Millions of people live, work and play near major highways. Half of all Americans are exposed to unhealthy levels of air pollution each day. This close proximity to high traffic areas and the resulting poor air quality can have a negative impact on overall public health. This is due to exhaust from our cars and trucks being more dangerous than people realize. A growing body of research shows how auto emissions pose a serious threat to our health. The key contributor to this problem are toxic compounds in gasoline known as aromatics. Aromatics are known or suspected carcinogens that make up 25% of a gallon of gasoline.
Aromatics are hydrocarbons that include benzene, toluene and xylene which are often referred to as the BTX group. Aromatics are the most energy inefficient, carbon intensive, and expensive components of gasoline. They often don’t fully combust in the engine, which is why aromatics are the primary source for the formation of ultra-fine particulates (UFPs) which are one of the most dangerous and harmful pollutants to come from vehicle exhaust.
WHY ARE THEY IN GAS?
When lead was removed from gasoline because it is classified as a poison, something was needed as a replacement for octane in fuel. Aromatics were preferred by the oil industry to provide the octane boost and they were already available at oil refineries. BTX compounds naturally exist in crude oil but are also created within the oil refinery, so this allowed refineries to tweak its processes in order to boost aromatics to the levels needed. However, since these aromatic compounds are classified as known or suspected carcinogens, health groups and clean air advocates have regarded aromatics as “the new lead”—trading a poison for a carcinogen. EPA has classified them as hazardous air pollutants but has moved slowly to control them. Without sufficient controls on aromatic levels used for octane, health risks from auto emissions will only increase.
WHAT ELSE IS IN GAS?
Aromatics are just one of the ingredients in gasoline, which is a mix of hundreds of chemicals and oil derived components. While aromatics make up about 25% of gasoline, the majority of gasoline is made from saturates, which is considered the good portion of gasoline compared to aromatics. Saturates are also found in crude and produced within an oil refinery. They are good for combustion and cleaner than aromatics, but don’t provide enough octane to be used alone. The non-oil component of gasoline is ethanol, which makes up 10% of gasoline nationwide and is reducing aromatic content because it is a much cleaner and higher octane additive.
WHY DOES OCTANE MATTER?
When you pull up to a gas pump, the numbers on the buttons represent the octane rating of the fuel. Octane is needed to prevent the air/fuel mixture in your engine from detonating prematurely causing a knock or pinging noise under high load. Back in the day, you would actually hear a knock under the hood when this happened but today with modern technology, the vehicles computer can adjust the ignition timing to reduce or eliminate knock. When this happens, and still happens a lot today, this adjustment of timing reduces the mileage and raises your cost per mile. Octane is added to fuel to resist this knocking. The higher the octane or number on the button, the better the prevention of knocking which means better fuel economy. Higher octane coming from an oil refinery is expensive and this is why premium fuels usually cost more than the regular 87 octane.
OCTANE SOURCES AVAILABLE
There are two commercially viable octane sources. The first is ethanol, a homegrown, clean burning fuel additive that currently makes up 10% of gasoline. Ethanol has the highest octane rating of any component in gasoline and is proven to reduce emissions. The second octane source is aromatics, toxic hydrocarbons produced at the oil refinery. Aromatics, which include known and suspected carcinogens like benzene and toluene make up 25% of fuel. Aromatics are the most carbon intensive and toxic compounds in gasoline, creating the worst tailpipe emissions.
CAN AROMATICS BE REPLACED?
Since aromatics do naturally occur in crude oil, it is not possible to completely remove them from gasoline. However, aromatics can be significantly reduced through the addition of ethanol. Since 10 percent ethanol blends, commonly known as E10, entered the market, it’s replaced eight billion gallons of aromatics annually. This is because refiners started using ethanol to increase octane and reduce aromatics. In order to improve public health and reduce aromatics further, ethanol at 15, 20 or even 30% can make a big difference and reduce today’s dangerous levels of these harmful aromatic additives.