We propose to develop a highly sensitive and portable device to monitor soot particle mass distribution from aircraft engine exhaust. The proposed method is based on sensitive electric charge measurement on soot particles of specific mass, which was selected via Lorentz force. Through extensive investigation on soot emission from internal combustion engines over the past four decades, it has been well known that engine soot particles are usually charged. Counting particle charge at specific mass could lead to the determination of both total particle count and mass. Currently commercially available electrometric measurements on charged particles suffer from rapid signal drift, which limits its applications on soot emission measurements. In our proposed design, an amplitude modulation scheme is included to eliminate the influence from signal drift and also improve detection sensitivity. The proposed soot mass distribution monitor will be less than 50 pounds in weight and consume approximately 300W electrical power. It will also be capable of being remotely controlled and operating under vacuum condition. Since most of the components are commercially available, total cost of the proposed device could be less than $30,000.