DEEP: Mobile Sources

Mobile Sources

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What are Mobile Sources?

Mobile sources include a variety of vehicles, engines and equipment, and can be classified as either on-road mobile sources (e.g. trucks, buses, passenger cars, motorcycles) or off-road mobile sources (e.g. construction equipment, lawn, garden and snow equipment, personal recreation equipment, locomotives, marine vessels etc.).

Why do Mobile Sources Matter?   

Mobile source pollution accounts for approximately fifty percent of all man-made air pollution emitted in Connecticut and throughout the Northeast. This pollution affects human health and our environment.
Emissions from mobile sources contribute to the formation of ground level ozone, which is the primary constituent of smog.  According to version 1 of the 2014 National Emissions Inventory (NEI), 21.4% of total volatile organic compound (VOC) emissions and 66.8% of total emissions of oxides of nitrogen (NOX) are shown to be transportation related.  Studies have shown that high concentrations of ozone are harmful to human health, wildlife, crops, and buildings.
In addition, whether fueled by gasoline or diesel fuel, mobile sources are significant contributors to measured levels of particulate matter (PM).  Mobile source particulate emissions consist mainly of very tiny, fine particles, also known as PM2.5, that are less than 2.5 microns in diameter.  Fine particulate matter is a major health concern and contributes to unsightly haze.
According to the US Energy Information Administration, in 2014, transportation emissions of greenhouse gases (GHG), made up 43% of the GHG inventory and are the leading source of GHG emissions in Connecticut.

The Future of Mobile Sources in Connecticut

Connecticut’s non-attainment status for ozone and maintenance status for particulate matter requires strategies designed to reduce emissions of NOX, VOCs, sulfur dioxide and PM2.5.  The transportation sector is a significant source of these pollutants.  Additionally, diesel-powered engines produce black carbon, a significant contributor to global warming, and emissions of toxic air pollutants, along with carbon dioxide (CO2) and PM2.5 .  Minimizing vehicle miles traveled (VMT) for the on-road sources is an important strategy to improve Connecticut’s air quality.  For more information, read Connecticut's Transportation and Air Quality Challenges.

State efforts to address Climate Change consider the substantial contribution of mobile sources to the state’s total annual emissions of CO2. The Global Warming Solutions Act calls for a minimum of an 80% reduction of GHG emissions from 2001 by 2050.  Many mobile source options are available, with implementation requiring a change in the transportation culture of Connecticut.

Connecticut’s Transportation Strategy Board (TSB) has also identified key transportation initiatives which integrate Connecticut air quality goals. To find out more about these initiatives and recommendations, read TSB’s 2007 report entitled “Moving Forward: Connecticut’s Transportation Strategy

More Mobile Sources Information
Electric Vehicles: EVConnecticut is preparing the state for a rapid and seamless integration of electric vehicles into the market by providing resources and information to owners of electric vehicles (EVs) and by expanding the availability of EV charging stations in Connecticut.
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You and Your Car, Reducing your Environmental Footprint: Cars are a major source of air pollution. Everything from the manufacture of your car to the way you drive can have an effect. Take the time to find and compare cars according to gas mileage, GHG emissions, air pollution ratings, and energy impact scores at
Vehicle Emissions: Vehicle emissions' testing, through the Connecticut Inspection and Maintenance Program, is one of the state's most effective ways to improve air quality. The program reduces air pollution by identifying vehicles with emissions above emission standards and requiring that they be repaired.
Clean Cars: The Connecticut Low Emission Vehicles II Program requires that all new vehicles sold in Connecticut, beginning with model year 2008, meet strict California emission standards.
Diesel Reduction Initiatives: Connecticut's multi-faceted reduction strategy includes construction equipment, school buses, and other diesel engines. Diesel Grants and Incentives help to implement these strategies. This includes information on DEEP’s planning efforts to reduce air pollution caused by Freight Movement.
Anti-Idling Efforts in Connecticut: Anti-idling programs provide a cost effective mechanism to improve air quality and reduce risk exposure from the potential health impacts of vehicle exhaust. Programs to fund anti-idling technologies are also valuable in reducing idling emissions from on-road fleets.
Fuels : There are many different types of mobile source fuels in use. Reformulated gasoline and diesel are two of the more commonly used fuels in Connecticut. Highway diesel fuel is regulated by the EPA to limit the sulfur content, assuring healthy air quality.


Gasoline Dispensing Facilities (GDF): A GDF is any stationary facility dispensing gasoline into the fuel tank of an on- or off-road motor vehicle, lawn and landscaping equipment, boat, test engine, or generator. Stage I, Stage II, and Onboard Refueling Vapor Recovery systems prevent the discharge to the atmosphere of gasoline vapors from the loading of gasoline into underground storage tanks (USTs) and the refueling of a motor vehicle’s fuel tank.


Mobile Sources and Climate Change: Mobile sources make a substantial contribution to the state’s total annual emissions of the greenhouse gas, carbon dioxide.  In addition, diesel-powered engines produce black carbon, a significant contributor to global warming.
Related Links (to EPA website)
Content Last Updated on September 10, 2018