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Study Suggests Unregulated Nano-sized Ultrafine Particles May Be Most Damaging Component of Air Pollution for Heart Disease

Representative histological photomicrographs. Red staining in sections of the aorta represents lipid and macrophage content, which are part of the atherosclerotic plaque development. Exposure to ultrafine particles shows highest degree of plaques. Click to enlarge.

A new study indicates that ultrafine particles—particles of less than 0.18 micrometers—from vehicle emissions may be the most damaging components of air pollution in triggering plaque buildup in the arteries, which can lead to heart attack and stroke. The findings appear in an open access article in the 17 January online edition of the journal Circulation Research.

A team from University of California, Los Angeles (UCLA); the University of Southern California; the University of California, Irvine; and Michigan State University contributed to the research, which was led by Dr. Andre Nel, UCLA’s chief of nanomedicine. The study was primarily funded by the National Institute of Environmental Health Sciences and the US Environmental Protection Agency (EPA).

It appears that the smallest air pollutant particles, which are the most abundant in an urban environment, are the most toxic. This is the first study that demonstrates the ability of nano-sized air pollutants to promote atherosclerosis in an animal model.

—Dr. Jesus Araujo, first author and assistant professor of medicine and director of environmental cardiology at the David Geffen School of Medicine at UCLA

The EPA currently regulates fine particles at 2.5 micrometers, but doesn’t monitor particles in the nano- or ultrafine range. These particles are too small to capture in a filter, so new technology must be developed to track their contribution to adverse health effects.

We hope our findings offer insight into the impact of nano-sized air pollutant particles and help explore ways for stricter air quality regulatory guidelines.

—Andre Nel

The UCLA research team previously reported that diesel exhaust particles interact with artery-clogging fats in low-density lipoprotein (LDL) cholesterol to activate genes that cause the blood-vessel inflammation that can lead to heart disease. (Earlier post.)

In the current study, researchers exposed mice with high cholesterol to one of two sizes of air pollutant particles from downtown Los Angeles freeway emissions and compared them with mice that received filtered air that contained very few particles.

The study, conducted over a five-week period, required a complex exposure design that was developed by teams led by Dr. Michael Kleinman, professor of community and environmental medicine at UC Irvine, and Dr. Constantinos Sioutas, professor of civil and environmental engineering at USC.

Researchers found that mice exposed to ultrafine particles exhibited 55% greater atherosclerotic-plaque development than animals breathing filtered air and 25% greater plaque development than mice exposed to fine-sized particles.

Pollutant particles are coated in chemicals sensitive to free radicals, which cause the cell and tissue oxidation. Oxidation leads to the inflammation that causes clogged arteries. Samples from polluted air revealed that ultrafine particles have a larger concentration of these chemicals and a larger surface area where these chemicals thrive, compared with larger particles, Sioutas noted.

Ultrafine particles may deliver a much higher effective dose of injurious components, compared with larger pollutant particles.

—Andre Nel

Scientists also identified a key mechanism behind how these air pollutants are able to affect the atherosclerotic process. Using a test developed by Dr. Mohamad Navab, study co-author and a UCLA professor of medicine, researchers found that exposure to air pollutant particles significantly decreased the anti-inflammatory protective properties of HDL cholesterol.

To explore if air particle exposure caused oxidative stress throughout the body—which is an early process triggering the inflammation that causes clogged arteries—researchers checked for an increase in genes that would have been activated to combat this inflammatory progression.

They found greater levels of gene activation in mice exposed to ultrafine particles, compared to the other groups. The next step will be to develop a biomarker that could enable physicians to assess the degree of cardiovascular damage caused by air pollutants or measure the level of risk encountered by an exposed person.

Previous studies assessing the cardiovascular impact of air pollution have taken place over longer periods of exposure time, such as five to six months. The current study demonstrated that ill effects can occur more quickly, in just five weeks.

The research team included investigators from the fields of nanomedicine, cardiology and genetics. Additional co-authors included Berenice Barajas, Xuping Wang, Brian J. Bennett and Ke Wei Gong of the David Geffen School of Medicine at UCLA, and Jack Harkema from the department of pathobiology and diagnostic investigation at Michigan State University.

Additional grant support was provided by the National Institute of Allergy and Infectious Diseases; the National Heart, Lung and Blood Institute; and the Robert Wood Johnson Foundation.




Just a few questions: Do diesel engines put out more particles of less than 2.5 micrometers than gasoline engines.

Another question concerns the filters used on diesel exhaust, do they filter particles of less than 2.5 micrometers? Or are they targeted to pass regulatory limits which do not address the whole range of particulate health impacts.

If diesels are significantly worse, and the tier 2, bin 5 fixes do not reduce those impacts, the whole resurgence of diesel engines should be put on hold.

It appears that filtering diesels is like filtering cigarettes, all show and no go.


Well! after 100 years of burning fossil fuels and millions of heart attacks, we can finally prove internal combustion engines are really death machines and smog is a euphemism for death gas.

Think long term. The future is solar power and electric drive. All the rest is an interim experience, including the current diesel hype.


About a decade ago researchers found that diesel exhaust particulates (DEP) in the range from 0.5 microns to 2.5 microns caused considerable lung inflamation in asthmatics.
It was even suggested that the rise in diesel engines could be responsible for the world wide increase in asthma. As it turns out this theory was not correct but it is generally accpted that (DEP) is a source of inflamation to many asthmatics.
Since DEP is an organic compound the immune system sees them as biological agents.

Yeah, just another reason to go towards electric drive.



A filter will only remove stuff *above* a certain limit. DPF reduces PM10+ (10 um); simultaneously, the diesel engine is operated in such a way, that the majority of soot particles is less than 10 um - because below that threshold, they are unregulated.

Interestingly, the old, stinking, black-smoke producing diesels emitted particles significantly larger than 10 um (that's the reason they could be seen that clearly). Particles of that size, however, would be trapped well before the areoles in the nose, throat and bronchies - in places where they could be removed from the body by normal caughing...

I feel that "clean" diesels made the issue about the respiratory health effects of their exhaust potentially much worse...

Gasoline Engines (lean burn) are not a significant source of particulates.

Electric Vehicles even less so (only rubber from the tires, iron and silicon from the brake pads...)

It's well past the time where general transportation should have gone electric...


It's settled then; Diesels are bad for your health.


Regarding gasoline engines, have a look at this.


Hello all, I recently found this site and I am very happy to be reading such insightful knowledge from knowledgable people. I have a question, a little off topic but I'll try to keep it short. What are your opinions of the movie, Who killed the electric car? I always like to consider alternative viewpoints before forming opinions but I haven't been able to find anything significant. Is it a fair assessment of the primary reasons why we are still devoid of EV's?


Imagine what the air in our cities will be like when the dead dinosaur burners are history.

MarkMC: Who killed ... was generally accurate but I think it fell down a little in their appraisal of the NiMH battery. IMHO the NiMH's functionality and economics are pretty marginal at best and I don't think they're good enough to support a mass migration to EVs (some here will disagree). Only now are we starting to see batteries good enough to support EVs (price is still an issue)


You kind of have to realize where we were during that period and the fact that the recent very fast rise in the price of gasoline has forced research and development of better batteries. I find it interesting what the people at Firefly have accomplished with their lead acid batteries. These could very well be the battery of choice for lower cost cars during the ramp up to electric drive vehicles; if they move them to mass production soon enough. see:


To address the points raised by Van in post #1, gasoline vehicles have been shown to emit levels of ultrafine PM that equal or exceed those of uncontrolled (unfiltered) diesel trucks under some common driving conditions (see

DPF (filters) has been shown to be very effective across the entire particle size range (see, slides 10 & 11,, slide 27).

Furthermore, it has been shown that most ambient ultrafine PM is secondary in nature, i.e., it is formed in the atmosphere by gaseous precursors, not directly emitted (Southern Oxidant Study). These ultrafines are typically formed by homogeneous nucleation of increasingly lower vapor pressure oxidation products which partition more and more into the solid (particle) phase. The primary gaseous precursors are VOCs, of which gasoline exhaust and fugitive gasoline vapors (evaporative gasoline emissions) are a very large portion of that inventory, up to 80% in southern California (Brown, et al; “Source apportionment of VOCs in the Los Angeles area using positive matrix factorization”. Atmospheric Environment, Volume 41, Issue 2, January 2007, Pages 227-237) and generally at least 50% in urban locations (Watson, et al; “Review of volatile organic compound source apportionment by chemical mass balance.” Atmospheric Environment, Volume 35, Issue 9, March 2001, Pages 1567-1584). Bottom line – gasoline vehicles are primarily responsible for ultrafines, not diesel.

winnipeg BioD

It should be no surprise that IC engines are bad for our health. The question for our society to decide is if the costs outweigh the benefits?
Also, if I read this article regarding gasoline engines correctly (thanks yesplease) spark ignition machines are at least as harmful to human health a are compression ignition ones.


Rafael Seidl

It's been known for some time that ultrafine particles pose the greatest risk for population health, because anything smaller than ~7 microns can pass through the alveolae in the lungs directly into the bloodstream.

Particles that fine are fairly rare in nature but there are multiple artificial sources. Diesel engines with high-pressure injection systems are indeed high on the list but so are dust from tire and brake pads, industrial furnaces, jet engines, poorly adjusted home heating appliances, even dust from certain soils used for agriculture. In addition, traffic and wind conspire to keep fine dust that would otherwise settle on the ground suspended in the air.

Btw, gasoline engines tend to produce a lot less PM than diesels by weight. However, very small quantities of the finest of the ultrafine particles - i.e. the ones that are the most dangerous - are emitted by both. For SI engines, this applies especially during engine warm-up, whenever the mixture has to be enriched to protect components doenstream and, if stratified GDI is applied. Worn engines that consume additional engine oil are also likely to emit more PM.


...nasty thing.
Thus, we should rather believe in the Franco-German car industry. Everything is fine, clean and enviromently friendly. get a TDI and have fun. Or rather not?

Harvey D

Nasty but very well known health hazards. Children in schools built within 1.0 Km from highways in France have much high lung and asthma problems.

Many cancers, lung, heart and other deseases could be avoided if we stop filling the air we breathe with man-made chemicals, multiple pollution and fine particles.

Lung cancer + heart problems created by tobacco smoking was evident for 50 years before we (the majority) did anything about it. Even then, almost 20% of us are not convinced.

All ICE machines, coal, oil and NG power plants, wood fireplaces, open fires, many BBQs, printers etc emit loads of fine particles and various pollution. Electrification seems to be the solution, even if the direct cost is higher. Sooner or latter we must account for health cost and other hidden cost to make the best choice.

Why always select the lowest direct cost solution if it endangers your health and cost many times more in hidden indirect cost in the mid and longer terms. We have to get over that childish acquired attitude.


Just to clear up a point of confusion here: do not confuse particle mass with particle number. The Tier/Bin ratings use mass, not number. 10 ug of PM10 will have ~million times fewer particles than 10 ug of PM 0.1. The primary epidemiological sensitivity is to size, so don't just look at the PM by mass numbers. Those are actually less useful than PM by number density, which is not routinely measured except in academic studies like SOS that Carl mentioned. You certainly won't find emission PM sizing in the EPA listings.

Do not think you get a pass if you use gasoline. Those studies which have actually looked have found that gasoline engines may put out much less PM by mass than diesel but equal to greater amounts by number. This is possible because the size distribution of gasoline PM is more skewed towards the ultrafine size fractions than is diesel PM. The higher vapor pressure of gasoline also leads to greater secondary aerosol formation, as Carl points out.

Of course, it would better to minimize burning FFs in general. You'll be in better shape -- that is, if you don't drop dead of a heart attack triggered by breathing in UF PM.


Just a note about PHEV and clean power.
I live in Northern NM and we get power from two coal fired plants. They recently offered customers the option of buying clean power which is most likely credits from somewhere else. The cost is an additional $8/100KWH/month. The problem is I must sign a one year contract to purchase in blocks of 100KWH per month and the amount is added to the electric bill.
Lets say my usage is about 300 KWH per month (this is correct for me) and I now pay 10 cents/KWH. If I sign up for clean energy of three blocks (300KWH) per month, they charge me an additional $24 per month and I pay even if I don't use it. This raises my bill from about $28 a month to $52/month.

This is not good. A large house would add $80/month to buy 10 blocks. I really don't think very many people will take this deal. Electric cars would make this much worse, though I am all for PHEVs.


Also don't forget :

1. PM from old aircraft engines
2. PM from Ship engines
3. PM from any military excercises
4. PM from burned forest / prairie
5. PM from solid rocket fuel
6. PM from Fireworks / firecrackers

Stan Peterson

@ MarkMC,
Who killed the EV1 was polemics, by liberal know nothings. They savaged the only auto maker who really tried to comply with the impossible demands of know nothing but true-believer who got themselves appointed as regulators.

The EV1 was a billion dollar waste of time and effort, using technology that was far too primitive to ever be widely adopted.

Liberals never let reality get in the way of a good witchhunt, especially when it diverts attention from their own lunacies however.

Only today, has the technology advanced to make substitutes for hydrocarbon fuels achieve the reasonable expectations of the marketplace. Notice that even today, on the verge of the elctrification era, the resultant proposed vehicles bear no facsimile to the the EV1, a barren technological "Tour-de-Force", both too expensive, and too limited to be adopted.

Stan Peterson

Modern western man has a lot cleaner environement than mankind has experienced in all previous generations. Western man doesn't live in smoky houses, cooking over wood or manure fueled stoves. He doesn't, by and large till large fields, and breathe the dust.

This discovery, if and when scientifically duplicated and confirmed, will be but another temporay obstacle to be regulated and reduced to well below tolerable levels.

Meanwhile the doctors and scienitsts will define the problem, the regualtors will issue limits, the manufacturers of many products will comply. And the lawyers will have found a new set of targets to demonize, to sue, and from whom to extort, a good living.

Life goes on...

Harvey D


Do you really believe what you're saying?

If you check the trend in new cancer cases (specially in western industrial countries) you will find an almost direct correlation with the 'not so clean' modern environment we live in.


Forgot to mention electrification of ground transport through nuclear fusion is just around the corner.(joke)
There is in my honest opinion some reason not to hammer the particulate issue too hard while not mincing words . It is Phsycplogically damaging.
If I had to consider that city living is the equivalent to a two pack a day habit for my children and those I care for, as is the case for many ie the majority of the global population.
The majority of humans live an urban lifestyle!
Many of these will qualify as per previous stated.
Do I / we need to be confronted with this on a daily basis? Do the benifits outweigh the costs? Is there an alternative? My answer I think is Not really. Not in the forseeable future.
There are choices we can make as individuals. The brown haze killer changes its spots via pollution conrolling legislation, and becomes deadlier and more invisible.

Jeff R

I'm curious whether the ultrafine particulate issue would be different for biodiesel. Anyone know?

50 mpg on biodiesel made from non-edible feedstocks is still a decent short to medium-term option while we wait for affordable BEVs. Or at least I hope it is...

joe padula

How about CNG plug in hybrid electrics?
No PM from CNG. Please correct me if I'm wrong.


@ Carl,

Thanks Carl, for edifying these "insightful and knowledgable people."

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