Diesel Engines and Public Health

Health impacts of diesel pollution

Diesel-powered vehicles, vessels, locomotives, and equipment account for over 60 percent of all nitrogen oxides (NOx) and more than 70 percent of all fine particulate matter (PM2.5) emissions from US transportation sources. Heavy-duty diesel vehicles alone account for 20 percent of all NOx and 25 percent of PM_2.5 pollution emitted by vehicles in the country.¹

The World Health Organization (WHO) classifies diesel exhaust as carcinogenic to humans, and ample research demonstrates that its components, which include PM 2.5 and NOx, a ground-level ozone precursor, are harmful for human health even at low concentrations and through short-term exposures.^{2, 3, 4, 5} 

Fine particulate pollution

Particulate matter, sometimes called soot, is created during the incomplete combustion of diesel fuel. Though just a fraction of the width of a human hair, particulate matter varies in size from coarse particulates (less than 10 microns in diameter, known as PM 10) to fine particulates (less than 2.5 microns, known as PM 2.5) to ultrafine particulates (less than 0.1 microns). Ultrafine particulates, which are small enough to penetrate the cells of the lungs, make up 80 to 95 percent of diesel soot pollution.  

Particulate matter irritates the eyes, nose, throat, and lungs, contributing to respiratory and cardiovascular illnesses and even premature death. Although everyone is susceptible to particulate pollution, children, the elderly, and individuals with preexisting respiratory conditions are the most vulnerable. A recent study found that the rates of nine common causes of death, including cardiovascular disease, lung cancer, and other prevalent fatal conditions, were associated with exposure even at concentrations of fine particulates lower than the current federal standards.⁶

The larger body of science clearly shows that communities of color and socioeconomically disadvantaged communities bear disproportionately higher exposures to PM _2.5 pollution, and despite significant reductions in ambient concentrations over the past 40 years, these communities remain exposed at similarly proportioned higher levels.⁷  

Impacts from nitrous oxides (NO_x)

Heavy duty diesel vehicles also emit significant levels of NOx, especially at lower speeds while driving through urban neighborhoods.⁸ NOx is particularly dangerous as it is both a pollutant itself and a precursor chemical leading to the creation of fine particulate and ground-level ozone pollution. Exposure to NOx pollution has been shown to inflict a number of respiratory health issues over both short- and long-term exposure, including reduced lung function and inflammation.

Long-term exposure to NOx has been directly linked to the development of asthma, while short-term exposure can trigger asthmatic symptoms.⁹ 

Ground-level ozone

Diesel emissions of NOx contribute to the formation of ground-level ozone, which irritates the respiratory system, causing coughing, choking, and reduced lung capacity. Ground-level ozone pollution, formed when NOx and hydrocarbon emissions combine in the presence of sunlight, presents a hazard for both healthy adults and individuals suffering from respiratory problems. Urban ozone pollution has been linked to increased hospital admissions for respiratory problems such as asthma, even at levels below the federal standards for ozone.^{10, 11}

Exposure is particularly harmful for more vulnerable populations, including the elderly and those with preexisting conditions. A recent study found a significant relationship between mortality among the Medicare population with small, short-term increases in ozone concentrations.¹² Ground-level ozone has also been shown to damage crops leading to measurable reductions in agricultural output worldwide and climate change will only further these impacts.¹³  

Electric vehicles are here

Today, over 100 models of electric trucks and buses are on the market, including delivery vehicles, tractor trucks, shuttles, and charter buses among others.¹⁴ Businesses now have the option to purchase electric trucks and busses that have significantly lower and more predictable fuel and maintenance costs. Electric trucks are ready for work now.¹⁵

The availability of zero-emissions trucks continues to grow rapidly and the difference between lifetime costs for electric and diesel trucks declines every year. The California Air Resources Board estimates that, from delivery vehicles to tractor trucks, electric trucks will have a favorable total cost of ownership (TCO) by 2030, due in part to existing state policies and decreasing technology costs.¹⁶

Public policy is needed

The landscape around electric trucks and buses has changed dramatically with recent developments in technology. The last time EPA considered heavy-duty truck emissions, electric vehicles were a future concept, but we can now completely eliminate tailpipe emissions from heavy-duty vehicles. While electric trucks are here to stay, the urgency of the climate crisis and health disparities in disproportionately impacted communities demands public policies to accelerate the national electric truck and bus market while providing some regulatory certainty to industry.¹⁸