Selected by SAE E31 committee as the standard for gas turbine nonvolatile particulate matter mass emissions measurements. Turbine engine (helicopter) tests at Wright Patterson LII signal analysis results in the determination of the mass concentration, volume concentration, active surface area, and primary particle diameter of the particulates. In this context, primary particle diameter refers to the geometrical diameter of the spherical black carbon based particles formed during the combustion of hydrocarbon fuels; often these particles fuse together in the combustor to form a single nonspherical larger particle known as an aggregate. LII does not measure the size of the aggregates emitted from the combustor.The measurements made with LII are produced with each laser pulse at a 20-Hz rate, permitting online time-resolved data collection and reporting of results in real time. Auto-compensating laser-induced incandescence (AC-LII) enhances the LII technique by recording the temperatures of the irradiated particles during the measurement process. This technique automatically compensates for any changes in the experimental conditions, including fluctuations in local ambient temperature, variation in laser fluence, laser beam attenuation by the particulate matter, or desorption of condensed volatile material. The LII 300 instrument produced by Artium Technologies distinguishes itself from other LII instruments by being the only commercially available instrument offering AC-LII. AC-LII is based on the use of a traceable calibration source to establish the spectral sensitivity of the instrument to incandescence.Measurement at two distinct spectral bands enables real-time two-color pyrometry to measure particle temperature. This automatically compensates for:• Fluctuations in local ambient temperature• Variation in laser fluence• Laser beam attenuation by the particulate matter• Desorption of condensed volatile materialThese are issues that often affect conventional laser -induced incandescence (LII).