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Northwestern/Princeton study explores air quality impacts of aggressive conversion to EVs

Researchers from Northwestern University and Princeton University have explored the impact on US air quality from an aggressive conversion of internal combustion vehicles to battery-powered electric vehicles (EVs). In a paper published in the journal Atmospheric Environment, they report on the findings from a suite of scenarios designed to quantify the effect of both the magnitude of EV market penetration and the source of electricity generation used to power them.

The exponentially increasing global market share of EVs has prompted research on their efficacy in reducing greenhouse gases, but comparatively little effort has focused on their impact on air quality. This despite evidence that suggests air pollution impacts from the transportation sector exceed those from greenhouse gases.

… The impact on air quality from the adoption of EVs can vary substantially between regions depending on existing transportation type and density, proximity to and type of power generation, and the region’s chemical regime (e.g., NOx-vs.VOC-limited for O3, NH3-rich vs. NH3-poor for PM). For example, states in the western US (WUS) generally produce a larger fraction of their electricity from renewable and/or “emission-free” sources (i.e., solar, wind, hydroelectric, and nuclear) as compared to the eastern US (EUS), where the electricity market is dominated by pollutant and precursor emitting combustion sources (i.e., coal, oil, natural gas, and biomass).

Most studies that have examined the impact of EVs report only changes in the total emissions associated with their adoption, but do not consider their spatial or temporal variation. … Thus to fully account for the complexity of changes to air pollution chemistry, emission changes should be used to drive a chemical transport model (CTM).

—Schnell et al.

In the study, the researchers applied a prototype version of the new-generation NOAA GFDL global Atmospheric Model, version 4,for their simulations.

To fully account for the complexity of changes to air pollution chemistry, the researchers took multiple variables into consideration:

  • Potential electric vehicles adoption rates;

  • Generation of electric vehicle power supply, including the current combustion-dominant mix, combustion-only sources and enhanced emission-free renewables;

  • Geographical locations; and

  • Seasons and times of day.

Among the findings:

  • Summer surface ozone (O3) decreases in most locations due to widespread reductions of traffic NOx emissions.

  • Summer fine particulate matter (PM2.5) increases on average and largest in areas with increased coal-fired power generation demands.

  • Winter O3 increases due to reduced loss via traffic NOx.

  • Winter while PM2.5decreases since larger ammonium nitrate reductions offset increases in ammonium sulfate.

Increasing the fraction of vehicles converted to EVs further decreases summer O3, while increasing the fraction of electricity generated by “emission-free” sources largely eliminates the increases in summer PM2.5 at high EV adoption fractions. Ultimately, the number of conventional vehicles replaced by EVs has a larger effect on O3 than PM2.5, while the source of the electricity for those EVs exhibit greater control on PM2.5.

—Schnell et al.


Air quality changes binned at each 10th percentile and averaged over the WUS (left column, west of 100°W) and EUS (right column, east of 100°W) for each EV adoption scenario (colors) shown for (a, b) O3, (c, d) PM2.5 for April-September, (e, f) PM2.5 for October-March, (g, h) (NH4)2SO4, and (i, j) NH4NO3. Schnell et al.

Across scenarios, we found the more cars that transitioned to electric power, the better for summertime ozone levels. No matter how the power is generated, the more combustion cars you take off the road, the better the ozone quality.

—first author Jordan Schnell, a postdoc with the Ubben Program for Climate and Carbon Science in the Institute for Sustainability and Energy at Northwestern

Particulate matter decreased in the wintertime but showed greater variation based on location and how the power was generated. Locations with more coal-fired power in their energy mix experienced an increase in PM during the summer. Locations with clean energy sources, however, saw reductions.

We found that in the Midwest, the increased power demands of EV charging in our current energy mix could cause slight increases in summer particulate matter due to the reliance on coal-fired power generation. However, if we transition more of the Midwest’s power generation to renewables, particulate matter pollution is substantially reduced. In the Pacific Northwester or Northeast, where there is already more clean power available, EV adoption—even with the current energy mix—will decrease particulate matter pollution.

—Jordan Schnell

The research was supported by the Ubben Program for Carbon and Climate Science and the National Science Foundation (grant number CBET-1848683).


  • Jordan L. Schnell, Vaishali Naik, Larry W. Horowitz, Fabien Paulot, Paul Ginoux, Ming Zhao, Daniel E. Horton (2019) “Air quality impacts from the electrification of light-duty passenger vehicles in the United States,” Atmospheric Environment, Volume 208, Pages 95-102 doi: 10.1016/j.atmosenv.2019.04.003


Another authoritative argument for the removal of coal from the electric grid energy mix, and for purchasing solar with that EV.


This confirms that more REs and electrified vehicles (BEVs, PHEVs & FCEVs) are required to reduce air pollution and GHGs.

Quebec Hydro will add three (3) more small HPPs to the existing 63 HPPs to deal with population growth and the arrival of many more electrified vehicles. The construction of major HPPs have been delayed for another 5+ years due to current over supply of generating capacities.

Another authoritative argument for the removal of coal from the electric grid energy mix

As if we needed one.

and for purchasing solar with that EV.

That's a non-sequitur.  If you're reliant on solar power for EV charging, what do you do on cloudy days?  What do you do in winter, which happens where most people in industrial societies live?

Nuclear does the job.  CGNP is suing to halt the closure of Diablo Canyon, arguing forcefully that the California decarbonization law forbids the replacement of emissions-free nuclear power with NG and coal.  This is something to keep an eye on.


aggressive conversion...
There is still a barrier with a perceived risky large capital purchase.
Until it becomes normal mainstream for all your neighbors to buy EVs, adoption rates will not be "aggressive".


CPUC plans to close the remaining nuclear plant in 2024 and 2025 when the license expires; claiming changes in the costs of renewables, and increasing community local generation, etc. I think a large factor is PG&E wants out of the power generation business, as well as the gas business, in favor of just maintaining the wires, their grid.

It appears in the absence of sun and wind, California imports power from other states as well as using in state natural gas plants. Plans call for huge battery storage to replace these peaker plants and to feather out the power...I'm thinking they will still import power as needed for backup. Although there are no coal plants in the state, who know how the imported power is generated.


High concentration of plastic nano-particles floating in the air, all the way to high mountain areas, is another potential harmful health problem that humanity will have to deal with soon.

It seems obvious that we have been attacked from pollution from CPPs, NGPPs, ICEVs, trains, ships. planes, many chemicals used for farming and pollution from many industries for 2+ centuries and that we may not have adapted enough to survive in good health?

Many species of birds, bees, butterflies, whales and fishes are already having problems to reproduce and survive.

Life expectancy has started to go down in many countries, including USA and the near future does not look very good for China and India.

Certainly solar is only part of the solution. But if your grid mix is less than ideal, a combo EV/PV purchase moves you closer to the goal, and saves you money.

Payback periods for residential can be as low as 6 years now if you’re a savvy consumer and get competitive installation bids.

Important point is that a consumer can make a personal choice. The aggregate of these personal choices can move the needle on air quality.


I fully agree with e.c.i.c that locally captured/stored solar energy and EV/PV will soon become competitive with CPPs/ICEV, specially where carbon emissions are taxed at $100/Ton. Are people and politicians ready to introduce a progressive carbon emission tax?

May be not (yet) in Ontario, Sask, Alberta, N-B etc.

shuta chantal

Why should we invest so much money on nuclear energy instead of renewable energy. Solar and wind energy must be the future (there is plenty of them) every other source is a waste of time and money.


A usable 100+ kWh battery (or total 125+ kWh) is required for all weather extended range BEVs. That battery pack currently cost $20K to $30+K and raises the average BEV price above the equivalent ICEVs price by about the same amount.

One way to reduce that difference to zero would be to lease the battery and pay for the battery"s lease with (daily/weekly) savings with lower cost electricity.

More REs could be progressively installed where/when required to meet increased demands. Partially used batteries could be used/recycled for lower cost fixed storage units.

More efforts and resources are required to accelerate the mass production of improved quicker charge batteries and associated quick charge facilities.

If we do not do it, China and EU will do it and we will have to try to catch up.

Why should we invest so much money on nuclear energy instead of renewable energy.

Because "renewable energy", taken to mean wind and solar, DOES NOT WORK.  Nobody has ever gotten rid of fossil fuels that way, because the need is for always-on energy which they cannot provide.  The only "renewable" that works is hydro, and we've already used all the good hydro sites.

Solar and wind energy must be the future (there is plenty of them)

There's plenty of BS, but it isn't the future.  As BS is recognized, it has to be replaced with new BS.  There's plenty of uranium, too.  The difference is, uranium works; BS doesn't.

every other source is a waste of time and money.

Complete inversion of reality.  Nuclear power is the only thing which has decarbonized energy sources on industrial scales.  Every "renewable" country has much higher per-kWh pollutant emissions than France, Sweden and Ontario.  Shut up and go away until you've got something that works.

shuta chantal

You said:
"Shut up and go away until you've got something that works"
How ignorant from you. Did I wrote something about working things?
Quoting wind, sun and fresh water as the only source source of renewable energy tells me already the dimension of your ignorance.
You, being a fan of these complex, heavy and inefficient plug ins just confirms it.
So I feel no need to answer you with facts.

And haven't you read?
Do you see a man who is wise in his own eyes? There is more hope for a fool than for him


NPPs are excellent sources of relatively clean energy if the four main associated issues could be solved:

1) reduce implementation time by 4X to 6X
2) reduce initial installation cost by 5X to 6X
3) select safer sites and improve public acceptance..
4) solved long term spent fuel disposal.

Most REs have none of the above issues and essential storage for 24/7 can be solved with improved energy generation/distribution management. One+ billion EVs with V2G bidirectional units could solve most of the inherent problems associated with a system with 50% to 60% REs .

In addition, excess energy from REs could be transformed to H2 and stored-distributed for small and large FCEVs and fixed FC generators as required..

I feel no need to answer you with facts.

That was obvious from the beginning.  If you cared a whit for facts you'd be taking your cues from Environmental Progress, not Greenpeace.

How ignorant from you. Did I wrote something about working things?

Hah, grammar went out the window.  Cognitive dissonance confirmed.

Quoting wind, sun and fresh water as the only source source of renewable energy tells me already the dimension of your ignorance.

ORLY?  Show me where ANYTHING else is being rolled out in quantity.  Hell, just show me any proof of feasibility.  I'm from Missouri:  SHOW ME.

You, being a fan of these complex, heavy and inefficient plug ins just confirms it.

Complex?  Who cares?  Heavy?  Hundreds of pounds lighter than a Tesla.  And inefficient?  I regularly beat 50 miles per gallon in hybrid mode, and I'm currently averaging over 132 MPG since new.

If every vehicle sold in the USA was a plug-in like mine, the USA would quickly become independent of imported energy.  Carbon emissions would plummet.  IT WORKS.  I'm proving it personally.

I think that's what bothers you:  your greewashing doesn't work, but tech does.  It has debunked your religion and you're all butthurt over it.

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