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Study finds rapid increases in nitrogen oxides may be as harmful to the heart as sustained levels

Rapid increases in pollution may be as harmful to the heart as sustained high levels, according to new research published in the European Journal of Preventive Cardiology. The authors urgently call for confirmatory studies as even residents of clean air cities could be at risk.

There is longstanding evidence that exposure to high concentrations of air pollution increases the risk for several diseases including heart attacks; accordingly, European Union (EU) statutory pollution limits are based on absolute upper values. However, this study investigated whether rapid increases in pollution increase the risk of heart attack, independently of an absolute threshold.

It also looked at whether an association between heart attacks and changes in air pollution exists in clean air cities where concentrations of air pollution vary but do not exceed EU limits.

Even though the ambient air in the city of Jena is comparably clean, the significant association between rapid changes in nitrogen oxides and onset of myocardial infarction (MI) suggests that the current EU statutory limits do not sufficiently protect against effects relating to the cardiovascular health of the population. A more specific definition and stricter implementation of statutory limits for rapid increases of nitrogen oxides are potentially needed to address this issue and to close this gap regarding the risk of MI.

The study was conducted in Jena, Germany, a city with 100,000 residents and only a few days over the last several years during which concentrations of some air pollutants exceeded EU daily limits. All patients living within 10 km of Jena who had a heart attack and were admitted to Jena University Hospital between 2003 and 2010 were included.

Each of the 693 patients served as his or her own control. Concentrations of air pollutants one, two, and three days before heart attack symptoms were compared to concentrations in the previous and following week. The researchers analyzed whether there were rapid variations in air pollution before the heart attack.

Increases of nitrogen oxides of more than 20 μg/m3 within 24 hours were associated with a more than doubled risk of heart attack. The researchers were surprised by the magnitude of the association.

Our study suggests that the risk of heart attack associated with nitrogen oxides depends on the dynamics and extent of increases, and not only on exposure to high concentrations.

The impact of rapid increases in air pollutants on heart health may be at least as important as absolute concentrations. The adverse effects of rapid rises in pollution can occur in smaller cities. Increases of nitric oxides by more than 20 μg/m3 within 24 hours happen more than 30 times per year in Jena, which is known as a ‘clean air’ city where statutory limits for nitric oxides are generally not violated.

—Senior author Dr. Florian Rakers, a researcher and doctor at Jena University Hospital

Ground traffic and especially diesel cars are the primary source of nitric oxides in the EU. The study did not investigate the cause of rapidly changing pollution levels, but Dr. Rakers said they could be due to irregular events that lead to more traffic than usual— example the start of holidays or meteorological conditions associated with smog.

Once our findings are replicated, the EU should discuss statutory limits on rapid increases of nitric oxides. This would require more efforts to reduce these air pollutants, such as banning diesel cars that exceed EU emission limits.

—Dr. Rakers


  • Rasche M, et al. (2018) “Rapid increases in nitrogen oxides are associated with acute myocardial infarction: A case-crossover study.” European Journal of Preventive Cardiology doi: 10.1177/2047487318755804



One more study to justify banning all diesel vehicles ASAP, specially in all city cores?

BEVs and FCEVs and many PHEVs could help to solve the problem?


Four out of four diesel cars tested by Equa in the U.S. have received an air quality rating of "A", which corresponds to meeting California's SULEV limit for NOx (<0.02 g/mile).

Europe is implementing RDE testing, which should preclude any diesel vehicle that exceeds the Euro6 NOx limit from being certified.


Cheating is very common. Very few or none meet all standards during all weather operation and from A to Z?


Based on personal communications with EPA, all diesel vehicles certified in the U.S. undergo months of rigorous extra testing, including real-world testing under a variety of ambient conditions using PEMS. The certification process has become so onerous that some manufacturers have pulled the certification requests.

The Equa tests are real-world tests conducted with PEMS.

According to ICCT:

"...Recent actions by California’s Air Resources Board and US EPA indicate that future LD diesel NOx emissions will be much closer to regulatory emissions limits. These actions include ARB’s newly-developed defeat device screening methods, which notably include the use of “special driving cycles and conditions that may reasonably be expected to be encountered in normal operation and use”. As a result, average NOx emission factors for future vehicles certified to Tier 3 standards are estimated to be within 30% of the certification limit, equivalent to 14 mg/km...."

Anenberg et al. "Impacts and mitigation of excess diesel-related NOx emissions in 11 major vehicle markets." Nature 545, 467–471 (25 May 2017), page S7


My personal communication with bodies who conduct on-road tests for EU member states confirms what Carl stated. NOx emissions are rapidly decreasing from new diesel cars to levels comparable to modern gasoline cars, i.e. practically zero. Moreover, it has also been shown that tailpipe PN emissions from modern diesel cars are lower than in ambient air in densely populated cities.


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