, such as rock, metal, or clay; vegetable, such as grain, flour,wood, cotton, or pollen; or animal, includ
31、ing wool, hair, silk, feath-ers, and leather. Dust is also used as a catch-all term (house dust, forexample) that can have broad meaning.Fumes are solid particles formed by condensation of vapors ofsolid materials. Metallic fumes are generated from molten metalsand usually occur as oxides because of
32、 the highly reactive nature offinely divided matter. Fumes can also be formed by sublimation,distillation, or chemical reaction. Such processes create submi-crometre airborne primary particles that may agglomerate intolarger particle (1 to 2 m) clusters if aged at high concentration.Bioaerosols are
33、airborne biological materials, including virusesand intact and fragments of bacteria, pollen, fungi, and bacterial andfungal spores. Individual viruses range in size from 0.003 to 0.06 m,although they usually occur as aggregates (droplet nuclei) and areassociated with sputum or saliva and therefore
34、are generally muchlarger. Most individual bacteria range between 0.4 and 5 m andmay be found singly or as aggregates. Intact individual fungal andbacterial spores are usually 2 to 10 m, whereas pollen grains are10 to 100 m, with many common varieties in the 20 to 40 mrange. The size range of allerge
35、ns varies widely: the allergenic mol-ecule is very small, but the source of the allergen (mite feces or catdander) may be quite large. See the section on Bioaerosols for moredetailed discussion.Liquid ParticlesMists are aggregations of small airborne droplets of materialsthat are ordinarily liquid a
36、t normal temperatures and pressure. Theycan be formed by atomizing, spraying, mixing, violent chemicalreactions, evolution of gas from liquid, or escape as a dissolved gaswhen pressure is released.Fogs are clouds of fine airborne droplets, usually formed by con-densation of vapor, which remain airbo
37、rne longer than mists. Fognozzles are named for their ability to produce extra-fine droplets, ascompared with mists from ordinary spray devices. Many droplets infogs or clouds are microscopic and submicroscopic and serve as atransition stage between larger mists and vapors. The volatile natureof mos
38、t liquids reduces the size of their airborne droplets from themist to the fog range and eventually to the vapor phase, until the airbecomes saturated with that liquid. If solid material is suspended ordissolved in the liquid droplet, it remains in the air as particulatecontamination. For example, se
39、a spray evaporates fairly rapidly,generating a large number of fine salt particles that remain sus-pended in the atmosphere.Complex ParticlesSmokes are small solid and/or liquid particles produced by in-complete combustion of organic substances such as tobacco, wood,coal, oil, and other carbonaceous
40、 materials. The term smoke is ap-plied to a mixture of solid, liquid, and gaseous products, althoughtechnical literature distinguishes between such components as sootor carbon particles, fly ash, cinders, tarry matter, unburned gases,and gaseous combustion products. Smoke particles vary in size, the
41、smallest being much less than 1 m in diameter. The average is oftenin the range of 0.1 to 0.3 m.Environmental tobacco smoke (ETS) consists of a suspensionof 0.01 to 1.0 m (mass median diameter of 0.3 m) solid and liquidparticles that form as the superheated vapors leaving burning tobaccocondense, ag
42、glomerate into larger particles, and age. Numerous gas-eous contaminants are also produced, including carbon monoxide.Smog commonly refers to air pollution; it implies an airborne mix-ture of smoke particles, mists, and fog droplets of such concentrationand composition as to impair visibility, in ad
43、dition to being irritatingor harmful. The composition varies among different locations and atdifferent times. The term is often applied to haze caused by a sunlight-induced photochemical reaction involving materials in automobileexhausts. Smog is often associated with temperature inversions in theat
44、mosphere that prevent normal dispersion of contaminants.Sizes of Airborne ParticlesParticle size can be defined in several different ways. Thesedepend, for example, on the source or method of generation, visibil-ity, effects, or measurement instrument. Ambient atmospheric par-ticulate contamination
45、is classified by aerosol scientists and the EPAAir Contaminants 11.3by source mode, with common usage now recognizing three pri-mary modes: coarse, fine, and ultrafine.Coarse-mode aerosol particles are largest, and are generallyformed by mechanical breaking up of solids. They generally have aminimum
46、 size of 1 to 3 m (EPA 2004). Coarse particles also in-clude bioaerosols such as mold spores, pollen, animal dander, anddust mite particles that can affect the immune system. Coarse-modeparticles are predominantly primary, natural, and chemically inert.Road dust is a good example. Chemically, coarse
47、 particles tend tocontain crustal material components such as silicon compounds,iron, aluminum, sea salt, and vegetative particles.Fine-mode particles are generally secondary particles formedfrom chemical reactions or condensing gases. They have a maxi-mum size of about 1 to 3 m. Fine particles are
48、usually more chem-ically complex than coarse-mode particles and result from humanactivity, particularly combustion. Smoke is a good example. Chem-ically, fine aerosols typically include sulfates, organics, ammonium,nitrates, carbon, lead, and some trace constituents. The modes over-lap, and their de
49、finitions are not precise.Recently, there has been increased interest in even smaller con-taminants, known as ultrafine-mode particles. Ultrafines have amaximum size of 0.1 m (100 nm) (EPA 2004). They are complexparticles for which the biggest source is reaction of gases with otherparticles. They also form as a result of degradation of larger parti-cles. Natural sources include volcanic eruptions, ocean spray, andsmoke from wildfires. Sources involving human activity includetobacco smoke, burning of fossil fuels, and emissions from cookingand office machines. Engineered ul
