Teledyne API has blended the needs of both government agencies and health effects researchers into a single new instrument, the Model 602 BetaPLUS Particle Measurement System. The instrument uses a dual-channel approach for the simultaneous measurement of PM10 and PM2.5, and PMC (PM Coarse) through the subtraction of the two measured parameters.
The instrument is designed for autonomous, continuous ambient air quality monitoring. It can operate unattended for 15 to 48 days, depending upon configuration and environmental conditions at the site. Each sampling cycle includes the storage of 60 individual data parameters, including both measurement data and diagnostic information. These parameters can be viewed in real-time with the included remote communications package, or sent directly to a digital data acquisition system for automatic interpretation and validation. Additionally, a service log is kept in a separate data buffer for more in-depth analysis of maintenance or service needs. There is a capacity for 1.5 years of continuous hourly data storage within these internal data buffers.
A patented, multi-step analytical process yields high performance results from a beta attenuation mass measurement technique. And because the analysis takes place in parallel with the sampling event, the instrument achieves an active sampling rate of >96%. This means that the instrument will actively sample the air for 58 minutes of a 60 minute sampling period, while still using a full hour for analysis.
The results of each analysis step are individually recorded providing in-depth diagnostics and further information regarding each sampling event. For example, naturally occurring background radiation is a known interferrent with beta attenuation mass measurement techniques. The Model 602 BetaPLUS instrument measures and accounts for this artifact. These natural count data are stored independently and can be analyzed further to provide information about the regional Planetary Boundary Layer (PBL). This PBL or atmospheric stability analysis can provide useful information about environmental factors affecting air pollution events.
In addition to removal of background radioactivity, the instrument uses a unique ‘spy filter’ to measure humidity related errors which can occur during analysis. The spy filter actively simulates the interactions of humidity on the filter media during the analysis period, allowing the instrument to account for these effects which can be significant in high humidity environments.
The instrument closely matches results derived using certified gravimetric manual samplers. Automatic leak checks and flow audits can be performed on each pneumatic channel before each sampling event with recorded results. The instrument also monitors and records relevant sampling parameters such as the temperature on the collection filters, the difference between ambient and filter temperatures (i.e. Delta T), and standard deviation of the continuous flow measurement. Target ranges for each of these parameters are defined by the user which can be set to transmit alarms, and can also help in automating the data validation process.
Additionally, two-point mass sensor calibration span checks are performed at user-defined intervals to ensure the instrumental measurement is continuously calibrated with respect to mass.