The U.S. Environmental Protection Agency has awarded $8 million for projects in 21 states and Puerto Rico to reduce diesel engine emissions through the agency’s Diesel Emission Reduction Act (DERA) program.

The grants will fund projects such as retrofitting older school buses to improve air quality for children riding to school, upgrading marine propulsion and agriculture engines, as well as replacing long haul truck engines, according to the EPA. Each project is designed to improve air quality and support economic growth in local communities.

The 21 projects will receive funding through the EPA’s DERA fiscal-year 2014 allocation. The selected projects are cost-effective and will impact fleets operating in areas that will benefit from additional steps to protect air quality and public health, the EPA said.

The DERA funding covers engine replacements, repowers, and idle reduction technologies to clean up a variety of older diesel engines, including those in heavy-duty trucks used at ports, delivery trucks, long haul trucks, marine vessels, school buses, and agricultural equipment.

Since the start of the DERA program in 2008, the EPA has awarded more than 700 grants in 600 communities across the country.