High-Throughput, Robotic System for Analysis of Aerosol Sampling Filters

Exposure to airborne particulate matter (PM) is the leading environmental risk factor for premature disease and death. The gold-standard method for determination of PM mass concentrations is gravimetric analysis of air sampling filters. The United States Environmental Protection Agency (US EPA) describes gravimetric analysis as the sole Federal Reference Method for the determination of PM2.5 and PM10 concentrations (particles with aerodynamic diameters ≤ 2.5 um and 10 µm, respectively) in air; this method is then used to establish equivalence for all other methods (e.g., light-scattering, beta-attenuation). Unfortunately, gravimetric filter analysis is tedious and prone to bias/imprecision unless strict quality control procedures are employed.

Gravimetric analysis requires quantifying the mass of PM accumulated on an air sampling filter (i.e., weighing the filter on an analytic microbalance before and after a timed air sample is collected at a pre-determined flow rate).

To reproduce results accurately in such a controlled environment, recognized procedures include similar approaches and performance limits, such as control of ambient temperature and humidity, electrostatic discharge of the filter prior to weighing, and rules for filter handling and equilibration.

The challenge of making precise and unbiased gravimetric filter measurements is compounded by the tedious, labor-intensive nature of the measurement. The weighing of filters is a time intensive step, and prone to human error. Each replicate measurement of a gravimetric filter can take several minutes. A trained technician, following EPA protocol, can manually weigh only 10-15 filters per hour.