New study of emissions and health impacts from EVs in China, including massive e-bike fleet
02 February 2012
A new study by researchers from the University of Tennessee, University of Minnesota, and Tsinghua University compares emissions (CO2, PM2.5, NOx, HC) and environmental health impacts (primary PM2.5) from the use of conventional vehicles (CVs) and electric vehicles (EVs)—including electric cars, bicycles and light scooters—in 34 major cities in China. The study’s findings highlight the importance of considering exposures—especially the proximity of emissions to people—when evaluating environmental health impacts for EVs, the team said.
In their paper, published in the ACS journal Environmental Science & Technology, Ji et al. note that the focus of their study was motivated in part by the unprecedented rise in popularity of electric two-wheelers in China. The massive upsurge in e-bikes in the country marks “the single largest adoption of alternative fuel vehicles in history, with over 100 million vehicles purchased in the past decade, more than all other countries combined.”
While conventional vehicle (CV) ownership and electricity consumption in China are both increasing rapidly—annual growth rates during the past decade were ∼25% and ∼10%, respectively—e-bike ownership is skyrocketing: 86% annual growth during the past decade (doubling time: ∼13 months). Ten years ago, e-bikes were nearly unheard of, with vehicle ownership rates 26× lower for e-bikes than for CVs. Today, e-bikes outnumber CVs 2:1.
For EVs, combustion emissions occur where electricity is generated rather than where the vehicle is used. In China, 85% of electricity production is from fossil fuels, of which ∼90% is from coal. Most electricity generating units (EGUs) in China lack advanced pollution controls. Compared to typical vehicle emissions, EGUs are often located further from population centers; therefore, the exposure and health impacts per mass emitted tend to be lower for EGUs than for CVs. The net result for China is that it is unclear a priori whether EVs are an environmental health benefit or disbenefit relative to CVs.—Ji et al.
The team evaluated five vehicle types (gasoline and diesel cars, diesel buses, e-bikes, e-cars) and considered how environmental impacts varied depending on the emission location. The study used an intake-based, rather than concentration-based, risk assessment for primary PM2.5.
The team found that using concentration rather than intake is suboptimal for health comparisons. Because electricity generation typically occurs farther from people than do tailpipe emissions, intake factors (iF) values are often lower for EVs than for CVs. For example, they noted, comparing PM2.5 averages per passenger-km, emissions are 5× higher for an e-car than for a bus, but health impacts from primary PM2.5 are about equal between the two modes. Comparing averages for e-bikes and buses, based on PM2.5 emissions the two modes are similar (30% higher for buses) but based on PM2.5 mortality rates, impacts are 7× greater for buses as for e-bikes.
Among their findings were:
The order-of-magnitude variability in EGU emission factors by region yields the same degree of variability in EV emission factors and with the same spatial pattern (highest in the Northeast because of heavy reliance on coal). EV emission factors vary by the city they are in; they estimated that an e-car (180 Wh/km in Beijing emits 220 gCO2/km, equivalent to a gasoline car with a fuel economy of 9 L/100 km (26 mpg US), whereas in Chengdu the same e-car would emit only 135 gCO2 km−1, equivalent to a gasoline car with a fuel economy of 5.6 L/100km (or 42 mpg US).
PM2.5 emission factors generally are lower for CVs (gasoline or diesel) than comparable EVs. However, intake fraction is often greater for CVs than for EVs because combustion emissions are generally closer to population centers for CVs (tailpipe emissions) than for EVs (power plant emissions).
For most cities, the net result is that primary PM2.5 environmental health impacts per passenger-km are greater for e-cars than for gasoline cars (3.6× on average), lower than for diesel cars (2.5× on average), and equal to diesel buses. In contrast, e-bikes yield lower environmental health impacts per passenger-km than the three CVs investigated: gasoline cars (2×), diesel cars (10×), and diesel buses (5×).
Compared to a new (Euro IV) gasoline car, average e-car emission factors are about the same for CO2 and 19× greater for PM2.5. E-bikes outperform cars, motorcycles, and buses on most emission metrics.
Well-to-station emissions represent a larger proportion of total emissions for CVs relative to EVs for many pollutants.
In terms of health impacts, e-cars typically perform better than diesel cars, worse than gasoline cars, and comparably to diesel buses; e-bikes perform much better than diesel cars and buses but are comparable to or slightly better than gasoline cars.
CO2 emissions (g/km) vary and are an order of magnitude greater for e-cars (135–274) and CVs (150–180) than for e-bikes (14–27).
China provides a useful case study because of the large number of EVs (in 2009, 100 million EVs) and because of government policies aimed at increasing the number of EVs. Unique aspects of China include the large population and coal-heavy electricity system. Our findings show that replacing gasoline cars with e-cars will result in increased CO2 from combustion emissions and all-cause mortality risk from primary PM2.5 in most cities. Health risks attributable to other pollutants, including secondary PM2.5, are uncertain. Lightweight EVs such as e-bikes can have environmental and health benefits because of their energy efficiency. Chinese policy makers should carefully proceed with deployment of plug-in vehicles and consider aggressive improvements in the power sector to realize anticipated gains in emissions and health.
Future research could explore whether results presented here hold for other countries and could model impacts of secondary PM2.5. We highlight one distributional aspect of CV versus EV emissions (urban-rural exposure differences), leaving for future research a more significant exploration of environmental justice.—Ji et al.
Shuguang Ji, Christopher R. Cherry, Matthew J. Bechle, Ye Wu, and Julian D. Marshall (2012) Electric Vehicles in China: Emissions and Health Impacts. Environmental Science & Technology doi: 10.1021/es202347q
This really shows that China needs to move from coal to generate electricity, rather than that they should not move to EV's.
High temperature vertions of their modular pebble bed reactor currently being finished which could be put in in place of the coal burning parts of existing coal plants but would use existing turbines and so on would do the job nicely.
Posted by: Davemart | 02 February 2012 at 07:05 AM
IGCC conversion might be possible for existing coal plants. It would cost, but it would pay back in efficiency gains as well as improved air quality and fewer adverse health effects.
Posted by: SJC | 02 February 2012 at 07:20 AM
It should be fairly obvious that a crowded city like Beijing would be better off if more people used e-bikes and public transport - from a traffic congestion and parking startpoint at the very least.
Obviously, the pollution is lower, even if the electricity comes from dirty coal power stations because the amount of energy required is so much lower.
It is interesting how poorly EVs fare compared to more modern gasoline cars, but I suppose power stations last longer than cars and the old ones are very polluting.
Sounds like they have to start fitting scrubbers etc. to their coal power stations, starting with the ones in / near cities.
If the Chinese take pride in their e-bikes, and treat them as a good thing ("The Chinese Way") rather than a temporary stage on the way to 4 wheeled mobility, they could actively promote them, and greatly reduce their pollution and congestion problems.
It is not realistic for everyone in a huge city to drive to work - you HAVE to use public or 2 wheeled transport, and 2 wheeled e-bikes would be easier in very hot summer weather than push bikes. (Although you could use p-bikes in the other seasons for fitness reasons).
Posted by: mahonj | 02 February 2012 at 07:23 AM
Converting to IGCC would also allow the production of scrubbed syngas for use as town gas. Substituting town gas for coal in both industry and coal stoves would clean up the air overnight.
Syngas can also be used in microturbines for local cogeneration, boosting the efficiency of gas use. I'm amazed that China hasn't done this on a large scale already.
Posted by: Engineer-Poet | 02 February 2012 at 07:45 AM
Considering the huge quantity of e-energy required in China, even NG powered power plants are not clean enough. Replacing or upgrading 400+ coal fired power plants with a combination of up-to-date nuclear plants, wind and solar power plants may be required to reduce current and future air pollution level.
Posted by: HarveyD | 02 February 2012 at 08:44 AM
If a coal plant is 30% efficient and an IGCC plant is 60% efficient, then you get the same power using half as much coal. If they have 100s of coal power plants, the energy saved could offset adding even more regular coal plants.
Posted by: SJC | 02 February 2012 at 09:04 AM
IGCC isn't 60% efficient; there's considerable overhead in the gasification process (and I suspect also the syngas cleanup). Wabash River hit 40%, and I believe I've seen figures of 45% for plants with all the modern improvements.
Ultrasupercritical steam beats IGCC by a few percent, though it's nowhere near as clean or versatile.
Posted by: Engineer-Poet | 02 February 2012 at 09:48 AM
In 2012 China will produce slightly more e-energy than USA.
Both countries rely heavily on fossil fuel (USA 71%, China 79%)
USA's have added many new fossil fuel power plants in the last 7 years; 0.6 MW in 2006 up to 8.8 MW in 2012 for an increase of 1466%.
China has also added many new fossil fuel power plants but at a much lower rate than USA for the same period.
China has built more higher efficiency, cleaner fossil fuel power plants than USA in the last 7 years.
We talk a lot about 60% efficient IGCC power plants but the average efficiency in lower in USA than in China. For the last 7 years, China's added plants have an efficiency of 44% versus 40% for USA's.
Do we believe that we are a lot better than we really are? Yes, most of the time.
Posted by: HarveyD | 02 February 2012 at 10:20 AM
Harvey, I have no idea what you are talking about.
'USA's have added many new fossil fuel power plants in the last 7 years; 0.6 MW in 2006 up to 8.8 MW in 2012 for an increase of 1466%.'
This is absolutely insignificant against the ~500,000MWe of baseload capacity in the US
'China has also added many new fossil fuel power plants but at a much lower rate than USA for the same period. '
They have been adding new coal plants at a rate of about 2,000MWe a WEEK for years.
Posted by: Davemart | 02 February 2012 at 10:39 AM
Dave...if you check the stats for a longer period you will note that China's new fossil fuel power plants rate has been going down in the last 7 years vs the previous 7 year period while USA's have been going up fast (from only 0.6 MW in 2006 to 8.8 MW of new plants in 2012). Those of us who claimed that USA did not build new fossil fuel power plants in the last 7 years got it all wrong. Those of us who claimed that USA is building CLEANER coal power plants and China is doing the opposite also got it all wrong. The cleanest fossil fuel power plants are being built in China while we talk about them.
Posted by: HarveyD | 02 February 2012 at 11:18 AM
IGCC probably is not, Combined Cycle is more efficient, but I do not know how much more. My point being, more efficient means producing the same power using less fuel.
Posted by: SJC | 02 February 2012 at 12:01 PM
The numbers that you give are utterly trivial.
Quoting a huge increase on something way, way less than 1% of the total means nothing.
I am also simply not going to bother looking up precise figures on Chinese fossil plant build as it remains by any reckoning massive.
Your point on the burn in Chinese plants becoming cleaner is valid enough, but you really should provide links when you make claims.
Here is one of them:
Posted by: Davemart | 02 February 2012 at 12:10 PM
Dave...I was referring to rate of growth based on increase of new fossil fuel power plants (MW) added in the last 7 years. In real numbers China is definitely growing much faster in mostly everything (cars, trucks, e-trains, sub-ways, highways, bridges, buses, e-bikes, batteries, computers, TV, cell-phones, tablets, etc) including energy produced/used to manufacture all those goods.
It takes a lot less energy to design a tablet (in USA) than to produce 60,000,000 of them in China.
Posted by: HarveyD | 02 February 2012 at 12:11 PM
"In general in service Combined Cycle efficiencies are over 50 percent on a lower heating value and Gross Output basis. Most combined cycle units, especially the larger units, have peak, steady state efficiencies of 55 to 59%"
Posted by: SJC | 02 February 2012 at 03:58 PM
Note that "combined cycle" and "integrated gasification combined cycle" are different beasts.
Posted by: Engineer-Poet | 02 February 2012 at 04:54 PM
That is true, just posting for reference.
Posted by: SJC | 02 February 2012 at 05:45 PM
"The average global efficiency of coal-fired plants is currently 28% compared to 45% for the most efficient plants"
"IGCC efficiencies typically reach the mid-40s, although plant designs offering around 50% efficiencies are achievable."
So the difference between 30% and 45% is significant. Build fewer plants, use less coal and/or produce more electricity.
While you are making synthesis gas, make synthetic fuels at night. Combine some biomass with the coal and do everyone a favor by making it more renewable and CO2 neutral.
Posted by: SJC | 02 February 2012 at 05:54 PM
China's new very large (up to 5000 MW) coal fired power plants have an efficiency of 44.2% but are still heavy polluters like most fossil fuel power plants.
That efficiency level is probably reached by most up-to-date current fossil fuel power plants. Future plants will do better (worldwide), making electrified vehicles a better choice.
Using more efficient (cleaner) power plants, more zero pollution power plants, more electrified vehicles (2 to 26 wheels) and less ICEVs, pollution per Km/passenger should go down progressively, worldwide.
Posted by: HarveyD | 03 February 2012 at 08:30 AM
I would say it would be the overall average of 100s of plants that matters when it comes to efficiency, coal usage and pollution.
IGCC can get the sulfur and mercury out of the coal before combustion. Those can be used to industrial purposes and the plant can become a synthetic fuel plant. You can not do that with advanced regular coal burning.
Posted by: SJC | 03 February 2012 at 09:12 AM
Assuming visible sunlight, which is apparently becoming rarer in Beijing, it seems like a 130 W solar panel would charge an e-bike in a few hours and last for years. The energy used per rider mile is on a scale so much smaller than an ICE powered vehicle.
Posted by: E-Biker | 07 February 2012 at 08:25 AM
China's research in Molten Salt Reactors will determine their future energy mix. If they can bring MSR to production stage in a few years that could really cement them as an industrial power-house.
Posted by: TexasDesert | 07 February 2012 at 08:05 PM