Dreaded New Pollutant: Rain

A funny thing happened to me yesterday driving through rural Virginia. I almost stared to cry, but it wasn’t over my 401 (k). Instead it was air pollution-in particular, a massive burst of ozone-that, for the first time in 24 years in that bucolic spot, burned my eyes. What provoked this unprecedented event?

Massive ozone “exceedences” occur when volatile organic compounds (VOCs) react with nitrogen oxides, which are produced by cars and industry, in the presence of strong sunlight and light winds. This has been known for a long time. What is unexplained is why this suddenly appeared in a rural, Mid-Atlantic setting.

It wasn’t because of changes in nitrogen oxides, produced by cars, power plants, and manufacturing. There’s been no sudden up-spike in the number of polluting cars. In fact, every new car that is sold, replacing an old beater, produces an increment of cleaner air.

Nor has there been an explosion of new power plants. As any utility executive will tell you, it takes many years from imagination to electricity to satiate the regulatory monster.

Nor has there been much of a general up-tick in economic activity, at least as can be surmised from both national GDP data and more regional estimators.

What has changed is this: In Summer 2003 the Mid-Atlantic region is greener than an Atlantic City crap table. Over much of the region, trees are the largest source of volatile hydrocarbons. Plants produce two of these, isoprene and terpenes, in huge quantities (one tree = nine new cars), and the more green material there is, the more they emit. For what it’s worth, 60 percent of the volatile organic compounds produced in Metro Atlanta are from trees, not people.

According to the U.S. Department of Commerce, the region where my eyes burned has just experienced its wettest spring (March-May) in 109 years of record keeping. In addition, the same place also experienced the record number of days with measurable rainfall for any calendar month, totaling a Seattle-like 22 days in May. June isn’t far behind, and together the two are likely to combine to an all-time record for number of rainy days that could stand for a century or two.

So, not only was it wet, there also were an amazing number of cloudy days. The two combined to produce abundant vegetation, an experiment you can repeat at home. Put plants under a grow-light, which produces a lot less photosynthetic light than the sun (mimicking a cloudy day), water them well, and then you will see a massive profusion of leaves. Anyone who grows his own tomatoes knows how they sprawl under such conditions.

More leaves = more isoprene and, in some cases, more terpenes. More of these, in the presence of nitrogen oxides, means more smog.

Of course, we put most of the nitrogen compounds in the air, by driving cars, consuming electricity (produced by combustion of fossil fuels), and simply making things. They won’t go away completely until we no longer burn this fuel, and that’s not going to happen anytime soon.

Don’t blame President Bush for rolling back some executive order from late in the Clinton administration that would have created an additional increment of nitrogen oxide reduction. There hasn’t been any change in emissions as a result. It takes more than a few months (often a decade or so) for regulatory changes to produce much that can be measured. In fact, if eastern visibility has changed very little in the last quarter-century.

Don’t blame global warming either: The same places that were so wet nearly set their records for the coldest spring as well.

Sorry, it was a new class of pollutant that made a lot of rural Mid-Atlantic residents cry on June 25. It was rain. May showers brought June pollution.