A gaseous and particulate source emissions sampling program has been conducted at a Portland Cement production plant in Rapid City South Dakota. The study was conducted to determine the cause of the formation of an opaque detached plume from the plants' dry process kiln. The instack opacity of the emissions was less than 10 percent while the opacity of the plume five to ten stack diameters from the mouth of the stack was in excess of 40 percent, thus giving an appearance of a detached plume. The sampling and analysis program included particulate emissions measurements, particle sizing and composition, and measurements of gaseous and particle ammonia, chloride, fluoride, and sulfur dioxide. Extensive process materials sampling and analysis were also conducted. Based on the resulting data one conclusion is that the opaque detached plume is the result of ammonium chloride particles formed by the reaction of gaseous ammonia and hydrochloric acid. It was also found that the ammonia in the cement plant was generated from the shale portion of the raw products when the raw product was passed through the heat exchanger.