indoor air pollutants a literature review

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Indoor air pollutants a literature review how to write a critique paper on an article

Indoor air pollutants a literature review

Additionally, owing to meteorological factors, the effects differed between inland and coastal regions. However, despite the changes, the pollutant concentrations in many regions e. Without the support of adaptive environmental strategies, the recent gains in air quality will be unsustainable. Share this article with your colleagues. Subscribe to our Newsletter. Aerosol and Air Quality Research has published over 2, peer-reviewed articles. Enter your email address to receive latest updates and research articles to your inbox every second week.

Other readers also read Subscribe to our Newsletter Aerosol and Air Quality Research has published over 2, peer-reviewed articles. Search keywords. Aerosol and Air Quality Research AAQR is an independently-run non-profit journal, promotes submissions of high-quality research, and strives to be one of the leading aerosol and air quality open-access journals in the world.

Ok Learn more. We use cookies on this website to personalize content to improve your user experience and analyze our traffic. The data that are available are compiled and analyzed in the report. Based on a review of the literature, it was possible to infer relationships between indoor and outdoor pollution and to identify factors that affect these relationships. The relationships identified must be considered tentative. Except for bacteria, and perhaps, for fungus spores, indoor pollution levels appear to be controlled primarily by outdoor concentrations.

Other factors that influence indoor pollution levels include internal activities and pollutant generation, atmospheric conditions and natural ventilation, time, location, type of building, and air conditioning and filtration systems. Indoor concentrations of pollen and reactive gases, expressed as a percentage of outdoor concentrations, decrease with increasing outdoor concentrations.


You need JavaScript enabled to view it. Cite this article: Rana, R. Aerosol Air Qual. Restricting human activities had an immediate impact on air pollution. Urban, industrial, and inland areas experienced larger drop in pollutants. Pollutants NO 2 arising from the road traffic movement reduced the most. Reported drop in air pollution varied significantly based on the time compared.

After screening the titles, abstracts and full texts of the retrieved results, two reviewers independently evaluated the relevant data. The majority of the eligible studies reported data from central China e. We found evidence of a substantial reduction in air pollution immediately after lockdown measures were implemented, with traffic-related NO 2 exhibiting the largest decrease.

The reported reductions in air pollution varied by region and period. Specifically, urban, industrial and highly populated areas of China experienced greater improvements in air quality than rural, residential and less populated areas. Additionally, owing to meteorological factors, the effects differed between inland and coastal regions.

Chapter 5 includes a summary of the major conclusions resulting from this review and suggestions for further research to define and evaluate indoor-outdoor pollution relationships. This approach was employed to permit better definition of indoor pollution as a function of outdoor pollution. The identifi- cation of relationships between indoor and outdoor pollution would permit the esti- mation of indoor levels from the outdoor data, which are more abundant.

The data represent a wide range of studies conducted for varying purposes under a wide range of conditions. Sulfur Dioxide Figure presents the ratio between indoor and outdoor SO2 concentrations expressed as percentage versus outdoor concentrations. With a few exceptions, the data follow a consistent pattern, as delineated in the figure. Indoor concentra- tions approach, or even exceed, outdoor concentrations when outdoor concentra- tions are low, but drop rather rapidly to about 50 percent of outdoor levels as outdoor concentrations increase up to about 20 pphm; then they drop more slowly to a value approaching 30 percent or less with further increases in outdoor levels.

These data generally support the relationship noted above, however. Indoor concentrations of sulfur dioxide and carbon monoxide as a function of outdoor concentrations. Little, Inc. Raw data on an hourly basis are included in Reference 8. For the low levels measured during the summer - generally between 3.

For a period of several days in a building that housed both offices and laboratories, indoor concentrations were greater than outdoor concentrations. Outdoor concentrations were on the order of 4 pphm, however, and indoor levels were only about 5 pphm. These results indicated that indoor concentrations could be expected to range from 4 to 28 percent of outdoor levels for outdoor concentrations greater than 0. Based on the data plotted, it would appear that indoor CO concentrations range from 80 to greater than percent for outdoor concentrations below 10 ppm, but range from 60 to 80 percent for outdoor concentrations above 10 ppm.

These conclusions must be viewed with some suspicion, however. All the data for outdoor concentrations below 10 ppm were obtained in Hartford, Connecticut, and all data for concentrations above 10 ppm were obtained in Moscow. A limited amount of data in addition to that presented in Table A-2 and Figure is available in the literature. Carbon Dioxide As might be expected, data for carbon dioxide CO2 do not follow the same pattern as data for other gaseous pollutants.

Except for emissions from smoking, cooking, and heating, the other pollutants are essentially produced outside, and indoor concentrations can be expected to be lower. Assuming that outdoor concentrations are normally around 0. Summary The data available for nitrogen dioxide, carbon bisulfide, hydrogen sulfide, and total gaseous acids Table A-3 are insufficient for identifying relationships.

From the data in Tables A-l through A-3, and in Figure , however, it appears that indoor concentrations of gaseous pollutants are generally lower than outdoor concentrations, but by less than 50 percent unless outdoor concentrations are high. At very low levels of outdoor pollution, inside concentrations sometimes exceed outdoor concentrations. A similar trend for CO is a possibility, but, for the present, it seems wiser to assume that indoor CO levels will be equal to or only slightly less than outdoor levels.

Concentrations of CO2, since it is produced inside, are normally higher inside than out. Indoor particulate concentrations as a function of outdoor concentrations. These conclusions may well prove to be unfounded, how- ever. Almost all the data for concentration by weight were obtained in one study conducted in Hartford, Connecticut, and the data for particle counts, although based on several studies, were obtained primarily in Japan for the Department of Home Economics of Osaka City University.

Three possible trends in the relationship between indoor and outdoor particu- late concentrations have been identified in the literature, as summarized, respec- tively, in the following three paragraphs. The first trend identified appears to be the best supported.

Ishido and his colleagues concluded, as a result of their studies in Japan, that, even in relatively air-tight buildings, ' and in schools and hospitals as well as in small rooms, indoor suspended particulate levels are completely under the influence of outdoor changes. They further concluded that the generation of dust by daily activities may have some effect, but that it is of relatively short duration and is not directly reflected in daily variations in indoor dust concentrations.

These conclusions are supported by statistical analyses of the results of two studies30' 32 which indicated that differences in indoor and outdoor concentrations were not significant at the 5 percent level. A study in Cincinnati indicated that "under normal atmo- spheric conditions, the main component of suspended matter in the home was drawn from outside air, while during 'smog1 periods the correspondence of the two measurements was even closer.

Indoor and outdoor concentrations were found to be about equal up to concentrations of micrograms per cubic meter J. When outdoor concentrations were above this level, the concentrations indoors were less than those outdoors; and, the higher the outside concentrations, the greater the percentage difference. It has also been noted that indoor and outdoor levels showed fair agreement when windows were kept open, but that indoor levels were sometimes less than half of outdoor levels when windows were closed, particularly at night.

In some instances, however, such as in the crowded classrooms where Romagnoli obtained his data, the presence and activities of people inside may be of greater importance than outdoor concentrations. The data in Figure indicate a tendency for at least slightly lower partic- ulate levels indoors. These data indicate indoor concentrations less than those outdoors in 42 of 44 instances 95 percent by weight and 19 of 25 instances 76 percent by particle count.

Thus, although indoor partic- ulate concentrations are generally lower than outdoor concentrations, the pattern is not consistent, and a significant number of instances when indoor concentrations were higher than those outdoors have been reported. There is some indication that the composition of indoor particles may differ from that of outdoor particles. In one study, median particle diameter inside was found to be 0. In an air- conditioned office building, 99 percent of the particles were smaller than 0.

In another study, 85 percent of indoor particles were found to be 1 micron or smaller, while only 74 percent of those outside were 1 micron or smaller. In Hartford, the smaller par- ticles associated with soiling index were found to penetrate buildings more read- ily than the larger particles associated with suspended particulate measurements. In still another study,30 the ash content of the particles was determined. The ash content of indoor samples ranged from 1.

Ash in outdoor samples ranged from 2. This difference, which was highly significant at the 1 per- cent level, indicates that indoor air contains more organic material than outdoor air. Higher organic contents for indoor particulates were also noted in the Hartford study. In summary, indoor particulate concentrations appear to be generally lower than outdoor concentrations, especially at high outdoor levels, and the compo- sition of the particulates inside is different from that outside.

As was the case for carbon monoxide, however, it seems best in light of the data presently avail- able to assume indoor concentrations approximately equal to outside concentrations. Bacterial, fungal, and plant spores including pollen , though "naturally, " endogenously generated, are con- sidered to be pollutants from a health effects standpoint mold and pollen aller- gies , for purposes of indoor air quality control air conditioning , when present in inordinate amounts, or when present because of human activity.

Spores Indoor and outdoor concentrations of total fungal spores are presented in Table A Fourteen of the remaining 15 are below 90 percent. Consideration of those values below 90 percent indicates that averages are around 40 percent mean 41 percent; median 38 percent; mode 30 to 40 percent. Thus it appears that in- door spore concentratiorfs generally range from 15 to 90 percent and average around 40 p. Consideration of the composition of the spores found indoors and outdoors indicates that indoor populations are not directly controlled by outdoor popula- tions.

Indoor and outdoor concentration ratios of the ten most commonly reported types of spores are summarized in Tables and Detailed data on which Table It should be kept in mind that the data in Table do not allow direct comparisons between indoor and outdoor concentrations; rather, the data indicate the relative distribution of each type of spore in the to- tal population, either indoors or out. These tables indicate that the spore com- position of inside air samples is quite different from that of outside samples.

Penicillium is the most common spore found both indoors and out. Considering indoor and outdoor populations separately, Penicillium generally constitutes a higher percentage of indoor fungus populations than of out- door populations Table Aspergillus is the next most common spore found, especially indoors. Although concentrations are generally lower indoors than out, Aspergillus is gen- erally a more commonly occurring member of the indoor population.

In at least one of the ten studies reported, Aspergillus was found to be present indoors but absent outdoors. Cladosporium, while not occurring as frequently as Aspergillus, often con- stitutes a higher percentage of the population, especially outdoors, in those cases where it has been identified.

It is also more prevalent in indoor samples than in outdoor samples. The remaining four commonly found spores constitute a higher percentage of the outdoor population than the indoor population in most instances. In summary, Penicillium, Aspergillus, and Mucor constitute a higher per- centage of indoor samples than of outdoor samples.

The remaining seven of the ten most commonly found fungus spores are more prevalent in outdoor samples. The same holds true for the less common fungi listed in Table A-6, except for Oospora, Monilia, Rhizopus, and Aleurisma. Although a few exceptions can be found in Tables A-6 through A-9 the same spores are normally found indoors and outdoors.

Several investigators have con- cluded from this fact and from the assumption that relatively few spores are pro- duced inside and released into the air that the most important source of airborne spores in normal clean, dry houses is the outside air.

It is possible that different spores are transported indoors at different rates, but it is also possible that the growth and multiplication of these spores inside especially those of Penicillium and Mucor have a greater influence than has been assumed. A limited amount of data is available on spore populations in house dust Table , as opposed to airborne spores, which are discussed above.

In the two locations studied, fewer genera of fungi were found in house dust than in air. The samples were made up exclusively of five of the most commonly found spores, and Penicillium was by far the most predominant genus. Aspergillus and Mucor were more abundant in dust than in either indoor or outdoor air in Spain.

Kentucky" Summer To facilitate comparison between concentrations in grains per cubic meter and number per sample, the med- ians were plotted coincident with each other. Thus it appears that indoor concentrations will vary from 85 to percent of outdoor concentrations for low levels to 1 to 20 percent at high levels.

Bacteria Data related to indoor and outdoor concentrations of bacteria are presented in Table A-ll. Indoor pollen concentrations as a function of outdoor concentrations, non-air-conditioned buildings. Japan, are exceptionally high compared to the other data, and these values have been excluded in the following analysis.

A great disparity is noted between data obtained in Japan and in the United States, however, perhaps because the Japanese data are for total bacteria while most of the U. The range for the U. The consensus of the investigators, however, is that in- door bacterial counts do not reflect fluctuations in the outdoor air.

Indoor bacterial concentrations do not appear to be directly related to outdoor concentra- tions. Several investigators have reported that the most important source of air- borne spores in clean, dry houses is the outside air. However, a number of sources of pollutants exist inside buildings, notably heating, cooking, and smoking.

In addition, activities - such as sweeping and dusting, dress ing, and drying clothes - that entrain dust can affect interior concentrations of sus- pended particulate and airborne spores as well as the rate of diffusion of gaseous pollutants. In addition, the nature and types of interior furnishings and finishes can affect the rate of adsorption of reactive gases.

These effects on interior pollutant concentrations are discussed below. Biersteker et al. However, in one year-old home presumed to have a faulty heater, in- door concentrations averaged 3. Table shows a comparison of SO-, concentrations for new and old coal-heated houses in Hartford.

The exceptionally high indoor concentrations for the old coal-heated house are pre- sumed to be caused by a faulty heating system. Indoor concentrations at this house were found to be unrelated to outdoor concentrations; peak values were related in- stead to the stoking periods of the furnace. Indoor concentrations at the new Table According to Chamber- lain, walls and ceilings should provide a perfect sink for SO2. The floor lac- quered cork , walls painted with emulsion paint , and treated wood surfaces were not.

Carbon Monoxide - Carbon monoxide is generated indoors by combustion smoking, heating, cooking. The effect of combustion can be seen in the data from Russia in Table Indoor concentrations in the natural-gas-equipped home meters from the plant were higher than those in a home without natural gas located closer to the plant. It seems reasonable to assume that gas stoves and garages are also a significant source of indoor nitrogen dioxide, but no data were found from which the magnitude of this effect could be evaluated.

The effects of stoves and garages on indoor CO concen- trations can be seen in Figure , which shows the CO concentrations in a house in Hartford having a gas range and an attached garage. Carbon monoxide concentrations in house with gas range and furnace and with attached garage. For this house, CO concentrations are generally much higher than and unrelated to outdoor levels. Peak concentrations in the kitchen correspond to the periods when meals are being cooked, and concentrations in the family room generally follow those in the kitchen rather than those outside.

For two periods in the record, when the car was being put into or taken out of the attached garage, the emissions from the garage are the controlling influence on both the family room and kitchen concentrations. Particulates Particulates are also generated by combustion heating, cooking, smoking. Smoking has been found to significantly increase particulate concentrations in- doors. Elevated counts persisted for a period of 1 to 3 hours. Seisaburo et al. These meas- urements Table indicate that particles are distributed rather uniformly from floor to ceiling because of activities of people during the day, but that during the night they tend to settle and become concentrated near the floor.

Table shows particle counts in Italian schools before, during, and after classes. The measurements made after class indicate that concentrations do not drop rapidly after activities have ceased. Table Thus higher values measured after class in two instances do not indi- cate a continuing increase in concentration. In an office with an air filtration system that reduced interior concentrations to 24 per- cent of outside levels, the amount of dust generated in a room was found to be pro- portional to the number of people in the room.

For these buildings, the ratio of internal generation to exterior concentration was estimated to range from 0 to 0. As stated in Chapter 2, the importance of internal generation of spores is not clearly established. Maunsell found, however, that activities such as cleaning and dusting cause spores to be entrained in the air.

The resulting increase in entrained spores was mainly in Penicillium, Cladospo- rium, Pullularia, and yeasts. Spores of larger sizes, which were absent in undisturbed air, were found to be present after dust was raised. Significant exceptions occur, however, when faulty oil- or coal-burning heating systems are encountered. Carbon monoxide is generated by smoking, cooking, and heating.

Attached garages are also a significant source. Particulates can also be generated indoors from combustion heating, cooking, smoking. Smoking, in particular, has been definitely identified as a significant source of particulates indoors. Indoor activities seem to enhance entrain- ment of particles already present indoors. Indoor concentrations of bacteria appear to be highly dependent on indoor liv- ing conditions and activities, but pollen concentrations are almost completely de- pendent on outdoor concentrations.

The importance of internal generation of spores is not clearly established, but, as with other particles, internal activities can play an important role in the entrainment of spores found indoors. Sulfur dioxide and probably other reactive gases as well is removed from interior air by adsorption, the rate of which is dependent primarily on the pro- perties of the interior surfaces and only slightly on the rate of transport to the surfaces.

Sampling for 1 day is shown in Figure On the evening illustrated, outside concentrations increased rather rapidly to about 12 ppm because of a light wind from a nearby interstate highway. Indoor concentra- tions remained around 5 ppm, about equal to the outdoor concentration before it increased.

Carbon monoxide concentrations for house in Hartford, Connecticut; September 22, After 2 hours, out- door concentrations had increased to about 16 ppm, but indoor concentrations were still significantly lower at 10 ppm. At this time, the wind direction changed, causing outside concentrations to drop rapidly to about 3 ppm. Inside concentra- tions remained high, however, and required 2. Studies in Cincinnati indicated that indoor and outdoor levels were in fair agreement when windows were open but that indoor concentrations were sometimes less than half of outdoor con- centrations when windows were closed.

Average indoor concentrations were found to be roughly 15 percent higher with windows open than with windows closed. When windows were open, penetration of pollen was quite different, but the amount of opening apparently made little difference. TIME Figure and the related discussion show how inside concentrations and the relation between indoor and outdoor concentrations can vary with time.

Indoor and outdoor concentrations of nonviable and viable particles, as well as of gases, have been found to vary on diurnal and seasonal bases, and the relationship between in- door and outdoor concentrations has also been found to vary in some cases. The time-related variations in indoor pollution levels that can be inferred from the literature are discussed in the following sections.

Gases Simultaneous study of atmospheric and indoor air for 24 hours for Russian homes in the vicinity of a plant with a blast furnace showed parallel changes in CO concentrations, as indicated in Table Similar diurnal patterns for carbon monoxide have been reported for American homes, that is, high concentrations in the late night and early morning hours, low concentrations later in the morning between 7 a.

The data do illustrate, however, that the indoor-outdoor relationship varies with time. Day and night concentrations of carbon monoxide inside and outside a num- ber of buildings were measured in Hartford, Connecticut, during the summer, fall, and winter Table A To better illustrate the diurnal patterns indicated by these data, ratios of the concentrations during the day to those during the night are given in Table Carroll Rd. Notable exceptions to this trend occur at the office buildings at Constitution Plaza CP.

A seasonal effect on the diurnal pattern can also be inferred from the data in Table In almost all cases, there is less difference between day and night concentrations in the summer than in the winter. With few exceptions, the ratios are lower during the day, corresponding to the higher concentrations noted above.

In the instance shown, which represents a relatively tight house with doors and windows shut, the lag time a- mounted to 2. Measurements of indoor and outdoor concentrations of total gaseous acid have indicated lag times of up to 2 hours 16 Particulates Figure shows the diurnal pattern obtained during the summer for a Jap- anese apartment.

The pattern may also be grossly applicable to the United States. It has been noted that daytime levels are higher than night levels, and the major peak at around 8 a. The effect of the lag time in the example illustrated is relatively minor, but it does result in indoor levels higher than outdoor levels twice during the period covered - "at about hours and from to hours.

Concentration of particles in an apartment in Toyonaka City, Japan, May , These values indicate that daytime concentrations of particulates are higher than night- time levels by as much as percent. For the houses, there is a greater difference between day- time and nighttime concentration inside than outside except, perhaps, during the fall.

The ratios generally increase from summer to winter, indicating that there is more variation in concentrations, both inside and outside, in the winter than in the fall and more variation in the fall than in the summer. For the offices and public buildings, the per- centages are slightly less during the day in summer and winter, reflecting the higher daytime concentrations noted above. For one of the houses, day and night percentages were nearly equal throughout the year; for the other, daytime per- centages were much higher than nighttime percentages.

This difference in behavior between suspended and soiling particu- lates is probably the result of size differences; the smaller soiling particles tend to stay suspended at night whereas the larger particles contributing to the day- time suspended particulate measurement tend to settle out at night. Indoor and outdoor particulate concentrations were determined on a seasonal basis in two Japanese studies ' and in the Hartford study mentioned above. Results of the Japanese studies are summarized in Table Some seasonal trends indicated by the Hartford data have been identified above as they relate to diurnal patterns.

Viable Particles Spores - Indoor and outdoor spore concentrations on a monthly basis have been reported for Tucson, Arizona, and Galveston, Texas. In Copenhagen, Denmark, concentrations of many of the common spores were noted to show seasonal variations. The seasons of peak concentrations were as listed on the following page. These data indicate that outdoor bacterial concentrations are from 2 to 9 times higher during the day than during the night Table Indoor concentrations were also higher during the day, but not as markedly so; factors for the living room were from about 1 to 7 and those for the bedroom, excluding November, were about 1 to 1.

In November, the concentrations in the bedroom were significantly greater at night than during the day. Further seasonal trends can be inferred from the data in Table These data indicate that concentrations both indoors and outdoors generally increase from winter to summer.

Summer concentrations up to 10 times winter levels have been reported. Also worthy of note are the differences in concentrations and composition of spore samples in Tables A-5 to A Exceptionally low concentrations characterize Arizona. The type of area considered, that is, urban, industrial, suburban, or rural, has a great effect on the concentrations encountered, primarily because of the re- lative proximity of these types of areas to various sources of pollutants.

As might be expected, concentrations of particulates, and probably also of gases, are higher in urban and industrial areas than in nonindustrial suburbs. Fungus spore concentrations may often be higher in rural areas than in urban or suburban areas, however, because of the presence 49 52 of cattle barns, storage bins, etc.

As expected, in- door concentrations generally become lower with increasing distance from the source. CO concen- trations in a dwelling 18 meters from a filling station, for instance, were found to be as high as 23 ppm and to average only about 8 percent less than those near the gas pump itself.

To a large extent, the effects of location discussed above pertain to outdoor as well as indoor pollution levels and could be predicted on the basis of indoor- outdoor pollution relationships such as those presented in Chapter 2 if such re- lationships have been established and if local outdoor concentrations are known.

Consider, for instance, the data in Table for SO2 concentrations in the vicinity of an industrial plant. This trend is still apparent for the much lower concentrations, both indoors and outdoors, in the area beyond the in- fluence of the plant. In some cases, internally generated pollutants, such as CO emitted from gas ranges or attached garages, can cause locally high concen- trations in certain areas of a building Figure Carbon Monoxide Carbon monoxide concentrations were measured in pairs of houses, office buildings, and public buildings in Hartford.

However, outdoor concentrations were generally lower in the vicinity of the homes than at the office and the public buildings. House, Carroll Rd. Mean concentration, ppm Indoor 3. Figure is a plot of the individual CO data from the Hartford study for the range of outdoor concentrations common to all three building types. Within this range 1. Particulates Particulate concentrations were also measured for the buildings in the Hart- fort study Table Again, however, outdoor pollution levels were lower in the vicinity of the houses.

Figure is a plot of the data for the range of common outdoor concentra- tions. A limited amount of data from Whitby et al. Outdoor concentrations for the homes fall between about 50 and o. Data for the offices and public buildings for this level of pollution generally fall within the data scatter band for the houses, but are concentrated in the lower portion of the band.

Presuming the outdoor concentrations to be similar, additional comparisons of this type can be made from the data reported in References 30, 32, and These data support the trend noted for o Figure In this in- stance, lower concentrations are reported for houses, but the ranges are still similar.

Summary Based on the limited CO and particulate data available primarily from Yocum et al. These data are limited, how- ever, to CO concentrations between 1. For these pollutants at these concentrations, pollution levels inside houses appear to be slightly higher than those inside offices and public buildings when similar outdoor concentrations pre- vail. It has been noted instead that the current employment of air conditioning is largely dictated by the economics of heating and cooling with little regard for changes in indoor air quality and how it is affected by outside pollutant levels, by air-condi- tioning system parameters, and by internal pollutant generation.

This study also revealed that ozone concentrations indoors were not generally affected by air conditioning. Air- conditioning systems with electrostatic precipitators actually caused a slight in- crease in ozone concentrations, but never enough to be of concern. Carbon monoxide, being unreactive, is not effectively removed by air- conditioning. This "fresh" air, however, was drawn from near street level during the time of the morning peak traffic period.

The dilution of this initial "charge" of CO provided by the 10 percent make-up air used during the remainder of the day was apparently not sufficient to reduce the indoor concentrations to the vicinity of the outdoor levels. An air-conditioning system that maintained a positive interior pressure was found to reduce indoor concentrations to 24 percent of outdoor levels.

This system employed two filters with high dust-removal efficiency. Electrical dust collectors have also been noted to be highly effective in eliminating indoor sus- pended particulate matter. Yocom et al. Thus, it is not clear whether the apparent reduc- tion at the offices was a result of the air-conditioning system or was, in fact, a result of higher outdoor pollution levels.

Significant reductions in indoor particu- late levels for the Boston study were found only for the air-conditioning system described above. In five other air-conditioned buildings, indoor-outdoor relation- 7 8 ships were about what one would expect for non-air-conditioned buildings.

These data indicate that air conditioning significantly improves indoor pollen concentrations. In conjunction with an air conditioner, neither the standard air-conditioner filter nor the special filter evaluated by Speigelman and Friedman59 was found to improve indoor pollen concentrations more than the air conditioner alone.

Concentrations of bacteria and spores may also be lower in air-conditioned buildings, but the data are highly limited and inconclusive. In one study, mold and bacteria in an air-conditioned room were found to be only 9 percent of those in a non-air-conditioned room with windows open. Summary The data available in the literature appear to support the conclusion drawn from the Boston study: i. Carbon monoxide, nitric oxide, and light hydrocarbons are difficult to remove without extensive pretreatment of the intake air.

Particu- late concentrations may be reduced slightly by the roughing filters commonly used in air conditioners, but more efficient filters must be used to obtain significant re- ductions. Pollen, in contrast to other pollutants, is practically eliminated by air conditioning, even without the standard roughing filters normally employed. Although they are not generally employed in the air-conditioning systems currently in use, air filtration and purification devices that could significantly re- duce the indoor concentrations of most pollutants are available.

Evaluations of the efficiency, application, and cost of those components are properly the subject of a separate report and are not covered here. In addition, Kalika et al. Discussions of techniques and methods are presented, how- ever, in References 71 through Measurement of pollution indoors presents problems that are not encountered in outdoor measurements.

For instance, noisy air samplers, such as the standard high volume sampler, are not acceptable inside buildings or near residences. As with outdoor pollution, particle size is important because it is re- lated to sedimentation, soiling, and health effects. Yocum et al. Some modifications have been made to their system in order to overcome operational difficulties experienced in early testing and to make possible the deter- mination of particle size distribution.

Reference 75 describes the gas analysis equipment used on submarines. This equipment should be effective and compact and could possibly be employed in indoor pollution measurements. Reference 16 describes a small sequence sampler for determining indoor sulfur dioxide concen- trations. A tape sampler for determining particulate concentrations is described in Reference 41, and Reference 76 describes methods for determining size distri- butions as well as concentrations with this type of sampler.

Reference 48 includes a discussion of the comparative limitation of sedimentation and the advantages of impaction for obtaining samples of airborne viable particles. The review of literature revealed many shortcomings in the methods that have been used for obtaining, analyzing, and presenting indoor-outdoor pollution data.

The data obtained were sufficient, however, to define possible trends and identify the factors that probably affect the relationships.

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Indoor air quality has been the object of interest for scientists and specialists from the fields of science such as chemistry, medicine and ventilation system design.

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The literature on the important indoor air pollutants, their sources, their effect on human welfare, and methods for controlling their presence is reviewed. Indoor Air Pollutants: A Literature Review. T.F. Cooke,. From the journal Reviews on Environmental Health. Indoor Air Pollutants: A Literature Review. T.F. Cooke,. DOI:; |; Published online: 01 Jul