Eight European Union countries exceeded the bloc's air pollution limits in 2011, down from 12 the previous year, the European Environment Agency said in a report published on Monday.
According to preliminary data, Denmark, Malta, the Netherlands and Sweden managed to bring their air pollution under the authorised levels in 2011.
But Austria, Belgium, Finland, France, Germany, Ireland, Luxembourg and Spain remained above the limits.
The EU's National Emissions Ceiling directive covers sulphur dioxide (SO2), nitrogen oxides (NOx), non-methane volatile organic compounds (NMVOCs) and ammonia (NH3).
Countries that exceed the authorised levels can in theory face fines.
"Although the new data shows some clear improvement between 2010 and 2011, Europe still needs to work hard to reduce air pollution," EEA executive director Jacqueline McGlade said in a statement.
"Emissions from transport are still a major problem, particularly in some cities."
A map published with the data showed that Paris, Marseille, Turin, Milan, Rome and several Czech, Polish and Bulgarian cities had the highest levels of particle pollution, with an annual average of more than 50 microgrammes per cubic metre.