“Temperature plays some role in the cleanliness of the air,” said Todd Miner, a meteorologist at Pennsylvania State University. One temperature-related case involves the chemical reactions that produce ozone. Higher temperatures combined with sunlight provide the conditions that promote ozone, which has well-known irritating effects on the respiratory tract. In general, winter weather systems promote the mixing of the layers of the atmosphere, diluting pollutants, and sometimes those systems import cleaner air from Canada, Mr. Miner said. But mixing can be inhibited in temperature inversions, which are more common in winter in most places. In an inversion, the temperature increases with altitude, rather than the more typical decrease. The inversion can cause pollutants to build up near the ground.
While winter certainly has its negatives, such as the wicked cold weather, it also has pluses. In a recent post, Paul Maxim, made note of the upside of the quietness of winter and snow. For me another plus is the extraordinary clear/clean skies and sweeping clouds.
I’m not certain the air is indeed cleaner in the winter but it seems so and I find myself looking at the sky more often amazed at the crispness. It’s as if it’s in sharper focus during the winter. There certainly seems to be a haze most of late spring, summer and early fall.