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- Perhaps most surprising was the discovery that there was “no apparent difference in secondary organic aerosol (SOA) formation between a Euro 5 light gasoline vehicle equipped with a GPF and a Euro 6b gasoline car without GPF.
- The research points out that gasoline vehicles are “major sources of SOA formation in urban areas,” which is dominated by the atmospheric oxidation of aromatic volatile organic compounds (VOCs) emitted as unburned fuel or formed during combustion.
- This trend began in the 1990s and accelerated in the 2000s, resulting in cities with high pollution levels as consumers purchased diesel vehicles regardless of their intended use.
A groundbreaking study from Germany’s Helmholtz Munich research center and the University of Rostock has challenged our understanding of vehicle emissions, suggesting that modern gasoline engines might actually be more harmful than their diesel counterparts.
The fall of diesel and rise of gasoline engines
Over the past decade, we’ve witnessed the unexpected demonization of diesel engines. This trend gained momentum following the Volkswagen emissions scandal uncovered by the EPA in 2015. Diesel vehicles, once promoted for their fuel efficiency, saw their market share plummet dramatically. In many European markets, electric vehicles now outsell diesel cars.
The automotive industry pivoted toward gasoline engines, which were widely assumed to be cleaner alternatives. Manufacturers implemented gasoline particulate filters (GPFs) to comply with emissions standards, similar to the technology diesel vehicles had used since the Euro 5 standards.
What the research reveals about gasoline emissions
The German researchers focused their study on a gasoline vehicle equipped with a particulate filter. Their findings, published in Science Advances, revealed something unexpected: while the freshly emitted exhaust gases showed no detectable toxic effects on human lung cells, these emissions became significantly more toxic after photochemical aging.
This natural transformation process, driven by sunlight and atmospheric oxidants, dramatically changed the nature of these emissions. The aged emissions caused substantial DNA damage and oxidative stress in both cancerous alveolar epithelial cells and normal bronchial epithelial cells.
The toxicity wasn’t just associated with newly formed particles but also with volatile oxygenated compounds like carbonyls generated during their time in the atmosphere.
No benefit from particulate filters
Perhaps most surprising was the discovery that there was “no apparent difference in secondary organic aerosol (SOA) formation between a Euro 5 light gasoline vehicle equipped with a GPF and a Euro 6b gasoline car without GPF.”
In plain English? The fancy particulate filters that were supposed to make gasoline cars cleaner don’t seem to be making much difference when it comes to overall emissions impact.
The current Euro 6d standard (similar to EPA standards in the US) measures emissions produced immediately after combustion, but doesn’t account for how these emissions behave once released into the environment. This is a major oversight since filtered emissions remain toxic when exposed to sunlight.
The bigger picture of vehicle emissions
The research points out that gasoline vehicles are “major sources of SOA formation in urban areas,” which is dominated by the atmospheric oxidation of aromatic volatile organic compounds (VOCs) emitted as unburned fuel or formed during combustion.
Recent studies have linked these secondary organic aerosols with increased risk of death from cardiorespiratory diseases in the United States.
(Ever notice how the air in cities sometimes has that distinctive smell on hot, sunny days? That’s photochemical smog – partly created by this exact process we’re talking about.)
Was diesel unfairly demonized?
The diesel engine remains one of the most efficient combustion technologies available. It’s ideal for heavy vehicles and drivers who rack up significant annual mileage. However, it’s less suitable for primarily urban driving or occasional use.
Modern diesel engines emit less CO₂ thanks to technologies designed to reduce emissions (EGR valves, particle filters, AdBlue catalysts, etc.). The same authorities that have been criticizing diesel for years are the ones who previously encouraged consumers to buy diesel vehicles.
This trend began in the 1990s and accelerated in the 2000s, resulting in cities with high pollution levels as consumers purchased diesel vehicles regardless of their intended use.
Now that diesel has been nearly eliminated from many markets, are we seeing a shift toward demonizing gasoline engines to push hybrid and electric vehicles? The timing of this research certainly raises questions about the future direction of automotive propulsion technologies.
As we navigate these complex environmental and technological issues, one thing is becoming clear: the atmospheric chemistry of vehicle emissions might be just as important as the raw emissions themselves when determining their real-world impact on human health.
