Sacramento -- The California Air Resources Board (CARB) last Friday agreed to open a 45-day public comment period on the use of clean diesel in the state, according to news reports. The South Coast Air Quality Management District (SCAQMD), the air quality regulators for Los Angeles and neighboring counties, implemented rules in 2000 that effectively banned fleet operators in the state from using diesel-powered vehicles. Though diesel fuel produces lower emissions of certain pollutants than gas, levels of particulate matter and nitrogen oxide are deemed unacceptable by CARB and SCAQMD. The District’s fleet rules imposed an economic disadvantage on the Southern California region by forcing fleet operators to purchase gas or natural gas-fueled vehicles, according to the California Chamber of Commerce.The diesel industry said in a prepared statement this week that diesel has made continuing improvements in cleaner engines and fuels and is on track to meet stringent federal emission reduction mandates that take effect in 2007. By 2007, the Diesel Technology Forum said, on-highway diesel engines will produce near-zero emissions and will be certified to the same emissions standards as natural gas.