Pollutant
Any substance, species produced either by a natural source or by human activity, which produces very adverse effect on the environment is called pollutant.
Some commonly known examples of pollutants are carbon monoxide, oxides of sulphur (SO2, SO3), oxides of nitrogen, pollens, dust particles etc.
Contaminant
A substance which does not occurs naturally in nature but is introduced by human activity into the atmosphere which affecting its composition is called contaminant.
The contaminant is classified as pollutant when it has some harmful effect.
Source
The site from which the pollution, contaminants originate is called source.
Sink
The material or medium by which it consumes or interacts with a long lived pollutant is called sink.
For example a marble wall acts as a sink for atmospheric sulphuric acid because of the reaction
Similarly, the oceans acts as a sink for atmospheric CO2 & other water soluble gases.
Receptor
Any thing which can be affected by the pollutants is called receptor.
For example. human being are the receptor of photochemical smog, which can cause irritation in the eyes and also breathing Problems.
Threshold limit value (TLV)
This indicates the permissible limit of a pollutant in atmosphere by which a healthy worker is exposed during each hour a day or 40 hours a week for life time without any adverse effects.
TLV are determined by experimentation on different animals by use of medical knowledge, epidemiology surverys and environmental studies.