This amazing unit simultaneously measures 6 mass concentration ranges (PM1, PM2.5, PM4, PM7, PM10 and TSP) displayed in mass mode, as well as five popular cumulative particle sizes (> 0.3, 0.5, 1.0, 5.0 and 10.0 microns) in count mode. Using a unique mass conversion, the Aerocet 531S particle counts from eight size ranges which are converted to mass using a proprietary algorithm for typical-density aerosols. Accommodation for special particulate with different densities is provided through user–programmable “K-factors”. The Aerocet 531S stores up to 6,257 records. These records can be viewed on the display, or transferred to a computer via USB or RS232. Our included Comet download utility makes file transfers easy in an Excel® formatted output. An optional temperature / relative humidity plug-and-play sensor immediately adds ambient temperature and relative humidity capabilities to displayed and logged data.