How to Drive Cleaner

Cars have gotten a bad reputation for being big contributors to air pollution. Smog is produced when hydrocarbons (like those in gasoline) and nitrous oxides (produced when combustion temperatures in an engine are excessively high) interact with the light from the sun to create a dirty fog.

But since the 1960s and 70s, car companies have been working to build cleaner engines that produce fewer pollutants. Modern cars, if maintained properly, are much more fuel-efficient and much less polluting. To keep cars and trucks running cleanly, owners must pay attention to vehicle maintenance.

Vehicle emissions (hydrocarbons, carbon monoxide, and nitrous oxides) come from three major car systems:

1. The exhaust pipe, which releases all three types of emissions into the air;
2. The crankcase, the engine case housing the crankshaft (the part of your engine that translates the push-pull motion of pistons into the rotating motion that allows the wheels to turn), which releases hydrocarbons; and
3. The hydrocarbon vapors that evaporate from the fuel system and fuel tank.

Modern engine design and devices developed specifically to control emissions help to limit the release of these pollutants. Modern cars also have internal computers which use sensors to monitor and control emissions. Keeping cars and trucks running cleanly involves maintaining all of these things.

There are literally dozens of different devices, sensors, and engine design aspects that mechanics can check and fix if a car fails an emissions test or if emission maintenance reminder lights come on, but here are some of the most common to be aware of:

1. A faulty oxygen (O2) sensor. This device is designed to measure the amount of oxygen in the exhaust gas, and when it isn’t working properly, the amount of toxic gases emitted can increase. The sensor malfunctioning can also lead to other problems, from overheating to poor acceleration.
2. A rich fuel mixture, meaning that the vehicle is burning excessive amounts of gasoline or diesel. This leads to production of high levels of carbon monoxide. This problem can be related to a faulty oxygen sensor or mass air flow sensor, or because of leaky fuel injectors or high fuel pressure, among other causes. Alternatively a fuel mixture that is too lean (too little fuel in the mixture) will cause problems as well.
3. A bad ignition system. If high levels of hydrocarbons are detected in an emissions check, this is a common cause. Improperly maintained ignition systems can have spark plugs, wires, and distributor caps that are defective or worn out, causing misfires.
4. Bad fuel metering. A computerized engine control and computerized fuel injection unit are designed to monitor and regulate the amount and rate of fuel usage. The goal of these devices in a gasoline engine is to get as close as possible to the ideal ratio of air to fuel, where all the fuel is burned without any excess air. Malfunctions in the computer system can cause fuel metering to be out of specification.
5. A bad air injection system. This system is designed to feed unburned, hot gases in the exhaust to keep them burning and so emit less hydrocarbon and carbon monoxide into the air. A malfunctioning air injection system will allow the vehicle to release high levels of these gases.
6. A bad EVAP (Evaporative Emission Control) system. This system is designed to prevent gasoline from the fuel system and gas tank from evaporating into the air by keeping it sealed. If this system isn’t properly maintained, even a parked car can release large amounts of vapors. Leaky gas caps, purge valves, and vacuums can be common causes of malfunction.

Proper maintenance of your vehicle can prevent most of these problems from occurring in the first place. Make sure to follow your owner’s manual’s recommendations for vehicle maintenance, and have your car inspected regularly to head off any potential malfunctions.