Kyle's Blog


The Coming Tyranny of Air Purification

Or, Why Adding an Air Purifier To Your Home is the Single Most Important Thing You Can Do to Improve Your Health

For Your Health

WHO Agrees?

The WHO factsheet on HAP and health states that 3.8 million premature deaths annually — including stroke, ischemic heart disease, chronic obstructive pulmonary disease and lung cancer are attributed to exposure to household air pollution.

Whats the solution?

Use of air cleaners and filters are one of the suggested strategies to improve indoor air quality. This review discusses the impact of air pollutants with special focus on indoor air pollutants and the benefits of air filters in improving indoor air quality.

The Contenders



The human lungs are excellent at air filtration but that is not what you want to be using yours for. In order to extract the 400 liters of oxygen that is crucial for survival, a total of 10,000 liters of air enters the lungs every day. The quality of air we breathe determines the health of the lungs as well as other organs. Thus, clean air is a basic requirement of human health. However, air pollution continues to pose a significant threat to health worldwide. The World Health organization (WHO) reports that seven million people die each year as a result of air pollution exposure, confirming that air pollution is now the world’s number one environmental health risk.

The impact of pollution on respiratory health is well known. The WHO factsheet reveal that, there exists a stronger link between air pollution exposure and cardiovascular diseases, such as strokes and ischemic heart disease, as well as between air pollution and cancer.

In the recently published analysis of the largest ever population based study on the distribution, causes and risk factors of a wide array of major diseases across the world, the Global Burden of Disease (GBD) study, exposure to air pollution and particulate matter was globally ranked as one of the top 10 risk factors for disease.

The quality of air inside homes, offices, schools, day care centers, public buildings, health care facilities or other private and public buildings where people spend a large part of their life is an essential determinant of healthy life and people’s well-being, says the WHO Guidelines for Indoor Air Quality. Hazardous substances emitted from buildings, construction materials and indoor equipment or due to human activities indoors, such as combustion of fuels for cooking or heating, lead to a broad range of health problems.

The Pyramid of Death



Exposure to air pollution can lead to a wide range of short- and long-term effects. Temporary short-term effects include discomfort such as irritation to the nose, throat, eyes, or skin or headaches, dizziness, and nausea. Air pollution can also cause respiratory conditions such as pneumonia or bronchitis.Long-term effects of air include heart disease, lung cancer, and respiratory diseases. That air pollution can cause exacerbations of pre-existing asthma is supported by accumulating evidence over several decades.

Several large studies suggest that pollutants exert significant effects on the cardiovascular system. It has been shown that for any increase in mortality caused by pollutants, two-thirds of the effect was accounted for by cardiovascular diseases.

Chronic exposure to pollutants results in vascular inflammation and acute exposure causes changes in blood flow and overall lung health. Increase in pollution has been linked to increased hospital admissions for congestive heart failure and heart disease.


Indoor air pollution is a complex mixture of pollutants migrating indoors from outdoor air and pollutants generated by multiple sources.

Documented evidence on indoor pollutants in the urban environment is somewhat limited. It is however, very apparent that there has been continuous deterioration of ambient air and human health with the increase in population, industrialization, and urbanization. Improper management of transport, primitive roads, high construction activity, and unplanned distribution of industries –all have led to an increase in the pollution levels. Residential complexes adjacent to industries related to dyes, textiles, timber and furniture, handicrafts, metals, chemicals, sandstone quarries and oil mills, etc., are responsible for a rise in a variety of indoor pollutants. Increasing emission of toxic pollutants such as particulate matter and green house gases like ozone, sulphur dioxide, nitrous oxide, etc., has been reported from various cities. Burning of fossil fuels by humans also adds up to pollute the atmosphere.

Tobacco smoke has been well recognized as an indoor pollutant, with severe health risks to children and elderly.


Pollutants are particulate matter and are described by their “aerodynamic equivalent diameter” (AED). Particles of the same AED tend to have the same settling velocity.

Particulate matter is subdivided into fractions based on where they deposit in human airways <10, <2.5, and <0.1 μm (PM10, PM2.5, and PM0.1).

Particles with a diameter greater than 10 μm have a relatively small suspension half-life and are largely filtered out by the nose and upper airway.

Those with a diameter between 2.5 and 10 μm (PM2.5–10) are classified as “coarse,” less than 2.5 μm as “fine,” and less than 0.1 μm as “ultrafine” particles.

Particles <10 μm in diameter are capable of entering the respiratory system, and particles <2.5 μm are capable of reaching the alveoli and ultrafine particles systemically affect the blood and organs such as the heart and even the brain.


Several measures are recommended to reduce exposure to contaminants of biological origin (dust mites, household pets, mold and mice) and non-biological origin (tobacco smoke, wood smoke, volatile organic compounds). With a better understanding of indoor pollutants, new and effective measures have evolved, including the development of indoor air filters.

Air filtration is frequently recommended as a component of environmental control measures. Indoor air filtration can be provided by whole house filtration via the home’s heating, ventilation, or air conditioning system, by portable room air cleaners, or a combination of the two.

The key attribute of any air filter, is a balance of the following:

Air flow to assure adequate ventilation.
Efficiency to filter out a range of small particle sizes.
Capacity to allow for reasonable cost-effective maintenance schedules without adversely affecting airflow and efficiency.
Currently available air purifiers usually use a multilayer filter system composed, often of a prefilter, a carbon filter, an antibacterial filter, and a HEPA filter.

The use of HEPA filters traditionally used in hospitals, has indeed been a significant inclusion to home air purifiers. A HEPA filter uses mechanical filtration to remove airborne particles. A HEPA filter is standardized at a minimum 99.97% efficiency rating for removing particles greater than or equal to 0.3μm in diameter.


A study by van der Heide et al., assessed the efficacy of air-cleaners with respect to their capacity to capture airborne allergen particles. Over a 6-month period, the efficacy of air filters to capture particulate matter and allergens was measured. The study included three interventions -application of active air-cleaners in living-rooms and bedrooms, placebo air-cleaners used in combination with allergen-impermeable mattress covers or active air-cleaners used in combination with allergen-impermeable mattress covers.

The last filter consisted of a high efficiency particulate air (HEPA)-type filter, filtering 70% of 0.3-μm particles and 95% of 1.0-μm particles. The air cleaners in this study clearly showed the capacity to capture substantial amounts of airborne dust particles and airborne allergens.

Another study, a randomized controlled trial, evaluated the effectiveness of free-standing air filters and window air conditioners in 126 low-income households of children with asthma. It was found that a reduction in PM, by an average of 69 to 80% suggested that while PM levels in homes with asthmatic children can be high, levels can be dramatically reduced using filters.

In a year-long, randomized, parallel-group study, Francis et al., measured the clinical outcomes for the use of indoor HEPA air cleaners of 30 adult asthmatics who were sensitized to, yet lived with an indoor cat or dog. Outcomes were statistically improved in the treatment group over the controls.

Another study by Sulser et al., compared sham versus HEPA portable room air cleaners in asthmatic children sensitized to cat or dog. A significant reduction in nocturnal symptoms including stuffy nose was observed in the HEPA filter group.

Exposure to particulate matter is associated with risk of cardiovascular events, as a consequence of oxidative stress and inflammation.

The effects of controlled exposure to indoor air particles were studied in a healthy elderly population. The study suggested that a reduction of particle exposure by filtration of recirculated indoor air for only 48 hours improved lung health elderly citizens and suggested that this may be a feasible way of reducing the risk of cardiovascular disease

In one study by Weichenthal et al. the benefits of an electrostatic air filter was assessed in residents from 20 homes. The indoor PM2.5 decreased substantially during the period when air filter was used relative to placebo and on average, air filter use was associated with a decrease in systolic blood pressure.


Despite the rapid rise in environmental pollutants, the causal pathways leading to adverse health effects is often complex and poorly understood.

Children, the elderly, and women are most vulnerable to potential indoor air pollution health effects because they spend more time in the home environment.

There are many sources of indoor air pollution. Air pollution inside homes consists of a complex mixture of agents penetrating from ambient (outdoor) air and agents generated by indoor sources. Indoor pollutants can vary in their potential health effects and intensity, as well as in their distribution across geographic areas, cultural backgrounds, and socioeconomic status. Exposure to indoor air pollutants can cause health effects ranging from sneezing and coughing to exacerbation of chronic respiratory disorders such as asthma and outcomes such as cardiovascular disease and even cancer.

Studies appear to suggest, that reduction in particulate matter and allergens results in reducing symptoms and in certain cases, preventing disease progression across all age groups, including the elderly and children. The evidence is apparent, in chronic respiratory diseases, such as asthma and in cardiovascular health.

Technologically advanced air filter systems are now available which efficiently remove particulate matter, resulting in significant health benefits to patients of asthma and cardiovascular disease.

KEY WORDS: Air filters, air pollution, cardiorespiratory health, enhancing indoor air quality, HEPA