Skip to Main Content View Text-Only

The City of Portland, Oregon

Office of Management & Finance

Bureau of Revenue and Financial Services

Phone: 503-823-5288

Fax: 503-823-5384

1120 SW 5th Avenue, Rm 1040, Portland, OR 97204

Clean Air Construction FAQs


Background Information - General

Background Information - Human Health

Clean Air Construction Initiative

Clean Air Construction Program

Background Information - General

1. What is the significance of the diesel engine?

It is not an exaggeration to say that diesel engines are crucial to modern life. The diesel is favored due to its high power output, fuel efficiency, and high torque at lower engine speeds. Because of these advantages diesel engines move the vast majority of commercial goods across Oregon and across the country. In addition, a large percentage of heavy construction equipment is powered by diesels. A variety of advanced technologies may promise a future with cleaner engine technology, however, the reliable and durable diesel will continue to play an important role in commercial activity for the foreseeable future. Despite its importance, the major problem associated with the diesel engine is the air pollution that it creates.

2. What is diesel exhaust?

Diesel exhaust is the result of burning fuel inside a diesel engine. This combustion process creates a complex mixture of gases, fine particles and toxic air pollutants. The major gases of concern are carbon monoxide, carbon dioxide, nitrogen oxides and nitrous oxide. The major particles are soot, hydrocarbons, sulfate, nitrate and metals including aluminum, iron, silicon, titanium and zinc. The exhaust also contains several dozen other types of gases and particles which are known to be toxic including formaldehyde, acetone and polyaromatic hydrocarbons (PAHs). The exact makeup of diesel exhaust varies and is dependent on things like vehicle type, fuel type, vehicle use or task, vehicle speed and whether the vehicle or equipment is properly maintained. Weather conditions such as air temperature can also influence the gases and particles that make up the diesel exhaust mixture.

3. What are the sources of diesel exhaust in Portland?

Diesel emissions by source

4. What are the problems associated with diesel exhaust?

Human Health Concerns (link to the next section)

Environmental Concerns: The pollutants released from diesel engines can be deposited on land and eventually find their way into water bodies. One result of this is acid rain which can cause forest damage. Another result is increased nitrates in wetlands, lakes and streams which can harm aquatic life and impact drinking water quality. Acid rain along with soot deposition can cause metal corrosion and reduce the useful life of buildings, bridges and other human made structures.

Environmental Justice: The harms associated with diesel exhaust are not distributed evenly. Communities nearer to the sources of diesel emissions are likely to experience disproportionate impacts. These are communities that live, work and play near busy truck and bus routes, areas of chronic traffic gridlock, freight terminals and construction sites. There is a disproportionate impact on African American and Latino populations in the Portland metro area. They face up to 3 times higher exposure rates since those communities tend to live in proximity to high development and transportation hub activities.

Climate: Diesel exhaust is the largest source of black carbon particles in the United States. When it comes to global warming, the importance of black carbon is second only to carbon dioxide. The black carbon particles are released to the atmosphere and absorb heat which can increase air temperatures. These particles can also fall on to snow and ice fields, absorb light and release heat which increases the rate of melting.

5. Why is the Portland Metro Area at a greater risk of exposure to diesel exhaust?

According to the Oregon Department of Environmental Quality (DEQ) Portland has a greater health risk from air toxics exposure than less densely populated areas of the state. DEQ has also identified that the air toxics of greatest concern in Portland are benzene, polycyclic aromatic hydrocarbons (PAHs) and soot from diesel engines. Since Portland is at greater risk of exposure to air toxics than other areas of the state and since the increased risk is primarily driven by products found in diesel exhaust, it is reasonable to assume that people living in the Portland Metro area are at a greater risk of exposure to diesel exhaust. This risk is primarily driven by the population density of the Portland Metro area, the number of vehicles that are on roadways, and the amount of construction, freight, marine and rail activity that occurs within the Metro boundary.

6. How can diesel exhaust be reduced or controlled?

The good news is that improved technology is currently available to significantly reduce the amount of pollution associated with the diesel engine. Improved engine design, idle reduction and cleaner fuels have helped to reduce diesel emissions. However, exhaust after-treatment technology including improved catalysts, diesel particulate filters and NOx reduction technology is essential to achieving the emissions reductions needed to significantly reduce the risk of harm. In addition, regular inspection and maintenance to keep the control technology operating properly is critical to keeping emissions rates low.

7. Why does the Clean Air Construction initiative focus on construction vehicles and equipment?

Construction equipment is designed and built to have a long useful life. It can be common to see 30-year-old equipment on job sites. These older vehicles do not have the advanced pollution control technology for NOx and fine particulates that comes standard on the US EPA Tier 4 equipment that is manufactured today. Also, there are few incentives for business owners to retrofit or replace older equipment if that equipment remains operational. Leveraging public dollars to reduce diesel emissions on public construction projects can help to reduce a large source of diesel emissions in the Portland area. And since these types of projects are within the city limits that means real reductions will occur near where people live and breathe.

Background Information - Human Health

1. What are the health impacts of diesel exhaust?

Exposure to diesel exhaust can have immediate health effects. Diesel exhaust can irritate the eyes, nose, throat and lungs, and it can cause coughs, headaches, lightheadedness and nausea. Exposure to diesel exhaust also causes inflammation in the lungs, which may aggravate chronic respiratory symptoms and increase the frequency or intensity of asthma attacks.

Diesel particulate matter is a known human carcinogen. There are also non-cancerous, long-term health effects associated with exposure which include asthma, heart disease, chronic lung disease, neurological damage and premature mortality.

2. What are the societal costs of diesel exhaust?

The levels of diesel pollution in Oregon result in significant public health impacts. Including:

  • Over 400 premature deaths
  • Over 140 non-fatal heart attacks
  • Over 25,000 work loss days

The monetized value of diesel pollution health impacts in Oregon exceeds $3 billion annually.

3. Who is most impacted by diesel exhaust?

Diesel engines are a major source of fine-particle pollution. The elderly and people with emphysema, asthma, and chronic heart and lung disease are especially sensitive to fine-particle pollution. Because children's lungs and respiratory systems are still developing, they are also more susceptible than healthy adults to fine particles. Exposure to fine particles is associated with increased frequency of childhood illnesses and can also reduce lung function in children.

Additionally, certain occupations expose people to higher levels of diesel exhaust, increasing their risk of negative health effects. These jobs include railroad workers, truck drivers, loading dockworkers, diesel mechanics and those who work in and around construction equipment. In total, this accounts for over 29,000 members of the Oregon workforce.

Clean Air Construction Initiative

1. What does the Clean Air Construction (CAC) initiative mean for my business?

If you are looking to work on an applicable public agency's construction project valued over that agency's applicable CAC threshold on or after January 1, 2020, you need to be aware of the CAC requirements. CAC requirements include two components, 1) Idle reduction requirements that go into effect January 1, 2020. 2) Phased-in diesel engine requirements - beginning with the oldest and dirtiest engines - go into effect January 1, 2021. See the CAC Requirements for specifics on the phase-in schedule.

2. What types of construction projects does the CAC initiative apply to?

The specific type of construction projects the CAC requirements apply to will vary by applicable public agency, depending on that agency's applicable contract dollar threshold and how construction was defined in a specific agency's CAC adoption document.

3. Why are public agencies in the Portland Metro area adopting Clean Air Construction requirements?

Levels of pollution from diesel engines in the Portland Metro area are above the State’s adopted health benchmarks. Diesel engines produce fine sooty particles that travel through the lungs into the bloodstream, where they cause numerous health impacts to the cardiovascular and nervous systems, including as a known carcinogen. The State of Oregon does not regulate diesel particulate matter and the impacts disproportionality impact people living in working in Portland Metro area. Given the lack of regulation, public agencies in the Portland Metro area are adopting the CAC requirements to reduce the air quality and health impacts that result from our projects.

4. Why does the idling requirement allow engines to idle for 5 min?

Diesel engines need to idle to cool down and rest between periods of heavy operation. Turning off a diesel engine before it has time to cool down can negatively impact engines life and performance. The CAC nonroad idling requirement also aligns with the State’s 5 min idling requirement for on-road vehicles in the public right of way.

5. Do idling requirements apply to trucks?

The CAC idling requirements only apply to nonroad diesel engines. Individual public agencies adopting the CAC requirements may have additional project site idling requirements included in contract requirements as per separate ordinances, resolutions, or policies.

6. Isn't turning the engine on/off to avoid idling bad for the engine?

No. In fact, idling can reduce engine life and wastes fuel and money.  Check out the following resources from other States: and

7. Why are the CAC engine requirements phased-in over so many years?

The CAC engine requirements phase-in approach was designed to reduce the burden of compliance on the contracting community while still maximizing emissions reductions over the long term. Contractors working on applicable projects will need to upgrade applicable equipment and vehicles, which can come at a significant cost. The phase-in schedule is intended to give contractors time to prepare and plan for upgrades in a manner the has the least impact on their business operations and does not impede their ability to compete for work on local public projects.

8. What if my supplier is delivering materials on a flatbed truck to the project site, are they required to meet the CAC?

The CAC requirements only applies to nonroad construction equipment and on-road cement mixers and dump trucks. Flatbed trucks and other delivery vehicles are not otherwise subject to the CAC requirements.

9. As a contractor, what do I need to do to demonstrate compliance?

Contractors (prime and sub-contractors, and applicable suppliers) will be required to submit to the CAC Program all requested diesel equipment/vehicle information needed to verify compliance, including confirmation that retrofit devices are maintained on the equipment in proper operating condition. Further details on the compliance process and required information will be developed as part of the program development in 2019-2020. While details are currently being developed, it is the intent that:

  • upon determining compliance with the requirements, the CAC Program will issue an equipment/vehicle decal for each compliant piece of equipment/vehicle, and that the decal must be displayed on the compliant equipment/vehicle at all times in a location readily visible by agency staff.
  • random on-site inspections by agency staff (or approved program operator) will be conducted on a project by project basis.
  • contractor and vehicle compliance information will be housed in a database accessible by all local public agencies that have adopted the CAC requirements to verify compliance across jurisdictions.

10. What if I can’t find a compliant piece of equipment?

Contractors may apply for exemptions to the diesel engine requirements on a per project basis in circumstances where:

  • The equipment/vehicle is required for an emergency (including for underground equipment operators).
  • The required emission control device would obscure operator lines of sight or otherwise impact worker safety, or the equipment is not able to be retrofit with a verified emission control device; and no compliant rental equipment is available within 100 miles of the job site.
  • The contractor can demonstrate that due to the uniqueness of the equipment/vehicle or similar special circumstances, it is not reasonable to comply with the diesel engine requirement for a specific piece of equipment/vehicle.

11. How do I find out if my construction equipment or vehicle engines are subject to the CAC requirements?

Review the Compliance Options Protocol steps.  The first few steps identify which construction equipment/vehicle engines are subject to the CAC requirements.

12. How do I determine compliance of an on-road vehicle?

Look up the engine model year and ensure all exhaust control systems are active and working properly. Vehicles with 2007 or newer engines and properly functioning exhaust control systems are compliant.

13. To determine compliance of nonroad equipment, how do I look up the engine Tier?

Engine tier can be looked up by knowing the engine model year and the horsepower of the equipment.  Reference the EPA Nonroad Ratings/Tier Chart.

14. What options are available to upgrade my vehicles/equipment for compliance with the CAC requirements?

There are a number of options for contractors to comply with the CAC requirements. For future purchases and capital investments contractors should:

  • Include CAC requirements in their plans for future vehicle/equipment purchases and replacements as vehicles and equipment reach their end of life.
  • Prioritize purchases of low carbon or alternative fuel equipment and vehicles, such as electric, biofuels, or compressed natural gas (CNG).

To upgrade existing equipment for compliance, contractors have several options at various price points, beginning with the lowest cost options:

  • Rent compliant vehicle/equipment for use on the job.
  • Retrofit vehicle/equipment with emission control devices
  • Repower existing vehicle/equipment with new Tier 4 engine for nonroad equipment
  • Replace engine with 2007 or newer engine for on-road engines
  • Purchase used vehicle/equipment that was 2014 or newer nonroad or 2007 and newer on-road.
  • Purchase new vehicle/equipment

15. How many public agencies have adopted the CAC requirements?

For a currently list of public agencies that have adopted the CAC requirements, check the Clean Air Construction Requirements page. 


Clean Air Construction Program 

1. Who do I contact with questions related to the CAC initiative?

Contact Stacey Foreman, City of Portland Sustainable Procurement Program Manager at Agency-specific questions (other than for the City of Portland) will be forwarded on to the appropriate agency-specific contact.

2. What support the program will provide the contractors?

Program details, such as contractor support, will be determined as part of the program development process in 2019-2020. At a minimum, the CAC Program will provide technical assistance and web-based resources to assist contractors in registering vehicles/equipment and determining CAC compliance. Other aspects of contractor support currently being considered and/or pursued include:

  • Utilization of State of Oregon VW Settlement money for grants that support diesel engine retrofits or replacements.
  • Assisting contractors with pursuing EPA DERA grant funds for diesel engine retrofits or replacements.
  • Low-cost financing partnerships with local financial institutions for diesel engine replacements.

In addition, per Resolution 37403, the City of Portland’s Bureau of Planning and Sustainability and Procurement Services will return to City Council in October 2019 with a proposal for funding assistance for COBID certified construction firms working on construction projects for the City to comply with the Clean Air Construction requirements.

3. If the City of Portland determines that my equipment and vehicles are compliant with the CAC requirements, will that approval be accepted by other agencies who adopt the CAC requirements and vice versa?

Yes. One of the main goals in taking a regional approach to developing the CAC initiative is to reduce the administrative burden on contractors by not having multiple standards and multiple compliance processes.