Automotive Air Pollution (for non-specialist citizens)

Introduction: While surfing the net recently (2021-02-15) I began bumping into articles and blog posts about the Volkswagen AG debacle currently going by the internet meme Dieselgate. Most contain a lot of errors, while some contain almost no facts. I believe this is partly due to the fact that many modern citizens skipped secondary school chemistry, or know next the nothing about technology. Simply put, Dieselgate cannot be fully understood without understanding things like:

  1. what is smog?
  2. how did initial industry efforts to reduce pollution only changed smog color?
  3. how do automobile manufacturers reduce smog this side of Y2K?
  4. what is the 'Cole's Notes' version of Dieselgate?

This article is not finished (I have been called away to deal with other more-pressing issues)

Setting the stage

Circa 1965 in North America, passenger automobiles and small trucks were powered by gasoline (petrol for you Brits) which was relatively cheap (45 cents per Imperial gallon in Canada). Buses and large trucks were powered by diesel which usually belched black smoke during acceleration. Since gasoline was cheap, and everyone wanted to go fast, every red-blooded male wanted to own a muscle car. But two were problems looming.

  1. POLLUTION: There has always been national clean air clean legislation in the USA (here are two examples: 1956 and 1963) but the American nation started thinking differently after Apollo 8 snapped pictures of a fragile-looking Earth from lunar orbit. With pressure from both political parties, Richard Nixon created the EPA (Environmental Protection Agency) on 1970-07-09 with a mandate to prosecuting environmental laws in order to protect air and water.

    comment: Nixon also created NOAA (National Oceanic and Atmospheric Administration) in 1970-10-03 after a federal government reorganization.
  2. PRICE: In 1973, a coalition of Arab nations attacked Israel in what is now known as the Yom Kippur War. The Nixon administration backed Israel which triggered the Arab nations to seek revenge by having OPEC embargo oil exports to North America. That immediately elevated the price per barrel of crude oil from $3 to $12. Since then the price of oil has skyrocketed and gasoline followed.


Smog has been around since before the start of the industrial revolution. Yellow Smog was first observed in Great Britain and was usually associated with burning high-sulfur coal (eg. Lignite is one example). I mention this here because non-technical people reported seeing yellow smog in California during the late 1960s where virtually no one was burning coal but every family seemed to own two cars. Also at that time, people reported seeing brown smog as well as gray smog.

Scientists and engineers know that the color of NO2 (nitrogen dioxide) can be perceived as reddish-orange to reddish-brown so now we have a possible explanation for the brown smog. In the presence of water, NO2 can be transformed to HN03 (nitric acid) which is pale yellow, and this is a possible explanation for yellow smog seen in California.

Grey smog is usually associated with soot produced by burning coal (or wood) but since California is a warmish state, engineers assumed this was unburned hydrocarbons from cars (so gasoline) or buses and trunks (so diesel). Since fuel was becoming expensive and pollution was in the rise, automotive engineers decided it was time to make vehicles more fuel efficient.

Improving Engine Efficiency

Energy is lost whenever any engine, either gasoline or diesel, is releasing unburned hydrocarbons (CHx), carbon monoxide (CO) or soot (C). Solutions include:
  1. increasing the oxygen/fuel ratio
    • Carburetors
      • Fifty-years ago, many vehicles employed a carburetor to mix fuel with atmospheric air before presenting it to a combustion engine. A carburetor is nothing more than a glorified perfume atomizer where the starting mixture is controlled by turning a screw (rich vs lean). In 2021 my property maintenance machines (snow blower, lawn mower, weed-wacker) still employ carburetors.
      • A simple carburetor tuned to work efficiently at sea-level might not behave properly when you drive to a mountainous area where atmospheric air pressure is lower, so mechanical feedback mechanisms were introduced to add-to, or subtract-from, the starting setting
    • Supercharger (and turbocharger)
      • Things were different in the aircraft industry where huge changes in pressure and temperature made carburetor use unreliable. So many non-jet aircraft designers employed superchargers to ensure that sufficient air and fuel were always available. Most people today seem to be unaware of the fact that superchargers predate the invention of powered flight and horseless carriages.
      • Initially, superchargers were only available on expensive most racing equipment as well as expensive European autos but as time moved forward they began to appear in the consumer space.
      • Alert: a supercharger "is a pump which requires power" which, almost always, comes from the engine via a crankshaft belt. Superchargers "powered by engine exhaust" are called turbochargers
  2. improving fuel evaporation from a liquid to a gas
    • according to Boyle's law, a supercharger (or turbocharger) will cause fuel droplets to evaporate as soon as the pressure is increased.
    • some solutions preheat the air-fuel mixture as it passes through the intake manifold  
  3. improving engine design
    1.  Wikipedia's article titled Chrysler's hemispherical engine is good so i won't repeat this here

Details about burning Gasoline ('petrol' for you Brits)

CO2 moleculeAt first glance it seems impossible (to a non-scientist) that:
burning one U.S. gallon (3.8 L) of octane (C8H18)
which weighs approximately 6 pounds (2.7 Kg)
will produce produce produce 18 pounds (8.16 Kg) of carbon dioxide (CO2)

However, most of the weight of CO2 does not come from the gasoline itself, but the oxygen from the atmosphere. When gasoline burns, the carbon and hydrogen separate. The hydrogen combines with oxygen to form water vapor (H2O) while the carbon combines with oxygen to form carbon dioxide (CO2). A carbon atom has an atomic weight of 12, and each oxygen atom has an atomic weight of 16, giving each single molecule of CO2 an atomic weight of 44 (12 + 2 x16 ). It now appears that that Carbon Capture and Storage (CSS) technology will never be practical since the required amount of energy to compress-store this volume of gas would be too large.

  • The players in this drama
    Substance Chemical Formula Notes
    Molecular Oxygen O2
    Octane (gasoline or petrol) C8H18
    Carbon Dioxide CO2
    Water H2O
    Molecular Nitrogen N2 an inert gas at room temperature
  • Atomic Masses from the Periodic Table:
    Element Atomic Number Atomic Mass
    Hydrogen 1   1
    Carbon 6 12
    Oxygen 8 16
  • (balanced) Burn Equation: 2 C8H18 + 25 O2 → 16 CO2 + 18 H2O (reference)
  • Gasoline Mass Calculation
    • Total octane mass (from the left-hand side of the equation):
      • 2 x ((C x 8) + (H x 18))
      • 2 x ((12 x 8) + (1 x 18))
      • 2 x (96 + 18)
      • 2 x 114 = 228
    • Total Oxygen Mass (from the left-hand side of the equation):
      • 25 x (O x 2)
      • 25 x (16 x 2)
      • 25 x 32 = 800
  • Carbon Dioxide Mass Calculation
    • Total Carbon Dioxide mass (from the right-hand side equation):
      • 16 x ((C x 1) + (O x 2))
      • 16 x ((12 x 1) + (16 x 2))
      • 16 x (12 + 32)
      • 16 x 44 = 704
    • Ratio: 704 / 228 = 3.09 (therefore the resultant CO2 is ~ 3 times heavier than gasoline)
  • Water Vapor Mass Calculation
    • Total Water Vapor mass (from the right-hand side equation):
      • 18 x ((H x 2) + (O x 1))
        • 18 x ((1 x 2) + (16 x 1))
      • 18 x (2 + 16)
      • 18 x 18 = 324
    • Ratio: 324 / 228 = 1.42 (therefore the resultant water vapor is ~ 1.4 times heavier than gasoline)

The Diesel Scandal (article scaffolding; this is not complete)

  • diesel engines are built to higher tolerances because they have much higher compression ratios
  • the compression ratio is so high that most engines do not require a spark plug
    • as each piston finishes "the compression stroke" the temperature rises (Gay-Lussas's Law) causing the fuel to automatically ignite
    •  some systems employ glow-plugs to to help start the engine on very cold days
  • Atmospheric Nitrogen is usually inert. But at the very high temperatures resulting from higher compression ratios, combined with very lean fuel (read as too much oxygen in order to enure that 100% of the fuel is burned), Diesel engines to convert atmospheric (diatomic) nitrogen (N2) into pollutants like these few of many:
    NO Nitrogen Monoxide
    Nitrogen Dioxide
    Nitric acid
  • In order to limit the production of these pollutants, diesel engines employ a chemical product known as AdBlue® which is injected into the exhaust system.
  • When the chemical runs low, a blue light (or LED) is illuminated on the dash telling the owner to visit the dealer (many people buy the chemical at a big box store then fill it up themselves)
  • Now the story gets weird:
    • Volkswagen upper management wanted to sell more diesel vehicles around the world as a greener alternative to gasoline engines; but the consumer grumbling about AdBlue along with some complaints that some drivers need to refill the AdBlue reservoir 3-4 times a year appeared to be limiting sales
    • Without consulting their engineers, management announced that Volkswagen was going to produce an diesel engine that did not require AdBlue. Rumor has it that they spent $100 million before giving up (if asked ahead of time, the engineers would have told management that what was being proposed was impossible)
    • So after spending a bunch of money with nothing to show for it, Volkswagen began selling diesel products which:
      • did not employ AdBlue
      • Volkswagen claimed were cleaner than other diesels but were actually dirtier
      • contained a software patch to the engine software (also called firmware) that could detect when the engine was being environmentally tested. At that time only, the system would alter engine parameters in such a way as to reduce engine performance (including temperature) which would reduce the production of nitrogen pollutants.
    • IMHO Volkswagen management was very naive because their competitors were also looking for solutions to eliminate AdBlue so would, most likely, be looking for a way to copy (or cross-license) Volkswagen's solution to this problem.


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Neil Rieck
Waterloo, Ontario, Canada.