I have read in a lot of places the PAN acts as a very good reservoir of nitrogen dioxide. I can't find much information on why though. All I have found is that PAN is thermally unstable and has a very short lifetime at typical tropospheric temperatures, but becomes much more stable at lower temperatures where it can exist for months. Apparently the ability of PAN to travel hundreds of miles in a cold air stream before decomposing to nitrogen dioxide is what makes PAN such a damaging pollutant. My question is what chemical properties make it decompose rapidly at temperatures around 20-30 degrees C, but exist for much longer at colder temperatures? Is it simply that the nitrogen-oxygen bond is very weak and will break at 20-30 degrees, but can withstand lower temperatures? Is PAN a particularly unreactive chemical species? What is it about PAN's chemistry that makes it a better nitrogen dioxide reservoir than other chemicals?