This instrumentation grant seeks funds to purchase a high precision robotic weighing system in support of new exposure tools and health studies. Obtaining this system is directly linked to our long term efforts to develop and use technologies that reduce the uncertainties associated with characterizing individual and population exposures to airborne particulate matter (PM), which has been identified as a critically-important area of research needed to improve the establishment of linkages between exposures to sized particles and adverse health effects (NRC, 2004). Specifically, a high precision robotic weighing facility is needed for weighing filters that are generated from the next generation of personal particulate monitor samplers that have been developed under the Genes, Environment and Health Initiative. These monitors have been designed to be light-weight and have extended run time by using low flow-rate pumps. The robotic weighing system made by Measurements Technology Laboratory (MTL) is an integrated system designed around the concept of being able to provide high precision gravimetric determinations of the particulate matter collected onto filters. The system comprises a tightly-controlled environmental chamber, an inertial mass weighing table, a microbalance and faraday cage, and a robotically controlled automatic sampler that transfers the filters from specially designed stainless steel petri-dishes to the microbalance. The whole system is controlled by software on a PC and the data are written automatically to a database that tracks quality assurance and generates reports. The robotic weighing system would be a major upgrade, replacing a manual weighing system and supporting the needs of an active user group, which we expect to grow with time due to the high precision and high throughput capabilities and lower costs. The system will be part of long running recharge center that is integrated into the Exposure Assessment Facility Core of the P30 Center of Environmental Health in Northern Manhattan that has a vibrant group of investigators carrying out public heath research related to environmental exposures. Institutional support from Columbia will insure that the system is in a state of the art, HEPA filtered laboratory and is well maintained for years to come, allowing time to expand the user group. Based on the experience of multiple groups that currently have the MTL system, we will be able to weigh particulate matter on filters with an uncertainty of d1 ?g, which opens up many new study designs including the use of the new miniaturized personal monitors that also monitor wearing compliance and estimate respiration rates. This ability to obtain such high precision (and accuracy) of gravimetric determinations of airborne PM concentrations, which is needed for certain applications such as the new generation of low flow air monitors is a primary justification of the need for this instrument. The ability to do this while increasing sample throughput (decreasing backlogs) and potentially lowering costs significantly will be a major benefit to all facility users.