The proposed rule would also reduce emissions of hydrocarbons from new portland cement kilns by 220 tons per year, a 38 percent reduction from projected future emissions levels. Some of these hydrocarbons are volatile organic compounds, which can contribute to the formation of ground-level ozone. Ground-level ozone can cause a variety of health problems because it damages lung tissue, reduces lung function, and makes the lungs susceptible to other irritants. Portland cement manufacturing is an energy intensive process in which cement is made by grinding and heating a mixture of raw materials such as limestone, clay, sand, and iron ore in a rotary kiln. The main source of air toxics emissions from a portland cement plant is the kiln.
Emissions originate from the burning of fuels and heating of feed materials.
Air toxics are also emitted from the grinding, cooling, and materials handling steps in the manufacturing process. EPA's published list of industry groups to be regulated includes portland cement manufacturing plants. EPA based the emission limit for hydrocarbons on the emissions levels that can be achieved through the pollution prevention technique of using clean feed materials. However, the rule does not dictate any particular type of air pollution control. Rather, the rule allows industry to use a variety of techniques to achieve the emissions limits.