Reviewing the thousands of Auto Asthma Index values gives us a first ever glimpse of real world vehicle performance. We found that vehicle pollution varies widely based on the year a particular vehicle was built, the vehicle type, the number of miles it has been driven, the automaker, and the care with which it was designed and assembled.
1. Many vehicles are big polluters.
2. Older vehicles pollute more.
3. Trucks, SUVs, vans, minivans, and oversized vehicles pollute more.
4. Vehicles driven more miles pollute more.
5. Vehicle pollution depends on the automaker.
6. Pollution from individual vehicles varies widely.
7. The best way to reduce smog depends on where you live.
Many vehicles are big polluters
Vehicles are a major source of the two types of chemicals that cause smog, volatile organic compounds (VOCs) and nitrogen oxides (NOx). Some of the factors that govern a new vehicle's emissions can be improved by employing new, more protective emissions control technologies. However, a striking number of today's newer vehicles (model year 2001-2006) still have scores of 7 to 10 on our Auto Asthma Index. A car with an Index of 7 emits 10 times more smog chemical pollution than today's cleanest cars (those with a score of 1). 9's emit 30 times more pollution and 10's are even worse. These are almost uniformly large vehicles—trucks, vans, and oversized vehicles—once intended as commercial vehicles, now common status symbols for passenger use.
Many newer vehicles score poorly on the Auto Asthma Index.
(Find an Auto Asthma Index Score for an newer vehicle.)
California's Smog Check data for thousands of vehicle models made between 1985 and 2000 offer a unique look at pollution from today's aging autos. Typical smog chemical emissions from the dirtiest of these models are over 1000 times the emissions of the cleanest models. We found notable trends toward increasing emissions for older vehicles, 'truck-type' vehicles (including trucks, SUVs, vans, and minivans), and vehicles driven more miles. However, almost all vehicles manufactured before 1996 have Auto Asthma Index scores of 9 or 10, indicating that they too emit at least 30 times the pollution of today's cleaner cars.
Older vehicles pollute more
Vehicle emissions have declined significantly since 1985, when little was done to capture hazardous pollutants generated by vehicle engines. Basic technologies such as the catalytic converter, developed to meet requirements of the Clean Air Act of 1970, were responsible for the earliest improvements in vehicle emissions. In the mid-1990s, on-board diagnostic tools came into use to monitor engine and emissions systems. They typically indicate when tailpipe emissions are 50 percent greater than the vehicle's allowable emissions.
Our analysis of Smog Check data show a dramatic decrease in vehicle emissions over time. Thus, older vehicles are responsible for a large share of overall vehicle emissions. Both technological improvements, and changing federal and California vehicle standards play a role in this decline, as well as the fact that newer vehicles have been driven fewer miles and have emissions systems that are in better repair.
Typical emissions from older model year vehicles are much higher than from year 2000.
(Find an Auto Asthma Index Score for an older vehicle.)
Vehicles manufactured between 1975 and 1984 are also required to receive a Smog Check. We did not include them in this analysis because so few of them are driven today. Due to outdated pollution control technology and high miles, these vehicles are among the dirtiest on the road. Most, if not all, would receive a score 10, and would emit many times more pollution that even mid-1990s vehicles.
Trucks, SUVs, vans, minivans, and oversized vehicles pollute more
The majority of EPA's vehicle certification laws and local Smog Check programs continue to allow trucks, SUVs, vans, minivans, and oversized vehicles to pollute more than passenger cars. Over the past decade, many automakers changed their vehicle design and emissions certification precisely to take advantage of these lax standards. These loopholes are gradually being phased out, but in the meantime, people in smoggy regions are stuck in neighborhoods choked with popular, and smoggier truck-type vehicles used as passenger vehicles.
Newer trucks, vans, and oversized vehicles pollute more than passenger cars.
Vehicles driven more miles pollute more
As vehicles are driven, the wear and tear on engines and pollution control equipment results in increased emissions. EPA estimates that a new car that has been driven 100,000 to 120,000 miles will emit 25 percent more pollution than the same model with just 50,000 miles. [EPA 1999] Our own analysis of Smog Check records for cars with lower and higher odometer readings finds a similar trend. Four-year old cars with 60 to 80,000 miles emit twice as many volatile organic chemicals per mile as those vehicles with less than 20,000 miles, and five times as many nitrogen oxide chemicals.
High miles cars emit two to three times more smog chemicals than low miles cars.
Vehicle pollution depends on the automaker
Some automakers show a commitment to manufacturing cleaner vehicles, while others do not. We analyzed automaker performance in both designing new vehicles that incorporate the cleanest pollution controls, and in how their older models hold up over time. Among the largest automakers, Honda, Mazda, Hyundai and Nissan stand out as consistently performing better than their competitors. Cars from General Motors and Daimler-Chrysler were consistently more polluting. Ford, Toyota, BMW, Volkswagen and Hyundai fell in the mid-range for Auto Asthma scores.
Affordable technologies exist to make vehicles much cleaner. Honda, Nissan and Ford have taken initiative to voluntarily adopt more stringent pollution controls for their vehicles ahead of federal mandates. [Friedman 2004] Automakers must continue to innovate and improve their records.
Average score for the Big 10 Automakers on the Auto Asthma Index, 2001-2006 vehicles.
(Find the best and worst automakers and learn what more automakers can do to improve air quality.)
Pollution from individual vehicles varies widely
There is a big difference between the cleanest and dirtiest vehicles on the road. California officials estimate that the dirtiest 10 percent of all cars and trucks—mostly older vehicles—spew out roughly 50 percent of the state's smog-forming emissions from vehicles. [Shafizadeh 2004] These highly polluting vehicles can be from models that are universally bad, reflecting poor technology and construction. When smog tested, a large percentage of these models may be flagged as "Gross Polluters," or vehicles that produce double or more the allowable pollution according to the California Smog Check program. [Shafizadeh 2004]
However, even typically clean models have a handful of extreme polluters. An example is the nearly 15,000 model year 2000 Honda Civics smog tested in 2004. EWG's Auto Asthma Index for a typical 2000 Honda Civic is 2. However, the dirtiest 3,700 cars in this group emit at least double this level of smog chemical pollution, and the worst 1,500 emit 6.5 times more pollution, receiving a score of 8 or worse on the Auto Asthma Index. Other vehicles show the same trend, with a large disparity between emissions from typical vehicles and a handful extreme polluters.
Total smog chemicals emitted from 2000 Honda Civics: The dirtiest cars emit 6.5 and 2 times the pollution of typical cars.
The best way to reduce smog depends on where you live
Smog formation is governed by the reaction of volatile organic compounds (VOCs) and nitrogen oxides (NOx) with sunlight in the atmosphere. The relative importance of each of these chemical groups to smog formation depends on local man-made and natural emissions sources, as well as on the climate in your region of the country.
Vehicles are a major source of both smog chemical pollutants. However, the effectiveness of different local smog control measures depends on which particular pollutant is more critical in the area where you live. In regions where one pollutant typically determines the amount of smog formation, we ranked vehicles exclusively on that pollutant (VOCs or NOx). In regions where both pollutants matter, we ranked vehicles based on the total smog chemical emissions they produce. (Check the best and worst vehicles for your town.)
REFERENCES
Environmental Protection Agency. 1999. Determination of NOx and HC Basic Emission Rates, OBD and I/M Effects for Tier 1 and Later LDVs and LDTs. Draft. EPA document 420-P-99-009
Friedman D, MacKenzie D. 2004. Automaker Rankings 2004: The Environmental Performance of Car Companies. Union of Concerned Scientists, Cambridge, MA. http://www.ucsusa.org/clean_vehicles/
vehicles_health/automaker-rankings-2004.html
Shafizadeh K, Niemeier D, Eisinger DS. 2004. Gross Emitting Vehicles: A Review of the Literature. Prepared for the California Department of Transportation, Task Order No. 27. Available at: http://aqp.engr.ucdavis.edu/Documents/Gross%20
