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Out of the Tailpipe Do cars or does industry contribute more to Houston's air pollution? That question seems to start a debate in Houston. In most cities the major source of air pollution is vehicles, so it may come as a surprise to learn that in the Houston area only one-fourth of ozone generating pollutants are produced by vehicles. (1) The enormous size of Houston's petrochemical complex explains why at least half the ozone-generating pollutants are produced by industry. So Houston is unique among other cities in that most of its ozone pollution comes from industry (including utilities) and not from cars. But that fact does not get drivers off the hook. There are still plenty of air pollutants coming from cars and other vehicles for the average citizen to do something about. Pollution levels from cars have been greatly reduced with the introduction of the catalytic converter and cleaner-burning gasoline. However, ozone levels in Houston and other cities have remained fairly constant or even gotten worse in the past 10 years. Some experts think the reason ozone levels have become stagnant is because the decreases gained by cleaner burning vehicles have been off-set by the increase in the number of vehicles. In other words, although each car is producing less pollution, there are now more cars making that pollution. The number of cars registered in Harris County has not shown much of an increase in the past fifteen years, but this does not reflect vehicles coming in from outside the county. However, there has been a 50% increase in the number of miles Harris County cars travel each year since 1980 (See figure 1 below). Last year, all vehicles registered in Harris County traveled a total of 45 million miles. (2) This increase in vehicle miles traveled (VMT) could be due to people living farther away from places they need to go - urban sprawl.
A closer look at the vehicles registered in Harris County reveals that the majority (70%) of the vehicles are passenger cars. However, light- duty trucks make up 27% of vehicles registered in the county and this number is growing. (3) The light-duty truck category includes what you would think -- small pick-ups -- but it also includes sport utility vehicles (SUVs), such as Suburbans, Expeditions. and mini-vans. Half of the new cars sold today are SUVs and more than a quarter of the vehicles on the road in Harris County are SUVs and light-duty trucks. The problem with these vehicles is that although they are used as passenger vehicles, they do not have the same pollution-control requirements as passenger vehicles. Light-duty trucks are allowed to pollute three times more and use 33% more gasoline per mile than another new vehicle used for the same purpose. (4) The EPA is proposing rules to lower emissions from all cars and to end the pollution disparity between cars and SUVs. However, some of these rules will not go into effect before 2009, and the largest, most polluting SUVs (like the Ford Excursion) are exempt. The EPA is expected to issue a final rule by the end of this year. 1
Air Quality Reference Guide for the Houston-Galveston Area, June
1998. Houston-Galveston Area Council |
