Thanks for the vote, A-A!
The worst thing about haze is usually flying NE in the morning and thinking "well its hazy, but ok", and then having to fly SW in the afternoon to get back. Then of course, the wind is often WSW in the UK, so many of our runways are 24 - 26, so the runway in use is directly into a lowering sun in haze - good news for noseleg manufacturers and the mechanics who fit them!
Two main types of hazy situations:
1- The ones when haze builds up day by day under high pressure - maybe ok for 3 or 4 days, then starts to get worse and worse day by day. Annoyingly, all non-pilot friends make a point of telling you it must have been a great flying day as the sun was shining and the sky was blue. (they only look up, not noticing its white near the horizon) - and your lesson or flight was cancelled or curtailed.
The haze (as stated earlier) in this case is pollution, so each days industrial and motor car output is added to the previous days, as high pressure clamps it down. (I seem to remember Easter 2003 had 10 - 14 days of 'great sunny weather' but by day 8 it was getting dangerous!)
2- the days when there is a definite temperature inversion or minor lapse rate which has the same effect, trapping in the pollution below, but offering the prospect of escaping above the inversion layer into super visibility if you CAN get above it. How do you know the inverson tops to decide if you can escape above? You might be able to spot it from the lapse rates on Metform 214. In practice, many pilots either keep climbing as it looks like the top is just above, in which case it never is, or they accept flying in the murk, perhaps later finding from another pilot that the clear air was only about 500' above them. ALTERNATIVE, and much simpler, look at the BALLOONING section of the metoffice aviation site, where it will tell you the expected inversion top in various parts of the country. (yes, i have asked them to copy it to somewhere more obvious!). Beware two things when flying above the inversion - (a) winds usually stronger, which may be good or bad for your fuel consuption and navigation, and (b) expect vibrations when re-entering the haze layer in the descent - can be worrying if you don't realise its 'normal'.