Next Thursday, the California Air Resources Board (CARB) will vote a proposal to reduce smog-forming and soot emissions from heavy-duty vehicles sold in the state over the next decade. While CARB has already moved forward to accelerate the adoption of electric trucks in the state, this latest proposal is a critical part of cleaning up the trucking sector until that broader transformation takes place.
Trucks are major contributor to California’s critical smog problem
The San Joaquin Valley and Southern California continue to have the worst air quality in country, in terms of both smog and particulate pollution (soot). Smog is ground level ozone and is formed from the reaction of volatile organic compounds (VOCs, from sources such as passenger vehicles, industrial processes, and even biogenic/natural processes) with nitrogen oxides (NOx, the largest sources of which are from heavy-duty trucks and construction equipment), in the presence of sunlight. In addition to smog, NOx reacts with other airborne compounds to form particulate pollution, and in LA and the San Joaquin Valley this secondary particulate matter is the leading contributor to their exceedance of federal air quality requirements. Heavy-duty trucks are the largest contributor to NOx in the state, and therefore substantial reductions in pollution from heavy-duty trucks is critical in order for California to improve its air quality.
Systemic racism, particularly through policies such as redlining, has led to communities of color being disproportionately affected by truck pollution. As such, these communities stand to benefit the most from policies targeting emissions reductions from heavy-duty trucks. (“Truck pollution” is defined as both primary particulate emissions and secondary particulate emissions resulting from smog-forming nitrogen oxides. “Most Exposed” represents the 1% of population with greatest exposure.)
Importantly, the impacts of truck pollution are not felt equitably, particularly in California. The San Joaquin Valley (including Bakersfield and Fresno) is most impacted along Highway 99, particularly among communities which are disproportionately non-White, including large Latinx and Southeast Asian populations. In Southern California, the areas along the I-10 freeway from LA to Riverside, and the area bounded by the I-605 and I-110 freeways from the port of Long Beach through LA are most affected, including communities like Lynwood and Huntington Park, which are virtually devoid of non-Hispanic White residents.
Our new analysis above shows clearly that nationwide, the communities with the largest exposure to truck pollution are disproportionately communities of color—and that’s especially true in California. While some of the reasons for this disproportionate impact are systemic and require massive shifts to address longstanding structural racism, cleaning up trucks is a relatively straightforward way to at least address a symptom, if not the cause, of this environmental injustice.
Federal inaction means states forced to step up
Emissions from heavy-duty trucks have been declining over time, thanks to federal requirements to limit diesel emissions that were fully phased-in in 2010. Unfortunately, while these standards have reduced NOx pollution from new trucks by 90 percent, nominally, the new diesel emissions controls do not function as well in real-world conditions as they do in tests. At low-speed and heavy-idling conditions, which can be of particularly significant concern around industrial areas like warehouses and ports, in-use truck emissions are as much as 7 times higher than the lab-test certification level at which the current federal standard is set, in part because engine temperatures are not high enough to keep the emissions controls operating efficiently. This has increased the public health risk from ozone in the region above what was anticipated, particularly from respiratory impacts like increased exacerbation of asthma.
Additional regulatory action is needed in order for the South Coast Air Basin (made up of Orange and parts of Los Angeles, Riverside, and San Bernadino counties) to meet national air quality standards. Even as the 2010 diesel standards continue to phase in, heavy-duty trucks remain the largest source of NOx emissions in the Basin (at 45 tons per day in 2023 and 43 tons per day in 2031) and are a prime opportunity for further reductions (Source: EPA).
Faced with continuing air quality challenges and standards which today are proving inadequate to the task, the South Coast Air Quality Management District pressed EPA to move forward on more stringent truck regulations back in 2016—however, the Obama administration prioritized the first-ever greenhouse gas and fuel economy regulations for heavy-duty vehicles, and the Trump administration has put its own Cleaner Trucks Initiative on indefinite hold. Prompted by need and, in part, by such federal inaction, California is moving forward with its own, stronger regulations.
Lower pollution, longer life, and better testing
First and foremost, CARB is proposing to lower the NOx standards on the current federal test procedure, from 0.2 grams NOx per horsepower-hour (a measure of energy) to 0.05 in 2024 and 0.02 in 2027 and beyond, a reduction of 90 percent.
CARB has proposed significant reductions (80-90 percent) in the emissions standards for new heavy-duty engines, including a new test cycle meant to capture operation under low loads (since there is no low-load standard today, the hashed bar represents the tested range of values for today’s 2010-compliant diesel engines). (Source: CARB)
Importantly, CARB is also proposing to extend the useful life and warranty period required of the emissions controls on their trucks. This would extend the period by which these emissions controls are required to be fully operational and protective and also puts the onus and cost for this operation on manufacturers rather than drivers. This rule will nearly double both the required useful life (for semi-trucks, this will increase from 435,000 miles to 800,000 miles in 2031) and warranty period (for semi-trucks, from 350,000 miles to 600,000 miles in 2031), reducing the additional lifetime emissions seen today which result from tampering and poor maintenance.
In addition to extending the warranty/useful life, CARB is working to better monitor real-world operation, including on limits for in-use emissions. Currently, the only in-use emissions limits are related to operation within the “not to exceed” (NTE) zone—this outdated process based on engine operations from 40 years ago captures less than 10 percent of real-world operation, making any limits virtually toothless. CARB is proposing to move to an approach similar to that already used in Europe that covers three main types of operating conditions: idling, low-load operation, and medium- and high-load operation.
Finally, to better ensure emissions reductions in real-world operation, CARB is proposing to add a new “low load” test cycle to the procedure and increasing constraints on “in-use” emissions. The low-load test cycle is focused on engine operations such as extended idling and low-speed operation currently not captured in the federal test procedure, areas of operation where today’s emissions controls are routinely either not operational or operating at very low efficiencies.
Approaching the transition to zero emission trucks
Importantly, CARB is also including for the first time ever a pathway to credit zero-emission trucks for pollution reductions. This policy is complementary to the state’s groundbreaking zero-emissions requirement under the Advanced Clean Trucks (ACT) standard, encouraging manufacturers to accelerate ZEV deployment.
Incorporating and crediting electric trucks in this rule is a key step to transitioning the entire new truck fleet to zero-emission vehicles for both climate and public health reasons and reflects both a recognition that diesel is approaching the limits of efficiency and emissions while acknowledging that electrification is mature enough to be phased into the industry in the timeframe of this rule.
While the ACT standard drives a minimum number of trucks to market over the next decade-plus, complementary incentives such as the ZEV credits found in this rule can help drive adoption beyond those minimum levels. While CARB did not appropriately consider the impact of ACT in the design of the incentive in its proposal, recognizing and incentivizing the end goal is critical to getting there faster, and we are optimistic that CARB will find an appropriate compromise to backstop to any additional diesel pollution while increasing zero-emission truck sales through this rule.
The California Air Resources Board approved the country’s first ever sales requirement on zero-emission trucks, accelerating the adoption of electric trucks over the next 15 years. While the Advanced Clean Trucks standard sets a floor for adoption, CARB’s ultra-low NOx standard could help further spur the transition to electrification of the heavy-duty vehicle fleet. (Source: UCS)
California moving first—feds should follow its lead
While strong action by California will significantly advance progress on both diesel emissions controls and progress towards attaining the state’s air quality goals, more than 60 percent of truck emissions in the state come from out-of-state trucks. For states in the Northeast that are dealing with similar air quality issues, out-of-state trucks are a critical issue. While many have expressed interest in adopting California’s stronger NOx rules, the best way to deal with the national problem of diesel truck pollution is a strong national standard.
The Trump administration began work on a Cleaner Trucks Initiative to set stronger emissions standards for trucks, progress on that has seemed to stall, and the administration itself has erroneously claimed that California’s proposal is “not attainable,” ignoring the reams of detailed research conducted by CARB and the Southwest Research Institute, research in which EPA technical staff themselves have been closely involved.
Regardless of who is President, EPA must move forward to address pollution from diesel trucks and accelerate the transition to even cleaner, zero-emission trucks—the need for further pollution reductions is clear, and the technology is available for diesel-powered trucks to meet both the 0.05 g/bhp-hr standard in 2024 and the 0.02 g/bhp-hr standard in 2027. With the long lifetime of every new truck sold, delay is costly, especially for the communities most affected by truck pollution—and we will pressure EPA to move forward with standards at least as strong as what California has proposed as quickly as possible to address this public health issue.