AIR pollution in Huddersfield has soared in the past 48 hours.
And the high readings mean bad news for asthma sufferers and others with breathing problems.
Readings taken from monitoring equipment in Huddersfield showed nitrogen dioxide readings soared to 107 parts per billion yesterday - four times the average for other parts of Yorkshire and almost twice as high as the centre of London.
And although today's reading was half that of yesterday, it was still well above average.
But there was some relief: the high readings lasted only a few hours before brighter weather dispersed the smog.
Andrew Simnett, Kirklees Council's senior environmental health officer, said: "It is a bit of a freak. It was the first time we had a reading exceeding the health standards for several years.
"The winter smog, as it is known, happens when cold air descends into the valleys and does not move.
Our monitoring station is in Leeds Road and is at low level, with the smog particles not being dispersed.
"People who are prone to breathing problems may have noticed difficulties yesterday and today but it was only temporary."