There’s end-of-the-year good news for almost everyone who breathes in Cascadia: particulate pollution is mostly declining, as is ground-level ozone pollution.

EPA released its Particle Pollution Reportlast week, which summarizes trends in concentrations of particulates: tiny specks of airborne pollution. Don’t think of happy little flecks like in Dr. Seuss’s Horton Hears a Who. Think of nasty little killers.

Aside from cigarette smoke (a form of pollution that roughly a quarter of adults pay to breathe), these particulates are the most worrisome form of air pollution in Cascadia for human health. Particulates come from burning fossil fuels and wood. They also come from tires rubbing on roads and brakes rubbing on wheels, from forest fires, dust kicked up in construction and roadwork, and many other activities. Some studies suggest that particulates shorten more lives than do roadway crashes in North America.

  • The most dangerous of particulates are the smallest ones, because they can lodge deep in our lungs and do the most mischief. Average airborne concentrations of these tiny particles, called “PM2.5” because they are “particulate matter of less than 2.5 micrometers in width,” have declined by 15 percent in the past five years in the Northwest’s major cities, as this map-chart shows. (Note that the EPA’s definition of the Northwest for this chart is larger than Cascadia. It extends further south and east.) The Northwest outdid the national rate of improvement and ended the period with the second lowest concentrations in the contiguous United States. Regional trends are here (pdf).


    These declines are part and parcel of larger, longer-running decreases in particulates concentrations achieved in the region since 1988. The Northwest slashed its overall particulates concentrations by 39 percent, the largest decrease of any region, and ended 2003 with the second lowest particulate concentrations in the United States, after the Northeast. The steepest decrease came between 1988 and 1996.

    Unfortunately, the Fraser Basin Council reports in its latest snapshot of regional trends (large pdf), (which we posted on here) that PM2.5 concentrations in the few places monitored are flat or even rising, as you can see in this chart.

    Fortunately, BC’s ground-level ozone concentrations (another major air pollutant) are on a long down trend, though there was a small uptick in 2001-2002. And overall, Cascadia is a low-ozone zone, compared to many parts of the world, as you can see on this global map from an remote-sensing project from Europe. (A large, high-resolution version of the map is available from that site.) On the map, Cascadia has only slight concentrations of ground-level ozone, indicated by the pale smudges around Puget Sound, for example. Of course, this is just one snapshot from space. At certain times in the summer, ozone levels can get bad, especially downwind from major cities, as we pointed out here.