By extending air-quality regulation to off-road vehicles and engines, the US Environmental Protection Agency has properly adjusted its aim in the fight against pollution.
EPA on Sept. 13 issued a final rule setting standards for emissions of three pollutants from new large industrial spark-ignition engines, recreational vehicles, and large diesel marine engines—all previously unregulated. EPA expects the move by 2020 to have cut total emissions from the affected engines by these amounts: hydrocarbons 72%, oxides of nitrogen (NOx) 80%, and carbon mon- oxide 56%.
At present, the affected engines contribute relatively little to estimated mobile-source emissions—hydrocarbons 9%, NOx 3%, carbon monoxide 3%, and particles, emissions of which won't be controlled, 2%. But their shares are leaping. Without controls, EPA says, they would roughly triple for hydrocarbons and NOx by 2020 and double for all but one of the others.
Dirty machines
Off-road vehicles and engines are countering the effectiveness of other air-quality controls. There was no good reason to extend their exemption from regulation. Snowmobiles, swamp buggies, and dirt bikes are dirty machines, many of them powered by inefficient two-stroke engines. It's time for them to clean up, as other vehicles have had to do. Compliant vehicles and engines will cost more than their predecessors to build, buy, and operate. That's the price of air quality.
The growing contribution to pollution by off-road vehicles is clear in the annual air-quality trends report EPA published this month. According to the report, air quality is improving most in the cities and suburbs where it has been—and remains—the worst. And it's deteriorating rapidly in many rural areas, including national parks, where snowmobiles and dirt bikes roam.
Overall improvement remains impressive. Since 1970, total emissions estimated for the six pollutants subject to control have fallen by 25% while the economy, population, and energy use have zoomed. In the last 20 years, the measured concentration of each of six monitored pollutants, some of which differ from the directly emitted substances EPA regulates, has fallen.
Here are the numbers: During 1982-2001, estimated emissions rose only for NOx—9%. Emissions of volatile organic compounds (VOCs) fell by 16%, of sulfur dioxide by 25%, of particles by 51%, and of lead by 93%. Emissions of carbon monoxide didn't change.
In the same period, measured concentrations of the six monitored pollutants all fell: nitrogen dioxide (the only measured nitrogen compound) by 24%, ozone by 18% in 1-hr testing and 11% in 8-hr testing, sulfur dioxide by 52%, carbon monoxide by 62%, and lead by 94%. Data were unchanged or not available for particles.
Ozone, which forms when VOCs and NOx combine in sunlight, is the most stubborn air pollutant and the main reason that 130 areas still don't comply with statutory air-quality criteria (out of 230 receiving the "nonattainment" designation in 1990). With VOC emissions and measured levels falling, NOx has emerged as the main ozone challenge. It also aggravates airborne concentrations of particles. While NOx emissions increased in 1982-2001, however, they have fallen since 1997 and were 3% lower in 2001 than they had been 10 years earlier.
So further reductions in ozone pollution are likely in cities and suburbs where controls already are strict on vehicles and other engines and where measured ozone levels have dropped by 20% in the past 20 years. In the past 10 years, ozone measurements have fallen by 5% in urban and 6% in suburban monitoring stations.
Welcome clampdown
Trends point the other way for rural areas. In 2001, 1-hr ozone levels recorded by rural stations were 11% below 1982 levels but less than 1% below 1992 levels. For the sixth straight year, average rural 1-hr ozone levels were greater than levels observed for urban sites but generally lower than those at suburban stations. Furthermore, average 8-hr ozone levels of 33 monitored national parks rose by almost 4% during 1992-2001. Six monitoring stations in five of the parks showed significant pollution increases. This can't result from the urban traffic congestion that universally symbolizes ozone pollution.
Smog and its precursors move, sometimes by hundreds of miles. To keep city air improving and rural air clean requires a clampdown on emissions from vehicles now smoking freely across the countryside. EPA made the right move.
