
Reviewing SMOG Prevention Measures
We have seen that areas with smog problems tend to be major cities as that is where there are lots of (dirty) vehicles. Smog is also an issue in areas close to major refineries such as the Texas basin where much of the refining capacity for that region is located (because of Texas oil and offshore oil from the Gulf of Mexico). So if there are 4 things needed to form smog, then we can reduce smog by reducing the precursors. There is not much we can do to block out the sun, or to reduce the outside temperature, so we are limited to reducing the precursor emissions of NOx and VOCs. In particular, we need to reduce or eliminate the anthropologic emissions of NOx and VOCs.
Reducing VOCs

We have already discussed reducing the volatility of the gasoline fuel as one method of reducing the VOC emissions. This takes place in the blending stage of the refinery operation. By limiting the quantity of the more volatile compounds, the gasoline will evaporate less. This results in the refinery having larger quantities of light compounds to dispose of (in less profitable ways) which raises the cost of the gasoline just as do all the approaches where something needs to be changed. This reduced volatility fuel is a "summer blend." The lower temperatures of Fall, Spring, and Winter reduce the gasoline emissions, and thus reduce smog formation because smog requires warm (mostly summer) temperatures.
So the summer blend is only used in the summer and only in those locations with poor air quality (non-attainment area). You might ask how do gasoline vapors escape? When you "fill her up" the first thing you do is open the cap to the gasoline tank. What happens next on a summer day? Hsssss.... Gasoline vapors escape! And it is not only from the open "gas" tank, but also other locations: from the engine, the exhaust, fuel lines, and the gasoline tank. One approach is to capture these vapors from the tank with special nozzle attachments on the metal part of the gasoline hose. While it won't capture all of the volatile gasses escaping from the moment you unscrew the cap, it will capture the vapors that will be displaced by filling the tank up with gasoline. These vapors are cooled back into a liquid and sent back to the refinery.
Other Approaches...
- Not overfilling the tank also prevents gasoline spills (and fires — how may people have you seen smoking while filling up?)
- Another approach is to fill up at times when the smog formation opportunities are lowest, such as in cooler evening hours (not enough sunlight and lower temperatures). This includes our use of the many gasoline-powered tools we tend to have, such as lawnmowers, weed whackers, etc. Filling up your lawnmower in the evening would also reduce VOC emissions.
- Oxygenated fuels also reduce VOC emissions because the oxygen within the fuel enhances the mixing process of fuel with oxygen, and so less fuel (VOCs) will escape the combustion process. The catalytic converter will also oxidize some of the escaping VOCs to water and carbon dioxide.
Reducing NOx From Vehicles
This table provides a quick summary of the methods used to reduce NOx emissions in vehicles. For those of you keeping score at home, the information here combines NOx emissions issues from this lesson, earlier lessons, namely Transportation (L05), and issues in upcoming lessons: Climate Change (L11 & 12), and Acid Deposition (L10).
Method | Result |
---|---|
Oxygenated Fuels | The addition of MTBE (or ethanol) in the summer reduces NOx by lowering the temperature of the combustion process. |
Alternative Fuels | Methane (compressed natural gas), ethanol, etc. will have lower levels of NOx emissions. |
Catalytic Converter | The NOx is reduced to N2 in the catalytic converter. It does not eliminate emissions but it will drastically reduce the emissions. However, all our gasoline vehicles have them, so this is not a solution to our current problems as it is already in place. |
Improved Catalytic Converters | One of the reasons to reduce sulfur from gasoline to very low levels is because the S (as a catalyst poison) would reduce the effectiveness of the catalytic converter. The new lower S standards (<30 ppm S in gasoline) allow for better catalytic converter operation and also newer more effective catalysts. |
Hybrid Cars | Hybrid cars manage to reduce pollutant emissions via a combination of higher efficiencies and perhaps by utilizing the electric engine in those already polluted areas such as the centers. In Europe, one proposal would require that gasoline-fueled vehicles be banned from the inner city parking areas thus encouraging the use of cleaner cars. Thus, a hybrid might function as a gasoline engine for the commute to work but as an electric engine when within the city. |
Emission Free Vehicles | Electric or fuel cell cars have no NOx emissions from the vehicle itself. Encouraging their use (fleet vehicles, tax credits, parking availability-fuel cell car only, and other approaches such as allowing these cars in high occupancy vehicle lanes with 1 driver and no passengers) would aid electric vehicle adoption. |
Getting Old Cars Off the Road | A few vehicles are the cause of much of the pollution. If we have a buy-back of your old Junker program (then squish the car and recycle it) we can remove them from the road. Emission checking (emission inspection along with the traditional vehicle inspection) is also a key component of ensuring the pollution control equipment within the car is functioning but also for failing super and high polluting vehicles. Emission Inspections are often required in vehicles in non-attainment areas. |
Efficiency and Conservation AGAIN! | Always a right answer! All the methods of increasing vehicle efficiencies, such as increases in MPG and passenger occupancy, and the uses and development of more efficient methods of public transportation, are again applicable here and are all discussed in detail in Lesson 5 for those of you who would benefit from a review. |