Appendix A

Glossary

Aerosol: A stable suspension of solid or liquid particles in air.

Air change rate: The volumetric flow rate of air entering a room divided by the net volume of air in that room (1/h).

Biological particle: Solid-phase material derived from biological organisms (e.g., bacteria and viruses, pollen, fungi, dust mites, endotoxins, and skin dander).

Bottom-up approach: A method of inventorying the chemical composition of the indoor environment by determining the chemical composition and/or emissions of every individual source object or material.

Consumer-grade sensor: An air quality sensor available to the public that measures, typically indirectly and with low sensitivity and/or precision, the concentration of a pollutant in the surrounding air. Sometimes called a “low-cost” sensor.

Dust: A material that builds up on surfaces, made up of settled particles, fibers, and biological matter that can be mechanically removed.

Exposome: The record of all exposures, both internal and external, that a person receives throughout a lifetime.

Indoor chemistry: Reactions involving indoor pollutants, occurring either in the gas phase or on surfaces.

Infiltration: Uncontrolled inward air leakage to conditioned spaces through unintentional openings in ceilings, floors, and walls from unconditioned spaces or the outdoors, caused by differences in pressure.

Intake rate: The amount of carrier medium crossing into the body per unit time for a given route of exposure (e.g., volume of inhaled air per unit time).

Interface: A surface forming a common boundary of two bodies, spaces, or phases.

Interstitial space: A hidden space within a building that is infrequently accessed by occupants (e.g., spaces where mechanical systems are located).

Mechanical ventilation: Ventilation provided by mechanically powered equipment, such as motor-driven fans and blowers, but not by devices such as wind-driven turbine ventilators and mechanically operated windows.

Microbial volatile organic compound (mVOC): Microbial organic compounds in the vapor state present in an indoor atmosphere.

Natural ventilation: Movement of air into and out of a space primarily through intentionally provided openings (e.g., windows and doors) or by infiltration.

Particle: A tiny droplet or fragment of condensed-phase matter suspended in air or settled on a surface; sometimes referred to in bulk as particulate matter (PM).

Partitioning: The transfer of molecules from one phase to another (e.g., from air to a surface).

Primary source: An item or material that directly emits or releases chemicals into the indoor environment.

Reservoir: Any surface or volume to which molecules can partition. Can act as both sources and sinks of chemicals.

Secondary source: A process or mechanism that creates new chemicals based on reactions between primary precursors.

Semivolatile organic compound (SVOC): An organic compound of intermediate volatility. SVOC definitions vary between organizations and fields of research. Detailed definitions define an SVOC based on chemical characteristics such as boiling point, vapor pressure, and/or molecular weight.

Sink: A reservoir that accumulates and stores chemicals for a long period of time.

Sorption: The process of a substance becoming captured by a condensed phase, or adsorption and absorption considered as a single process.

Stack effect: The movement of air into and out of buildings, chimneys, flue gas stacks, or other containers, driven by density differences between indoor and outdoor air (caused by differences in temperature). The stack effect is also referred to as the chimney effect, and it helps drive natural ventilation and infiltration.

Surface: The top-most (or outermost) region of any solid or liquid material accessible to chemicals present in air.

Top-down approach: A method of inventorying the chemical composition of the indoor environment by measuring the total chemical composition of the gas, particle, dust, and surface phases.

Under-reported chemicals: Species that have historically received less attention from researchers and are not extensively documented in the scientific literature (for the purposes of this report, not to be confused with another common definition, which is the deliberate act of reporting a lower level than what is present).

Volatile chemical product (VCP): Consumer products made from petrochemicals, including pesticides, coatings, printing inks, adhesives, cleaning agents, and personal care products, that contain volatile organic compounds.

Volatile organic compound (VOC): An organic compound that easily evaporates at ambient temperatures. VOC definitions vary between organizations and fields of research. Detailed definitions define a VOC based on chemical characteristics such as boiling point, vapor pressure, and/or molecular weight.