Robert Charlson glances at a stand of dark pines a few hundred yards away, across the flat gray waters of Lake Washington. This air looks pretty clean,’’ he says.
It sure does. A cold scent of fresh water is blowing off the lake behind the parking lot of the National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Laboratory in Seattle. Sparrows are cheeping all around as they flit among the red and gold leaves of trees in full autumn display. There’s a constant scritch-scritch sound coming from the lawn, where a flock of Canada geese, each approximately the size of a well-fed third grader, is munching grass. The sensible compacts in the parking lot aren’t belching exhaust, and even the smoke coming from one of NOAA’s boxy white buildings looks like harmless water vapor. It’s hard to imagine how the atmosphere could be any cleaner and still have any modern, car-driving, industry-dependent people in it.
Well, let me tell you, it’s not clean,’’ Charlson says. See the trees on the other side of the lake?’’ He points east. If it were really clear, you’d be able to see every branch over there. Instead, some of the details are lost because some of the light reflected from the trees isn’t reaching us. On its trip across the lake, the light is slogging through a thin haze of solid specks and liquid globules, most of which are sulfur compounds. Some of these particles are as small as viruses; some are no bigger than a handful of molecules. Belched forth from smokestacks and car exhausts, these airborne particles, or aerosols, don’t absorb much light, so they don’t appear dark. But light that strikes an aerosol doesn’t pass through it, either--it just bounces off at a new angle. The more haze, Charlson says, the more this optical scattering degrades the view.
Charlson, a professor of both atmospheric sciences and chemistry at the University of Washington in Seattle, has been studying aerosols since the 1960s, when standard textbooks said optical scattering would never be measured accurately (among the first of Charlson’s half-dozen patents is for a device that does just that). Like a nineteenth-century explorer painstakingly drawing hills and streams on the blank spots that were once labeled here there be tigers, he has spent 30 years creating an almanac of details about what he calls this peculiar state of material floating around in the atmosphere.
As a result of his work, one feature of haze is now very clear: there’s much more at stake than the view. Our whole climate is in jeopardy. Just as aerosols scatter light traveling from one side of a lake to another, they also interfere with light coming in to Earth from the sun. Some of it’s being reflected back, Charlson says. It goes right out into the blackness of space.
