In times of widely publicized environmental issues, namely global warming, the transportation sector is often bemoaned for its contribution to carbon emissions. Though diesel exhaust certainly exhibits detrimental effects on the atmosphere, its effects on the human body attract less attention. The World Health Organization estimates that urban air pollution, to which vehicles are a significant contributor, kills 1.2 million people every year.
On Sept. 9, Prof. Oliver Gao, civil and environmental engineering, who focuses on the nexus of transportation, air quality and energy, discussed his ongoing research on the effect of different fuels on air quality measurements.
Transportation-related air pollution is a significant issue across the globe. In 2005, the Clean Air Task Force reported that fine particle pollution from diesels (fuel used in internal combustion engines) shortens 21,000 Americans’ lives each year, including 3,000 early deaths from lung cancer. 400,000 people suffer each year from asthma attacks.
This is illustrated in the South Bronx, New York’s asthma hot spot and one of the poorest sections in the city. The region’s highways, waste transfer stations, and meat, fish and flower markets, which serve Manhattan, are some of the busiest in the world. Before 7 a.m. each day, smoke-spewing trucks have already released noxious fumes into the air. These diesel particles cause asthma rates to rise four to five times higher than the national average.
Diesel particles, along with gas particles, make up diesel exhaust, which promotes a 7.5 times greater risk of cancer than the combined total cancer risk from all other air toxins in the nation, according to the Clean Air Task Force. Particles are classified according to size and composition, and the most dangerous particles are “ultrafine.” In comparison, a human hair is 60 micrometers, and an ultrafine postulate is 0.1 micrometer.
Ultrafine particles can bypass human respiratory system mechanisms and penetrate into the lungs. In addition to airways and blood vessels, new research suggests that ultrafine particles can also harm the brain.
Lilian Calderón-Garcidueñas at the National Institute of Pediatrics in Mexico City tracked children in the city for four years, and observed that they suffered from cognitive impairments in memory, problem solving and judgment, as well as deficiencies in their sense of smell compared with age-matched children from a city with better air quality.
At the Harvard School of Public Health, Shakira Franco Suglia’s group conducted research that suggests children’s minds may be especially susceptible to inflammation caused by ultrafine particles. This inflammation causes nerve cell damage, which resembles characteristics of Alzheimer’s or Parkinson’s diseases.
Although the EPA acknowledges the dangers of ultrafine particles, it regulates emissions according to particle mass, not particle number (P.N.). Gao’s research indicates that large, coarse-mode particles (a micrometer or more in diameter) dominate in terms of particle mass, whereas ultrafine particles dominate in terms of number.
Gao and his group collected particle measurements while going through New York City as a typical traveler. They found that particle mass was highest in underground stations (possibly due to dust), while P.N. was highest on urban streets. Ultrafine particles emitted by traffic are highest along streets but drops off significantly around 100 yards away.
Gao studied the connection between P.N. measurements and vehicle operations. His findings have challenged notions that new energy technologies are better for humans.
$100,000 hybrids, for example, do not reduce PN concentration. In contrast, diesel particle filters, which only cost $10,000 to $15,000, can reduce P.N. concentration by 99 percent. Gao’s group tested filtered vegetable oil biofuel supplied by Ithaca Biodiesel, and found that biofuels not only reduced greenhouse gas emissions but also particle number concentrations. B20 (20 percent biodiesel and 80 percent petroleum diesel) can reduce P.N. concentration by 36 percent.
The debate of particle mass versus P.N. and biofuel versus hybrid diesel-electric is the more pertinent in light of the $50 billion transportation infrastructure plan, “Renewing and Expanding America’s Roads, Railways, and Runways,” announced by President Obama on Sept. 6.