Smog is not simply a result of human air pollution. It's highly dependent on natural weather conditions, as this summer's heat wave demonstrates.
The blanket of sweltering, stagnant air has trapped harmful ground-level ozone in the Baltimore-Washington basin, causing decidedly unhealthy air quality for more than a dozen days so far. That's more than in all of 1994, according to government air monitoring stations.
It's a reminder that sunlight is a key ingredient in production of ozone, or smog; it's needed to cook the nitrogen oxide and hydrocarbon pollutants of vehicles, factories and furnaces to create ozone. And a reminder that winds can swiftly dilute and disperse a potentially unhealthy pocket of dirty air.
But the high levels of ozone along Maryland's smog belt this summer also emphasize that smog is not disappearing, despite a panoply of technologies and controls applied to the problem for more than a decade. Human growth generates more air pollutants, even as we tighten emissions standards.
This summer's smog also illustrates that air pollution is a pernicious vagabond. State readings, for example, show Harford and Anne Arundel counties to have the worst levels. The reasons include transient traffic loads, wind patterns and weather conditions, not a relative concentration of industry or population in those two metro jurisdictions. (It's one reason why draconian commuter limit proposals for urban centers were highly fallible.)
Smog conditions are perceptibly improved in the metro region since air quality standards were tightened in 1990. In the 1980s, the Baltimore region averaged 20 days of unhealthy smog levels; this decade, the average is about 8 days.
But there is renewed scientific concern that soot, the tiny powdery particles formed by combustion, may still be a cause of human mortality in the U.S. The first air pollution controls addressed this particulate smokestack matter, which was thought to be under tight control.
So there is no justification to declare victory and abandon the fight for clean air, especially when there is evidence that unhealthy effects are felt at ozone levels below the federally set danger levels. The weakest members of society -- children, the elderly, the sick, those with respiratory conditions such as asthma and emphysema -- remain most vulnerable to the effects smog. But we all may feel it in the lungs and the head when pollution and the weather get together to mix up this potent witches' brew.
