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:

what is smog?
how did initial industry efforts to reduce pollution only changed smog color?
how do automobile manufacturers reduce smog this side of Y2K?
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.

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.
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

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 (CH_x), carbon monoxide (CO) or soot (C). Solutions include:

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
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
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)

At 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
NO2	Nitrogen Dioxide
HNO3	Nitric acid