I see that the observer/forecaster at Leeming is reporting present weather 05 'haze' in their 0700 UTC observation this morning.
When I started work there almost 48 years ago now that would never have been the case.
Leeming was always smoke central back then, and with winds in the north or northeast or from the south it was always present weather 04 smoke haze, and none of the 05 haze that was always reported in southern SYNOPs by the likes of Heathrow or Gatwick.
The use of 04/05 present weather was almost a cultural thing, and the boundary between its use extended from the Wash to Birmingham, south of that line smoke haze was rarely reported outside stubble burning.
I realise that things are much cleaner these days, but I would like to bet that much of that haze is industrial in origin, either from Teesside or imported from our friends in Europe.