Posted on June 26, 2017 by Charles Morris
Conventional wisdom has it that diesel engines are dirtier than gas engines because they emit more particulate matter - tiny bits of soot that can cause serious damage to human lungs. However, a new study led by the Swiss research institute Empa (via Gas2) has found that some gas engines spew forth much more particulates than diesels.
Above: Tailpipe emissions from internal combustion engine gasmobiles are a major source of greenhouse gas emissions and pollutants harmful to human health (Image: Living on Earth via Pittou2, Flickr CC BY-NC 2.0)
The researchers studied the emissions of 7 gas vehicles equipped with direct fuel-injection systems, and found that they emit from 10 to 100 times more particulates than modern diesel engines - more, in fact, than older diesel engines with no particulate filters.
“Once inhaled, these particles remain in the body forever,” explains project leader Norbert Heeb. Evidence shows that they can penetrate the membrane of the air sacs in the lungs and get into the bloodstream. And it gets worse: “Liquid or solid chemical toxins from the combustion process... accumulate on the surface of the particles, which can then smuggle these substances into the bloodstream - like a Trojan horse.”
Those nasty combustion products include benzo(a)pyrene, a known carcinogenic substance that’s found in all kinds of smoke and soot (including cigarette smoke). The World Health Organization (WHO) considers even a tiny dose of benzo(a)pyrene harmful. Levels in vehicle exhaust were found to be as much as 1,700 times above the safe limit established by the EU.
Above: An alarming amount of particulate emissions are coming from gasoline engines (Image: Gas2 via Bosch)
Not all gasoline engines form particulates in the exhaust. The culprit appears to be a modern innovation: direct fuel injection. In older electronic fuel injection systems, fuel is added to the combustion chamber at the end of the exhaust stroke. In direct-injection engines, the fuel is added after the end of the intake stroke. This gives the fuel less time to evaporate, says Heeb, resulting in more unburned hydrocarbons and thus more soot.
Automakers began adopting direct injection because it allows more precise control of the fuel delivery process, leading to better fuel economy and lower carbon dioxide emissions. The new study seems to be one of the first to test direct-injection engines for anything other than CO2.
Heeb and his team urge automakers to begin equipping their cars with particulate filters. “New exhaust emission technologies launched on the market typically need about 13 years to become fully effective,” writes Heeb. “Only after that period of time will 9 out of 10 cars in the vehicle fleet be replaced. So, the faster particle filters are mandatory in gasoline cars, the better it will be for everyone’s health.”
Above: Cities like Beijing are pushing for electric vehicles in order to reduce emissions (Youtube: CGTN)
Particulate matter is only part of the toxic mixture that hovers around cars and roads. We all regularly breathe in nitrogen oxides, volatile organic compounds, ozone, carbon monoxide, benzene and other nasties. In a recent article in the Guardian, Professor Sir David King, chief scientific adviser for the English government, warns that levels of air pollution are often far higher inside cars than outside them, as indicated by several studies. A study in Copenhagen found that a driver breathed in more pollution than a cyclist on the same road. Outside, the emissions are diluted by the surrounding air, but inside a car, the dirty air circulates and builds up.
As Sir King notes, the UK is considering a ban on smoking in cars, in order to protect children, but the wee bairns may actually be at greater risk from air pollution. “You may be driving a cleaner vehicle but your children are sitting in a box collecting toxic gases from all the vehicles around you.”
One automaker is fitting its vehicles with filters that clean the air that drivers and passengers breathe. The heavy-duty HEPA filter was first available in Tesla's Model X (and later in its Model S) and it's about 10 times larger than an ordinary car filter. Tesla claims it is “100 times more effective than premium automotive filters” and that it removes “at least 99.97% of fine particulate matter and gaseous pollutants, as well as bacteria, viruses, pollen and mold spores.” In 2016, the company tested the filter, and found that not only did it scrub the cabin air clean, but even began to vacuum up pollutants from the outside air.
Above: Tesla putting its HEPA filter and "Bioweapon Defense Mode" to the test (Image: Tesla)
Even as legacy vehicles get dirtier, electric vehicles (EVs) are clean and getting cleaner. Numerous studies have found that, thanks to their far greater efficiency, EVs in general produce less emissions than gas vehicles, even if powered by coal-generated electricity. However, the mix of power sources varies widely among different parts of the world, so EVs end up being greener in some regions than in others.
A new report from the Union of Concerned Scientists, which updates and expands upon an earlier study from 2015, found that driving electric is now cleaner than driving a typical gas-burner everywhere in the US. Furthermore, the electric advantage is growing as more regions are cutting their use of coal and increasing investment in renewable energy sources. The new analysis is based on updated data from the EPA, which shows reduced greenhouse gas emissions from power generation in most of the country over the past five years.
According to the new study, in 70 percent of the US, driving electric produces fewer emissions than driving a gasoline car that gets 50 mpg (a figure met by only the Toyota Prius and the new Hyundai Ioniq). On average, today’s EVs are as clean as a hypothetical gas vehicle that gets 73 mpg.
Above: For over 70% of Americans, driving an electric vehicle results in fewer emissions than even a 50 MPG gasoline vehicle (Source: Union of Concerned Scientists)
“Driving electric is one of the best choices a consumer can make to reduce emissions in their own lives,” said David Reichmuth, Senior Vehicles Engineer at UCS. “As the electric vehicle market has emerged over the last five years, electric vehicles are better than a 50 mpg gasoline car for 70 percent of Americans, up from 50 percent. It’s been remarkable to see the improvements.”
Of course, it’s not enough to consider only tailpipe emissions. What about the pollution produced in manufacturing a vehicle? Several studies have examined the cradle-to-grave life cycle of an EV, including a recent offering from Like Tesla. Producing an electric vehicle, especially one with a large battery pack like Model S or Model X, requires a lot of energy - that’s one of the reasons Tesla decided to bring the battery manufacturing process in-house at its Gigafactory. According to Like Tesla, manufacturing an electric car actually produces more greenhouse gas emissions on the front end than manufacturing a comparable legacy car.
Above: Looking at how electric vehicles are better from the 'cradle to the grave' than their gasoline counterparts; Editor's Note: This was filmed before the latest Union of Concerned Scientists report which means that EVs numbers have actually improved even more since this video was published (Youtube: Like Tesla)
However, once the vehicle leaves the factory, the equation is reversed. An internal combustion vehicle will produce more emissions than its electric cousin with every mile driven. Like Tesla found that, over its lifetime, a typical internal combustion vehicle will produce 160,000 pounds of greenhouse gas emissions, compared to 82,000 pounds for a Tesla Model S (smaller and more efficient EVs, such as a Nissan LEAF, will produce even less).
Another oft-cited environmental hazard is rare earth metals, which are used in all kinds of modern products, from cars to consumer electronics. Tesla has long avoided them, as it stated in 2012: “Tesla does not use rare earth metals in our batteries or our motors. Typically rare earth metals apply to DC motors, which use magnets. One of the reasons we use an AC induction motor is it does not require magnets, which often contain rare earth metals.” Tesla also recycles the vast majority of metals used in its battery packs.
Some EVs (and legacy vehicles) do use rare earth elements, but the clear trend in the industry is to phase out their use. Automakers and motor suppliers are developing new technology to recycle rare earths, minimize their use, or stop using them entirely.