BS EN ISO 9223:2012

1   Scope This International Standard establishes a classification system for the corrosivity of atmospheric environments. It

— defines corrosivity categories for the atmospheric environments by the first-year corrosion rate of standard specimens,

— gives dose-response functions for normative estimation of the corrosivity category based on the calculated first-year corrosion loss of standard metals, and

— makes possible an informative estimation of the corrosivity category based on knowledge of the local environmental situation.

This International Standard specifies the key factors in the atmospheric corrosion
  of metals and alloys. These are the  temperature-humidity complex , pollution by sulfur dioxide and airborne salinity. 
Temperature is also considered an important factor for corrosion in areas outside
  the temperate macroclimatic zone. The  temperature-humidity complex  can be evaluated in terms of  time of wetness . Corrosion effects of other pollutants (ozone, nitrogen oxides, particulates) can
  influence the corrosivity and the evaluated one-year corrosion loss, but these factors
  are not considered decisive in the assessment of corrosivity according to this International
  Standard. 
This International Standard does not ...