22 Indoor Air Pollution

Dr. Vijay Shridhar

Contents

Introduction
Sources of indoor air contaminants
The various factors attributing to indoor air pollution
Types of indoor air pollutants
Health impact of indoor air pollution
Regulations, guidelines and standards for indoor air pollution
control measures for improving indoor air quality
The Indian scenario of indoor air pollution
References

Introduction

When we think of air pollution, we probably think of things like smog, power plant emission and emissions from vehicles. These are all examples of outdoor air pollution, but indoor air can be polluted too. Pollutants are any harmful contaminants in the air; therefore, indoor air , which is closely connected with outdoor air can not escape from the effects of out door contamination. Even things or activities present indoor are also contribute largely in indoor air pollution. Indoor air pollution is a very real and dangerous thing because indoor air is far more concentrated with pollutants than outdoor air. We also spend most of the time inside the building in comparison to out door activities. There are many sources of indoor air pollution, but they are different for city and villages, commercial region to industrial region, and developed & developing nations.

Indoor air pollution refers to chemical, biological and physical contamination of indoor air. It may result in adverse health effects. The Indoor air quality is determined by the concentrations of pollutants and thermal (Temperature and Relative Humidity) conditions that has impact on the comfort and performance of occupants. The air indoors presents a more complex mixture of these contaminants in a localized area than outdoor environment. The four elements: source, HVAC system, pollutant pathways and occupants are involved in development of IAQ( Indoor Air Quality) problems. The air quality status of a building/ enclosed space is therefore directly associated with the health of its occupants. A number of factors associated with indoor air have its impact on quality. These may include Inadequate ventilation and poorly designed ventilation systems. Flow of outdoor air contaminants into the internal spaces Extreme of temperature and humidity levels Combustion activities Making use of cleaning products, paints, printers, pesticides and other VOCs generating products etc.

The adverse impact of indoor air is a concern both in rural and urban context and has been ranked among the top five environmental health risks to the public by Environmental Protection Agency (EPA). It becomes therefore extremely important to understand all the aspects associated with it viz; sources, factors, types, impacts and standards associated with different pollutants. Some of these are being described here:

Sources of Indoor Air Contaminants

The source of pollutants in indoor environment will depend on the type of the space/ area being analyzed. Thus accordingly three categories of buildings have been classified as industrial buildings, Offices or residential areas. The importance of a source inside is determined by the amount of pollutant emitted and toxicity of these emissions. The principle sources of indoor air pollution can be categorized into following four groups: (i) combustion, (ii) building material, (iii) the ground under the building, and (iv) bioaerosols.

Some of the major sources of different forms of pollutants being released indoors are as follows:

Combustion of solid fuels in households often takes place in simple, poorly designed and maintained stoves. This kind of combustion contributes directly to low energy efficiency, and high pollutant concentration adding pressure on fuel resources. The low combustion efficiency of stoves leads to the release of products of incomplete combustion comprising mainly of Carbon monoxide and respirable particles (RSPM) as well as a large numbers of Volatile Organic compounds and SVOC(Semi volatile organic compound). The household coal combustion usage produces differing levels of sulphur dioxide (SO2) and certain toxic elements such as fluorine and arsenic.

Environmental Tobacco Smoke (ETS) refers to the mixture of primary smoke exhaled by smokers and the secondary smoke produced by the burning tobacco between puffs. It contains a wide range of irritating compounds and carcinogens such as nicotine, nitrosamines, PAHs, CO, CO2, NOx, acrolein, formaldehyde and hydrogen cyanide etc.

Some of the Inorganic gases are found in contaminated indoor air include CO2, CO, SO2, NO2, ozone (O3), hydrogen chloride (HCl), nitrous acid (HNO2), nitric acid vapour (HNO3) and radon. The primary cause of these emissions is fuel combustion and occupants expired air. HCl is introduced by transportation and by decomposition of polyvinyl chloride (PVC) while HNO3relates to the penetration of outdoor HNO3 formed in photochemical smog episodes and HNO3 formed indoors via reactions involving O3, NO2 and water vapour. Radon-222, an odourless, colourless, and tasteless noble gas, is an isotope produced as a result of the decay of radium-226, which is found in the Earth’s crust as a decay product of uranium. Primary sources of radon in buildings are the soil beneath and adjacent to buildings, domestic water supplies (e.g. well water) and building materials. The soil radon is transported indoors by means of convection i.e., due to indoor–outdoor temperature differences and pressures associated with winds. Synthetic asbestos fibers in buildings are found in spray-applied fireproofing, ceiling tiles, thermal insulation, sound insulation, fabrics, filtration components, plasters and acoustic surface treatments.

Indoor organic compounds comprising VOCs , SVOCs and Particulate matter are released from a variety of building materials such as vinyl tile and coving: compounds include phthalate esters, 2-ethyl-1-hexanol), carpets (4-PCH, 4-VCH, styrene), linoleum (C5–C11 aldehydes and acids), particleboard (formaldehyde, other aldehydes, ketones) and power cables (acetophenone, dimethylbenzyl alcohol). Other sources include paints (texanols, ethylene glycol,pinene, butoxyethoxyethanol), paint thinners (C7–C12 alkanes), paint strippers (methylene chloride), adhesives (benzene, alkyl benzenes), caulks (ketones, esters, glycols) and cleaners (2-butoxyethanol, limonene, 2-butanone, frying foods (1,3-butadiene, acrolein, PAHs), smoking (nicotine, aldehydes, benzene, PAHs), dry cleaned clothing (tetrachloroethylene), deodorizers (p-dichlorobenzene), showering (chloroform), moulds (sesquiterpenes) and pesticides (chlorpyrifos, diazinon, dichlorvos).

A diverse forms of biological particles have always been inhabiting the indoor environment including the microorganisms (viruses, bacteria, fungi and protozoa) pollen grains, animal dander and fragments of insects and mites and their excretory products, volatile organic compounds emitting from plants and animals. Dander consists of fine skin and hair/feather particles (and associated dried saliva and urine). The main sources of dander in indoor environments are usually cats and dogs, but rats and mice (whether as pets, experimental animals or vermin), hamsters, gerbils (a species of desert rat), guinea pigs and cage birds may be additional sources. The mites are associated particularly with dust, but fragments of these microscopic relatives of spiders and their excretory products (faeces) may be present in indoor air. The chief source of viruses indoors is by transmission from person to person contact, by coughing and sneezing although some may be recirculated through HVAC system. The bacterial population chiefly divided as Gram positive originate from mouth, nose, nasopharynx and skin and include Staphylococcus epidermidis, S. aureus and species of Aerococcus, Micrococcus and Streptococcus. Fungus may be present as unicellur cells in air or colonize substrates as a network (mycelium) of filaments (hyphae). These filamentous fungi produce numerous aerially dispersed spores, from microscopic sporing structures in moulds and from large sporing structures in macrofungi. Protozoa such as Acanthamoeba and Naegleri are microscopic unicellular animals which feed on bacteria and other organic particles in humidifiers, reservoirs and drain pans in HVAC systems.

The Various Factors Attributing to Indoor Air Pollution It can be categorized as follows:

Location of building: The location of a building can have direct association with the type of indoor pollutants. Thus buildings in close proximity of highways or busy thoroughfares may exhibit high concentration of particulates and other pollutants while those nearby industries may have higher amount of chemical based gaseous pollutants.

Building Design and maintenance: The improper building design and construction flaws may also contribute to indoor air pollution. The buildings may suffer from poor foundations, roofs, ceilings, windows and door openings promoting the influx of outdoor pollutants. The non compliance with the updating of HVAC system needed for accommodating any redesigning process may also lead to infiltration of outdoor pollutants such as particulates, vehicle exhaust, parking garage contaminants, etc.

Renovation Activities: The renovation processes like painting and polishing may cause the distribution of various gaseous pollutants and other by products throughout the building.

Building Materials: The presence of damp structural surfaces (e.g., walls, ceilings) or non-structural surfaces (e.g., carpets, shades), may be source of different forms of pollutants including dust, dust mites, microbes, particulates etc. contributing to the indoor air pollution.

Occupant Activities: Building occupants may use a number of cosmetic and daily used products including perfumes or colognes, detergents, soaps etc. which count among the major pollutant sources.

Local Exhaust Ventilation: These include such regions with insufficient local exhaust ventilation like kitchens, laboratories, maintenance shops, salons, toilet rooms, laundry rooms and other specialized areas.

Control of odors and contaminants by diluting them with outdoor air if there is appropriate flow of air that mixes them with room air.

Thermal Comfort

A number of variables, including personal activity levels, uniformity of temperature, radiant heat gain or loss, and humidity interact to determine whether people are comfortable with the temperature of the indoor air. The activity level, age, and physiology of each person affect the thermal comfort requirements of that individual. Uniformity of temperature is important to comfort. When the heating and cooling needs of rooms within a single zone change at different rates, rooms that are served by a single thermostat may be at different temperatures. Temperature stratification is a common problem caused by convection, the tendency of light, warm air to rise and heavier, cooler air to sink. If air is not properly mixed by the ventilation system, the temperature near the ceiling can be several degrees warmer than at floor level.

Some other technical factors like, the kind of activity being performed within its premises, non compliance with the product (pesticides, disinfectants, products used for cleaning and polishing) usage, gaseous emissions from the combustion sources (from smoking, kitchens, cafeterias and laboratories), and cross contamination coming from other poorly ventilated zones which then diffuses towards neighbouring areas and affects them. The presence of stagnant water relates to the dominance of various types of biological contaminants, with an amount impregnated into materials, exhausts etc. The defective maintenance of humidifiers and refrigeration towers also contribute to the microflora.

As regards anthropogenic activity, three main sources of contamination from outdoor environment include: combustion in stationary sources (power stations); combustion in moving sources (vehicles); and industrial processes. The major contaminants emitted by these sources are carbon monoxide, oxides of sulphur, oxides of nitrogen, volatile organic compounds (including hydrocarbons), polycyclic aromatic hydrocarbons (PAHs) and particles. The vehicular combustion contributes as a source of carbon monoxide and hydrocarbons along with more harmful oxides of nitrogen. Combustion in stationary sources and industrial processes produces oxides of sulphur. These also generate more than half of the particles emitted into the air by human activity, and industrial processes can be a source of volatile organic compounds. A number of naturally generated contaminants such as particles of volcanic dust, soil and sea salt, and spores and microorganisms are propelled through the air. The contaminants apart of being introduced from outside sometimes follow a path where they are first expelled out of the building and then return inside as intakes from of the air conditioning system among other sources of pollutants indoors include infiltration through the foundations of the building (e.g., radon, fuel vapours, sewer effluvia, fertilizers, insecticides and disinfectants).

Types of Indoor Air Pollutants

A major list of indoor air pollutants that can be spread through a building, can be categorized under three basic forms i.e., biological, chemical, and particle.

Health impact of Indoor Air Pollution

The indoor air quality has become an important concern for public health as people spend majority of their time indoors. It is a well established fact that the air pollution may lead to chronic and acute respiratory diseases and affect the medical prognosis of already existing diseases as well. Further, in terms of the impact on human health, respiratory diseases have been ranked third following cardiovascular diseases and cancers.

The impact of smoke from solid fuels has been related to acute respiratory infections (ARI) in young children. Also the elevated risk of chronic obstructive pulmonary disease (COPD) and lung cancer in women cooking over biomass fires and working in exposed atmosphere of smoky coal (containing sulphur and large quantities of smoke and PAHs) respectively have also been observed. Among other evidences of solid fuel smoke are risk of developing cataracts, tuberculosis, asthma attacks and adverse pregnancy outcomes.

Available data indicates that Environmental Tobacco Smoke (ETS) exposure is a significant health risk factor in adults, children and Infants. Smoking in workplace has been directly regarded with to cancer and chronic lung disease. The breast cancer and pulmonary tuberculosis are among other direct effects. Chronic Bronchitis due to cigarette smoking among workers of certain occupation based exposures as to coal, cement and grain, silica aerosols, vapours generated during welding, and to sulphur dioxide is quite common.

The concern about carbon monoxide is primarily for its acute poisoning—i.e. its ability to bind strongly to haemoglobins. An acute exposure to high levels of CO from improperly operated and maintained appliances is the leading cause of poisoning death.

The harmful effect of exposure to Ozone include breathing problems, reduce lung function, exacerbate asthma, irritate eyes and nose, reduce resistance to colds and other infections, and speed up ageing of lung tissue. Further indoor O3 may generate secondary pollutants by means of chemical reactions occurring inside thus aggreviating the problem. For example, several terpenes are used indoors as solvents in consumer products (e.g. d-limonene contained in lemon scented detergents, a-pinene contained in pine scented paints) which can react with O3 to form ultra-fine and fine particles, aldehydes, hydrogen peroxide, carboxylic acids, reactive intermediates intermediates, and free radicals including the hydroxyl radical. These Ozone generated secondary pollutants are strong airway irritants and may exhibit respiratory and cardiovascular effects.

The decaying process of radon makes the particles slightly radioactive and thus expose lung tissue when they deposit during breathing. Three types of radiation (α, β, γ) are emitted during the process with a capability to ionize atoms leading to cell damage. Radon exposure is of primary concern amongst uranium miners and others with a high risk of developing lung cancer.

Some of the VOCs and SVOCs like benzene, styrene, tetrachloroethylene, 1,1,1-trichloroethane,trichloroethylene, dichlorobenzene, methylene chloride and chloroform are mutagenic and/or carcinogenic in nature causing long term toxic effects. Many others may cause sensory irritation (e.g. aldehydes) and central nervous system symptoms (e.g. pesticides). Their adverse affect have also been observed in neurobehavioural performance, lung function and nasal inflammation.

The term Sick building syndrome is used to describe the cases in which building occupants experience acute health and comfort effects that are apparently linked to the time they spend in the building, nut in which no specific illness or causes can be identified. The Building related illness(BRI) is a term referring to illness brought on by exposure to the building air where symptoms of diagnosable illness are identified( certain allergies or infections)

A small percentage of population may be sensitive to a number of chemicals in indoor air, each of which may occur at very low concentration. The existence of this condition which is known as Multiple Chemical Sensitivity(MCS) is a matter of considerable controversy. Some of the effects associated with different biocontaminants include: Pollen grains contain substances (allergens) which may cause in susceptible, or atopic, individuals allergic responses usually manifested as “hay fever”, or rhinitis. Dander is a source of potent allergens which can cause bouts of rhinitis or asthma in susceptible individuals. A host of diseases like Pneumonia and Influnza are caused by different forms of viruses.

Regulations, guidelines and standards for Indoor Air Pollution

A number of different international Organizations have given standards and guidelines associated with different aspects of Indoor air quality. WHO has given long back some guidelines to control indoor air pollutants. Presently Indian agency does not have any guidelines or regulation for indoor air. Two of these are described hereunder:

The Occupational Safety and Health Administration (USA, Department of Labor) in 1970 adopted a set of exposure guidelines and consensus standards in the workplace as OSHA regulations. The guidelines were meant to address the most common workplace complaints about IAQ, which are typically related to temperature, humidity, lack of outside air etc. thus setting an airborne concentration limits which are legally enforceable. The different airborne exposure limits as established by OSHA include:

Permissible Exposure Limit (PEL): It is the maximum allowable limit that is representative of a worker’s exposure, averaged over an 8-hour a day.

Short-term Exposure Limit (STEL): It is the allowable limit that represents a worker’s exposure, for a time period averaged over 15 minutes.

Ceiling Limit (C): The maximum airborne concentration to which a worker is exposed that should not be exceeded.

A number of Different Acts have been established by OSHA that comply with various aspects of Indoor Air pollution. Some of the applicable OSHA Standards are:

29 CFR 1910.94, Ventilation., 29 CFR 1910.1000, Air Contaminants.

ASHRAE (American Society of Heating, Refrigerating and Air-conditioning Engineers) is an international organization that deals with the advancement of Science for HVAC & R (heating, ventilation, air-conditioning, and refrigeration). It offers more than 175 guidelines describing the uniform methods of testing, specify design requirements, and recommend standard practices and over 4000 standards for the design and maintenance of indoor air environments.

(1) OSHA – Permissible Exposure Limit

(2) ASHRAE – Standard 55

(3) WHO air quality guidelines – global update 2005 and WHO guideline value for the ―classical‖ air pollutants (WHO 1999)

(4) The National Ambient Air Quality Standards (NAAQS) were developed by the U.S Environmental Protection Agency (EPA) under the Clean Air Act (last amended in 1990). These standards are applicable for both outdoor and indoor contaminant levels

Control measures for improving Indoor Air Quality

There are three basic strategies to improve indoor air quality:

Source Control

Usually the most effective way to improve indoor air quality is to eliminate individual sources of pollution or to reduce their emissions. Some sources, like those that contain asbestos, can be sealed or enclosed; others, like gas stoves, can be adjusted to decrease the amount of emissions. In many cases, source control is also a more cost-efficient approach to protecting indoor air quality than increasing ventilation because increasing ventilation can increase energy costs.

Ventilation Improvements

Another approach to lowering the concentrations of indoor air pollutants in your home is to increase the amount of outdoor air coming indoors. Most home heating and cooling systems, including forced air heating systems, do not mechanically bring fresh air into the house. Opening windows and doors, operating window or attic fans, when the weather permits, or running a window air conditioner with the vent control open increases the outdoor ventilation rate. Local bathroom or kitchen fans that exhaust outdoors remove contaminants directly from the room where the fan is located and also increase the outdoor air ventilation rate.

It is particularly important to take as many of these steps as possible while you are involved in short-term activities that can generate high levels of pollutants — for example, painting, paint stripping, heating with kerosene heaters, cooking, or engaging in maintenance and hobby activities such as welding, soldering, or sanding. You might also choose to do some of these activities outdoors, if you can and if weather permits.

Advanced designs of new homes are starting to feature mechanical systems that bring outdoor air into the home. Some of these designs include energy-efficient heat recovery ventilators (also known as air-to-air heat exchangers). Ventilation and shading can help control indoor temperatures. Ventilation also helps remove or dilute indoor airborne pollutants coming from indoor sources. This reduces the level of contaminants and improves indoor air quality (IAQ). Carefully evaluate using ventilation to reduce indoor air pollutants where there may be outdoor sources of pollutants, such as smoke or refuse, nearby. The introduction of outdoor air is one important factor in promoting good air quality. Air may enter a home in several different ways, including: through natural ventilation, such as through windows and doors through mechanical means, such as through outdoor air intakes associated with the heating, ventilation and air conditioning (HVAC) system through infiltration, a process by which outdoor air flows into the house through openings, joints and cracks in walls, floors and ceilings, and around windows and doors.

Infiltration occurs in all homes to some extent. Natural ventilation describes air movement through open windows and doors. If used properly natural ventilation can at times help moderate the indoor air temperature, which may become too hot in homes without air-conditioning systems or when power outages or brownouts limit or make the use of air conditioning impossible. Natural ventilation can also improve indoor air quality by reducing pollutants that are indoors. Examples of natural ventilation are:

Opening windows and doors
Window shading such as closing the blinds

Most residential forced air-heating systems and air-conditioning systems do not bring outdoor air into the house mechanically, and infiltration and natural ventilation are relied upon to bring outdoor air into the home. Advanced designs for new homes are starting to add a mechanical feature that brings outdoor air into the home through the HVAC system. Some of these designs include energy efficient heat recovery ventilators to mitigate the cost of cooling and heating this air during the summer and winter.

Air Cleaners

There are many types and sizes of air cleaners on the market, ranging from relatively inexpensive table-top models to sophisticated and expensive whole-house systems. Some air cleaners are highly effective at particle removal, while others, including most table-top models, are much less so. Air cleaners are generally not designed to remove gaseous pollutants.

The effectiveness of an air cleaner depends on how well it collects pollutants from indoor air (expressed as a percentage efficiency rate) and how much air it draws through the cleaning or filtering element (expressed in cubic feet per minute). A very efficient collector with a low air-circulation rate will not be effective, nor will a cleaner with a high air-circulation rate but a less efficient collector. The long-term performance of any air cleaner depends on maintaining it according to the manufacturer’s directions. Another important factor in determining the effectiveness of an air cleaner is the strength of the pollutant source. Table-top air cleaners, in particular, may not remove satisfactory amounts of pollutants from strong nearby sources. People with a sensitivity to particular sources may find that air cleaners are helpful only in conjunction with concerted efforts to remove the source.

Alternative fuels

The largest reductions in indoor air pollution can be achieved by switching from solid fuels (biomass, coal) to cleaner and more efficient fuels and energy technologies such as:

liquid petroleum gas (LPG) biogas producer gas electricity solar power

Improved stoves

In poor, rural communities where access to alternative fuels is very limited and biomass remains the most practical fuel, pollution levels can be lowered significantly by using improved stoves. These stoves, provided they are adequately designed, installed and maintained, are effective in reducing smoke because of better combustion, lower emission levels and potentially also shorter cooking times.

Interventions to the living environment

Improved ventilation of the cooking and living area can contribute significantly to reducing exposure to smoke. There are a number of ways to achieve better ventilation of the living environment including:

chimneys smoke hoods (with flues) eaves spaces enlarged and repositioned windows (cooking window)

Interventions to user behaviour

Changes in user behaviour can also play a role in reducing pollution and exposure levels. For example, drying fuel wood before use improves combustion and decreases smoke production. Keeping young children away from smoke reduces exposure of this most vulnerable age group to health-damaging pollutants.

Such changes in user behaviour are unlikely to bring about reductions as large as those expected from a fuel switch or the installation of a hood or chimney. However, they should be seen as important supporting measures for other interventions.

The Indian Scenario of Indoor Air Pollution

The foremost factor responsible for indoor air pollution in the country is burning of fossil fuel for cooking. About 1/4 of ambient PM2.5 comes from household cook fuels. Based on the study conducted to estimate the total burden of disease (mortality and morbidity) associated with the use of solid fuels and exposure on vulnerable section, indoor air pollution is responsible for ~ 1/5th casuality related to air pollution in India. The attributable risks calculated on the basis of demographic conditions and patterns of each disease provides evidence with high confidence the occurance of acute respiratory infections (ARI), chronic obstructive pulmonary disease (COPD), and lung cancer. Estimates for tuberculosis (TB), asthma, and blindness are of intermediate confidence. Indoor air pollution was found to be a major risk factor contributing in a total of 4–6% of the Indian national burden of disease.

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Suggested Reading:

Gilbert M. Masters, Wendell P. Ela., Introduction to Environmental Engineering and Science., IIIrd edition. PHI Publication
Andrew R W Jackson & Julie M Jackson ., Environmental Science: The Natural Environment and Human Impact 2nd edition., Longman publication
Parker C. Reist, Introduction to aerosol science., 1984. Macmillan Publishing Company, New York.
John H. Seinfeld, Spyros N. Pandis., Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, 3rd Edition (2016)., John Wiley & Sons
www.who.int/indoorair/interventions/en/
www.epa.gov/indoor-air-quality-iaq/improving-indoor-air-quality