Clean air legislation and pollutants—a review
Tightened emissions standards resulted first in evaporative emission control systems and sealed crankcases.
A switch to unleaded fuel (no small accomplishment) enabled manufacturers to use catalytic converters, and then came closed loop engine management systems with oxygen sensors, and reformulated gasoline blends. According to Downstream Alternatives: “With the introduction of so-called Tier One vehicles in 1999 hydrocarbon (HC) emissions have been reduced by 98% compared to pre-control era vehicles. Likewise, automotive emissions of oxides of nitrogen (NOx) have been reduced 90% below control pre-levels.”2 Because of California’s severe air quality issues, tougher laws enacted there have led the nation; and some northeastern states have adapted tougher-thanfederal standards like those in the Golden State. OEs may thus find a given engine package certifies for sale under federal emissions standards, but not for California, et al.
According to EPA figures, the average 2000 and 2001 model year vehicle emitted between 27.4 and 36.3 pounds of smog forming pollution (primarily NOx and HC) for every 15,000 miles—about the average driven per year.
Knowledgeable automotive technicians monitor five automotive tailpipe emissions important for air quality: CO, HC, O2, CO2 and NOX. Carbon monoxide (CO) and hydrocarbons (HC) are deadly and were the first to be regulated and measured in the service bay; high readings are the result of partially burned or unburned fuel, respectively.
Later, monitoring of O2 (oxygen) and CO2 (carbon dioxide) was added to better understand the combustion process; high O2 means a possible misfire, while increasing CO2 indicates increased combustion efficiency. Diesels of course are also monitored for particulate matter as small as 2.5 microns (PM2.5). CO2 is now recognized as a contributing greenhouse gas.
NOx is the greenhouse gas most associated with photochemical smog and ozone. NOX comes from
NOx is caused by high combustion chamber temperatures (over 3000 degrees), hence the need for relatively lower compression ratios, retarded ignition timing, and EGR systems to reduce nitrous oxide emissions. Environmentalists are also concerned about as-yet unregulated emissions like aldehydes and sulfur dioxide.
Emissions standards have tightened with each year’s passing and tend to vary according to state and locality, along with how they are to be measured.
Different emissions tests are performed in various state and localities.
Some programs may call for simply monitoring emissions with the vehicle unloaded and taking samples at two different engine speeds. This is usually referred to as a two-speed idle (TSI) test. More recently, emissions tests have gone increasingly high-tech to match the more sophisticated technology used in engine control systems. This has brought about the need for dynamometer- based emissions tests, otherwise known as loaded-mode testing. Initially, EPA accepted only the I/M240, an emissions test performed under varying loads and speeds. Eventually, EPA also accepted the ASM (Acceleration Simulation Mode) test, which evaluates emissions with the vehicle at a steady speed and load. Inasmuch as conditions have changed when measuring emissions, so have the measurement techniques.
Historically, automotive technicians have used “concentration” sampling to measure the level of exhaust pollutants, expressed as either a percentage or in parts per million (1% equates to 10,000 ppm). Concentration sampling is an integral part of emissions programs using the two-speed idle test (TSI) and also the more recent ASM test. A shortfall of the concentration method is that it measures the concentration of pollutants only; it does not account for the difference in exhaust volume between smaller and larger engines. For example, if a 2.0L engine and a 6.0L engine showed the same concentration readings, the 6.0L engine would theoretically produce three times the pollution because it has three times the displacement.
To offset the shortfall of concentration sampling, constant volume sampling (CVS) was adopted, which provides pollutant readings in grams per mile.
CVS uses a “make-up” air system to supplement the volume of exhaust from the tailpipe, regardless of engine displacement, so that exhaust volume has no bearing on overall emissions readings. The variance in displacements of smaller versus larger engines is no longer an issue. CVS is an integral part of the I/M240 test performed at centralized testing facilities.
|Emission Standard Programs|
|Tier 1||The least stringent emission standards|
|A voluntary program to sell cleaner vehicles nationwide. The average emission level must meet LEV, or better, emission standards (see table below).|
|California||California has special authority under the Clean Air Act to set their own emission standards because of unique air quality problems.|
|Tier 2||New standards for cars and trucks, to be phased in from 2004 through 2009, that are optional from 2001 to 2003.|
|Emission Standard Level (listed from least clean to cleanest)|
|T1||Tier 1||The least stringent emission standards|
|TLEV||Transitional Low Emission Vehicle||More stringent than Tier 1 standards for hydrocarbons (HC)|
|LEV||Low Emission Vehicle||More stringent than TLEV standards for both hydrocarbons (HC) and nitrogen oxides (NOx)|
|ULEV||Ultra Low Emission Vehicle||More stringent than LEV standards for HC|
|SULEV||Super Ultra Low Emission Vehicle||Even more stringent standards than ULEV for both HC and NOx|
|ZEV||Zero Emission Vehicle||The strictest emission standard, permitting no emissions|
|Source: EPA; www.epa.gov/autoemissions/about.htm|
|The Greenest Vehicles of 2003|
|Make & Model||Specifications||Emission
|Honda Insight||1.0L 3, auto CVTa||SULEV||57||56||57|
|Honda Civic GX||1.7L 4, auto CVT [CNG]b||SULEV*||30||34||53|
|Toyota RAV4 EV||Electricc||ZEV||3.7||2.9||52|
|Toyota Prius||1.5L 4, auto CVTa||SULEV||52||45||52|
|Honda Civic Hybrid||1.3L 4, auto CVTa||SULEV||48||47||51|
|Honda Civic HX||1.7L 4, manuala||ULEV*||36||44||43|
|Nissan Sentra||1.8L 4, manuala||SULEV||28||36||42|
|Toyota Echo||1.5L 4, manuala||LEV*||35||43||42|
|Toyota Corolla||1.8L 4, manuala||ULEV*||32||40||41|
|Honda Civic||1.7L 4, manuala||ULEV*||32||38||40|
|Ford Focus||2.3L 4, manual||SULEV||25||33||39|
|Ford Focus Wagon||2.3L 4, manual||SULEV||25||33||39|
|a Configurations of these models with other transmissions and emission standards score nearly as well.|
|b Compressed natural gas (CNG) vehicle fuel economy given in gasolineequivalent miles per gallon.|
|c Electric vehicle fuel economy given in miles per kilowatt-hour.|
|* California-certified vehicle available nationwide.|
|Source: American Council for an Energy-Efficient Economy|
New Vehicle Emissions Certification
Vehicle emissions are monitored and measured by the EPA using a standardized federal test procedure (FTP) on virtually all vehicles sold or brought into the U.S. Evaporative emissions—volatile organic compounds (VOCs)—are measured in a sealed test cell (known as a “shed”), and tailpipe emissions are measured on a dyno using the constant volume sampling (CVS) or “mass” method. CVS measures the relative weight of pollutants in meaningful grams per mile during a load mode test. Vehicles must be precisely driven at a variety of speeds and loads following a “trace” designed to simulate real world conditions. Based on these results, vehicles are classified as to their clean air potential (see below).
Vehicle Clean Air Ratings: What’s It all About?
Ever tightening emissions standards for on-road vehicles have resulted in EPA compliance timetables with designations like Tier O, Tier One, LEV, ZEV and so forth.
Under the National Low Emissions Vehicle (NLEV) program, manufacturers may sell a variety of vehicles and average their emission levels; indeed, manufacturers sell flexiblefuel vehicles (an FFV can burn up to 85% ethanol) and apply clean air credits against their more polluting yet popular gas guzzlers.
Vehicles are rated according to vehicle emission standards as LEV, ULEV, SULEV, or ZEV; ratings are based on vehicle year of manufacture, by the maximum allowable amount of VOCs evaporated, and tailpipe emissions. For example, vehicles rated SULEV are ahead of the 2004 schedule and qualify as such because they emit virtually no VOC emissions and very low tailpipe emissions—about 75% less than a ULEV. The gasoline powered 2000 Nissan Sentra CA (clean air) qualifies as SULEV because of its zero evaporative emissions and use of three catalysts. Toyota’s gasoline burning Prius qualifies as SULEV because the Atkinson Cycle engine only runs part-time for extremely low grams per mile. A small percentage of zero emission vehicles (ZEVs) are presently mandated in California; ZEVs are principally battery electric vehicles (BEVs) or could be hydrogen fuel cell vehicles (FCVs); even wind and solar powered vehicles might one day be included.
Obviously, along with clean/green vehicle technology, cleaner petroleum fuels help to reduce emissions. The EPA regulates the amounts of pollutants (like sulfur) in both gasoline and diesel fuel. In geographical areas where CO and NOx have contributed to “non-attainment” (i.e. where ozone levels exceed EPA limits) these areas have benefited from the use of oxygenated gasoline.
Likewise, the use of reformulated gasoline (RFG) has helped certain areas to meet clean air standards.
When the Minneapolis-St. Paul area had concerns about rising levels of ozone, officials collaborated with a local fuel supplier to deliver fuel which exceeded present fuel standards: “Our testing has confirmed it to be low-sulfur and low-benzene. When it was introduced in the fall of 1999 (about 6 years ahead of EPA tier II sulfur standards), it represented the first time such a proactive move was made by a fuel supplier and retailer.” said Tim Gerlach, Twin Cities Clean Cities Coordinator and Director of Outdoor Air Programs for the American Lung Association of Minnesota. Alternate fuels burn even cleaner. Despite the cleanest of gasoline or diesel fuel, engines properly outfitted and integrated with alternate fuel systems show a drastic reduction of tailpipe emissions when burning alternate fuels. Honda’s literature notes that its Civic GX (a dedicated CNG vehicle) has “the world’s cleanest burning internal combustion engine …with an emissions level of just 1/10 the ULEV standard.” See the accompanying charts for a better understanding of Vehicle Emission Standards, how alternate fuel emissions compare to RFG, and which vehicles are the cleanest.
Over the years impressive strides towards clean air improvements have been made, thanks to improved vehicles - and clean fuels.
More vehicles are being driven more miles however, and clean air problems for major metropolitan areas persist. Each summer cities experience alarming numbers of “code red” ozone-level days when children, the aged, and those with respiratory problems are urged to stay indoors. Thus health, environmental and conservation organizations alike actively support the use of clean fuels and vehicles.
We, as automotive professionals, can partner with these efforts by staying well informed, trained, and equipped to keep today’s vehicles running properly for low emissions.
Furthermore, we can opt for using cleaner/greener fuels in our vehicles, and promote the clean fuels choice whenever possible to our customers.
Source: Rob Rodriguez (ASE)