So long as you own a vehicle, you will, at regular intervals have to put gasoline (petrol) in the tank. On several occasions (especially when there is looming or imminent fuel scarcity) people get to the fuel station and utter the phrase “fill it up” or “fill-up”. Most often, the attendant takes it literarily and makes sure the tank is filled till it spills over, sometimes rocks the vehicle a bit and add more till saturation.

What most people however are unaware of is that, a lot of damage is being done to the vehicle and eventually to the owner’s finances and the environment.

When we think of vehicle emissions, we often think of the dirty stuff coming out of the exhaust. The internal combustion process creates noxious chemicals that are released into the air as we drive. But tailpipe emissions are controlled using a variety of systems like catalytic converters, and exhaust gas recirculation systems.

However, there is another type of emission that comes from our cars. They’re called evaporative emissions. The gasoline in your fuel tank and fuel lines slowly evaporates over time, releasing volatile organic compounds into the air.

Because of their harmful nature, carmakers are required to install evaporative emissions control systems onto every new car and truck they build.

The fuel we put in our cars contains more than 150 chemicals, including benzene, toluene and sometimes even lead. These ingredients can cause dizziness, breathing problems and headaches when they’re inhaled. Inhaling large amounts of fuel fumes can even cause death.

For these reasons, carmakers are required to install systems on their vehicles that help mitigate gasoline evaporations. Environmental regulation in the United States began in earnest in the early 1970s, and as a result, cars have had evaporative emission control (EVAP) systems ever since. These systems are designed to store and dispose of fuel vapors before they can escape into the atmosphere.

A typical system consists of a small canister full of charcoal, valves, hoses, and vents in the fuel lines and a sealed fuel tank cap. When fuel evaporates inside the tank, the excess vapors are transferred to the charcoal canister. They’re stored there until they can safely be transferred back to the engine to be burned.

When that’s ready to happen, a valve creates a vacuum that draws the vapors into the engine. Fresh air is also drawn in through the vents and valves to mix with the vapors for better combustion. These systems can be controlled mechanically, or like on most on newer cars, through the engine’s computer. The computer tells the valves when to purge the canister of vapors. This typically happens when the car is in motion, rather than at idle. It’s just one example of some of the behind-the-scenes technology that you’ll likely never see or feel.

As you may expect, things can go wrong with the EVAP system, too. If the canister fails to purge or does so under the wrong conditions, it can hamper the performance and emissions of your vehicle. When this happens, you may find that the entire system needs to be replaced.

The good news is that there are things you can do to prevent your gasoline from evaporating (or at least slow the process down a little). First and foremost, make sure your fuel cap is secured tightly. If you don’t have a fuel cap, get one. Seriously. That old rag you stuffed in there isn’t doing you any favors. Fuel can escape right out of your tank if it’s not airtight.

Second, whenever possible, park in the shade. Even though modern cars have advanced EVAP systems to prevent too much evaporation from occurring, gas does still evaporate from the tank, especially when the car is parked in the sun. This is even worse when it’s extremely hot outside. Parking in the shade helps keep the entire vehicle cooler and reduces fuel evaporation.

Buy your fuel in the early morning or later at night. It’s warmer in the afternoon and early evening, which means evaporation is more prevalent. That’s why you’re sometimes hit with that nasty smell at fuel stations during the heat of the day.

Most important of all, DO NOT over-fill your fuel tank. Quite a number of fuel stations are now equipped with automatic shut-off dispensers, STOP filling the tank when the nozzle clicks-off. This gives room for the fuel to expand (especially in the afternoon).

When the tank is over-filled, as against vapor going into the charcoal canister, raw fuel (liquid) flows in, causing damage to the parts on the EVAP system, thereby leading to increased emission.

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