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This glossary provides clear, concise definitions of key terms related to Indoor Air Quality (IAQ) in multi-family properties to support professionals in understanding the science, technology, and standards that drive healthier indoor environments.

Airborne Particulates (PM) – Tiny solid or liquid particles suspended in the air, including dust, pollen, and smoke. Measured in micrometers (PM2.5 and PM10).
Air Changes Per Hour (ACH) – The number of times the air within a space is replaced with fresh air in an hour. Higher ACH means better ventilation.
Air Exchange Rate – The rate at which indoor air is replaced with outdoor air through ventilation systems.
ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) – A professional organization that sets indoor air quality and HVAC standards.
AQI (Air Quality Index) – A standardized measure of air pollution levels, commonly used to report outdoor air quality but relevant for indoor monitoring.

Bacteria – Microorganisms that can be airborne and contribute to indoor air pollution. Some bacteria can cause illness when inhaled.
Bioaerosols – Airborne biological particles, including mold spores, bacteria, and viruses, which can impact IAQ and health.
Building-Related Illness (BRI) – A diagnosable illness caused by poor IAQ, often associated with mold, bacteria, or chemical exposure.

Carbon Dioxide (CO₂) – A naturally occurring gas that can accumulate indoors due to poor ventilation, leading to drowsiness, headaches, and reduced cognitive function.
Carbon Monoxide (CO) – A colorless, odorless gas produced by burning fuel that can be deadly at high concentrations. Common in environments with faulty heating equipment.
CASPR (Continuous Air & Surface Pathogen Reduction) – A technology used in IAQ management to reduce airborne and surface contaminants.
Clean Air Delivery Rate (CADR) – A measure of how effectively an air purifier removes particles from the air.
Chronic Obstructive Pulmonary Disease (COPD) – A respiratory condition that can be aggravated by poor IAQ.
Combustion Pollutants – Harmful gases and particles produced by fuel-burning appliances, including stoves, fireplaces, and generators.

Dander – Tiny, often microscopic flakes of skin shed by animals and humans that contribute to indoor allergens.
Decibels (dB) – A unit used to measure noise levels, relevant to HVAC systems that impact guest comfort.
Duct Cleaning – The process of removing dust, debris, and contaminants from HVAC ducts to improve IAQ.

Electrostatic Precipitator – An air filtration technology that uses electrical charges to remove airborne particles.
Environmental Tobacco Smoke (ETS) – Secondhand smoke, a major indoor pollutant in hospitality environments where smoking is allowed.
Epidemiology – The study of how environmental factors, including IAQ, affect public health.

Filtration Efficiency – The ability of an air filter to capture and remove airborne particles.
Formaldehyde (CH₂O) – A volatile organic compound (VOC) found in furniture, carpets, and adhesives, which can cause respiratory issues and irritation.
Fungi – Mold and mildew that can grow in humid environments and negatively impact IAQ.

Gas-phase Filtration – A method used to remove gaseous pollutants from the air using activated carbon or other absorbent materials.
Green Building Certification – Certifications such as LEED (Leadership in Energy and Environmental Design) that promote sustainable and IAQ-conscious building practices.
Ground-Level Ozone (O₃) – A pollutant that can enter buildings from outdoor air and cause respiratory problems.

HEPA (High-Efficiency Particulate Air) Filter – A type of air filter that removes at least 99.97% of airborne particles as small as 0.3 microns.
Humidity – The amount of moisture in the air; ideal indoor humidity is 40-60% for IAQ optimization.
HVAC (Heating, Ventilation, and Air Conditioning) – The system that regulates indoor air quality, temperature, and humidity.

IAQ (Indoor Air Quality) – The condition of the air inside a building, measured by pollutants, humidity, and ventilation.
IAQ Sensor – A device that detects pollutants like CO₂, VOCs, and PM2.5 in real time.
Indoor Air Pollution – Contamination of indoor air by harmful substances, including chemicals, mold, and smoke.

LEED (Leadership in Energy and Environmental Design) – A widely recognized certification program for sustainable and IAQ-friendly buildings.
Legionella – A bacteria that thrives in water systems and can cause Legionnaires’ disease, a severe respiratory illness.

MERV (Minimum Efficiency Reporting Value) – A rating that measures the effectiveness of air filters, with higher numbers indicating better filtration.
Mildew – A type of mold that grows in damp environments and can impact IAQ.
Mold Spores – Airborne particles released by mold, which can trigger allergies and respiratory issues.

Negative Air Pressure – A condition where indoor air pressure is lower than outdoor air pressure, which can help contain contaminants.
NIOSH (National Institute for Occupational Safety and Health) – A U.S. organization that sets standards for workplace safety, including IAQ guidelines.

Off-Gassing – The release of VOCs and other chemicals from building materials, furniture, and carpets.
Ozone (O₃) – A reactive gas used in some air purifiers but harmful in high indoor concentrations.

PM2.5 – Fine particulate matter smaller than 2.5 micrometers, capable of penetrating deep into the lungs and bloodstream.
PM10 – Larger particulate matter, up to 10 micrometers in size, which can cause respiratory irritation.
Pathogens – Microorganisms, such as viruses and bacteria, that can be transmitted through the air.

Radon – A radioactive gas that can seep into buildings from soil and cause lung cancer.
Relative Humidity (RH) – The percentage of water vapor in the air relative to the maximum amount the air can hold.
Reentrainment – When pollutants removed from the air re-enter the indoor environment due to poor filtration.

Sick Building Syndrome (SBS) – A condition where building occupants experience health issues linked to poor IAQ, but no specific illness can be identified.
Smart IAQ Monitoring – The use of AI-powered sensors to track and improve indoor air quality in real-time.

TVOCs (Total Volatile Organic Compounds) – The total concentration of multiple VOCs in indoor air.
Tobacco Smoke Residue – Chemical residues left by smoking that can linger in indoor spaces, affecting IAQ.

Ventilation Rate – The amount of fresh air introduced into a space, crucial for maintaining IAQ.
VOCs (Volatile Organic Compounds) – Chemicals emitted from paints, cleaning products, furniture, and other materials, which can affect air quality and health.

WELL Building Standard – A certification that emphasizes IAQ and other wellness-related building features.
Workplace IAQ – Indoor air quality standards specific to office and hospitality environments.