The enervating shroud of smog hanging over Central Maryland this summer is an irritating reminder that ozone pollution is not disappearing.
Stagnant air 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, with another month left in smog season.
Smog is not merely a result of human air pollution. It's highly dependent on natural weather conditions, as this summer's heat wave demonstrates.
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 strong winds can swiftly dilute and disperse a potentially unhealthy pocket of dirty air.
Despite a range of human technologies and controls applied for two decades, smog remains a problem. Human growth generates more air pollutants, even as we tighten emissions standards on smokestacks and auto exhausts.
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.)
But smog conditions have noticeably 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; in this decade, the average is about 8 days.
Now there is renewed scientific concern that soot, the tiny powdery particles formed by combustion, may still be a cause of human mortality. The first air pollution controls aimed at this particulate matter, which was thought until recently to no longer pose a major health threat.
So there is ample reason to continue the fight for clean air, especially when there is increasing 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 smog's effects. But we all may feel it in some way when pollution and the weather combine to mix up this potent witches' brew.