If not North in March then what?

Dear all,

We are traveling with my girlfriend to Thailand for 16 days from 8th of March this year. Our original plan was the usual one I suppose, couple of days in Bangkok, then Sukhothai for a day, Chiang Mai for a few after that a flight down south for a bit of much needed sun and island hoping and flying back from Bangkok.

This was before we realised he North is shrouded in smoke, I suppose we did not do a proper research and relied too much on Lonely's description of the month as the end of the high season. Although we tried to persuade ourselves, that Chiang Mai will be probably all right it seems the smoke issue gets pretty bad with flight cancellations whatever last year (and some years before).

Anyway, I would like to ask, does anybody know if Sukhothai gets their share of the big smoke? Everybody speaks of Chiang Mai and the surrounding areas. Also does the slash and burn (and the resulting pollution) applies to other parts, like the Mekong region?

If this all is true, does anybody know of a good alternative to the North's pull of hill tribes, green mountains and the likes? (In particular Lang San Park or Khao Yai National Park or any recommendation).

Thank you for all your recommendations. I suppose I could risk it and go up North either way, but our time is extremely limited and this is a trip we have been thinking about for a good while and can not repeat anytime soon, so I would hate to battle my way through an otherwise beautiful part of the country.

Gabriel;