Table Of Contents

Glossary Glossary
Introduction
About this Guide
Chapter 1
Why Indoor Air Quality Matters
Chapter 2
Indoor Air Quality and Human Health
2.1 — Air Quality and Respiratory Health
2.2 — Air Quality and Heart Health: What the Research Shows
2.3 — Air Quality and Cancer Risk
2.4 — Air Quality and the Nervous System
2.5 — Air Quality and Pregnancy
2.6 — Air Quality and Productivity
2.7 — How Air Quality Affects Your Sleep and What You Can Do About It
Chapter 3
Sources of Indoor Pollutants
3.1 — Biological Sources and Indoor Air Quality
3.2 — Indoor-Origin Sources
3.3 — Outdoor-Origin Sources
Chapter 4
Efficacy and Application of Air Purifiers
4.1 — Background and Evidence Base
4.2 — Health Benefits of Air Purifiers
4.3 — Air Purifiers vs. Biological Contaminants
4.4 — Air Purifiers vs. Indoor-Origin Pollutant Sources
4.5 — Air Purifiers vs. Outdoor-Origin Pollutant Sources
Glossary
Jargon & Assorted Big Words
The Definitive Guide to IAQ Definitive Guide to IAQ Glossary

Jargon & Assorted Big Words

1,3-Butadiene
C₄H₆

A colorless, flammable volatile organic compound with a mild gasoline-like odor used in the production of synthetic rubber and plastics; exposure occurs mainly through industrial processes, vehicle exhaust, and tobacco smoke and can irritate the eyes and lungs, affect the nervous system, and increase the risk of cancer.

Acrolein
C3H4

A clear or yellow volatile organic compound with a burnt, sweet, pungent odor used as an intermediate in the synthesis of acrylic acid and as a biocide; formed from the burning of organic matter including tobacco, gasoline, or oil, it causes eye, nose, and throat irritation and respiratory congestion following inhalation exposure.

Activated Carbon

A highly porous form of carbon with a vast internal surface area that removes contaminants from air and water through adsorption; produced by thermally or chemically “activating” carbon-rich materials such as coconut shells, wood, or coal to create a network of microscopic pores effective for trapping gases and vapors.

Air Exchange Rate
AER, ACH

The rate at which indoor air is replaced by outdoor or conditioned air within an enclosed space, typically expressed per hour; it represents how effectively pollutants are removed and serves as a key indicator of ventilation efficiency and indoor air quality.

Alcohols

A class of organic compounds containing one or more hydroxyl groups bonded to saturated carbon atoms; many, such as ethanol and methanol, are liquid, polar, and water-soluble, and are widely used as solvents, fuels, disinfectants, and chemical intermediates.

Aldehydes

A class of organic compounds containing the formyl group, typically formed by oxidation of alcohols; many have distinct odors and are used in solvents, perfumes, and manufacturing, while some, such as formaldehyde, are reactive irritants affecting the eyes, skin, and respiratory system.

Aluminum Compounds

A group of largely colorless inorganic substances in which aluminum typically occurs in the +3 oxidation state; they include oxides, hydroxides, halides, and aluminates used in water treatment, ceramics, and catalysts, while some forms may contribute to particulate or dust exposure affecting the respiratory system.

Ammonia
NH₃

A colorless gas with a pungent odor released from wastes, fertilizers, and fuel combustion; exposure primarily affects the eyes, skin, and respiratory tract, causing coughing, irritation, and, in high concentrations, burns or lung injury.

Aromatic Hydrocarbons

A group of ring-structured organic compounds with delocalized pi electrons, including benzene, toluene, and xylenes, widely used in fuels and solvents; many are volatile and toxic, with prolonged exposure linked to blood and nervous system effects.

Arsenic
As

A naturally occurring metalloid found in soil, water, and air, often contaminating groundwater and food; inorganic forms are highly toxic and carcinogenic, linked to skin, lung, and bladder cancers as well as cardiovascular, developmental, and endocrine effects.

Asthma

A chronic respiratory condition in which the airways become inflamed, narrowed, and filled with mucus, making breathing difficult; symptoms such as wheezing, coughing, chest tightness, and shortness of breath are often triggered by allergens, cold air, exercise, smoke, or stress, and can cause severe attacks if untreated.

Aspergillus

A genus of common molds found worldwide in soil, dust, and indoor air; most species are harmless, but some, such as Aspergillus fumigatus and Aspergillus flavus, can cause aspergillosis, a group of respiratory infections and allergic reactions that occur mainly in people with asthma, cystic fibrosis, or weakened immune systems.

Benzene
C₆H₆

A colorless volatile organic compound found in crude oil and gasoline and used in manufacturing and solvents; exposure occurs mainly through inhalation of vehicle exhaust, tobacco smoke, or industrial emissions and is linked to blood disorders and leukemia.

Benzene, Toluene, Ethylbenzene, and Xylenes
BTEX

A group of volatile organic compounds found in petroleum, fuels, and solvents that evaporate easily and are toxic to the nervous, immune, and hematopoietic systems; exposure—mainly from fuel vapors, smoke, or contaminated water—can cause dizziness, nausea, and organ damage, while benzene is a known human carcinogen and ethylbenzene a possible carcinogen.

Benzo[a]pyrene
BaP, C₂₀H₁₂

A carcinogenic polycyclic aromatic hydrocarbon formed during incomplete combustion of organic material and found in tobacco smoke, vehicle exhaust, coal tar, and charred foods; its metabolites bind to DNA, causing mutations linked to lung, skin, and bladder cancers, as well as developmental, immune, and reproductive effects.

Black Carbon
BC

A component of fine particulate matter produced by incomplete combustion of fuels and biomass; it absorbs sunlight, warms the atmosphere, reduces the reflectivity of snow and ice, and poses risks to both human health and the climate.

Bronchitis

An inflammation of the bronchial tubes that carry air to and from the lungs, usually causing coughing and mucus production; it may be acute, a short-term viral illness that resolves within weeks, or chronic, a long-term condition often linked to smoking or air pollution and classified under chronic obstructive pulmonary disease.

Cadmium
Cd

A toxic metal used in batteries, coatings, and pigments that accumulates in the body through food, smoke, or workplace exposure, damaging kidneys, bones, and the cardiovascular system and increasing cancer risk.

Carbon Dioxide
CO₂

An invisible, odorless gas produced by human respiration and combustion, commonly used indoors as a proxy for occupancy and ventilation effectiveness.

Carbon Monoxide
CO

A colorless, odorless gas produced by incomplete combustion of fuels that reduces the blood’s oxygen-carrying capacity, causing headaches, dizziness, and potentially fatal poisoning.

Chlorine
Cl₂

A greenish-yellow gas with a sharp, irritating odor used in disinfection and manufacturing; it is highly reactive and corrosive, forming acids when combined with moisture and posing respiratory and eye hazards at low concentrations.

Chromium
Cr

A hard, steel-gray metal used in stainless steel, plating, and pigments; trivalent chromium is an essential nutrient for glucose metabolism, while hexavalent chromium is a toxic, carcinogenic industrial compound.

Chronic Obstructive Pulmonary Disease
COPD

A group of progressive lung diseases, most notably chronic bronchitis and emphysema, that cause airflow blockage and make breathing difficult.

Cladosporium

A common genus of molds found indoors and outdoors on damp surfaces and decaying material; it produces airborne spores that can trigger allergic reactions, asthma, and respiratory irritation, though infections are rare and most species are not dangerous to humans.

(U.S. EPA) “Clean Room”

A designated space in your home where doors and windows are closed, indoor pollution sources are avoided, and air is filtered—ideally with a HEPA- or MERV 13-based air purifier—to reduce exposure to wildfire smoke and protect indoor air quality until conditions improve.

Conjunctivitis

An inflammation of the membrane covering the white of the eye and eyelids, commonly called pink eye, caused by viral or bacterial infection or allergies and resulting in redness, irritation, and discharge.

Coronaviruses

A large family of respiratory viruses named for their crown-like surface spikes; most cause mild illnesses such as the common cold, but three strains—SARS-CoV, MERS-CoV, and SARS-CoV-2—have caused severe and sometimes fatal diseases in humans.

Escherichia coli
E. coli

A group of bacteria normally found in the intestines of humans and animals; most strains are harmless, but certain types—such as Shiga toxin-producing E. coli (STEC)—can cause severe gastrointestinal illness, urinary tract infections, and sometimes kidney failure.

Fibrosis

The formation of excess fibrous connective tissue within an organ or other body tissue, usually as a response to chronic injury, inflammation, or infection; characterized by collagen buildup and scarring that can stiffen tissue, impair function, and, in severe cases, lead to organ damage.

Fine Particulate Matter
PM₂.₅

Tiny airborne particles with diameters <2.5 µm that can penetrate deep into the lungs and enter the bloodstream, posing serious risks to human health.

Formaldehyde
CH₂O

A colorless, flammable volatile organic compound with a strong odor used in building materials, household products, and manufacturing that can irritate the eyes, skin, and respiratory system and increase cancer risk with long-term exposure.

Heating, Ventilation, and Air Conditioning
HVAC

An integrated system that regulates indoor temperature, humidity, and air quality by combining heating, cooling, and ventilation components; designed to maintain comfort and remove contaminants through principles of thermodynamics, fluid mechanics, and heat transfer.

High Efficiency Particulate Air Filter
HEPA Filter

A pleated mechanical air filter capable of removing at least 99.97% of airborne particles 0.3 µm in diameter—the most penetrating particle size—with larger and smaller particles captured at even higher efficiency.

Hypersensitivity Pneumonitis

An inflammatory lung disease caused by an immune reaction to inhaled allergens such as mold, bird proteins, or dust; repeated exposure leads to inflammation and scarring of the alveoli, producing cough, shortness of breath, fever, and fatigue that may become chronic if not treated or exposure continues.

Indoor Air Quality
IAQ

The air quality within buildings and structures, especially as it relates to the health and comfort of occupants.

Infiltration Factor

The fraction of outdoor particulate matter that penetrates and remains suspended indoors.

Influenza

A contagious viral infection of the nose, throat, and lungs, also called the flu, that causes sudden fever, cough, sore throat, muscle aches, fatigue, and chills; spread mainly by respiratory droplets, influenza can range from mild to severe and is best prevented through annual vaccination and good hygiene practices.

Lead
Pb

A soft, dense metal once used in pipes, paints, and gasoline; toxic even at low levels, it accumulates in the body and damages the brain, kidneys, and nervous system, especially in children.

Legionella

A genus of waterborne, Gram-negative bacteria that spread through inhaled aerosols from contaminated plumbing or cooling systems, causing Legionnaires’ disease (a severe pneumonia) and Pontiac fever (a milder flu-like illness).

Limonene
C₁₀H₁₆

A citrus-scented liquid hydrocarbon found in orange and other fruit peels, used as a flavoring, fragrance, solvent, and cleaning agent; though naturally derived, it can irritate skin and is toxic to aquatic life.

Manganese
Mn

A hard, silvery metal used mainly in steel and aluminum alloys to improve strength and corrosion resistance; also an essential nutrient needed in trace amounts for metabolism and bone formation, though excessive exposure can cause neurological damage resembling Parkinson’s disease.

Minimum Efficiency Reporting Value
MERV

A rating developed by ASHRAE that represents a filter’s ability to capture airborne particles from 0.3 to 10 µm, ranging from MERV 1 (lowest efficiency) to MERV 16 (highest efficiency).

Microbial Volatile Organic Compounds
MVOCs

Volatile organic gases released by microorganisms such as molds and bacteria during metabolism; responsible for musty or earthy odors in damp environments, these compounds can irritate the eyes, nose, and throat and contribute to headaches, fatigue, or respiratory symptoms in sensitive individuals.

Mycotoxins

Toxic compounds naturally produced by certain molds (e.g., Aspergillus, Penicillium, Fusarium) that can contaminate foods such as grains, nuts, spices, dried fruits, and coffee; exposure can cause acute poisoning or long-term effects including immune suppression, liver and kidney damage, and cancer.

Nicotine
C₁₀H₁₄N₂

A highly addictive chemical naturally found in tobacco plants and present in all tobacco products, including cigarettes, e-cigarettes, and smokeless tobacco; it alters brain function to cause dependence and cravings but is not the primary cause of smoking-related diseases, which result mainly from the thousands of toxic combustion byproducts in tobacco smoke.

Nitrogen Dioxide
NO₂

A reactive gas produced mainly by fuel combustion that irritates the airways, worsens asthma, and contributes to the formation of ozone and particulate matter.

Nitrogen Oxides
NOₓ

A collective term for nitric oxide and nitrogen dioxide, reactive gases formed mainly during high-temperature fuel combustion; they contribute to smog, acid rain, and tropospheric ozone formation, posing risks to respiratory health and the environment.

Organic Acids

A broad class of carbon-based weak acids—most commonly carboxylic acids—found throughout living organisms and the environment; compounds such as acetic, citric, and lactic acids play key roles in metabolism, food preservation, and industry.

Organic Nitrates

A class of carbon-based compounds that release nitric oxide, causing smooth-muscle relaxation and vasodilation; used medically to treat angina, they also occur naturally in vegetables, are added to processed meats as preservatives, and form in the atmosphere as secondary pollutants from nitrogen oxides.

Oxidation

A chemical process in which a substance loses electrons, often seen as the gain of oxygen or loss of hydrogen, increasing its oxidation state and always occurring alongside a reduction reaction.

Ozone
O₃

A highly reactive gas found in both the stratosphere, where it protects life by blocking ultraviolet radiation, and the troposphere, where it forms through sunlight-driven reactions with volatile organic compounds and nitrogen oxides, harming health by irritating the lungs and contributing to smog.

Particulate Matter
PM

A mixture of solid particles and liquid droplets suspended in air; fine particles can penetrate deep into the lungs and even reach the bloodstream, causing adverse health effects.

Peroxyacetyl Nitrate
PAN, C₂H₃NO₅

A secondary pollutant formed when hydrocarbons and nitrogen oxides react in sunlight; it is a key component of photochemical smog, more stable than ozone, capable of long-range transport, and causes eye and lung irritation when it decomposes to release nitrogen oxides and promote ozone formation.

Personal Care Products
PCPs

A broad class of hygiene and cosmetic products—such as shampoos, deodorants, lotions, and perfumes—that emit volatile and semi-volatile compounds linked to respiratory irritation, migraines, allergic and endocrine effects, as well as secondary pollutant formation.

Penicillium

A genus of ascomycete fungi widespread in soil and decaying matter, Penicillium includes more than 300 species important in nature, medicine, and food production; some cause food spoilage or produce mycotoxins, while others yield the antibiotic penicillin or are used in cheesemaking.

Phthalates

A group of chemical compounds used mainly to make plastics more flexible and durable; phthalates are widespread in consumer products but can leach into food, air, and dust, where exposure is linked to hormonal disruption, reproductive toxicity, and respiratory problems.

Polycyclic Aromatic Hydrocarbons
PAHs

A class of chemicals formed during the incomplete combustion of fuels and other organic materials that adhere to airborne particles and contribute to indoor and outdoor air pollution; several are known carcinogens, and others are associated with respiratory, immune, and reproductive effects from long-term exposure.

Quaternary Ammonium Compounds
QACs

A class of synthetic chemicals used as disinfectants, surfactants, and preservatives that kill microbes by disrupting cell membranes but can cause skin, eye, and respiratory irritation with repeated exposure.

Radicals

Atoms, molecules, or ions with unpaired electrons that make them highly reactive, driving key processes like combustion, polymerization, and atmospheric chemistry but also causing cellular damage and oxidative stress in living organisms.

Rhinitis

Inflammation or irritation of the nasal passages that causes congestion, runny nose, sneezing, and itching, commonly triggered by allergens such as pollen, dust mites, or animal dander, or by nonallergic factors like smoke, odors, and temperature changes.

Rhinoviruses

Small RNA viruses that are the leading cause of the common cold, spreading through respiratory droplets and surfaces to infect the nasal passages and occasionally causing severe illness or asthma attacks, with no current vaccine or specific antiviral treatment.

Semi-Volatile Organic Compounds
SVOCs

Organic chemicals with higher boiling points and lower vapor pressures than volatile organic compounds, found in products like pesticides, flame retardants, and plasticizers, that persist on surfaces and dust and are linked to respiratory irritation, endocrine disruption, developmental effects, and cancer.

Siloxanes

Organosilicon compounds used in products like cosmetics, lubricants, and sealants that contain alternating silicon and oxygen atoms in their molecular backbone; valued for flexibility and stability but of emerging concern due to persistence, bioaccumulation, and potential aquatic toxicity.

Stachybotrys

A slow-growing mold that colonizes wet, cellulose-rich materials and produces trichothecene mycotoxins; Stachybotrys chartarum (“black mold”) is often found in water-damaged buildings and can aggravate allergy and asthma symptoms, though evidence for severe systemic toxicity in humans is limited.

Staphylococcus aureus

A Gram-positive bacterium commonly found on the skin and in the nasal passages that can act as an opportunistic pathogen, causing infections ranging from minor skin lesions to life-threatening diseases such as sepsis, pneumonia, and endocarditis, with some strains resistant to multiple antibiotics.

Terpenes

A large class of volatile hydrocarbons produced by plants that give characteristic scents to materials like pine, citrus, and lavender; they serve ecological roles in pollination and defense, are widely used in fragrances and cleaners, and can form irritants indoors through reactions with ozone.

Tetrahydrocannabinol
THC, C₂₁H₃₀O₂

The main psychoactive cannabinoid in cannabis that binds to receptors in the brain and body, producing euphoria, altered perception, and relaxation; used medically for certain therapeutic applications, though chronic use can impair memory, coordination, and cause dependence or cannabinoid hyperemesis syndrome.

Ultrafine Particles
UFPs

Airborne particles <0.1 µm in diameter that penetrate deep into the lungs and bloodstream, contributing to cardiovascular, respiratory, and systemic health effects.

Volatile Organic Compounds
VOCs

Gaseous pollutants released from natural and human sources—including combustion, building materials, and consumer products—that can accumulate indoors and cause short- and long-term adverse health effects.

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