A mobile emission reduction credit (MERC) is an emission reduction credit generated within the transportation sector. The term “mobile sources” refers to motor vehicles, engines, and equipment that move, or can be moved, from place to place. Mobile sources include vehicles that operate on roads and highways ("on-road" or "highway" vehicles), as well as nonroad vehicles, engines, and equipment. Examples of mobile sources are passenger cars, light trucks, large trucks, buses, motorcycles, earth-moving equipment, nonroad recreational vehicles (such as dirt bikes and snowmobiles), farm and construction equipment, cranes, lawn and garden power tools, marine engines, ships, railroad locomotives, and airplanes. In California, mobile sources account for about 60 percent of all ozone forming emissions and for over 90 percent of all carbon monoxide (CO) emissions from all sources.