BST. 15° but the air was still breathable. For now. We are supposed to be in for the mother of all inversions. :( Speaking of inversions, I found this info on why indoor air quality is cleaner than outdoor during an inversion. It is not related to furnace filters but air temperature!! "Inside vs. Outside The deal with our particulate is that so much of it is ammonium nitrate (NH4NO3). Ammonium nitrate happens to be volatile at warmer temperatures and stable at cold temperatures. In our case, the cold temperatures help to keep NH4NO3 as a particle, but once you go indoors the particulate tends to volatilize into it gas phase components. Therefore, indoor air quality is a whole lot better than outdoors. DAQ has done a fair bit of work on this very issue. They conducted numerous studies inside/outside schools. I think they may have worked at Hawthorne among others. Dr. Steve Packham at DAQ would be the contact on that." Google wasatch weather weenies for more good info | 