Terminology
A useful list of definitions encountered in air quality
legislation is given below:
Standard
This is a numerical value usually
relating to an atmospheric concentration of a pollutant species
which can be broadly taken to represent a certain degree of
environmental quality. A standard is based on the assessment of the
effects of a pollutant on either human health or ecosystems.
Objective
This is a
policy target and can be thought of as a standard with an attached
timescale within which it should be achieved. It must be noted
however, that many objectives are couched in terms of a permitted
number of breaches in a given timescales i.e. expressed on a
percentile basis.
Limit Value
This is a
legally binding parameter which must not be breached. A limit value
for a pollutant is couched in terms of an objective as above. Note
that for an individual pollutant, differing limit values covering a
variety of dates for compliance, averaging period or receptor may
be applicable. Failure to achieve a limit value on the part of an
European Union (EU) Member State may render that Member
State liable to European Commission instigated infraction
proceedings.
Target Value
This is similar to a limit value but is more
aspirational in nature i.e. should be considered as a value to be
attained by all necessary, reasonable means not entailing
disproportionate costs. Target values therefore are not legally
binding.