At a Glance
Researchers at Colorado State University have developed an automated filter analysis system for high-throughput gravimetric mass and optical black carbon measurements of filter-based aerosol samples. The Automated Air Analysis Facility (AIRLIFT) system (1) increases sample throughput, (2) achieves good analytic figures of merit, i.e. bias, precision, and limit of detection, (3) reduces personnel burden, and (4) serves as a platform for multiplexed analysis of air sampling filters. Furthermore, the AIRLIFT system is compliant with US EPA gravimetric filter analysis requirements.
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.
The AIRLIFT system automates this process, reducing human error and maintaining the strict controlled environment necessary for precise gravimetric measurements. It includes seven subsystems, as depicted in Fig. 1: (a) an enclosure; (b) a data acquisition/control system; (c) a robotic filter management system; (d) a weighing apparatus; (3) and an optical black carbon analysis system; (f) a sample tracking system; and (g) a system for active environmental control. Details of each subsystem can be found in the publication linked below.
Figure 1 illustrates a schematic view of the AIRLIFT system. Lower-case letters and dotted lines designate subsystems.
- Automation of optical Black carbon analysis
- Greatly increase filter analysis throughput
- Meets or exceeds US EPA requirements for filter weighing
- Ability to configure system to include additional spectroscopic analyses
- Additional quality assurance capabilities that include incorporation of photos/videos
- Achieves the levels or measurement repeatability necessary for air quality related studies
- Reduces tedious time-consuming process of manually weighing filters by a factor ~4
- Capable of analyzing approximately 260 filters per day
- Air quality monitoring
- Direct application in organizations who work directly or indirectly with aerosol related air quality