Transportation Sector Emissions

EM – July 2023: This month, EM considers how environmental policy can help reduce emissions from cars, trucks, and ports and drive the uptake of zero-emission vehicles, fuels, and technologies.
by Edward Carr and Bryan Comer

The transportation sector is the largest source of greenhouse gas (GHG) emissions in the United States, representing 28.5% of total GHG emissions in 2021. Within the transportation sector, light-duty vehicles are the largest contributor, at 57.1%, followed by freight trucks (25.9%); aircraft (7.5%); rail (2.1%); and vessels (2.0%). Similarly, addressing the public health impacts of criteria emissions—including particulate matter (PM), ozone, nitrogen oxides (NOx), and carbon monoxide (CO)—will require continued reductions in these pollutants from the transportation sector. In 2023, mobile sources will account for approximately 54% of anthropogenic NOx emissions, 5% of anthropogenic direct PM2.5 emissions, and 19% of anthropogenic volatile organic compound (VOC) emissions. Light- and medium-duty-vehicles will account for approximately 20%, 19%, and 41% of 2023 mobile source NOx, PM2.5, and VOC emissions, respectively.

The benefits of reductions in criteria pollutant emissions occur over a broad range of populations in both urban and rural communities. There are currently 15 PM2.5 nonattainment areas with a population of more than 32 million people and 57 ozone nonattainment areas with a population of more than 130 million people who will all benefit from cleaner air with fewer exceedances. Further, the U.S. Environmental Protection Agency (EPA) has proposed strengthening the annual PM2.5 standard to between 9 and 10 micrograms per cubic meter, which will require further emissions reductions to reach these levels.

For their part, automakers have relied on a range of electrification technologies—including hybrid electric vehicles (HEVs), plug-in electric vehicles (PHEVs), and battery-electric vehicles (BEVs)—to reduce emissions. These technologies have advanced rapidly in the past several years, while battery costs have dropped such that BEVs and PHEVs have become a growing mix of their product lines, leading to increasing diversity of battery electric vehicles planned for high-volume production going forward. As a result, zero and near-zero tailpipe emissions technologies have become more feasible and cost-effective than ever before.

The development in vehicle electrification is driven, in part, by the need to compete in the global market, as zero-emission tailpipe transportation policies continue to be implemented by governments across the world. Auto manufacturers also compete in a global market for market share that is becoming increasingly electrified. China is now the leading producer of electric vehicles: China sold 6.8 million vehicles in 2022, while the United States sold just 800,000. This trend is being further accelerated globally, with at least 20 countries, as well as numerous local jurisdictions, having announced goals to shift all new passenger car sales to zero-emission vehicles in the coming years, including Norway (2025); Austria, the Netherlands, Denmark, Iceland, India, Ireland, Israel, Scotland, Singapore, Sweden, and Slovenia (2030); Canada (2035), Chile, Germany, Thailand, and the United Kingdom (2035); and France, Spain, and Sri Lanka (2040). 

Additionally, several U.S. states have acted to shift the light-duty fleet toward zero-emissions. In 2022, California finalized the Advanced Clean Cars II rule, which requires zero tailpipe emissions by 2035 for all new passenger cars, trucks and sport utility vehicles sold in the state, with similar initiatives in New York, Massachusetts, Washington state, and Oregon.

Similarly, electrification or hydrogen fuel cells for freight transportation is also occurring with state mandates being set for the 2040s. While ocean-going vessels and aircraft emission reductions are mainly being pursued at the international level due to their global operations, strong efforts continue by state and local governments to reduce their emissions while at port or airports where nearby communities may reside. For example, California currently requires container ships, refrigerated cargo vessels, and cruise ships to comply with its at-berth regulation, which requires the use of shore power or other approved emission control strategy while docked in California ports; this expands to other ship types, including tankers and roll-on/roll-off vessels, in the mid-2020s.

Continue reading the full July 2023 issue of EM.


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