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Georgia Tech study finds link between sulfate, metallic particles from vehicles and adverse health impacts

Metals from brakes and other automotive systems are emitted into the air as fine particles, lingering over busy roadways. Now, researchers at Georgia Institute of Technology have shown how these vehicle-emitted metals—such as copper, iron and manganese—interact with acidic sulfate-rich particles already in the air to produce an aerosol that, when inhaled, is more likely to cause oxidative stress and impact respiratory health. Their study is published in the ACS journal Environmental Science & Technology.

The study, which was sponsored by the National Science Foundation and the US Environmental Protection Agency, showed how the metals are emitted mainly in an insoluble form but slowly become soluble after mixing with sulfate. In other words, the sulfate plays a key role in making metals soluble before they are inhaled, which could explain the association of sulfate with adverse health impacts, the researchers said.

Oxidative potential (OP), referred to as the ability of particles to generate ROS [reactive oxygen species] by consumption of antioxidants and/or generation of oxidants, has been used as a health-based exposure measure of PM in several recent studies. … To mitigate adverse health effects, ambient particle OP sources, and atmospheric transformations that alter OP, need to be known.

A number of aerosol components have been found to correlate with aerosol OPDTT [dithiothreitol]. These include bulk water-soluble organic carbon (WSOC), humic-like substances (HULIS) and highly oxygenated organic aerosols, and more specific aerosol components, such as polycyclic aromatic hydrocarbons (PAHs), quinones, and water-soluble transition metals (e.g., manganese (Mn) and copper (Cu)). Source apportionment points to incomplete combustion from biomass and fossil fuels (gas and diesel engines), and sources associated with transition metals, such as mineral dust and resuspended road dust from tire or brake wear.

In contrast to OPDTT, correlations suggest that transition metals (i.e., Cu) are the main aerosol component contributing to OPAA [ascorbic acid], with road-traffic a major source.

—Fang et al.

For the study, the team collected size-segregated ambient PM from a road-side and representative urban site in Atlanta, GA. They then measured elemental and organic carbon, ions, total and water-soluble metals, and water-soluble OP (using a high-throughput analytical system that simulates the toxic response that such a mix would have on cellular organisms).

Sulfate was spatially uniform and found mainly in the fine mode, whereas total metals and mineral dust cations were highest at the road-side site and in the coarse mode, resulting in a fine mode pH < 2 and near neutral coarse mode.

The team found that soluble metals and OP peaked at the intersection of these modes; the researchers concluded that this demonstrates that sulfate plays a key role in producing highly acidic fine aerosols capable of dissolving primary transition metals that contribute to aerosol OP. Such sulfate-driven metals dissolution may account for sulfate-health associations reported in past studies, they suggested.

That’s the smoking gun. The sulfate essentially dissolves those metals; when you breathe in those particles, the metals could be absorbed directly into the blood stream and cause problems throughout the body. For the first time, a mechanism emerges to explain why small amounts of acidic sulfate can adversely affect health.

—Athanasios Nenes, a professor and Georgia Power Scholar in the School of Earth & Atmospheric Sciences and the School of Chemical & Biomolecular Engineering

While the sample taken from the testing site located farther away from the highway had less particulate metal, there was still enough to cause an increase in the oxidative potential, showing that roadway pollution could travel through the air and potentially cause problems in surrounding areas as well.

Dust from brakes and tires isn’t the only source of metals in the air. Incinerators and other forms of combustion also produce mineral dust and metallic particles, which could mix with sulfate to trigger a similar reaction.

The researchers noted that while the amount of particulate sulfate in the southeastern United States has decreased during the past 15 years as sulfur dioxide emissions from power plants have fallen, there’s still enough acidic sulfate in the air to keep the pH of particles very low, in the range of 0 to 2, transforming insoluble ambient metals to a soluble form.

There’s a chain reaction happening in the air above busy highways. Acidic sulfate in the atmosphere comes into contact with those metals emitted from traffic and changes their solubility, making them more likely to cause oxidative stress when inhaled.

Vehicle tailpipe emissions are going down, but these kinds of emissions from braking will remain to some extent, even if you drive an electric car. Therefore, this kind of process will continue to play out in the future and will be an important consideration when we look at the health effects of particulate matter.

—Rodney Weber, a professor in Georgia Tech’s School of Earth & Atmospheric Sciences and corresponding author

This material is based upon work supported by the National Science Foundation under Grant No. 1360730 and the U.S. Environmental Protection Agency under Grant No. RD834799. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation or the U.S. Environmental Protection Agency.


  • Ting Fang, Hongyu Guo, Linghan Zeng, Vishal Verma, Athanasios Nenes and Rodney J. Weber (2017) “Highly acidic ambient particles, soluble metals and oxidative potential: A link between sulfate and aerosol toxicity,” Environmental Science & Technology doi: 10.1021/acs.est.6b06151



So, acid rain and metalic brake shoes are unhealty combination. Sulfur dioxide emississions of coal plants and Nox emissions of diesel engines not good either. But, the more we know the more environmentally friendly we can design our power plants and autos. Fuel suppliers have drastically lowered sulfur content. Diesel technology has improved vastly. Gasoline engines utilize exhaust gas and ethanol to decrease Nox. Coal power plants within U.S. have much lower emissions. Problem is developing nations. We could do much more working on their problems than continually working our EPA to cost more to acheive less.


Most BEV's use regenerative braking, requiring a minimized use of mechanical braking, which is a double plus for BEV's.


We are certainly participants in a big experiment.

" I feel like I woke up in the wrong universe"

We are entering a new epoch that may become accepted Anthropocene.
It be cheekily suggested a rival title based on ocean plastic pollution is the 'Plasticine'.

This another example of accelerating rates of change.

"It took billions of years for most of the Earth's minerals to form but scientists say hundreds more have been created in the years since the Industrial revolution.

These 'new minerals' have been created by chance, when substances that would otherwise have never encountered one another came into contact as a result of human activity.

Robert Hazen, a mineralogist at Washington's Carnegie Institution for Science is pushing for these 'man made' minerals to be accepted as real minerals, and wants to discover even more.



Regen braking would help but not enough hybrids out there.

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We need to ban sulfat in all gasoline and diesel. It can be removed but it will make the gas more expensive.

Globally 7 million people are killed prematurely by air pollution each year from the coal, oil and gas. This is totally unacceptable and we need to stop this ASAP. Ban new coal power plants and ban using diesel vehicles inside cities.


Regen braking certainly contributes to a considerable reduction of those metals used in brake linings. An even greater effect would be achieved by the usage of ceramic brake linings. The reduction would not be the only positive effect; ceramics endure far higher temperatures, last much longer and are far more reliable and safer than metal additives. Of course, ceramics are also more expensive. The final question is; do you want to die younger and cheaper or older and more expensive?


Most board rooms want profits, the externalities are not their concern.


ICEVs producers and end users + CPPs operators should be legally suied for XX $T, like tobacco coompanies were and still are.

Wonder why our 100,000++ lawyers have not done it? A strong class action would acellerate the switch to BEVs/FCEVs. A single $1/year per ICEV user ($250,000,000/year) in USA (only) could et the ball rolling.

We should not wait for politicians to do it because they will not.

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