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Understanding Vehicle Smog

Do you breath in the stuff that comes out the tail pipe of your vehicle?

Someone else does!

We have all driven behind an old vehicle (or diesel truck) that gives off a lot of "smell" and soot/ fumes .... and you do not want to breath those smells either, they are toxic! 

Fortunately vehicles do not last forever, and the vehicles that replace old ones are almost always much cleaner (in terms of their operating emissions). That said, even the cleanest vehicles emit something dirty and toxic... tire dust for example is released by fuel cell and electric vehicles the same way that tire dust is released by conventional vehicles.
A great example of particulate matter emissions! 

Smog brings to mind places like Mexico City, Beijing China, and Los Angeles California. Smog is a soup of funky toxic chemicals suspended in the air. Soot from diesel engines and coal power plants, that fine particulate matter that causes asthma, lung cancer and chronic obstructive pulmonary disorder; known as PM, it is a major component of urban smog. 


Particulate Matter, the fine dust/ soot released from the incomplete combustion of fuels / the dark funk you see emitted from diesel trucks and buses and older diesel passenger cars. Due to the health effects of particulate matter, various governments have created regulations both for the emissions allowed from certain types of pollution sources (motor vehicles, and for the ambient concentration of particulates. Many urban areas in the U.S. and Europe still frequently violate the particulate standards because of the over-use of private and commercial vehicles.

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Irritating ground level ozone that disturbs the mucus membranes in our eyes, mouths and lungs. It forms when VOC and HC emissions (fuel vapor fumes) bake in the sunlight, where the UV energizes chemical reactions that form Ozone.

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VOC's from fuel that exits tailpipes un-burned (incomplete combustion). People literally huff on fuel vapors to get high breathing in VOC's. Sadly, we are all exposed to persistent low levels of these same chemicals from traffic corridors. Un-burned gasoline vapors exit the exhaust of a vehicle as HC or hydro-carbon, a regulated air pollutant. We all breath these fumes, some of us more than others, and it is the daily low level exposure over long periods of time that causes the negative health problems associated with breathing in transportation emissions or smog.

Read about the health effects of breathing gasoline vapors:

VOC/ HC Fumes/ Vapor/ Smoke  : Image From
Acid Rain

NOX and SOX : Oxides of sulfur and nitrogen from vehicle emissions mix with water vapor to form weak sulfuric and nitric acids in the rain water. This rains down on infrastructure accelerating the corrosion of metal and destruction of oxide/ silicate bonds in cement, masonry and rock and stone. Acid rain causes billions of dollars worth of accelerated degradation of human infrastructure. 

NOX is a generic term for mono-nitrogen oxides NO and NO2 (nitric oxide and nitrogen dioxide). They are produced from the reaction of nitrogen and oxygen gases in the air during the combustion of fuels, especially at high temperatures and pressures (inside engines). 

NOx gases are formed everywhere where there is combustion – like in an engine, because the air being sucked into the engines is primarily composed of Nitrogen. When this nitrogen rich air is reacting with the fuel in the engine to burn producing power and heat, some of the nitrogen reacts with the oxygen in the air at the high temperatures and pressure in the combustion, forming NOX emissions. 

Sulfur Oxides are oxides of sulfur that form when sulfur is present in the fuel (mostly a problem with low quality and cheap diesel fuels). When the sulfur burns inside the engine, it reacts and forms sulfur oxides, which then exit in the exhaust stream. In the environment, sulfur oxides react with water to form weak sulfuric acid and ultimately acid rain.

Acid rain also poisons natural water systems like lakes and rivers. Acidification of these eco-systems by acid rain disrupts their ability to support life. 

Nitrogen Dioxide Red Orange Color Over Madrid Spain
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Carbon Monoxide: it is the gas that kills many people every year when they run engines *vehicles or power generators* without adequate ventilation indoors. Some people even commit suicide by intentionally running their vehicles in a closed garage until the carbon monoxide levels from the exhaust reach deadly levels.

Carbon monoxide forms from incomplete fuel combustion: in a reaction where oxygen levels are insufficient to completely oxidize the carbon from the fuel into CO2. 

CO reacts with other ground level air chemicals to form ground level ozone. CO is a psychoactive gas, producing mild intoxication when it is inhaled. Many smokers derive joy from this because the incomplete combustion occurring in their cigarettes produces psychoactive quantities that augment the effects of the tobacco. 
Inhaling elevated levels of CO from a dirty transportation corridor is mildly toxic. It is not the CO alone that is the problem, it is the CO level along with all of the other smog forming chemicals in the emissions that forms the harmful rainbow of chemicals in smog.


Carbon Dioxide = What we exhale = major product of the combustion of fuel.

Burning fossil fuels such as coal and petroleum is the leading cause of increased industrially released CO2. CO2 is the majority component of vehicle emissions.

CO2 in water forms carbonation (think soda pop), but in the lakes and oceans and rivers this increased acidity is bad for many lifeforms.

Transportation emissions release CO2 at such a large scale that these CO2 emissions have a measurably negative effect on climate, weather and ecological systems.


Often emissions test for CO+CO2 as a measure of combustion efficiency. An ideal burning of a hydrocarbon would only release water vapor and carbon dioxide.

CH4 + 2 O2 → CO2 + 2 H2O + energy

Methane + Oxygen -> Carbon Dioxide + Water 

Unfortunately engines are far from ideal, and the real chemistry of combustion is very complicated as a result. The pollutants in exhaust are what we call the byproducts of combustion.

Bad fuel air ratios that cause noxious emissions are caused by the engine operating outside of its ideal rpm range. Engines have only one speed at which they produce the best ratio of power output to low emissions. 

Unfortunately to work with transmissions for variable vehicle speed and power output variation, engines must operate over a wide range of speeds from idle to redline.

You can read a very interesting article about how engines work on 

Ars Technica: More Bang Less Buck : Going Farther on Less

Incomplete combustion also causes particulate matter and VOC/ HC to form. These dust/ soot/ vapors are extremely toxic: they are the parts that give some of the color and most of the nasty smell to vehicles exhaust and smog.  

Toxic vehicle emissions are especially notable in older vehicles with inefficient engines, but you can smell them in the exhaust of newer vehicles too; they are most pungent when the engine is cold and first starting up after having cooled off completely. Warm engines burn more cleanly than cold engines. Using a block heater for example to preheat the engine can dramatically reduce cold start emissions, especially in very cold climates. 

At idle an engine produces excess VOC/ HC because the engine cannot burn its fuel completely at low speeds. These emissions react with sunlight (photo-chemical smog) forming hundreds of compounds in smog, and contributing greatly to ground level or tropospheric "bad" Ozone. 

Traffic congestions that causes stop and go traffic results in a lot of engine idling, and thus increases the amount of HC/ VOC in the air hanging around the traffic corridor. You can see and smell the plumes of smog forming over interstate 5 in California when stop and go traffic is combined with low wind conditions and warm temperatures. You can almost always "Smell" stop and go traffic congestion. 

SOX's, NOX's, CO and VOC's / HC's in vehicle emissions are the chemicals responsible for smog formation. All engines that "burn" a fuel release smog forming emissions.

Vehicles that burn oil or petroleum products and distillates (gasoline, diesel, natural gas, propane or another hydrocarbon) all suffer from incomplete and non-ideal combustion that produces nasty smelly and toxic smog forming emissions. 

Hydrogen combustion engines are one example where the only emission is water. The high cost of hydrogen, and technical difficulties in storing it efficiently, make hydrogen impractical as a fuel for internal combustion engines. Hydrogen is more feasible to use in fuel cells because the fuel cells make much more efficient use of the hydrogens potential chemical energy. Within the next 10 years hydrogen fuel cell vehicles will become widely available to consumers. 

Essentially a hydrogen fuel cell vehicle is an electric vehicle with a chemical battery that can be refilled quickly at a hydrogen refueling station. Fuel cells produce electricity from the fuel they consume, and are often referred to by the name of the fuel used "hydrogen fuel cell".

Technical problems and cost problems with fuel cell manufacturing and hydrogen production and distribution have prevented large scale commercial application of fuel cells in vehicle power systems thus far. Honda's FCX-Clarity is an example of a fleet functioning prototype fuel cell vehicle in use today by customers of lease the vehicle from Honda for $600 per month. 

The CO2 emitted by vehicles is a major source of anthropogenic carbon release. It is this vehicle emission CO2 and CO2 released from Coal Power that has politicians talking about carbon offsets and carbon trading credits and carbon sequestration.

Atmospheric sciences have created a lot of evidence to support the conclusion that vehicle emissions are affecting and in many ways accelerating climate change. The term "global warming" is often applied to this phenomenon, but the term "warming" does not match up with our observations: some regions are cooling down. As the climate changes weather patterns change. Some areas will flood more now while other areas will experience longer and more sever drought. With climate change we should observe odd changes in weather patterns throughout the world that "break" historical records.

The release of CO2 at the scale involved with transportation increases the green-house effect in earths atmosphere, which subsequently affects climate and weather by trapping more of the suns thermal energy in our atmosphere. Transportation carbon emissions at the global scale are having wide ranging climate consequences that include drought, flood, changes in weather patterns and increased storm system energy. Study how a hurricane forms and think about how the net increase in trapped solar energy will affect hurricane formation and intensity.

Emissions Controls

A wide range of different technologies are employed to reduce smog forming emissions. Catalytic converters for example use the waste heat in the exhaust to energize a ceramic/ metal "sponge" of catalysts metals that break down many of the toxic emissions into their non-toxic constituent chemical parts, facilitating post combustion reaction completion and chemical reduction of noxious emissions species like NOX, CO, VOC and SOX.

The US Clean Air act was pivotal for the development of emissions reduction technology. Robust scientific and technological development in emissions control systems resulted from government policies derived from the clean air act "pushing" industry to clean up. Public policy can be a major source of inspiration for the private sector. Public policy that rewards "positive" business practices tends to be far more effective than public policy that punishes "bad" business practices. Automakers were given all sorts of positive incentives to develop effective and durable emissions controls technologies, and they did. Modern cars are at least two orders of magnitude cleaner than the carbureted gas guzzlers of 50 years ago.

Sadly much of the innovation gained in engine design was applied to making engines more powerful, rather than making them more fuel efficient. A 2.4L 4 cylinder engine from a 2012 vehicle makes as much power and torque as a 4.0L engine from the early 1990's: while releasing dramatically less smog forming emissions. Despite impressive refinements of engine design, most vehicles still only achieve poor fuel economy (around 23MPG real world). This is partially due to the fact that vehicles are much larger today than they were in the past. As the American people have become larger, so have our vehicles. So the innovations in engine design have been "eaten" up by making smaller more powerful motors that pull larger vehicles: while the fuel economy remains relatively unchanged. In engineering you cannot get something for nothing, and all of the rewards gained in engine innovation were applied to increasing power output, durability, and cleaner emissions in smaller engines.

Modern vehicle emission control systems combine catalyst technology with vapor recovery, advanced engine control, precise fuel control, variable valve control, air injection, and re-circulation technology.

Technologies that rapidly heat up the engine help to reduce cold start emissions (some of the worst). Particulate filtering technology is applied to modern "clean" diesel vehicles. Variable valve timing, direct injection, displacement reduction combined with turbo-charging: there are a number of technologies and methods that automakers are using to improve fuel economy while also reducing emissions.

One largely ignored aspect of vehicle design is aerodynamics. Look at an aircraft and compare it to a vehicle! Aircraft have to be aerodynamic to function efficiently at high speeds. Automakers have ignored aerodynamic design because it is a complex area of refinement that requires a lot of computer simulation testing and wind tunnel testing. The boxy shape of most vehicles (even ones with rounded edges) is an intrinsically inefficient design for cutting through the air efficiently. 

A vehicle really does have to cut through the air, air is a fluid (gas) and it is heavy when you move through it at high speeds. Try sticking your head out the window of a car traveling at 100MPH and you can feel the weight force of the air pushing against you. It turns out that at 50MPH, most vehicles have to apply a lot of energy just to push the air out of the way, because of their boxy designs. Teardrop and egg shapes do better (think of the Nissan Leaf and Toyota Prius). 

Aesthetics seem to be the driver of vehicle aerodynamic design... vehicle purchases are emotional in nature, and people like to buy new vehicles that strike a visual cord in their perceptual centers. One area that automakers can improve without affecting the look of a vehicle is the underside (underbody). A well engineered system of underbody panels can make the car cut through the air more smoothly, reducing emissions and improving fuel economy. At the manufacturing level, adding these panels adds a few hundred dollars to the cost of making a vehicle. It would be nice if they at least offered these smooth underbody setups as an option, if they are not going to apply them outright to the designs. Many DIY vehicle nerds have added home spun "smooth" underbody setups to their vehicles: mostly in the "hypermiling" community with zealous hypermiling enthusiasts. 

Hypermiling is a set of driver practices employed to allow the driver to exceed the EPA fuel economy rating of their vehicle. An Australian couple known as the Taylors recently set a hypermiling record in VW passat. Look at the following article for an example.

Tires are another area of fuel efficiency that have been largely neglected by society until recently. LRR or low rolling resistance tires incorporate special compounds that reduce "flex" that wastes energy in the tire, and compounds that keep the tires "cooler" so they flex less. Putting LRR tires on your car can boost your fuel economy by %1 to %5, depending on how your drive and what kind of vehicle you are putting them on. I recently replaced the tires on my Prius with Michelin Energy Saver A/S (ironic for me because my name is Aaron Schwarz [AS] and I am passionate about energy saving/ conservation). I will need more time to track the data, but it looks like I am seeing a 2MPG boost from the new tires, and another 1MPG boost from a "more gentle" "smooth and steady" driving style.

Too much steel: another problem with most vehicles is the over-use of heavy steel. While modern high strength steel reduces that amount of steel used in a vehicle, the steel is still very heavy. Using aluminum it is possible to reduce the weight of a normal passenger vehicle by 600lbs or more. Some auto-makers like Audi used this kind of weight saving to improve performance of their expensive luxury vehicles. Mainstream consumer vehicles have only limited applications of light weight metal alternatives to steel. The reason that steel is widely used in auto manufacturing comes down to prior capital investment that auto makers put in steel fabrication infrastructure: in essence the automakers are all tooled up to cut, stamp, form and weld steel: switching to composites or other metals would require a massive investment in new tooling and production equipment. This is the reason that high strength light weight composites like carbon fiber are used in low volume niche market performance vehicles like the Tesla Roadster.  

Light and Full Hybrid Vehicles 

To address the fundamental shortcomings of an engine that must operate over a range of RPM speeds and power output levels, hybrid vehicles blend power from an electrical system with the engine to reduce emissions and improve fuel economy. 

Regenerative Breaking: hybrid vehicles run their electric motors backwards when the vehicle is being slowed or going down a hill. The energy generated by running the electric motor backwards is stored in the primary traction battery or energy storage system. This energy is then available when the driver requests power from the drive train by depressing the gas pedal.

In a hybrid vehicle a computer blends power from the battery and electric motor with the power from the internal combustion engine to improve the overall dynamics of the power-train: delivering substation improvements in fuel economy; %30 to %50 better fuel economy along with dramatic reductions of emissions; %70 to %90 improved. A Toyota Prius is a good example of a full hybrid that gets great fuel economy (~49MPG real world) while also emitting dramatically cleaner exhaust (90% reduction). These features of the Prius along with the huge interior cargo space afforded by the hatchback design helped Toyota sell millions of hybrids featuring Toyota's class leading Hybrid Synergy Drive technology. 

A mild hybrid is a vehicle with a much smaller electric power system. Typically these vehicles employ an advanced version of "idle stop" to prevent the engine from running when the vehicle is stopped at a traffic signal for example. Idle Stop is available as an option on some vehicles. Mild hybrids typically employ electric assist to the drive-train, such as in Honda's IMA (integrated motor assist) technology. While this system is much less expensive, much less powerful and not as efficient as Toyota's HSD hybrid synergy drive system, the IMA system from Honda still improves fuel economy while reducing emissions. 

Electric Vehicles

The Nissan Leaf, Tesla Roadster, Tesla Model S, and Mitsubish I-MiEV are examples of current electric vehicles. Many electric vehicles are soon to launch from dozens of automakers. 

With electric vehicles, the tail pipe is in the grid. The power used to charge the electric vehicle comes from some energy source. In a region where the energy is mostly from renewable sources like wind, hydro and solar, an electric vehicle is exceedingly clean because the power used to charge the vehicle is from non-carbon sources (non-smog forming sources ;) 

In a region where coal power is the major grid energy source, an electric vehicle is still cleaner than a gasoline or diesel vehicle when you calculate the coal emissions associated with charging the electric vehicle. One way or the other, electric vehicles are much cleaner in terms of their net emissions! 

See also: 

Plug-in Hybrids

Future Hybrids

Electric Vehicles are Cool


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