Abstract: A pollutant emissions monitoring system and a method of measuring pollutant emissions, particularly fly ash, of gas passing through stacks of coal-fired boilers. An all optical-based emission monitor has an opacity monitor and a flow rate monitor connected to a remote data processing facility by a single fiber optic cable. A timing/calibration wheel assembly initiates measurement cycles and calibrates the opacity monitor. A first beamsplitter polarizes a collimated light beam from a light source into two collimated light beams, an upstream and a downstream beam. A second beamsplitter receives the collimated light beams, reflects a portion of the light beams to the flow rate monitor and passes the remainder of the light beams to a retro-reflector.