AirPhoton Nephelometers provide laboratory level real time particulate measurements in a robust field deployable design. The IN Integrating Nephelometer models provide three wavelength measurements of light scattered by particulate matter, over the angular range from 7° to 170°. Employing an innovative design, the forward and backward scattering measurements are made completely independently. LED technology is used to make these measurements at 450nm, 532nm and 632nm, and to a sensitivity better than 10-7m-1. Internal sensors measure and log temperature, relative humidity and pressure.