Its survey of 1,600 cities in 91 countries revealed that nearly 90% of people in urban centres breathe air that fails to meet levels deemed safe.
The WHO says that about half of the world's urban population is exposed to pollution at least 2.5 times higher than it recommends.
Air quality was poorest in Asia, followed by South America and Africa.
"Too many urban centres today are so enveloped in dirty air that their skylines are invisible," said Dr Flavia Bustreo, the WHO's assistant director-general for family, children and women's health.
"Not surprisingly, this air is dangerous to breathe."
Health risks
The WHO currently sets safe levels of air quality based on the concentration of polluting particles called particulate matter (PM) found in the air.
It recommends that levels of fine particles called PM2.5 should not be more than 10 micrograms per cubic metre on average over a year, and slightly larger pollutants, called PM10, should not reach more than 20 micrograms per cubic metre on average.
But the Urban Air Quality database showed that many areas were breaching these levels.
Some cities in Asia showed extremely high levels of pollution. Peshawar in Pakistan registered a PM10 level of 540 micrograms per cubic metre over a period of two months in 2010, while Delhi in India had an average PM2.5 of 153 micrograms per cubic metre in the same year.
Cities in South America, including Rio De Janeiro in Brazil, also fared badly.
But the WHO says it is still lacking data, especially from cities in Africa, where poor air quality is a growing concern.
The most recent figures suggest that seven million people around the world died as a result of air pollution in 2012. It is estimated that 3.7 million of these deaths were from outdoor air pollution.
The WHO calls its the world's single largest environmental health risk, and links poor air quality to heart disease, respiratory problems and cancer.
"We cannot buy clean air in a bottle, but cities can adopt measures that will clean the air and save the lives of their people," said Dr Carlos Dora from the WHO.
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Fermanagh's All-Star nominee Sean Quigley has also been given a one-match ban following an incident in the Athletic Grounds game.
Both counties can appeal against the fines while there may also be an attempt to overturn Quigley's ban.
Several players from both teams got involved in jostling in the tunnel.
A row involving up to 20 players erupted in the wake of Tony Kernan's black card for tripping Quigley.
Tempers flared as referee Cormac Reilly blew the half-time whistle and the row continued as the players made their way down the tunnel.
Reilly booked Aidan Forker and James McMahon before the second half started while the game also had numerous late and cynical hits.
As it stands, Quigley's ban will rule him out of Sunday's Division 2 game against Laois.
Both Castlebar Mitchels and Crossmaglen Rangers have also been fined by the GAA's Central Competitions Control Committee following disturbances on the sideline in the closing stages of their recent All-Ireland Club Football semi-final.
Castlebar have been hit with a 1,500 Euro penalty with Crossmaglen fined 1,000 Euro.
Once again, appeals are highly likely.
The World Health Organization says air pollution in many of the world's cities is breaching its guidelines.
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Armagh and Fermanagh have been handed 5,000 Euro fines following the half-time disturbances in last weekend's Football League Division 2 game.