Crying In the Rain

A funny thing happened in rural Virginia on June 25, 2003. There was a spontaneous outbreak of tears. No, people weren’t crying over the stock market (things are looking better, at the moment). Nor were those tears shed over anything personal. The culprit was air pollution; in particular, a massive burst of ozone that for the first time in memory produced a 1960s-vintage, L.A.-style eye-burner.
     Things only get this bad when volatile organic compounds react with the nitrogen oxides produced by cars and industry in the presence of strong sunlight and light winds. This relationship has been understood for a quite some time. It was the basis for the original California ozone regulations. What seems inexplicable is how such a phenomenon could erupt in a rural, mid-Atlantic setting. What was different about this year and the year before, or any prior year for that matter?

NOx, NOx, Who’s There?

It wasn’t the oxides of nitrogen.

It doesn’t stand to reason that there was a sudden spike in the number of polluting cars. Every new car sold replaces an old beater, and produces an increment of relatively cleaner air.

Nor did a host of new power plants spring up, overnight. Any utility executive will tell you that it is years (sometimes a decade or longer) from imagination of a power station to production of electricity.

It certainly didn’t have its origin in an up-tick of economic activity, as a quick scan of national, regional, or state GDP will reveal.

What was different is this: thanks to an abundance of rainfall and snowmelt, the mid-Atlantic states got greener than a craps table in Atlantic City. Over much of the East coast, trees are the largest source of the volatile hydrocarbons required to produce smog. The trees produce two major precursors of ozone–isoprene and terpenes–in vast quantities (one tree equals nine new cars). The more vegetal matter, the greater the emissions. Remember Ronald Reagan being ridiculed for his “killer trees” remark? He knew.

East Beats West
Nasty smogs like the June 2003 surprise used to be l’air du jour for Los Angeles. Think back to the cover of Tim Buckley’s “Greetings From L.A.” album (now only available as an expensive, imported CD on Amazon.com). California cleaned up its act by pioneering auto emission regulations. While things still can get a little soupy out there, terrible and irritating smogs have been pretty much engineered out of the L.A. Basin. Fact is, the rest of us have adopted (either by law or default) the same emission standards. So why were eyes burning on the Right Coast? Like the bumper sticker says, “Trees are the answer.”

While not devoid of trees, urban California by removing automobiles and some industries as sources of volatile organic compounds reduced a large fraction of its air pollution problem. But the same isn’t true out East where conservation and forest management have combined to produce a virtual jungle. There is more abundant tree biomass along the eastern seaboard than there has been for at least three hundred years. When viewed from the air, Washington, Atlanta, Richmond and Charlotte appear to have been chopped out of a very aggressive vegetative cover only too willing to reclaim open space. Cities in the Golden State were hacked out of open grassland.

According to Georgia Tech scientist Bill Chameides (1980), about sixty percent of airborne VOCs in metro-Atlanta have their origin in vegetation. In rural areas such as the eye-stung region in June, the figure approaches 100 percent. No matter how you slice it, the airborne load is substantial. In the presence of a very small amount of nitrogen oxides, those VOCs will combine under hot and undisturbed conditions to produce nasty smog.

Water, Water Everywhere
According to the U.S. Department of Commerce, the East has just experienced its wettest spring (March-May) in 109 years of record keeping. There were a record number of days with measurable rainfall totaling a Seattle-like twenty-two days in May 2003. June wasn’t far behind. Together, May and June are likely to combine for an all-time record in the number of rainy days–a record that might stand for a century or two.

Not only was it wet, there were an amazing number of cloudy days. That combination produces abundant vegetation. You can test the hypothesis at home. Put plants under a grow-light (which produces a lot less photosynthetic light than does the sun, thereby mimicking a cloudy day), water them well and, voila, you will see a massive profusion of leaves. More leaves mean more isoprene and, in some cases, more terpenes. Add those in the presence of nitrogen oxides and you’ve got the fixin’s for smog.

So, Who’s to Blame?
Our Green buddies are apt to blame President Bush for the yucky air. They’ll point out that he recently rolled back an Executive Order from late in the Clinton Administration that would have created an additional increment of nitrogen oxide reduction from East Coast power plants. That’s a nice try, but it would take more than a few months (and probably a decade or so) for those regs to produce anything that could be measured. Judging from the lack of any visibility trends in the Mid-Atlantic in recent years (see Figure 1), oftentimes there’s no palpable result. Failing to pin the tail on the elephant, the same folks are apt to transfer the blame to global warming exacerbated by Bush/Cheney distancing from the tenets of the Kyoto Protocol. But that doesn’t pass muster, either. The same places that were so wet darn near set a precedent for the-coldest-spring-on-record, too.

It seems there was a new class of pollutant that made a lot of rural Easterners cry on June 25th. Move over CO2, it was rain!

Reference
Chameides, W.L., et al., 1988. The role of biogenic hydrocarbons in urban photochemical smog: Atlanta as a case study. Science, 241:1473-1475.

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