Most of the 8 years or so I lived there I was a smoker, so dodgy nasal secretions and hacking up crap were going to happen one way or another.

The contrast was most apparent to me within a few days of when I moved back here from Australia.

These days I live on the south coast, it's quieter, there seems to be adequate work (and I'm trying to make my own). I'd rather move abroad again than back to the city.

The black snot is mostly a zone 1 thing, though. I live in zone 5 and commute to zone 2. No black snot for me. Used to live at Marble Arch and work at Holborn, though, and the black snot was constant... Plenty of opportunity to work in London and avoid the most horrible snot / commute issues..

No black snot for me (ever!) despite doing KX/Finsbury Park to Vauxhall (with a further train at each end) and back five days a week for many years.

My commute (when not cycling) is now just a single commute from Zone 2 to Zone 1. Never a seat on the way in but it's just 18 minutes.

That's good stuff, thanks.

One thing I would say is that I've heard that no matter where one lives in London, the black snot goes away pretty quickly after moving there. I find that hard to believe (because: "why?") but so many people have told me it I think it must be true, except now you've said that for you it was constant so I don't know what to think any more.

Another thing is that "Plenty of opportunity to work in London and avoid the most horrible snot / commute issues.." fills me with hope! Cheers!

The black snot always comes back for me if I spend a day in the centre, after 13 years here now, but I haven't lived in the centre for 10 years so maybe it's improved somewhat... Who knows..

The key living-wise is to get to know the suburbs. There's a huge degree of variability in ease of commuting. I live in Croydon, which is about as far South as you can be and still be in London. It has a largely undeserved bad reputation (mostly because the centre was rebuilt extremely unsympathetically after the war), but is green and leafy, extremely cheap for London, and most importantly is extremely well connected - I moved here from Barnes in zone 3, and I can get in to the centre about twice as fast now despite living substantially further away.

Work wise, for technology jobs, there's quite a bit both East and West of the centre, and it's worth considering that a lot of larger tech companies actually have large offices outside of London, particularly Slough, Reading and surrounding areas. (e.g. you'll find Oracle, Microsoft, Amazon and many others in that corridor)

I work in Chelsea now, and so can easily bypass the centre entirely (I go in to Clapham Junction in South London, which takes 10 minutes, and have one stop from there to work - another 5 minutes train)

1999 - Visited London - Black snot 2001 - Lived in London - Normal snot 2002 - Moved out, but visited - Black snot 2003 to 2006 - Visited - Black snot 2006 - Moved back to London - Normal snot since and use tube every day.

I visited Berlin two weeks ago and got black snot after 1 day of using their metro system.

The cause? To quote Nelson Muntz - "That's like asking the square root of a million. No one will ever know."

I got black snot in Berlin after cycling behind an annoying bus for half an hour, but never otherwise. And the square root of a million is ten to the third power – as for the square root of ten million…nobody will ever know :)