A real time laser PM measurement instrument has been developed at AEI. The instrument is designed to allow test engineers to understand both steady state and transient PM characteristics during development work and ultimately provide a composite indicator of what portions of the test cycle contribute to the overall cycle PM during the FTP in a CVS cell. This capability can then be used to tune the engine for lowest overall total emissions. Work to date in test cells at AEI shows excellent sensitivity and turndown ratio for PM measurements both pre and post diesel particulate filters (DPFs). When used in conjunction with a multi-port sampling system to draw exhaust samples from different exhaust manifold locations, differences in cylinder-to-cylinder variation may also be quantified.