Tool 28 - Some Technical Concepts and Terms Explained

Units and Abbreviations


Conversion Factors

Terms and Definitions


Units and Abbreviations

Compound* Explanation
BaP benzo[a]pyrene, is the best known and most-measured PAH
CO Carbon Monoxide
CO2 Carbon Dioxide
NOx Oxides of Nitrogen
PAH Policyclic aromatic hydrocarbons
PAN Peroxyacetyl nitrate
PVC Polyvinyl Chloride
PM10 Particulate Matter of 10 microns or less
SPM Suspended Particulate Matter
SO2 Sulfur Dioxide
TSP Total Suspended Particles
VOC Volatile Organic Compounds
NMVOC Non- Methane Volatile Organic Compounds


g gram
mg milligrams (10-3 grams)
µg microgram (10-6 grams)
ppm parts per million (volume/volume)
ppb parts per billion (volume/volume)
mg/m3 milligrams per cubic metres
µg/m3 micrograms per cubic meter

* For descriptions of pollutants, see Tool 4.


Conversion Factors*

  25oC,1 atm

Sulfur dioxide

1 ppm = 2,860µg/m3
1mg/m3 = 0.35 ppm
Carbon Monoxide
1 ppm = 1.145mg/m3
1mg/m3 = 0.873 ppm
Nitric Oxide
1ppm = 1,230 µg/m3
Nitrogen Dioxide
1 ppm = 1,880µg/m3
1 µg/m3 = 0.000532 ppm
1 ppm = 3.19mg/m3
1mg/m3 = 0.313 ppm
Hydrogen Sulfide
1ppm = 1.5mg/m3
1mg/m3 = 0.670 ppm
Vinyl Chloride
1ppm = 2.589mg/m3
1 mg/m3 = 0.386 ppm
Toluene 1ppm = 3.75 mg/m3
1 mg/m3 = 0.226 ppm
Trichloroethylene (TCE)
1ppm = 5.4mg/m3
1mg/m3 = 0.18 ppm
1ppm = 6.78mg/m3
1 mg/m3 = 0.14 ppm
1 ppm = 4.2mg/m3
1mg/m3 = 0.24 ppm
1 ppm = 1.2mg/m3
1mg/m3 = 0.833ppm
Peroxyacetyl nitrate
1 ppm = 5mg/m3
Carbon Disulfide
1 ppm = 3.13mg/m3
1mg/m3 = 0.32 ppm
Ethylene dichloride
(1,2-Dichloroethane, DCE)
1ppm =4.12mg/m3 (at 20oC)
1mg/m3 = 0.242 ppm
1 ppm = 3.47mg/m3
1 mg/m3 = 0.28 ppm
1 ppm = 2mg/m3

*For conversions between ppm, ppb, mg/m3 and ug/m3: MolWeight x PPM = 24.45 x mg/m3 or MolWeight x PPB = 24.45 x ug/m3

For additional unit conversions see the attached Conversion Table.


Acute Health Effects:
Those immediate health effects resulting from exposure to an episode of air pollution e.g. asthma attack. In certain conditions, acute episodes of air pollution are also associated with an overall increase in respiratory and cardiovascular mortality.

Adverse Effect:
Any effect that may affect the performance of the whole organism or that reduces an organism's ability to respond to an additional pollutant.

Background Concentration:
The normal concentration of a particular air pollutant occures naturally in the environment (also without any human activity). This is determined by the natural characteristics of an area like the presence of deserts, volcanoes, etc.

A substance that causes abnormal, uncontrolled growth of cells or cancer, like lung cancer or leukaemia. This includes benzene, benzo-a pyrene (BaP) and heavy metals like lead, arsenic, nickel, cadmium etc.

Carcinogenic and Toxic Health Effects:
Those health effects resulting from exposure to carcinogenic (cancer causing) substances.

Cardiovascular Disease:
Heart related disease

Chronic Health Effects:
Those health effects owing to long term exposure to lower levels of pollution e.g. bronchitis resulting from SO2 exposure, or the increased respiratory and cardiovascular mortality observed in a number of epidemiological studies due to exposure to particulate matter. (ENDS, 1994)

Cost Benefit Analysis (CBA):
An analysis of the costs of pollution abatement versus the benefits to be derived from such abatement measure: both of which are expressed in monetary terms.

Cost Effective Analysis (CEA):
An analysis of the costs of abatement measures whose benefits are expressed in physical terms such as reduced emissions or reduced concentrations.

Dispersion Model:
A dispersion model is a software programme that assesses/calculates the concentrations of a specific pollutant on the basis of the emissions of the polluting activity sectors, at a certain point in time and space. These models account for geographic factors such as wind speed, temperature and direction. e.g. CAR International, IMMIS LUFT, BLB etc., Dispersion models help to limit the complex and often expensive ambient air monitoring since it calculates the ambient air quality in a given area and identifies where the emissions are likely to have an impact. However, regular monitoring will remain important to validate the models and determine the natural background concentration.

Any measurable air contaminant, pollutant, gas stream, or unwanted sound from a known source which is passed into the atmosphere

Emission Control Device:
Any device that is placed in a system to reduce the amount of air pollutants released into the environment.

Emission Factor:
This is a constant which relates the emission of a certain compound to the input or output of another compound by the same source, e.g. the emissions of SO2 by a factory can be estimated from its coal consumption. Emission factors are useful in cases where emissions data are missing. They can be used to make a rough estimate of emissions, based on economic activities, traffic and number of households, followed by the use of dispersion models to assess concentrations.

(OR: a numerical estimate of the mass of one or more air contaminant produced by a given amount of material processed by an industrial facility or, in the case of transportation sources, per mile driven (by a given vehicle using a particular fuel). It is important to note if the emission factor is for an uncontrolled source or one with properly functioning air pollution control equipment. This factor is used to arrive at a rough estimate of the total air emissions for a facility or a geographical area.)

Emission Inventory:
A compilation of estimated air emissions by pollutant from smokestacks, cars and other emission sources in a given area.

Emission Standards:
Legal limits on the degree or quantities of pollutants that are permitted to be discharged to the atmosphere from specific sources or process, e.g. emissions from vehicles or from industrial sources.

Environmental Impact Assessment (EIA):
The process of analyzing the probable environmental effects, both positive and negative, of a proposed project, programme or policy and suggesting ways to mitigate the adverse effects, including the identification of alternatives or other ways of implementing parts of it.

A series of short-term air pollution events that significantly alter the ambient air quality of an affected area.

Lowest Achievable Emission Rate:
Any technology or combination of technologies and process controls that result in the lowest possible emission of a given air pollutant. The technology must be reasonably demonstrated to be appropriate and reliable for the given application.

Lowest Observed Adverse-Effect Level (LOAEL):
The lowest experimental dose of a chemical at which there is statistically or biologically significant increase in the severity or frequency of a toxicity effect.

Mobile Sources:
Those sources of pollution that emit pollutants along their path of movement e.g. road transport and off road mobile sources.

A substance that causes mutation or the alteration of the basic genetic structure of any living organism

No Observed Adverse Effect Level (NOAEL):
The highest experimental dose of a chemical at which there is no statistically or biologically significant increase in the frequency or severity of a toxicity effect between an exposed group and its appropriate control.

Respiratory Effects:
Air pollution problems related to the respiratory/ breathing difficulties, sometimes resulting in acute effects like asthma and fatal heart attacks.

Stationary Sources:
Those sources of air pollution that emit the pollutants from a fixed-point e.g. industrial plants, power generation facilities, domestic cooking and heating, agricultural activities etc.

The point below which the environment is not harmed by any pollutant.

Threshold Value:
Denotes the concentration of a pollutant below which no negative effects are expected.

Threshold Level:
The minimum dose of a toxic substance that causes harmful effects in any ecosystem.

Threshold Limit Value (TLV):
The concentration of an airborne contaminant to which workers may be exposed regularly without adverse effect. The TLV recognizes that there are some individual variations among workers and that maintaining exposures within the limits may not prevent discomfort or aggravation of a pre-existing condition in some individuals. Most TLVs represent average exposures and some fluctuations during the day is possible without causing adverse effects.

The distance separating one wave crest from the next in any uniform succession of traveling waves.