Development of a Low-Cost Particulate Matter Monitor

The purpose of this project is to develop an inexpensive device that monitors concentrations of airborne particulate matter (PM). The goal is a particulate monitor that is small, lightweight, portable and quite sensitive. PM is a major public health issue, and there is an urgent need for inexpensive devices that monitor PM in epidemiological studies of aerosol exposure effects and exposure to pollutants such as diesel exhaust, environmental tobacco smoke, and power plant emissions. Such tools could also be applied to ventilation control for better indoor air quality with lower energy expenditure, monitoring airplane cabin air quality and improving industrial hygiene. The PM monitor described in this report could thus be of substantial value to the State of California.

This project is based on initial work at LBNL to monitor airborne particulate matter concentrations by using thermophoresis — motion of particles induced by a thermal gradient — to deposit particles on a piezoelectric resonator whose resonant frequency falls in proportion to the mass deposited. The present project uses microfabricated elements as the thermophoretic source and the mass-sensing resonator. (The acronym MEMS — for micro-electro-mechanical system, applies to this type of system.) The project is the result of collaboration between researchers at LBNL and the Berkeley Sensor and Actuator Center (BSAC) on the Berkeley campus of the University of California. The MEMS PM monitor currently has a limit of detection of 18 μg m^-3 for 24 hour sampling. Several large instrument manufacturers have expressed commercial interest in this device, as well as in use of its mass-sensing module in other instruments.

During this study, the optical component of the device was not fully implemented and has been left for future efforts. Suggested improvements in the current prototype include use of integrated thermal correction, reconfiguration of the resonator for increased particle collection area, increased thermophoretic collection efficiency using an increased temperature gradient, and shielding the resonator electronics from deposition of ultrafine particles.

Final Report to the Innovative Clean Air Technologies Program, California Air Resources Board and California Energy Commission, Contract Number 02-5