The European Union said Thursday that 23 of its 27 member nations have failed to meet clean air standards put in place four years ago.
Just Finland, Lithuania, Luxembourg and Ireland have stayed within the limits on particulate matter concentrations.
The bloc said it has taken legal action against 10 member states that are not in compliance and have not requested a possible deadline extension.
These countries were sent a first warning letter that begins a lengthy legal procedure that could end in fines. They are Cyprus, Estonia, Germany, Italy, Poland, Portugal, Slovenia, Spain, Sweden and Britain.
Eleven countries have taken advantage of a rule allowing them more time.
Two others, Romania and Bulgaria, were given until March 31 to file for an extension because of their recent accession to the EU.
The European Union warns that particulate matter can cause asthma, heart problems, lung cancer and premature death.
