The Trump Administration has proposed to roll back successful US clean car and fuel economy standards and to take away California’s—and other states'—ability to set clean car standards of their own. My colleague, Luke Tonachel, explains the basics of this dumb and harmful proposal here.

Buried deep in the Trump proposal is the recognition that the rollbacks, if enacted, may have effects on some states’ State Implementation Plans, or SIPs—documents that states that do not meet federal air quality standards are required to give to EPA to show how they will come into compliance, or attainment, with those standards. This is more than just some nerdy paperwork, as I will explain below.

Let’s take the Los Angeles region as an example. The local South Coast air basin is not meeting the (old) federal 80 ppm standard for ozone (smog) and must meet that standard by 2023. Due largely to tailpipe emissions from cars and trucks, the South Coast has little chance of meeting the standards by that date, but if the Trump rollback plan goes into effect its chances will drop to near zero.

There are three main reasons for this. First, because the Trump plan is designed to weaken GHG and fuel economy standards at a time when auto vehicles miles traveled are increasing, there will be more auto exhaust emitted in the South Coast air basin (and everywhere else in the US). Auto exhaust contains oxides of nitrogen (NOx), a key ingredient, along with volatile organic compounds, in the formation of ozone in the atmosphere. In general, more NOx means more ozone, and the federal ozone target will get farther away.

Second, the Trump Administration may attempt to kill California’s zero emission vehicle (ZEV) requirements based on an unprecedented attempt to revoke federal waivers that have been granted to the state since the 1990s. But the benefits of ZEVs extend beyond lower GHG emissions—because no fossil fuel is combusted, no oxides of nitrogen (NOx), a key ingredient of smog are emitted either. So, fewer ZEVs means more ozone, and the federal ozone target will get farther away.

Third, gasoline consumption would increase, and much of the gasoline consumed in California is produced and refined in California through processes that also emit oxides of nitrogen. Again, more ozone is the net result.

Even worse, when this rollback to U.S. clean car standards is mixed with the twenty or so rollbacks to other EPA clean air-related standards including rules limiting emissions from oil and gas drilling and standards reducing emissions of mercury and other toxic emissions, the ability of states to obtain healthy air will be at risk.

What happens if a state or region misses its SIP target date? It’s not good. The federal government can come in and take over local regulation of air pollution. All federal transportation funding is frozen—and most big transportation projects like subways or light rail depend on federal dollars. Air quality permits get much tougher to obtain because of increased offset requirements, putting the brakes on economic expansion and major retrofits of older facilities. Local air regulators like the South Coast Air Quality Management Board may need to crack down tighter on stationary sources such as oil refineries to achieve NOx reductions that they had anticipated to obtain from mobile sources—now denied them by the Trump Administration. Regulation of mobile sources by regulators such as the California Air Resources Board (CARB) may also get tougher in order to make up for the increased NOx emissions due to the rollbacks. Indeed Mary Nichols, the head of CARB, has been recently quoted as saying that California will need to make up this gap by looking to other sources—such as petroleum refineries—to regulate further or even more drastic measures such as phasing out internal combustion engine vehicles. Her statement does illuminate the seriousness of the problem that the Trump Administration has caused by proposing the SAFE rule.

California is not alone in facing these problems. Other states have enacted clean car and zero emission vehicle rules similar to California’s and SIP compliance in those states may also be at risk. For states with significant exposure to coal-fired electricity generation, the Trump proposal to kill the Clean Power Plan and other clean air standards may also increase the difficulty of meeting Clean Air Act requirements.

To avoid these results, the federal government would need to force states to rewrite their SIPs to weaken then, a process that will take years and result in lengthy litigation. In the meantime, air quality in Los Angeles and other cities also struggling to meet air quality standards will only get worse, while future economic expansion will become doubtful. Whether the Trump Administration intends this chaos and disruption is a mystery, but the negative consequences of its clean cars and fuel economy rollbacks are clear.