An emissions study for arsenic was conducted at a 300-MW coal-fired plant that was equipped with an electrostatic precipitator (ESP). The input and output streams, such as coal, slag, ESP ash, and flue gas that contained the post-ESP particulates, were collected. Gaseous arsenic was sampled using United States Environmental Protection Agency (USEPA) Method 29, and the arsenic concentrations in the samples were measured using inductively coupled plasma-atomic emission spectrometry. The mass balance recovery of arsenic estimated in this study was 87.2%. The arsenic concentration in the stack gas was 2.5 mug/Nm(3). Approximately 0.53% of the coal-derived arsenic was incorporated into slag, 84.6% of the arsenic was found on the fly ash that was collected by the ESPs, and 2.16% was found in the vapor phase. The relationship between arsenic concentration and ash particle size was also assessed, and arsenic was significantly concentrated in the small-sized particles. The modes of occurrence of arsenic in ash samples were studied using a modified sequential chemical extraction method. The extractable fraction was 13.78%-25.27% of the total arsenic in the fly ash particles, from the four ESP hopper samples. The arsenic concentrations found in the different extraction fractions were as follows: 74.73%-86.22% in the residue; 11%-19% in carbonate-bound, surface oxide-bound ions; 2.7%-6.0% in readily extractable ions; and 0.076-0.27% in water-extractable form. There were no appreciable differences in the arsenic solubility fractions between the different particle sizes of fly ash.