Diesel vs Clean Diesel: A Visual Comparison of Cityscapes

Diesel vs. Clean Diesel: How Much Healthier Are Today's Engines?

Samir D’Costa in Climate & Environment May 2025 • 3 min read.

"A deep dive into how modern diesel engines stack up against their older counterparts, exploring the science and regulations that drive cleaner air."

For over a century, diesel engines have been the workhorses of industry and transportation. But these engines have also been a source of public concern due to the harmful health effects associated with their emissions. These concerns have spurred significant advancements in emission control technologies and stricter regulations.

The introduction of new standards by the Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) in 2001 marked a turning point. These regulations pushed manufacturers to innovate, leading to the development of new technology diesel engines (NTDEs), often referred to as 2007-compliant diesel engines.

So, how do these modern engines compare to their older, pre-2007 counterparts? This article explores the findings of the Advanced Collaborative Emissions Study (ACES) and other research to provide a clearer picture of the impact of these technological advancements on our health and environment.

Pre-2007 Diesel Engines: A Cloud of Health Concerns

Diesel vs Clean Diesel: A Visual Comparison of Cityscapes

Before the 2007 regulations, diesel engines emitted significantly higher levels of particulate matter (PM) and nitrogen oxides (NOx), both of which pose serious health risks. Studies on pre-2007 diesel exhaust (DE) revealed a range of concerning effects.

Early research focused on diesel exhaust particulate (DEP) extracts. Kotin et al.'s studies in the 1950s demonstrated that DEP extracts were both toxic and carcinogenic in mice, with different strains showing varying susceptibility. The studies showed:

DEP extracts could induce tumors when applied to the skin of mice.
The toxicity and carcinogenicity of DEP varied depending on the animal strain and sex.
Even low levels of DEP could cause harm over time.

Further studies, such as those by Huisingh et al., identified that the mutagenic components of DEP were primarily found in the neutral fraction, containing polynuclear aromatics, phenols, ethers, and ketones. These findings highlighted the potential of DEP to cause DNA mutations.

The Road Ahead: Cleaner Air for Future Generations

The transition to 2007-compliant diesel engines represents a significant step forward in reducing the harmful effects of diesel emissions. The ACES findings, combined with other research, suggest that these new technologies have effectively reduced measurable tissue damage associated with reactive oxygen species.

Everything You Need To Know

What were the main health concerns associated with older diesel engines?

Pre-2007 diesel engines released substantial amounts of particulate matter (PM) and nitrogen oxides (NOx), which posed serious health hazards. Studies highlighted concerning effects of diesel exhaust (DE). Early research on diesel exhaust particulate (DEP) extracts, such as those by Kotin et al. in the 1950s, showed that DEP extracts were both toxic and carcinogenic in mice, able to induce tumors. Later research, including that of Huisingh et al., identified mutagenic components within the neutral fraction of DEP, containing polynuclear aromatics, phenols, ethers, and ketones. This contrasts sharply with the emission profiles of newer engine technologies.

What drove the development of 2007-compliant diesel engines?

2007-compliant diesel engines are a result of regulations set by the Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) in 2001. These regulations pushed for advancements in emission control technologies, leading to the development of New Technology Diesel Engines (NTDEs). These new engines drastically cut pollution compared to older models, improving air quality and public health.

What health risks were identified in studies of diesel exhaust particulate (DEP)?

Diesel exhaust particulate (DEP) extracts were found to be toxic and carcinogenic. Kotin et al.'s research demonstrated that applying DEP extracts could induce tumors in mice. The severity varied based on factors such as the animal strain and sex. Additionally, even low levels of DEP were found to cause harm over time, emphasizing the potential health risks linked to exposure from pre-2007 diesel engines. Further studies identified the presence of mutagenic components, underlining the significance of emission control.

How has the transition to newer diesel engines affected health outcomes?

The Advanced Collaborative Emissions Study (ACES) and other research provide a clearer picture of the positive impact of modern diesel engines. The findings suggest that 2007-compliant diesel engines have significantly reduced measurable tissue damage associated with reactive oxygen species, indicating improvements in air quality. This is a direct result of the new technologies that resulted from the regulations.

Why is the shift from pre-2007 diesel engines significant?

The evolution of diesel engine technology, specifically the transition from pre-2007 engines to 2007-compliant models, represents a pivotal advancement. The older diesel engines were a major source of PM and NOx emissions, contributing to adverse health outcomes. The regulations and new technologies have effectively reduced these emissions, promoting healthier air quality and mitigating associated risks. These changes reflect a proactive approach toward environmental health and safer air.