Electric trucks, electric forklifts, upgrading tractors and pump engines to Tier 4, implementing conservation management practices on the farm, low VOC pesticides, vapor recovery on our farm gasoline tanks; at what point does it end? Especially when no one else in the country is doing it. In fact, no competitor in this country, or the world for that matter, must implement the stringent air quality measures that California growers have to. And it isn’t even close! But isn’t that enough?

Not according to the California Air Resources Board (CARB), which recently held a workshop on Tier 5 engine technology for offroad engines. Yes, that’s right, Tier 5. 

CARB staff is starting work on potential amendments to the off-road diesel engine standards in what they are calling the Tier 5 rulemaking. The Tier 5 rulemaking aims to reduce oxides of nitrogen (NOx) and particulate matter (PM) emissions from new, off road compression-ignition engines compared to what is allowed by today’s Tier 4 final emission standards. It will likely include more stringent exhaust standards for all power categories, including those that do not currently utilize exhaust aftertreatment like diesel particulate filters and selective catalytic reduction. At the workshop, staff indicated they are considering possible elements to achieve NOx standards up to 90% more stringent and PM standards up to 75% more stringent than today’s Tier 4 standards. First-time CO2 emission standards for off-road engines may also be proposed. Other possible elements include enhancing in-use compliance, proposing more representative useful life periods, and developing a low load test cycle. Staff is also investigating first-time, off-road, on-board diagnostics requirements and encouraging the development of zero-emission off-road equipment. Staff plans to bring a proposal to the Board in 2025, with implementation of the Tier 5 standards expected to begin in 2029. That is less than five years away, and there isn’t even an engine on the drawing board!

So how does CARB intend we get there? According to information published by the Association of Equipment Manufacturers, CARB intends to take several steps to ensure that aftertreatment systems perform as intended in the field.  It breaks down as follows:

Aftertreatment aging. CARB has developed what it refers to as the DAAAC, or Diesel Aftertreatment Accelerated Aging Cycle. It’s a new protocol designed to better estimate the aging of aftertreatment devices in off-road equipment.

Selective Catalytic Reduction (SCR) inducements. CARB is looking to codify that guidance into its proposed Tier 5 rule. This could force engine and equipment manufacturers to make additional changes. For instance, both a warning lamp and audible alarm will be required when various system sensors detect low diesel exhaust fluid (DEF) or DEF quality tampering, culminating with idle or engine shutdown if the fault mode isn’t corrected within a certain timeframe.

Low load cycle. This proposed standard impacts engines in the 56- to 560-kW range. A new test cycle has been developed to include an extended idle period. This is to account for the impact idle time has on emissions because CARB says its data suggests off-road engines idle anywhere from 30% to 50% of the time.

Idle NOx requirement. This proposed standard impacts all power categories. Engines in the 56- to 560-kW range will satisfy this requirement by satisfying the low load cycle requirement mentioned above. All other power categories have their own idle requirements. To comply with the NOx idle test, engines need to reach a pre-determined temperature at 3.5% rated power for 30 minutes. If the engine can’t meet the idle NOx requirement specified for that power category, an engine shutdown system will be required.

But it doesn’t stop there. A new CARB provision will require all Tier 5 engines that have an electronic control unit to meet certain diagnostic requirements. Engines that incorporate an SCR must have an onboard monitoring and diagnostics system, while engines without an SCR can utilize an onboard diagnostic system.

But one must ask why? Isn’t CARB pushing everything to go electric? It triggers many questions. Why would manufacturers bother to spend the significant resources to tool up and make compliant engines for only a short period of time? Furthermore, why would manufacturers spend the resources to make engines only for California? If they do end upmaking a Tier 5 engine, what will it cost? These are exactly the questions we are asking CARB. California agriculture has been devastated by the cost impacts of California-only air quality regulations that make it difficult, if not impossible, to compete in a world marketplace as agriculture does. The time has come. CARB, enough is enough.