Lower sulfur fuel produces fewer particles, and allows use of particulate filters. These systems can greatly reduce emissions of oxides of nitrogen and particulate matter. Welders are often exposed to hazardous gases and airborne particulate matter. Used backwash water contains high concentrations of particulate material. This can be used to remove both particulate and gaseous hazards. Diesel engines produce lower hydrocarbon and emissions, but greater particulate and pollution, than gasoline engines. Welders are often exposed to dangerous gases and particulate matter. Welders are also often exposed to dangerous gases and particulate matter. Marine carbon is further separated into particulate and dissolved phases. Emission of various particulate and volatile substances has been suggested as specific causes. The EPA has defined acceptable concentrations of particulate matter in the air. The reduction in ozone and other particulate matter can benefit human health. Silicon carbide is also used in a sintered form for diesel particulate filters. There are several methods of helping to reduce the particulate matter emissions from coal-fired plants. Particulate matter concentrations are consistently above the norm.