Car Exhaust - Air Pollutants
In cities across the globe, the personal automobile is the single greatest
polluter, as emissions from more than a billion vehicles on the road add up to a
planet-wide problem. Driving a private car is a typical citizen's most air
polluting activity. The negative effects of automotive emissions are maximum
when you sit in traffic surrounded by cars trucks and buses, their engines idling. Everyone
sitting in a traffic jam is getting poisoned.
The Combustion Process
Gasoline and diesel fuels are mixtures of
hydrocarbons (made of hydrogen, oxygen and carbon atoms.) Hydrocarbons are
burned by combining with oxygen. Nitrogen and sulphur atoms are also present and
combine with oxygen when burned to produce gases. Attempts to reduce exhaust emissions from gasoline and diesel engines have been
compromised by limitations of testing, inherent flaws in the design and
inadequate maintenance of emission control devices.
Diesel engines a pose different emission control problems than gasoline
engines. Diesels require more
sophisticated and expensive components than the catalytic converters fitted to
gasoline engines. Diesel emissions contain nitrogen oxide gases and carbon
particles, the smallest of which contribute to lung and heart disease. Increases
in airborne fine particulate matter increases the risk for myocardial
infarctions, strokes and heart failure. Particle deposition in the lungs
activates the sympathetic nervous system and triggers the release of systemic pro-inflammatory responses. Brook
and Rajagopalanb stated: "Higher circulating levels of inflammatory cytokines cause vascular
endothelial dysfunction and activation of vasoconstrictive pathways while
blunting vasodilator capacity. At the molecular level, the generation of
oxidative stress with the consequent up-regulation of redox sensitive pathways
appears to be a common mechanism of these pro-hypertensive responses. Due to the
ubiquitous, continuous and often involuntary nature of exposure, airborne fine
particles may be an important and under-appreciated worldwide environmental risk
factor for increased arterial BP.
Typical Engine Combustion Emissions
Fuel + Air => Hydrocarbons + Nitrogen Oxides + Carbon Dioxide + Carbon
Monoxide + Sulphur Dioxide+ water
Hydrocarbon emissions are fragments of fuel molecules, only partially burned.
See Toxicity Hydrocarbons in
Hydrocarbons react in the presence of nitrogen oxides and sunlight to form
ground-level ozone, a major component of smog. Ozone irritates the eyes, nose,
throat and damages the lungs. A number of exhaust hydrocarbons are also toxic,
some with the potential to cause cancer.
Nitrogen Oxides Under high pressure and temperature conditions in an
engine, nitrogen and oxygen atoms react to form nitrogen oxides. Nitrogen
is a brownish toxic gas, an important air pollutant. The air
of cities with high levels of car ownership has a distinctly brown tinge. NO2
combines with water in the air to form nitric acid
- acid rain. A complex chemistry involves NO2
combining with hydrocarbons to form the photochemical
smog that poisons city dwellers. Sunlight
converts unburned hydrocarbons to more reactive molecules such as aldehydes and
ketones which generate peroxyacyl radicals that react with NO2
forming peroxyacyl nitrates(PANs).
Catalytic converters in car exhaust systems reduce air pollution in the best case by breaking down
NO2 and N20 to nitrogen (N2) and
Nitrous oxide (N2O) also known as "laughing gas" has medical uses, but is a
pollutant in the air. N2O,
for example gives rise to nitric oxide (NO)
which reacts with and depletes ozone. N2O
a combustion product but also originates from forest fires, lightning storms nitrogen-based fertilizers and manure from farm
animals. According to the US EPA industrial sources make up only about 20% of
all anthropogenic sources of N2O, including the burning of fossil
fuel in internal combustion engines. Indoor gas burning appliances generate N2O. It is also
a major greenhouse gas and air pollutant with about 300 times more global-warming potential than carbon dioxide.
Carbon Monoxide Carbon monoxide (CO) is a colorless, odorless,
poisonous gas, a product of incomplete burning of hydrocarbon-based fuels.
Carbon monoxide consists of a single carbon atom and a single oxygen atom linked
together (CO), the product of incomplete combustion of fuel. Most CO is produced
when air-to-fuel ratios are too low in the engine during vehicle starting, when
cars are not tuned properly, and at higher altitudes, where thin air reduces the
amount of oxygen available for combustion. Two-thirds of the carbon monoxide
emissions come from transportation sources, with the largest contribution coming
from cars. In urban areas, the passenger vehicle contribution to carbon monoxide
pollution can exceed 90%. Read more about
Carbon Dioxide U.S. Environmental Protection Agency (EPA) originally
viewed carbon dioxide as a product of "perfect" combustion, but now views CO2 as
a pollution concern. Carbon dioxide is a greenhouse gas that traps the earth's
heat and contributes to Climate Change
Particle Pollution and Human Disease The U.S.
Environmental Protection Agency (EPA) defines fine-particle air pollution,
PM10, particulate matter 10 micrometers or less in diameter. Suspended particles
in the air create aerosols that are important to the behavior of whole
atmosphere and play a role in determining human disease. Natural sources of
atmospheric particles are volcanoes, dust storms, spontaneous forest fires,
tornadoes and hurricanes. Clouds are a product of aerosols that seed the
formation of water droplets. Human air pollution now dominates aerosol
production over cities with negative health effects. Thick aerosols are obvious
as haze and contain a complex system of particles with adherent toxic gases such
as sulphur dioxide. Air pollution is associated with increased hospital
admissions for cardiovascular diseases with increases in acute morbidity and
mortality. D'Ippoliti et al studied 6531 patients in Rome who were
hospitalized for acute myocardial infarction from January 1995 to June 1997. Air
pollution data were taken from 5 city monitors. Positive associations were found
for total suspended particulates, NO2
and CO. The strongest and most consistent effect was found for total suspended particulates.
Hydrocarbon pollutants also
escape into the air through fuel evaporation - evaporation causes significant
hydrocarbon pollution from cars on hot days when ozone levels are highest.
Evaporative emissions occur several ways:
Diurnal: Gasoline evaporation increases as the temperature rises
during the day, heating the fuel tank and venting gasoline vapors.
Running Loses: The hot engine and exhaust system can vaporize gasoline
when the car is running.
Sitting Evaporation: The engine remains hot for a period of time after
the car is turned off, and gasoline evaporation continues when the car is
Adding Fuel: Gasoline vapors are always present in fuel tanks. These
vapors are forced out when the tank is filled with liquid fuel.
(See Cars and Pollution US EPA Fact Sheet OMS-5)
Benzene is the main toxin in the hydrocarbon fraction of
exhaust. Benzene and other less known hydrocarbons are produced in petroleum
refining, and are widely used as solvents and as materials in the production of
various industrial products and pesticides. Benzene also is found in gasoline
and in cigarette smoke. Other environmental sources of benzene include gasoline
(filling) stations, underground storage tanks that leak, wastewater from
industries that use benzene, chemical spills, and groundwater next to landfills
containing benzene. Exposure to benzene can cause cancer, especially leukemias
and lymphomas. Benzene has a suppressive effect on bone marrow and it impairs
blood cell maturation and amplification.
Polycyclic aromatic hydrocarbon (PAH)
PAHs are a group of chemicals that are formed during the incomplete burning
of coal, oil and gas, garbage, or other organic substances. PAHs can be man-made
or occur naturally. A few of the PAHs are used in medicines and to make dyes,
plastics, and pesticides. They are found throughout the environment in the air,
water and soil. There are more than 100 different PAH compounds. Although the
health effects of the individual PAHs vary, the following 15 PAHs are considered
as a group with similar toxicity: acenaphthene, acenaphthylene, anthracene,
benzanthracene, benzopyrene, benzofluoranthene, benzoperylene,
benzofluoranthene, chrysene dibenzanthracene, fluoranthene, fluorene,
indenopyrene, phenanthrene, pyrene.
Long term solutions require reduced combustion of all kinds. While
vehicles with new energy sources such ethanol, biofuels, propane and natural gas
can contribute to reduced air pollution, their benefit is limited if vehicle use
continues at current intensities. If you pay more money to buy a hybrid car, but
drive it more, you have contributed little to solving air pollution problems. If
you buy a gas guzzling clunker and use only one gallon of gas to go 15 miles
each week, you have contributed more to the solution.
The problem with all alternative fuels is that the manufacture of fuels
requires energy, distribution with a manufacturing infrastructure that consume
energy, often derived from burning fossil fuels. No alternative fuel is ideal.
Switch to Biofuels
Ultimately cars might burn hydrogen in fuel cells, but
despite working prototypes, a hydrogen economy is a distant fantasy. There are
many problems to be solved before hydrogen can replace fossil fuels as a
portable energy source. The biggest problem is that producing hydrogen requires
a large amount of energy. In Canada, there are opportunities to dam rivers and
produce electricity with falling water, a non polluting, renewable energy
resource. A more problematic energy source would be be nuclear reactors that
"burn" uranium or plutonium. Even if new non-polluting energy sources are developed,
hydrogen storage and distribution requires a new, very expensive infrastructure that could
replace gasoline and diesel fuels.
With once rich countries such as the USA on the verge of bankruptcy and
facing the extensive repairs of already aging, derelict infrastructures, adding
a new, unprecedented development costs seems unlikely. Unless, of course the
priorities in the US shift dramatically. The US, for example, could adopt a
sane, smart strategy, reduce its military budget by 50% and invest the money and
skills in rebuilding the country's infrastructure with new sustainable energy
Car Emissions Testing - The Volkswagen Scandal
in Sept. 2015 a scandal erupted when Volkswagen, the world's largest car
manufacturer, was caught cheating on emission tests of their diesel engines. In
testing lab conditions, VW could show conformity with emission standards.
Subsequent independent testing of VW diesel vehicles in road tests revealed high
levels of nitrogen oxides emitted in real operating conditions. Errors in media
reports proliferated with talk of defeat devices and software that would fool
emission tests. Relevant engineering data was not available but likely the cause
of the problem was the Nitrogen Oxide converter (aka NOx storage catalytic converter ) that required injections of unburned fuel to keep the
converter clean and functional. The exhaust output was supposed be free of nitrogen oxides.
The computer that controlled fuel injection was programmed to inject more fuel than was needed for combustion for
about 2 seconds per minute. The fuel reaching the converter would burn increasing the temperature in the converter. Burning the diesel fuel in the converter would likely increase the emission of other air pollutants.
The software functioned optimally for emissions testing and turned down or off when the
engine was in service. The NO converter was a poor design that would increase
fuel consumption and decrease engine performance if the converter was operated for full
Jack Baruth advocated the end of diesel cars and pickup
trucks. He stated: "Western democracies encouraged diesel even though they were
perfectly aware of the health hazards posed by diesel particulate exhaust. Those
risks are far better documented than even the most "settled" climate science,
and they are very real. Eurocrats chose
diesel in order to be seen to be doing something about global warming, and the
manufacturers had to abide by their choice. The result? Paris has had to ban
cars for hours or even days at a time because of smog. According to The
Guardian, "diesel-related health problems cost (the British National Health
Service) more than 10 times as much as comparable problems caused by petrol
fumes. Last year the UN's World Health Organization declared that diesel exhaust
caused cancer and was comparable in its effects to secondary cigarette smoking.
And that was when people thought that these diesels were meeting pollution
standards! Now, of course, we know that many of them were not, and that even the
diesel cars that weren't designed to cheat the tests are not performing in the
real world the way they do in the test labs. In other words, diesel-powered
automobiles are killing people, and in not inconsiderable numbers. The jury is
in and the evidence is clear." (Jack Baruth. Road & Track. Oct 2015)
A review in the Science journal, Nature, questioned the
relationships between auto manufacturers and regulatory bodies: "Among the
questions raised by the scandal that allowed the German car maker Volkswagen to
sell 11 million vehicles containing software that cheats emissions tests, many
will ask why the regulators failed to notice and halt the practice. The answer
is not complicated. Regulated industries exert massive, discreet pressure on
regulators such as the US Environmental Protection Agency (EPA), to stop them
doing their jobs properly."
To put the VW scam in perspective, the company's diesel
cars are uncommon in in the USA and Canada and only contributed a small amount to air
pollution, compared with other sources, even with high nitrogen oxide emissions.
The big problems were corporate cheating and deliberate
violation of public trust. It appears that this deception will cost VW several
billion euros and is an embarrassment for all of Germany. Regulatory agencies
have been alerted to their limitations and will be changing testing procedures
for all new engines that include monitoring emissions during real driving tests
in real driving conditions.
Selective Catalytic Reduction
The best method of cleaning diesel exhaust is Selective Catalytic Reduction
(SCR) which converts oxides of nitrogen (NOx) emissions into benign nitrogen gas
and water. SCR can deliver near-zero emissions of NOx. The NOx reduction process
starts with an efficient engine design that burns clean Ultra Low Sulfur Diesel
(ULSD) and produces inherently lower exhaust emissions—exhaust that is already
much cleaner due to leaner and more complete combustion. The vehicle’s onboard
computer regulates the addition Diesel Exhaust Fluid (UREA) in precisely metered
spray patterns into the exhaust stream just ahead of the SCR converter where the
conversion happens. Together with the catalyst inside the converter, the mixture
undergoes a chemical reaction that produces nitrogen gas (N2) and water vapor.