I can't speak for this year because I have not been there yet but....

I was there in 1999, 2000, & 2001 and it was pretty bad back then...Fumes don't ever bother me but i was wearing the facemask things they give out.

Stayed away for a few years, then went in 2007, 2008, and last year and I noticed a big difference. Still a hint of fumes occasionally but nothing like in the past. Was told they had more ventilation and were using low emission fuel now.

the last 2 years i was stripped down to a t-shirt until late in the event when I would throw on a hoodie...when it's EXTEMELY cold outside it's a bit chilly in the building but if its above 15-20 degrees out the building is pretty comfy.

Disclaimer....fumes rarely if ever bother me, even standing beside a 410 idleing to get heat, as rich as they are, my eyes burn but my nose/throat are fine. I am sure people with respritory issues or people who are sensitive to fumes would have a much different opinion of the expo center than I do.