Guide to Air Cleaners in the Home

Introduction.Indoor air pollutants are unwanted, sometimes harmful materials in the air. Indoor air pollution is among the top five environmental health risks. Usually the best way to address this risk is to control or eliminate the sources of pollutants, and to ventilate a home with clean outdoor air. The ventilation method may, however, be limited by weather conditions or undesirable levels of contaminants contained in outdoor air. If these measures are insufficient, an air cleaning device may be useful. Air cleaning devices are intended to remove pollutants from indoor air. Some air cleaning devices are designed to be installed in the ductwork of a home’s central heating, ventilating, and air-conditioning (HVAC) system to clean the air in the whole house. Portable room air cleaners can be used to clean the air in a single room or specific areas, but they are not intended for whole-house filtration. The following pages will provide information on different types of air cleaning devices and how they work.

Please Note: EPA neither certifies nor recommends particular brands of home air cleaning devices. While some home air cleaning devices may be useful in some circumstances, EPA makes no broad endorsement of their use, nor specific endorsement of any brand or model. This document describes performance characteristics associated with several types of air cleaners sold to consumers for home use. It does not discuss the effectiveness of air cleaners installed in the HVAC systems of large buildings, such as apartments, offices, schools, or public buildings.

Under Federal pesticide law, manufacturers of ozone generators must list an EPA establishment number on the packaging. This number merely identifies the facility that manufactured the product. Display of this number implies neither EPA endorsement nor that EPA has found the product to be safe or effective.

Some portable air cleaners sold in the consumer market are ENERGY STAR qualified. Please note the following disclaimer on their packaging: “This product earned the ENERGY STAR by meeting strict energy efficiency guidelines set by EPA. EPA does not endorse any manufacturer claims of healthier indoor air from the use of this product.”

Indoor Air Pollutants.Pollutants that can affect air quality in a home fall into the following categories:

Particulate matter includes dust, smoke, pollen, animal dander, tobacco smoke, particles generated from combustion appliances such as cooking stoves, and particles associated with tiny organisms such as dust mites, molds, bacteria, and viruses.

Gaseous pollutants come from combustion processes. Sources include gas cooking stoves, vehicle exhaust, and tobacco smoke. They also come from building materials, furnishings, and the use of products such as adhesives, paints, varnishes, cleaning products, and pesticides.

Understanding the Types of Air Cleaning Devices.Before deciding whether to use an air cleaning device, several questions should be considered:

What types of pollutants can an air cleaner remove?

How is the performance of an air cleaner measured?

Will air cleaning reduce adverse health effects?

What other factors should I consider?

What Types of Pollutants Can an Air Cleaner Remove?

There are several types of air cleaning devices available, each designed to remove certain types of pollutants.

Particle Removal.Two types of air cleaning devices can remove particles from the air − mechanical air filters and electronic air cleaners. Mechanical air filters remove particles by capturing them on filter materials.

High efficiency particulate air (HEPA) filters are in this category. Electronic air cleaners such as electrostatic precipitators use a process called electrostatic attraction to trap charged particles. They draw air through an ionization section where particles obtain an electrical charge. The charged particles then accumulate on a series of flat plates called a collector that is oppositely charged. Ion generators, or ionizers, disperse charged ions into the air, similar to the electronic air cleaners but without a collector. These ions attach to airborne particles, giving them a charge so that they attach to nearby surfaces such as walls or furniture, or attach to one another and settle faster.

Gaseous Pollutant Removal. Gas-phase air filters remove gases and odors by using a material called a sorbent, such as activated carbon, which adsorbs the pollutants. These filters are typically intended to remove one or more gaseous pollutants from the airstream that passes through them. Because gas-phase filters are specific to one or a limited number of gaseous pollutants, they will not reduce concentrations of pollutants for which they were not designed. Some air cleaning devices with gas-phase filters may remove a portion of the gaseous pollutants and some of the related hazards, at least on a temporary basis. However, none are expected to remove all of the gaseous pollutants present in the air of a typical home. For example, carbon monoxide is a dangerous gaseous pollutant that is produced whenever any fuel such as gas, oil, kerosene, wood, or charcoal is burned, and it is not readily captured using currently available residential gas-phase filtration products.

Pollutant Destruction.Some air cleaners use ultraviolet (UV) light technology intended to destroy pollutants in indoor air. These air cleaners are called ultraviolet germicidal irradiation (UVGI) cleaners and photocatalytic oxidation (PCO) cleaners. Ozone generators that are sold as air cleaners intentionally produce ozone gas, a lung irritant, to destroy pollutants.

Ozone is a lung irritant that can cause adverse health effects. UVGI cleaners use ultraviolet radiation from UV lamps that may destroy biological pollutants such as viruses, bacteria, allergens, and molds that are airborne or growing on HVAC surfaces (e.g., found on cooling coils, drain pans, or ductwork). If used, they should be applied with, but not as a replacement for, filtration systems.

PCO cleaners use a UV lamp along with a substance, called a catalyst, that reacts with the light. They are intended to destroy gaseous pollutants by converting them into harmless products, but are not designed to remove particulate pollutants.

Ozone generators use UV light or an electrical discharge to intentionally produce ozone. Ozone is a lung irritant that can cause adverse health effects. At concentrations that do not exceed public health standards, ozone has little effect in removing most indoor air contaminants. Thus, ozone generators are not always safe and effective in controlling indoor air pollutants. Consumers should instead use methods proven to be both safe and effective to reduce pollutant concentrations, which include eliminating or controlling pollutant sources and increasing outdoor air ventilation.

In addition to understanding the different types of air cleaning devices, consumers should consider their performance, as explained in the next section.

How is the Performance of an Air Cleaner Measured?There are different ways to measure how well air cleaning devices work, which depend on the type of device and the basic configuration. Air cleaning devices are configured either in the ductwork of HVAC systems (i.e., in-duct) or as portable air cleaners.

In-duct Particle Removal.Most mechanical air filters are good at capturing larger airborne particles, such as dust, pollen, dust mite and cockroach allergens, some molds, and animal dander. However, because these particles settle rather quickly, air filters are not very good at removing them completely from indoor areas. Although human activities such as walking and vacuuming can stir up particles, most of the larger particles will resettle before an air filter can remove them.

Consumers can select a particle removal air filter by looking at its efficiency in removing airborne particles from the air stream that passes through it. This efficiency is measured by the minimum efficiency reporting value (MERV) for air filters installed in the ductwork of HVAC systems. The American Society of Heating, Refrigerating and Air-Conditioning Engineers, or ASHRAE developed this measurement method. MERV ratings (ranging from a low of 1 to a high of 20) also allow comparison of air filters made by different companies.

Flat or panel air filters with a MERV of 1 to 4 are commonly used in residential furnaces and air conditioners. For the most part, such filters are used to protect the HVAC equipment from the buildup of unwanted materials on the surfaces such as fan motors and heating or cooling coils, and not for direct indoor air quality reasons. They have low efficiency on smaller airborne particles and medium efficiency on larger particles, as long as they remain airborne and pass through the filter. Some smaller particles found within a house include viruses, bacteria, some mold spores, a significant fraction of cat and dog allergens, and a small portion of dust mite allergens.

Filters with a MERV between 7 and 13 are likely to be nearly as effective as true HEPA filters. Pleated or extended surface filters.Medium efficiency filters with a MERV of 5 to 13 are reasonably efficient at removing small to large airborne particles. Filters with a MERV between 7 and 13 are likely to be nearly as effective as true HEPA filters at controlling most airborne indoor particles. Medium efficiency air filters are generally less expensive than HEPA filters, and allow quieter HVAC fan operation and higher airflow rates than HEPA filters since they have less airflow resistance.

Higher efficiency filters with a MERV of 14 to 16, sometimes misidentified as HEPA filters, are similar in appearance to true HEPA filters, which have MERV values of 17 to 20. True HEPA filters are normally not installed in residential HVAC systems; installation of a HEPA filter in an existing HVAC system would probably require professional modification of the system. A typical residential air handling unit and the associated ductwork would not be able to accommodate such filters because of their physical dimensions and increase in airflow resistance.

Some residential HVAC systems may not have enough fan or motor capacity to accommodate higher efficiency filters. Therefore, the HVAC manufacturer’s information should be checked prior to upgrading filters to determine whether it is feasible to use more efficient filters. Specially built high performance homes may occasionally be equipped with true HEPA filters installed in a properly designed HVAC system.

There is no standard measurement for the effectiveness of electronic air cleaners. While they may remove small particles, they may be ineffective in removing large particles. Electronic air cleaners can produce ozone − a lung irritant. The amount of ozone produced varies among models. Electronic air cleaners may also produce ultrafine particles resulting from reaction of ozone with indoor chemicals such as those coming from household cleaning products, air fresheners, certain paints, wood flooring, or carpets. Ultrafine particles may be linked with adverse health effects in some sensitive populations.

In-duct Gaseous Pollutant Removal.Although there is no standard measurement for the effectiveness of gas-phase air filters, ASHRAE is developing a standard method to be used in choosing gas-phase filters installed in home HVAC systems. Gas-phase filters are much less commonly used in homes than particle air filters. The useful lifetime of gas-phase filters can be short because the filter material can quickly become overloaded and may need to be replaced often. There is also concern that, when full, these filters may release trapped pollutants back into the air. Finally, a properly designed and built gas-phase filtration system would be unlikely to fit in a typical home HVAC system or portable air cleaner.

In-duct Pollutant Destruction. UVGI cleaners may not reduce allergy or asthma symptoms. There is no standard measurement for the effectiveness of UVGI cleaners. Typical UVGI cleaners used in homes have limited effectiveness in killing bacteria and molds. Effective destruction of some viruses and most mold and bacterial spores usually requires much higher UV exposure than is provided in a typical home unit. Furthermore, dead mold spores can still produce allergic reactions, so UVGI cleaners may not be effective in reducing allergy and asthma symptoms.

There is no standard measurement for the effectiveness of PCO cleaners. The use of PCO cleaners in homes is limited because currently available catalysts are ineffective in destroying gaseous pollutants from indoor air. Some PCO cleaners fail to destroy pollutants completely and instead produce new indoor pollutants that may cause irritation of the eyes, throat, and nose.

Portable Air Cleaners.Portable air cleaners generally contain a fan to circulate the air and use one or more of the air cleaning devices discussed above. Portable air cleaners may be moved from room to room and used when continuous and localized air cleaning is needed. They may be an option if a home is not equipped with a central HVAC system or forced air heating system.

Portable air cleaners can be evaluated by their effectiveness in reducing airborne pollutants. This effectiveness is measured by the clean air delivery rate, or CADR, developed by the Association of Home Appliance Manufacturers, or AHAM. The CADR is a measure of a portable air cleaner’s delivery of contaminant-free air, expressed in cubic feet per minute. For example, if an air cleaner has a CADR of 250 for dust particles, it may reduce dust particle levels to the same concentration as would be achieved by adding 250 cubic feet of clean air each minute. While a portable air cleaner may not achieve its rated CADR under all circumstances, the CADR value does allow comparison across different portable air cleaners.

Many of the portable air cleaners tested by AHAM have moderate to large CADR ratings for small particles. However, for typical room sizes, most portable air cleaners currently on the market do not have high enough CADR values to effectively remove large particles such as pollen, dust mite, and cockroach allergens. Some portable air cleaners using electronic air cleaners might produce ozone, which is a lung irritant. AHAM has a portable air cleaner certification program, and provides a complete listing of all certified cleaners with their CADR values on its Website at www.cadr.org.

Will Air Cleaning Reduce Adverse Health Effects?The ability to remove particles, including microorganisms, is not, in itself, an indication of the ability of an air cleaning device to reduce adverse health effects from indoor pollutants. The use of air cleaning devices may help to reduce levels of smaller airborne allergens or particles. However, air cleaners may not reduce adverse health effects completely in sensitive population such as children, the elderly, and people with asthma and allergies. For example, the evidence is weak that air cleaning devices are effective in reducing asthma symptoms associated with small particles that remain in the air, such as those from some airborne cat dander and dust mite allergens. Larger particles, which may contain allergens, settle rapidly before they can be removed by filtration, so effective allergen control measures require washing sheets weekly, frequent vacuuming of carpets and furniture, and dusting and cleaning of hard surfaces. There are no studies to date linking gas-phase filtration, UVGI, and PCO systems in homes to reduced health symptoms in sensitive populations.

Additional Factors to Consider.When making decisions about using air cleaning devices, consumers should also consider:

Installation: In-duct air cleaning devices have certain installation requirements that must be met, such as sufficient access for inspection during use, repairs, or maintenance.

Major Costs: These include the initial purchase, maintenance (such as cleaning or replacing filters and parts), and operation (such as electricity).

Odors: Air cleaning devices designed for particle removal are incapable of controlling gases and some odors. The odor and many of the carcinogenic gas-phase pollutants from tobacco smoke will still remain.

Soiling of Walls and Other Surfaces: Ion generators generally are not designed to remove the charged particles that they generate from the air. These charged particles may deposit on room surfaces, soiling walls and other surfaces.

Noise: Noise may be a problem with portable air cleaners containing a fan. Portable air cleaners without a fan are typically much less effective than units with a fan.

Conclusion.Indoor air pollution is among the top five environmental health risks. The best way to address this risk is to control or eliminate the sources of pollutants, and to ventilate a home with clean outdoor air. The ventilation method may, however, be limited by weather conditions or undesirable levels of contaminants in outdoor air. If these measures are insufficient, an air cleaning device may be useful. While air cleaning devices may help to control the levels of airborne allergens, particles, or, in some cases, gaseous pollutants in a home, they may not decrease adverse health effects from indoor air pollutants.

(http://www.epa.gov/iedweb00/pubs/airclean.html)

Carbon Monoxide (CO)

Carbon monoxide is an odorless, colorless and toxic gas. Because it is impossible to see, taste or smell the toxic fumes, CO can kill you before you are aware it is in your home. At lower levels of exposure, CO causes mild effects that are often mistaken for the flu. These symptoms include headaches, dizziness, disorientation, nausea and fatigue. The effects of CO exposure can vary greatly from person to person depending on age, overall health and the concentration and length of exposure.

Sources of Carbon Monoxide.Unvented kerosene and gas space heaters; leaking chimneys and furnaces; back-drafting from furnaces, gas water heaters, wood stoves, and fireplaces; gas stoves; generators and other gasoline powered equipment; automobile exhaust from attached garages; and tobacco smoke. Incomplete oxidation during combustion in gas ranges and unvented gas or kerosene heaters may cause high concentrations of CO in indoor air. Worn or poorly adjusted and maintained combustion devices (e.g., boilers, furnaces) can be significant sources, or if the flue is improperly sized, blocked, disconnected, or is leaking. Auto, truck, or bus exhaust from attached garages, nearby roads, or parking areas can also be a source.

Health Effects Associated with Carbon Monoxide.At low concentrations, fatigue in healthy people and chest pain in people with heart disease. At higher concentrations, impaired vision and coordination; headaches; dizziness; confusion; nausea. Can cause flu-like symptoms that clear up after leaving home. Fatal at very high concentrations. Acute effects are due to the formation of carboxyhemoglobin in the blood, which inhibits oxygen intake. At moderate concentrations, angina, impaired vision, and reduced brain function may result. At higher concentrations, CO exposure can be fatal.

Levels in Homes.Average levels in homes without gas stoves vary from 0.5 to 5 parts per million (ppm). Levels near properly adjusted gas stoves are often 5 to 15 ppm and those near poorly adjusted stoves may be 30 ppm or higher.

Steps to Reduce Exposure to Carbon Monoxide.It is most important to be sure combustion equipment is maintained and properly adjusted. Vehicular use should be carefully managed adjacent to buildings and in vocational programs. Additional ventilation can be used as a temporary measure when high levels of CO are expected for short periods of time.

ALERT: Put generators outside.

Never use a generator inside homes, garages, crawlspaces, sheds, or similar areas. Deadly levels of carbon monoxide can quickly build up in these areas and can linger for hours, even after the generator has shut off.

Keep gas appliances properly adjusted.

Consider purchasing a vented space heater when replacing an unvented one.

Use proper fuel in kerosene space heaters.

Install and use an exhaust fan vented to outdoors over gas stoves.

Open flues when fireplaces are in use.

Choose properly sized wood stoves that are certified to meet EPA emission standards. Make certain that doors on all wood stoves fit tightly.

Have a trained professional inspect, clean, and tune-up central heating system (furnaces, flues, and chimneys) annually. Repair any leaks promptly.

Do not idle the car inside garage.

Measurement Methods.Some relatively high-cost infrared radiation adsorption and electrochemical instruments do exist. Moderately priced real-time measuring devices are also available. A passive monitor is currently under development.

Exposure Limits.OSHA Note: This guideline summarizes pertinent information about carbon monoxide for workers and employers as well as for physicians, industrial hygienists, and other occupational safety and health professionals who may need such information to conduct effective occupational safety and health programs. Recommendations may be superseded by new developments in these fields; readers are therefore advised to regard these recommendations as general guidelines and to determine whether new information is available.

[OSHA PEL] The current Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for carbon monoxide is 50 parts per million (ppm) parts of air (55 milligrams per cubic meter (mg/m(3))) as an 8-hour time-weighted average (TWA) concentration [29 CFR Table Z-1].

[NIOSH REL] The National Institute for Occupational Safety and Health (NIOSH) has established a recommended exposure limit (REL) for carbon monoxide of 35 ppm (40 mg/m(3)) as an 8-hour TWA and 200 ppm (229 mg/m(3)) as a ceiling [NIOSH 1992]. The NIOSH limit is based on the risk of cardiovascular effects.

[ACGIH TLV] The American Conference of Governmental Industrial Hygienists (ACGIH) has assigned carbon monoxide a threshold limit value (TLV) of 25 ppm (29 mg/m(3)) as a TWA for a normal 8-hour workday and a 40-hour workweek [ACGIH 1994, p. 15]. The ACGIH limit is based on the risk of elevated carboxyhemoglobin levels [ACGIH 1991, p. 229].

About Carbon Monoxide Detectors.CPSC Recommends Carbon Monoxide Alarm for Every Home (January 18, 2001 CPSC Release # 01-069). The U.S. Consumer Product Safety Commission (CPSC) recommends that every home should have a carbon monoxide (CO) alarm. CPSC also urges consumers to have a professional inspection of all fuel-burning appliances − including furnaces, stoves, fireplaces, clothes dryers, water heaters, and space heaters − to detect deadly carbon monoxide leaks. CPSC recommends that every home should have at least one CO alarm that meets the requirements of the most recent Underwriters Laboratories (UL) 2034 standard or International Approval Services 6-96 standard.

(http://www.epa.gov/iaq/co.html)

Greenhouse Gas Emissions

Greenhouse Gas Overview.Gases that trap heat in the atmosphere are often called greenhouse gases. This section of the EPA Climate Change Site provides information and data on emissions of greenhouse gases to Earth’s atmosphere, and also the removal of greenhouse gases from the atmosphere. For more information on the science of climate change, please visit EPA’s climate change science home page.

Some greenhouse gases such as carbon dioxide occur naturally and are emitted to the atmosphere through natural processes and human activities. Other greenhouse gases (e.g., fluorinated gases) are created and emitted solely through human activities. The principal greenhouse gases that enter the atmosphere because of human activities are:

Carbon Dioxide (CO2): Carbon dioxide enters the atmosphere through the burning of fossil fuels (oil, natural gas, and coal), solid waste, trees and wood products, and also as a result of other chemical reactions (e.g., manufacture of cement). Carbon dioxide is also removed from the atmosphere (or “sequestered”) when it is absorbed by plants as part of the biological carbon cycle.

Methane (CH4): Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from livestock and other agricultural practices and by the decay of organic waste in municipal solid waste landfills.

Nitrous Oxide (N2O): Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of fossil fuels and solid waste.

Fluorinated Gases: Hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride are synthetic, powerful greenhouse gases that are emitted from a variety of industrial processes. Fluorinated gases are sometimes used as substitutes for ozone-depleting substances (i.e., CFCs, HCFCs, and halons). These gases are typically emitted in smaller quantities, but because they are potent greenhouse gases, they are sometimes referred to as High Global Warming Potential gases (“High GWP gases”).

Greenhouse Gas Inventories.A greenhouse gas inventory is an accounting of the amount of greenhouse gases emitted to or removed from the atmosphere over a specific period of time (e.g., one year). A greenhouse gas inventory also provides information on the activities that cause emissions and removals, as well as background on the methods used to make the calculations. Policy makers use greenhouse gas inventories to track emission trends, develop strategies and policies and assess progress. Scientists use greenhouse gas inventories as inputs to atmospheric and economic models.

To track the national trend in emissions and removals since 1990, EPA develops the official U.S. greenhouse gas inventory each year. The national greenhouse gas inventory is submitted to the United Nations in accordance with the Framework Convention on Climate Change.

In addition to the U.S. inventory, greenhouse gas emissions can be tracked at the global, state and local levels as well as by companies and individuals:

Many other countries also develop national greenhouse gas inventories, which can be compiled into global inventories. EPA works with developing and transition countries to improve the accuracy and sustainability of their greenhouse gas inventories. EPA has developed Greenhouse Gas Inventory Capacity Building templates and software tools targeting key sources, emissions factors, good practices, institutional infrastructure and use of the latest IPCC guidelines on greenhouse gas inventories.

Many state and local governments prepare greenhouse gas inventories, and EPA provides guidance and tools to assist them in their efforts.

Corporate greenhouse gas inventories provide information on the emissions associated with the operations of a company.

Individuals produce greenhouse gas emissions through everyday activities such as driving and using air conditioning or heating. EPA provides an online calculator for estimating personal emissions.

The Intergovernmental Panel on Climate Change (IPCC) publishes internationally accepted inventory methodologies that serve as a basis for all greenhouse gas inventories, ensuring that they are comparable and understandable. The 2006 IPCC Guidelines were completed and accepted by the IPCC in May 2006.

Emission Trends & Projections.Estimates of future emissions and removals depend in part on assumptions about changes in underlying human activities. For example, the demand for fossil fuels such as gasoline and coal is expected to increase greatly with the predicted growth of the U.S. and global economies.

The Fifth U.S. Climate Action Report concluded, in assessing current trends, that greenhouse gas emissions increased by 17 percent from 1990 − 2007. Over that same time period, the U.S. GDP increased by 65 percent and population increased by 21 percent. The dominant factor affecting U.S. emissions trends is CO2 emissions from fossil fuel combustion, which increased by 21.8 percent over the 17-year period, while methane and nitrous oxide emissions decreased by 5 percent and 1 percent, respectively. The declines in methane emissions are mostly due to increased collection and combustion of landfill gas, as well as improvements in technology and management practices at natural gas plants. The decline in nitrous oxide emissions is largely due to the installation of newer N2O control technologies in motor vehicles throughout the past decade. Fluorinated substances (HFCs, PFCs, and SF6) accounted for 2 percent of total U.S. GHG emissions in 2007. The increasing use of these compounds since 1995 as substitutes for ozone depleting substances has been largely responsible for their upward emissions trends. (Fifth U.S.Climate Action Report, 2010)

Many, but not all, human sources of greenhouse gas emissions are expected to rise in the future. This growth may be reduced by ongoing efforts to increase the use of newer, cleaner technologies and other measures. Additionally, our everyday choices about such things as commuting, housing, electricity use and recycling can influence the amount of greenhouse gases being emitted.

The United States government prepares projections of emissions and removals of all greenhouse gases.

EPA has developed several Climate Leaders Offset Project Methodologies that use a standardized approach to determine project eligibility, address additionality, select and set the baseline, identify monitoring options, and quantify reductions. This approach seeks to ensure that the GHG emission reductions from offset projects meet four key accounting principles − they must be real, additional, permanent, and verifiable.

To be eligible as offsets, project activities must be surplus to regulation. Projects are also required to demonstrate additionality by achieving a level of performance with respect to emission reductions and/or removals that is significantly better than business-as-usual. Business-as-usual is determined from similar, recently undertaken or planned practices, activities or facilities in the same geographic region. This level of “performance” may be defined as an emissions rate, a technology standard or a practice standard. Data used in setting the performance standard is primarily collected from publicly available historic data (although planned or projected activities may be used in certain cases as well). The performance standard approach minimizes the risk of accepting a project that is not additional or rejecting a project that is additional. A performance standard approach also reduces the complexity, cost, and subjectivity of constructing individual project-specific reviews.

(http://www.epa.gov/climatechange/emissions/index.html)

26. Climate Change − Health and Environmental Effects

Throughout the world, the prevalence of some diseases and other threats to human health depend largely on local climate. Extreme temperatures can lead directly to loss of life, while climate-related disturbances in ecological systems, such as changes in the range of infective parasites, can indirectly impact the incidence of serious infectious diseases. In addition, warm temperatures can increase air and water pollution, which in turn harm human health.

Human health is strongly affected by social, political, economic, environmental and technological factors, including urbanization, affluence, scientific developments, individual behavior and individual vulnerability (e.g., genetic makeup, nutritional status, emotional well-being, age, gender and economic status). The extent and nature of climate change impacts on human health vary by region, by relative vulnerability of population groups, by the extent and duration of exposure to climate change itself and by society’s ability to adapt to or cope with the change.

The Intergovernmental Panel on Climate Change (IPCC, 2007) concluded:

Human beings are exposed to climate change through changing weather patterns (for example, more intense and frequent extreme events) and indirectly through changes in water, air, food quality and quantity, ecosystems, agriculture, and economy. At this early stage the effects are small but are projected to progressively increase in all countries and regions.

Given the complexity of factors that influence human health, assessing health impacts related to climate change poses a difficult challenge. Furthermore, climate change is expected to bring a few benefits to health, including fewer deaths due to exposure to cold. Nonetheless, the IPCC has concluded that, overall (globally), negative climate-related health impacts are expected to outweigh positive health impacts during this century (IPCC, 2007). At the same time, the quality of medical care and public health systems in the United States may lessen climate impacts on human health within the U.S.

Direct Temperature Effects.The U.S. Environmental Protection Agency has produced the Excessive Heat Events Guidebook with the National Oceanic and Atmospheric Administration (NOAA), the Centers for Disease Control and Prevention (CDC), and the Department of Homeland Security (DHS). Municipal officials in both the U.S. and Canada provided useful information that can be used to help the public cope with excessive heat.

Designed to help community officials, emergency managers, meteorologists, and others plan for and respond to excessive heat events, the guidebook highlights best practices that have been employed to save lives during excessive heat events in different urban areas and provides a menu of options that officials can use to respond to these events in their communities.

Climate change may directly affect human health through increases in average temperature. Such increases may lead to more extreme heat waves during the summer while producing less extreme cold spells during the winter. Rising average temperatures are predicted to increase the incidence of heat waves and hot extremes. In the United States, Chicago is projected to experience 25 percent more frequent heat waves and Los Angeles a four-to-eight-fold increase in heat wave days by the end of the century (IPCC, 2007). Particular segments of the population such as those with heart problems, asthma, the elderly, the very young and the homeless can be especially vulnerable to extreme heat.

Extreme Events.Extreme weather events can be destructive to human health and well-being. The extent to which climate change may affect the frequency and severity of these events, such as hurricanes and extreme heat and floods, is being investigated by the U.S. Global Change Research Program. An increase in the frequency of extreme events may result in more event-related deaths, injuries, infectious diseases, and stress-related disorders.

Climate-Sensitive Diseases.Climate change may increase the risk of some infectious diseases, particularly those diseases that appear in warm areas and are spread by mosquitoes and other insects. These “vector-borne” diseases include malaria, dengue fever, yellow fever, and encephalitis. Also, algal blooms could occur more frequently as temperatures warm — particularly in areas with polluted waters — in which case diseases (such as cholera) that tend to accompany algal blooms could become more frequent.

Higher temperatures, in combination with favorable rainfall patterns, could prolong disease transmission seasons in some locations where certain diseases already exist. In other locations, climate change will decrease transmission via reductions in rainfall or temperatures that are too high for transmission. For example, temperature and humidity levels must be sufficient for certain disease-carrying vectors, such as ticks that carry Lyme disease, to thrive. And climate change could push temperature and humidity levels either towards or away from optimum conditions for the survival rate of ticks.

Though average U.S. and global temperatures are expected to continue to rise, the potential for an increase in the spread of diseases will depend not only on climatic but also on non-climatic factors, primarily the effectiveness of the public health system (WHO, 2003).

The IPCC has noted that the global population at risk from vector-borne malaria will increase by between 220 million and 400 million in the next century. While most of the increase is predicted to occur in Africa, some increased risk is projected in Britain, Australia, India and Portugal (IPCC, 2007).

Tick-borne Lyme disease also may also expand its range in Canada. However, socioeconomic factors such as public health measures will play a large role in determining the existence or extent of such infections. Water-borne diseases may increase where warmer air and water temperatures combine with heavy runoff from agricultural and urban surfaces, but may be largely contained by standard water-treatment practices.

Air Quality.The EPA Office of Research and Development’s Global Change Research Program has been investigating and supporting research on the effects of climate change on U.S. air quality.

Many individual research projects examining the effects of global change on U.S. air quality have been funded through Office of Research and Development’s STAR grant program. Summary information and progress reports from these and other STAR grants can be found at EPA’s National Center for Environmental Research .

Climate change is expected to contribute to some air quality problems (IPCC, 2007). Respiratory disorders may be exacerbated by warming-induced increases in the frequency of smog (ground-level ozone) events and particulate air pollution.

Ground-level ozone can damage lung tissue, and is especially harmful for those with asthma and other chronic lung diseases. Sunlight and high temperatures, combined with other pollutants such as nitrogen oxides and volatile organic compounds, can cause ground-level ozone to increase. Climate change may increase the concentration of ground-level ozone, but the magnitude of the effect is uncertain. For other pollutants, the effects of climate change and/or weather are less well studied and results vary by region (IPCC, 2007).

Another pollutant of concern is “particulate matter” also known as particle pollution or PM. Particulate matter is a complex mixture of extremely small particles and liquid droplets. When breathed in, these particles can reach the deepest regions of the lungs. Exposure to particle pollution is linked to a variety of significant health problems. Particle pollution also is the main cause of visibility impairment (haze) in the nation’s cities and national parks. Climate change may indirectly affect the concentration of PM pollution in the air by affecting natural or “biogenic” sources of PM such as wildfires and dust from dry soils.

Other Health Linkages.Other, less direct linkages exist between climate change and human health. For example, regional climate change impacts on agricultural yields and production are likely to grow over time, with the most negative effects expected in developing countries. This is expected to increase the number of undernourished people globally and consequently lead to complications in child development (IPCC, 2007).

Climate change may also contribute to social disruption, economic decline, and displacement of populations in certain regions (PDF) (22 pp, 915K, About PDF), due to effects on agricultural production, already-scarce water resources, and extreme weather events (e.g., Schwartz and Randall, 2003). These issues are likely to be more severe in developing countries, and may worsen human health and well-being in affected regions (IPCC, 2007).

(http://www.epa.gov/climatechange/effectshealth.html)

Не нашли, что искали? Воспользуйтесь поиском по сайту: