Response characteristics of scattered light aerosol sensors used for control monitoring

The response characteristics of scattered light aerosol monitors used in control monitoring applications were evaluated. In this report, "control monitoring" refers to continuous, fixed point monitoring used to ensure that dust controls are effective. Instruments evaluated included the following: an ATI-722, which uses a white light source; a RAM-S, which uses a LED source; and a PCAM-TX, which uses a LED source and provides a correction for particle size. The linearity of the monitors was evaluated from 0.5-10 mg/m3 with the use of coal dust as an aerosol. This concentration range was broken up into two smaller ranges since it was not possible to generate an aerosol with a constant size distribution over the entire range. All instruments showed a linear response with concentration for constant dust size distribution. The size sensitivity of the instruments was determined by passing a test aerosol through a series of impactor stages and measuring the mass response of each instrument relative to the indicated mass response of an Aerodynamic Particle Sizer (APS). The particle size was varied from 2-14 microns. The mass response of the instruments relative to the APS over this size range varied from as low as 0.1 to as high as about 5. The PCAM provides data that indicate changes in the size distribution of the aerosol being monitored. A simple model was developed to relate the net response of each test instrument to various log normal size distributions. The user of the instruments has to be aware of particle size changes in the aerosol being monitored since changes in the size distribution will affect the relationship between the response of the instruments and the mass concentration. Guidelines for instrument use are given in order to show how the instruments can be applied to the continuous monitoring of dust in the workplace.