New Vehicle Emissions Deceptively Clean

Researchers at Carnegie Mellon University have found that newer gasoline vehicles emit less particulate matter, but vapors in the "cleaner" exhaust form particulate matter long after exiting the tailpipe. These secondary particles, can be just as harmful to human health.

Mechanical Engineering Professor Allen Robinson and his research team investigated the formation of secondary organic aerosol (SOA) and the effects that more stringent vehicle standards could have on SOA formation. SOA is a major component of atmospheric fine particles, which negatively affect the human body and the earth’s climate.

Robinson and his colleagues found that emissions from newer vehicles meeting more stringent emissions standards formed less SOA than older vehicles, thus replacing older vehicles with newer vehicles will reduce pollutants in the air. The team also discovered that the formation of SOA strongly depends on nitrous oxides (NOx), which are abundant in cities and other areas with high motor vehicle traffic.

The team’s research highlights the importance of addressing SOA pollution in cities from Los Angeles to Pittsburgh."Overall, we found that new and stricter regulations for gasoline vehicle tailpipe emissions will not be that effective at reducing human exposure to secondary organic aerosol because of changing NOx levels," Robinson said. "This feedback illustrates the complex coupling between different pollutants, which must be accounted for in models used to develop control strategies."

"About 23 million Americans live in areas that violate the current federal standard for fine particulate matter," Robinson said. "SOA is a major component of those particles, and bringing these areas into compliance - so that all Americans breathe cleaner, safer air - will likely require addressing SOA pollution."