Supra truck refrigeration units from Carrier Transicold now meet the U.S. Environmental Protection Agency (EPA) Tier 4 emissions standard, according to the company. The units' Tier 4 diesel engines not only meet EPA particulate matter and NOx standards, but also comply with California Air Resources Board (CARB) requirements. The engines are now standard on Carrier Supra 550, 650, 750, 850 and 950 models, as well as its Genesis R-90 units.