Comparing local data / Reducing exposure to VOCs / Spotlight On: Route 2 Commuters, Inc.
Vermonters' predominant exposure to air pollution now results not so much from industrial sources but increasingly from our everyday activities, such as our daily driving and heating our homes.
Changing lifestyles have increased the distances we are willing to travel to and from work, expanded the number and types of recreational and special-purpose vehicles we drive, and changed the size and character of our homes. In addition, tourism draws more cars carrying visitors to our scenic attractions and resort locations. These changes continue to increase total statewide annual vehicle miles traveled (Figure 1).
As Vermonters, we have always had to contend with two major influences on our behavioral patterns and lifestyle choices. Our winters are long and cold, and our small towns and villages are dispersed across a mountainous state. We use energy - gasoline to power our cars and heating fuels to warm our homes - to overcome these influences. The resulting release of emissions during combustion of these fuels produces most of the air pollutants released in Vermont. After declining somewhat in the early 1980s, our energy appetite has increased steadily in recent years.
Even with the overall increases in energy use in Vermont, we have managed to maintain a relatively low per capita energy use level (11th lowest, according to the U.S. Energy Information Administration). Unfortunately, per capita energy use in Vermont has risen during the past two decades and now has returned to the same levels prior to the oil crisis of 1973.
Which of the two basic energy uses (home heating oil or motor vehicle gasoline use) creates more air pollution in Vermont, and what have been the trends of these emissions? To answer that question, consider the emissions of a single pollutant: Volatile organic compounds (VOCs), a class of air pollutants that includes some of the more toxic and carcinogenic chemicals.
The amount of volatile organic compounds produced by burning home heating oil is only a small fraction of that generated by the pumping and combustion of gasoline (Figure 2). Filling our gas tanks accounts for more than 2,000 tons of VOCs per year in Vermont. Refueling emissions have been increasing annually since they are directly related to the amount of gasoline sold. Gasoline refueling causes roughly 20 times the total VOCs released from all residential fuel oil combustion. Motor vehicle emissions are still by far the largest component. Because of federal motor vehicle emission standards, this component has been declining during the past 20 years although the volume of traffic has been increasing steadily statewide.
The data presented so far indicate that local air quality probably is more dependent on our use of motor vehicles and our use of gasoline as a transportation fuel than on any other influence, based on the magnitude of annual statewide emissions associated with the source categories. Statewide emissions, however, do not reflect an individual's exposure. The changing exposure to air pollutant emissions resulting from the growth in vehicle traffic and the increase in gasoline usage is not felt equally everywhere in Vermont.
Emissions from highway traffic primarily affect the immediate vicinity of the roadside. Similarly, vehicle refueling creates local areas of more dense emissions of VOCs, particularly in urban areas. Trends in daily traffic counts along sections of a roadway can be used to compare the relative potential for exposure to automobile-generated VOCs with exposure at gas stations.
Comparing local data
Based on Agency of Transportation highway traffic count data, trends in the volume of daily traffic flow (and by inference, air emissions) during the past 20 years reflect to some extent the nature of Vermont's changing landscape during this time. To make estimates of vehicle emissions along roadsides more comparable to gasoline service station emissions, the estimates in Figure 3 show tailpipe emissions along a 500-foot length of roadway. This is equivalent to assuming that a person standing near the roadway only is exposed to the closest 500 feet of the road. The figures reveal a gradual reduction in exposure to VOC emissions for locations near both urbanized roads (Route 7 in Shelburne) and in a relatively rural portion of Windham County along both Interstate 91 and Route 5. Current levels of emissions range from about one-half ton per year in the rural areas to more than one ton per year along Route 7 in Shelburne. These trends imply that exposures to VOCs along roadsides from traffic flow have been declining generally at all locations in the state.
This encouraging result of vehicle VOC-emission control - which would have been even more impressive had total vehicle miles traveled not increased - is in strong contrast to what is happening to exposure in the vicinity of gasoline service stations. Annual exposure to VOCs near gas stations depends on the annual fuel sales at each station. Because gasoline sales have increased steadily at the average service station, rising roughly in proportion to the number of vehicle miles traveled in Vermont, exposure to VOCs near service stations is increasing. For example, a relatively large service station that sold 750,000 gallons of gasoline in 1974 is now pumping close to 1 million gallons annually today. Emissions of VOCs at this gas station during the past 20 years have risen from less than 8 tons per year to more than 10 tons, or 10 times the emissions of VOCs generated annually by vehicle traffic along a typical 500-foot section of a busy roadway.
Reducing exposure to VOCs
Control of gasoline vapors at service stations involves two components. First, the proper fittings need to be installed on storage tanks and on tanker trucks to allow vapors released during filling to return to the tanker truck and not escape to the atmosphere. This is called Stage I vapor recovery, and it has been implemented in Vermont for several years.
Second, the gas pump hoses we use for refueling our cars need special nozzles. These nozzles return the vapors to the station's underground tanks and prevent them from escaping to the atmosphere. This is called Stage II vapor recovery. Vermont has recently adopted Stage II regulations which will ensure the capture of more than 1,200 tons of VOCs annually by the year 2000.
Car and van pools have the potential to counter some of the growth in vehicle miles traveled and, therefore, to reduce air pollutant emissions and the subsequent harmful effects on the environment and our health. A clear example of the benefits of such van pools may be shown from the Route 2 Commuters, Inc. van pool experience. This van pool has operated successfully between St. Johnsbury, Montpelier, and Waterbury for more than 10 years. It serves state employees most directly, but could be a model for others throughout Vermont. Fifteen subscribers ride the van regularly on the St. Johnsbury to Montpelier/Waterbury sector, with four other regular subscribers riding the Montpelier to Waterbury sector.
Using the one-year period from April 3, 1995 to March 29, 1996 for a calculation based on the actual ridership during this time period, the van pool resulted in an estimated reduction of 3,875 gallons of gasoline for commuting purposes. This equates to an estimated reduction of 690 pounds of nitrogen oxides, 604 pounds of volatile organic compounds, some of which are carcinogenic, and 5,002 pounds of carbon monoxide for this one-year period. More than 130,000 miles of vehicle travel were eliminated during this year by the use of the van pool by these 19 riders.
In addition to being good for the environment, this van pool provides financial benefits as well. The overall average cost per mile was found to be 6.7 cents per mile for each rider, compared to more than 30 cents per mile for a commuter driving alone in a typical sedan.