following assumptions about the shape and refractive index of the particles, an aerosol number and size distribution can be obtained (in practice, particle concentration in a certain number of discrete size bins is usually reported). Optical particle counters permit real time measurement particle size distribution and (unlike gravimetric methods) include any volatile component of the aerosol; however , the assumptions, required to derive the instrument calibration curves dictate that care is required when comparing optical particle counter measurements with, for example, filter or TEOM data, on in any situation where the particle population may vary significantly from the standard used to calibrate the instrument (typically, monodispherse, polystyrene latexspheres). Typical instrument performance is to measure particles over a diameter range of 0.1-10 ไมโครเมตร, divided into 10-20 size bins. Optical particle or dust monitors are frequently handheld units, used to monitor industrial and occupational health-related aerosol exposure, in addition to performing environmental measurements.