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  Clearing the air

Study shows cars, light trucks are falsely portrayed as the major cause of smog

By Dennis R. Heinze
Regional Editor
Published: Jan/Feb 2000

Automobiles are often pointed at as the primary source of our nation’s smog, but based on a new study, they should be applauded instead.

Cars and light trucks cause less than 24 percent of the emissions that lead to ground-level ozone problems in 25 major cities, according to a study based on state data submitted to the Environmental Protection Agency. By contrast, the study found that the majority of emissions that lead to smog come from other sources, such as power plants, industries and even households.

CarThe study, "Clearing the Air," is the third such analysis of EPA data performed by AAA. While AAA supports continuing efforts to improve the nation’s air quality, it has performed the studies because cars and trucks are often falsely portrayed as the major cause of smog in cities.

In fact, harmful emissions from cars and light trucks have declined at a faster rate than all other sources, and are expected to continue to decrease over the next decade.

Across the country, ground-level ozone continues to be a pervasive summertime air pollutant. Ozone is not emitted by any particular source, but rather forms in the atmosphere when emissions of volatile organic compounds (VOC) and oxides of nitrogen (NOx) react in the presence of sunlight and heat.

Since any process that burns fuel–in cars and trucks, homes and factories–will generate ozone-forming VOC and NOx emissions, all sources must be scrutinized, not just cars. Trends vary from area to area, but in general, the significance of auto and light truck emissions in all study areas has declined substantially.

For instance, in New Orleans, VOCs from automobiles have decreased by 80 percent between 1970 and 1999, and are projected to decrease by 87 percent between 1970 and 2005. Automobiles currently account for just 10 percent of the area’s VOC emissions, compared to 27 percent in 1970. VOC emissions from light trucks–including sport utility vehicles and minivans–have decreased by 45 percent since 1970 and are expected to decrease by 53 percent between 1970 and 2005.

These emission decreases among cars and light trucks were recorded despite a 140-percent increase in the number of vehicle miles traveled since 1970.

While autos and light trucks accounted for 36 percent of VOCs in 1970, they now account for just 19 percent of the ozone-causing VOCs in New Orleans. And by the year 2005, they are expected to account for just 16 percent of the VOC emissions and 7 percent of NOx emissions.

Meanwhile, harmful emissions from other "on-road mobile" sources such as buses, large trucks and motorcycles now account for 6 percent of VOCs in New Orleans, double their rate in 1970.

Now surpassing autos in VOC emissions are “off-road mobile” sources, which include aircraft, locomotives, boats and lawn and garden equipment. These sources account for 15 percent of VOCs in New Orleans, compared with 9 percent in 1970.

The largest category of man-made VOC emission is from stationary sources, which make up 60 percent of the VOC emissions and are projected to account for 68 percent of the emissions in 2005. These sources include industries, utilities, commercial establishments and households.

NOx emissions from autos in New Orleans have decreased by 38 percent between 1970 and 1999, and are projected to drop 60 percent between 1970 and 2005. Autos account for just 5 percent of the NOx emissions in New Orleans, and light trucks account for 4 percent. The majority of NOx emissions (73 percent) come from stationary sources.

Similar VOC and NOx emission decreases in cars and light trucks were found in the Baton Rouge area.

In fact, VOCs from cars decreased by 77 percent between 1970 and 1999 and now account for just 9 percent of Baton Rouge’s VOC emissions compared to 20 percent in 1970. Light truck VOC emissions have declined by 43 percent from 1970 to 1999.

Autos and light trucks now account for just 18 percent of the ozone-causing VOCs in Baton Rouge, a significant decrease from 30 percent in 1970. By the year 2005, they are expected to account for just 15 percent of VOC and 12 percent of NOx emissions.

As in New Orleans, off-road mobile sources have surpassed autos in VOC emissions. While they accounted for just 5 percent in 1970, they now make up 12 percent of the VOCs in Baton Rouge.

Stationary sources produce the most smog-producing emissions in the area, making up 66 percent of the VOC emissions. They are projected to account for 72 percent of those emissions in 2005.

AAA is calling attention to this new information to send a message to federal, state and local air quality officials to go beyond simply targeting passenger vehicles if they hope to make any more real progress in cutting ozone pollution.


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