Man-made air pollutants are disappearing. Carbon monoxide dioxide? Way down. Nitrogen dioxide? Way down. Sulphur dioxide? Way down. Have you heard much about that? The pollution protestors, who played a useful role, have moved onto new fund-raising areas without saying thank you for the improvement in the old ones. The Fraser Institute updates their data with 35 year charts current to 2009.
(C0 comes mostly from incompletely burnt fuel for transportation and 19% forest fires.)
(N02 mostly comes from transportation, and the petroleum and power generating industries.)
(S02 comes mostly from refining minerals, the petroleum industry and coal-fired power generation.)
(Acid rain comes from N02 and S02 mixing with water vapour).
A couple other areas are touched on. Over half of the volatile organics in the air come from unpaved and paved roads. Less than a quarter of the ultrafine particulates are directly produced by human activity with the rest coming from forest fires and being created in secondary reactions in the atmosphere. This has been declining to some degree as well.
The report is available as a free download at the link.