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Study links California regulations, significant declines in cancer risk from exposure to air toxics

A study by a team from the California Air Resources Board (ARB) has found that the collective cancer risk from exposure to seven toxic air contaminant (TACs) has declined 76% during the period from 1990 to 2012, and linked that result from air quality regulations targeting these TACs. The study appears in the ACS journal Environmental Science & Technology.

Of the seven TACs, diesel particulate matter (DPM) is the most important; DPM is emitted mainly from trucks and buses and is responsible for most of the airborne cancer risk in California, according to ARB. However, in the study DPM is not measured directly. Based on a novel surrogate method, DPM concentrations declined 68% during the period, even though the state’s population increased 31%; diesel vehicle-miles-traveled increased 81%; and the gross state product (GSP) increased 74%.

Credit: ACS, Propper et al. Click to enlarge.

The nearly 70% drop in DPM coincided with actions taken over the years, beginning in the 1990s, to reduce diesel emissions. In the 1990s, California adopted a reformulated diesel fuel program; started a heavy-duty diesel truck roadside inspection program; implemented particle pollution standards for urban transit buses; and established standards for off-road diesel engines. In 2006, California began requiring ultra-low-sulfur diesel fuel.

Estimating DPM
For the study, the researchers estimated ambient DPM concentrations using oxides of nitrogen as a surrogate, combined with scaling factors derived from the ratio of DPM emissions to total NOx emissions as obtained from the ARB inventory.
Basin-wide annual average ambient NOx concentrations (1990−2012) were calculated using hourly average measurements from over 200 monitoring sites.
The following assumptions were made: (1) ambient DPM concentrations are proportional to NOx concentrations in each air basin; (2) emissions are well-mixed on basin-wide time scales, and (3) background NOx concentrations can be neglected.
Full details on the methodology are presented in the supplementary materials for the paper.

Following the establishment of California’s statewide Truck and Bus Rule in 2008, California began requiring diesel particulate filters on trucks, reducing diesel particulate matter from the exhaust gas of diesel engines.

Based on monitoring data, concentrations of benzene; 1,3-butadiene; perchloroethylene; and hexavalent chromium declined 88–94%. (The reduction of benzene and 1,3-butadiene was largely the result of California gasoline reformulation in 1996, ARB said.) Also, the ambient and emissions trends for each of these four TACs were similar. Formaldehyde and acetaldehyde, which are formed in the air photochemically from volatile organic compounds (VOCs), declined only 20–21%.

The paper makes clear that further significant reduction in cancer risk to California residents is expected to continue as a result of continued implementation of air toxic controls. Such controls are part of broader statewide transportation initiatives, including the Truck and Bus Rule and more than a dozen rules focused on diesel equipment serving ports and railyards. Neighborhoods in freight corridors, including those near ports, will especially benefit.

ARB regulations have reduced air toxics emissions from vehicles and their fuels, from stationary sources and from consumer products since the mid-1980s. In response to public concern, the California Legislature passed the Toxic Air Contaminant Identification and Control Act in 1984. Since then, ARB has implemented regulations to limit TAC emissions. In 1987, the California Legislature passed the Air Toxics “Hot Spots” Information and Assessment Act, which requires businesses to reduce risks from exposure to emitted TACs.


  • Ralph Propper, Patrick Wong, Son Bui, Jeff Austin, William Vance, Álvaro Alvarado, Bart Croes, and Dongmin Luo (2015) “Ambient and Emission Trends of Toxic Air Contaminants in California” Environmental Science & Technology doi: 10.1021/acs.est.5b02766


Account Deleted

BBC now writes that 11 million VW cars has the defeat devise that allows VW to pollute up to 40 times their legal level. That compares to the pollution from 440 million extra cars for many years! This is insane!

It is a problem that VW only apology for a breach of trust between VW and its customers and the public. However, it is far more serious than a breach of trust that in a legal sense is not a crime. We know that WHO has linked air pollution to 7 million premature death per year globally. Stated differently, 12% of all people on our planet dies prematurely because of air pollution. In order for that number not to increase further it is extremely important that the legislation on air pollution limitations is respected in all industries. The auto industry is responsible for a large part of the total global air pollution and therefore also a large share of those 7 million premature death per year that can be linked to air pollution. When a car company like VW manufacture cars that cleverly can emit 10 to 40 times the legal level of air pollution while avoiding detection at normal EPA test procedures it is far more serious than a breach of trust. It is VW committing mass murder in the USA on a scale that outperforms 9/11. It is simply not enough to say we are sorry you can't trust us. VW needs to pay up in a big way that will hurt them seriously financially so that they cannot afford to commit mass murder in the USA a second time and so that other automakers also get the message that air pollution is not to be taken lightly as people's lives in massive numbers depend on those systems that limit air pollution. I sincerely hope that the legal end game of VW's defeat devise is a 18 billion USD penalty to VW so that VW and the industry start to treat this issue with the seriousness that it demands.

WHO on 7 million air pollution death.



You've made some assumptions that may not pan-out.

NOx requirements are less strict outside of the US and Canada, so a NOx level that's "up to 40x the limit" in the US will be much closer to compliance in the rest of the world. In other words, you can't just multiply 11 million times 40 and "compare to the pollution from 440 million extra cars." 10.5 of those 11 million were probably nearly compliant or fully compliant in their delivery market, so they wouldn't have been much worse than competing cars.

Also, as the article above alludes, NOx is only one pollutant. We don't know that VW diesels were non-compliant for DPMs and other pollutants.

Account Deleted

Your nitpicking is not going to change the fact that people at VW indirectly have committed mass-murder not just in the US but everywhere those 11 million affected diesel cars have been sold. This case is clearly bigger and more lethal than BP's Horizon disaster and the punishment of VW must be administered accordingly.

Another issue is why we allow industries globally to create enough air pollution to kill 7 million people per year prematurely. One reason is off cause that every time a politician support tougher air pollution legislation they lose funding and their opponent get more funding from the polluting industries. It is really hard to do the right thing in this case because of the involved economic interests. Air pollution is not something we need to accept. We should not accept that 7 million people dies every year for reasons that are entirely political in nature. Air pollution can be fixed and these people can be saved with tougher pollution legislation, tougher monitoring and harder punishment whenever this legislation is disobeyed.


VW and 1,000,000+ other local and international polluters should have been severely punished year and/or many decades ago. Premature deaths, cancers and many other related illnesses and associated health care cost would have been greatly reduced.

The total savings in USA alone would have been enough to fund much higher subsidies ($10K to $20K) for the initial purchase of electrified vehicles to further reduce pollution, GHG and imported oil.

Too bad that California is more or less alone in seriously fighting pollution in North America.


If VW TDI had been clean, the numbers might have been better.

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