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Perfluorinated Compound (PFC)

A family of fluorine-containing chemicals with unique properties to make materials stain- and stick-resistant.


An element found in the earth’s crust that has applications in various industrial processes, however runoff from factories, agricultural practices and natural deposits can lead to high concentrations in water.


A naturally occurring metal found in ore deposits; the most common form of antimony is antimony trioxide, which is used as a flame retardant.


Enters groundwater and surface water by dissolution of rocks and soils, from atmospheric fallout and biological decays and waste disposal.


Metallic element that enters water sources through natural deposits, but contamination most commonly occurs through corrosion of copper or brass.


Widely used as a precursor to various materials such as detergents, dyes, pesticides, Styrofoam, nylon and other synthetic fibers.


A naturally occurring component of crude oil and a combustion byproduct.


Typical applications include solvents for the printing, rubber and leather industries as well as ingredients in paper and fabric coatings.


A chlorinated hydrocarbon used as a dry cleaning solvent, an additive in textile processing and metal degreasing that has been linked to cancer.


Among the most widely used pesticides in the United States and among the most commonly detected pesticide in drinking water.


Widely used in agriculture as an herbicide to control weeds; high levels of simazine exposure over a short period can cause weight loss and blood damage.


A non-selective herbicide used in many pesticide formulations; exposure may result from its normal use due to spray drift, residues in food crops and from runoff into drinking water sources.

2,4-Dichlorophenoxyacetic Acid (2,4-D)

A major herbicide that is very susceptible to running off or leaching into ground and surface water sources.


A highly irritating, greenish-yellow gaseous halogen, capable of combining with nearly all other elements, produced principally by electrolysis of sodium chloride and used widely to purify water, as a disinfectant and bleaching agent.


A disinfectant formed when ammonia is added to chlorine and is commonly used as a secondary disinfectant in public water systems.


Chlorine in water can combine with organic matter to form compounds called disinfectant byproducts (DBPs), such as trihalomethanes.

Haloacetic Acid

When chlorine and chloramine are added to water and react with other organic matter to produce haloacetic acids known as a disinfectant byproduct (DBP), these can damage internal organs and the nervous system in elevated concentrations and can lead to cancer.


Small amounts are required for a healthy diet, but higher amounts may cause neurological damage.


Sodium is consumed as sodium chloride in common salt. It is a vital nutrient, but unhealthy in high amounts.


Sulfates occur naturally and can erode into water supplies; the health effects of sulfates are uncertain, but ingesting large amounts has been linked to negative health effects.


Necessary for healthy blood circulation, but excessive iron particles in water can provide a shelter for disease-causing bacteria.


Bacteria and microscopic algae and fungi, especially those living in a particular site or habitat.

Oxidized Lipids

A lipid, any of a diverse group of organic compounds including fats, oils, hormones and certain components of membranes that are grouped together because they do not interact appreciably with water, combined chemically with oxygen.


A potentially toxic and potentially cancer-causing substance that can be naturally present in uncooked, raw foods in very small amounts.


A chemical that is made from petroleum or natural gas.

Units and Measures

Sound Pressure Level (SPL)

Sound pressure level (SPL), also known as acoustic pressure, is the pressure variation associated with sound waves. Usually measured in decibels, the acoustic pressure is a ratio between the measured value and a reference value; a common reference is threshold of hearing or the minimum sound level that the average person can hear.

Air Changes Per Hour (ACH)

A measure of how many times the volume of air within a defined space is replaced, used in the context of building ventilation and air tightness.

Candela (cd)

Measurement of luminous intensity and the SI base unit of light.

Clothing Insulation (CLO)

Clothing insulation is the resistance to heat transfer provided by clothing measured in clo (1 clo = 0.155 m²K/W = 0.88°F ft²h/BTU).

Color Rendering Index (CRI)

Comparison of the appearance of 8 to 14 colors under a light source in question, to a blackbody source of the same color temperature. CRI or Ra refers to the average of the first 8 comparisons and R9 describes the lighting accuracy on red surfaces.

Correlated Color Temperature (CCT)

Spectral distribution of electromagnetic radiation of a blackbody at a given temperature. For example, the color temperature during the daytime is approximately 15,000 K, while during sunset is approximately 1,850 K.

Decibel (dB)

A unit of measurement for sound. The decibel is a logarithmic unit so an increase in 10 decibels equals an increase by a factor of 10.

Dry Bulb Temperature (DBT)

Temperature of air measured by a thermometer freely exposed to the air but shielded from radiation and moisture. This temperature is usually thought of as air temperature and it is the true thermodynamic temperature. Dry bulb temperature does not take humidity into account.

Equivalent Continuous Level (LAeq)

The time averaged sound pressure level on the A-weighted scale, converted to decibels.

Frequency (f)

The number of times an event repeats itself per a specified unit of time. Hertz (Hz) is a common unit for frequency and equals cycles per second i.e. 1 Hz = 1 cycle/second. Most commonly used with waves (sound and light) and is the number of times the wave repeats itself at its particular wavelength.

Relative Humidity (rH)

Ratio of partial pressure of water vapor in the air to the saturation pressure of water vapor at the same temperature and pressure.

Illuminance (Lux)

Amount of light passing through a given area in space. Measured in lux or foot-candles.

Light Reflectance Value (LRV)

Rating from 0 (black) to 100 (white) describing the amount of visible and usable light that reflects from (or absorbs into) a painted surface.


Measure of luminous flux, derived from the SI base unit candela, and therefore weighted to the eye's sensitivity to light; 1 W of light at 555 nm equates to 683 lumens.

Luminance (cd/m²)

Measurement of how bright a surface or light source will appear to the eye. Measured in candela/m² or foot-lamberts.

Luminous Flux

Total luminous output of a light source, measured in lumens. Weighted to the eye's visual sensitivity.

Luminous Intensity

Radiant power weighted to human vision, describing light emitted by a source in a particular direction. Measured by the candela.

Maximum Contaminant Level Goal (MCLG)

Concentration of a substance in drinking water believed to result in no adverse effects. Derived from on Population Adjusted Dose and estimated daily water consumption, fraction of exposure from water and body weight.

Maximum Contaminant Levels (MCL)

Enforceable water quality limits for a substance, based on the Maximum Contaminant Level Goal, but taking into account technology and cost limitations of treatment.

Mean Radiant Temperature (MRT)

The uniform surface temperature of an imaginary black enclosure in which an occupant would gain or lose the same amount of radiant heat as in the actual non-uniform space; MRT is a primary driver of human thermal comfort, roughly equal in influence to air temperature.

Metabolic Rate (MET)

Rate that chemical energy in the body is converted to heat and mechanical energy.

Noise Isolation Class (NIC)

Field test for determining the sound transmitting abilities of a wall. Higher NIC values indicate better sound insulation i.e. more effective sound cancellation between spaces. NIC specifications are defined in ASTM Standard E366.

Reverberation Time (RT)

Time it takes for sound to decay. The most commonly used reverberation time is RT60, the time it takes for the sound level to decrease 60 decibels. Additional reverberation time measurements are RT20 and RT30, for decreases of 20 and 30 decibels, respectively.

Sound Transmission Class (STC)

A laboratory method for determining the sound transmission through a wall. Higher STC values indicate more effective noise isolation than lower ones. STC specifications are found in ASTM Standards E90-09 and E1425.

Wavelength (λ)

The distance between two points on a wave in which the wave repeats itself. Often used to describe light waves.

Noise Criteria (NC)

Define the sound pressure limits of the octave band spectra ranging from 63-8000 Hz. The noise criteria equals the lowest curve which is not exceeded in the spectrum.


Unit of illuminance, one lux being equivalent to one lumen per square meter.

Footcandle (fc)

Unit of illuminance, equivalent to one lumen per square foot.

Spatial Daylight Autonomy (sDA)

Percentage of floor space where a minimum light level (for example 300 lux) can be met completely for some proportion (for example 50%) of regular operating hours by natural light.

Annual Sunlight Exposure (aSE)

Percentage of space in which the light level from direct sun alone exceeds a pre-defined threshold (such as 1000 lux) for some quantity of hours (such as 250) in a year.

Minimum Efficiency Reporting Value (MERV)

Value assigned to an air filter to describe the amount of different types of particles removed when operating at the least effective point in its life.

Equivalent Melanopic Lux (EML)

A measure of light used to quantify how much a light source will stimulate melanopsin’s light response.

Walk Score®

A measurement that takes into account a building inhabitants’ physical output; it is recommended a building obtains a Walk Score® of 70 or greater.

Parts per Billion (PPB)

Measurement of the mass of a chemical or contaminate per unit volume of water.


The concentration of an air pollutant (e.g. ozone) is given in micrograms (one-millionth of a gram) per cubic meter air or μg/m³.

Parts Per Million (PPM)

A unit of measurement to express very dilute concentrations of substances.

PicoCurie per Liter (pCi/L)

A non-SI unit of radioactivity.

Cubic feet per minute (CFM)

Measures the mass of gas that passes through a certain point.


Roughness rating of a physical surface, averaged in micro-meters & micro-inches.

Milliwatt (mW)

Unit of measurement for electromagnetic radiation, equal to 1/1000 watt. Not weighted to biological responses such as vision.

Nephelometric Turbidity Units (NTU)

Measure the turbidity of water.

Visible Transmittance (VT)

Amount of light in the visible portion of the spectrum that passes through a glazing material.

A-Weighted Decibel (dBA)

Acoustic decibel modified using "A-weighting" to adjust the frequency-dependent response of human hearing.

Noise Reduction Coefficient (NRC)

Average value that determines the absorptive properties of materials.

Impact Insulation Class (IIC)

Extent to which a physical structure blocks out sound, typically used in describing flooring, a higher IIC reduces footfall noise, and other impact sounds.