Beta Attenuation Mass Monitors A Discussion of Technology

1. Beta Attenuation Mass MonitorsA Discussion of Technology Dennis Hart Met One Instruments, Inc.

2. Overview • History of beta gauge technology • Theory of operation • Beta gauge advantages • Beta gauge safety • BAM-1020 technical overview • E-BAM technical overview • What’s next in beta technology • Conclusion

3. History of Beta Technology • 1930s - Beta attenuation measurement technology first developed for industrial processes. • 1970s - Beta attenuation adapted to measure particulate by Sibata Scientific of Japan. • 1990s - BAM-1020 developed with reduced size and advanced microprocessor control. • 2002 - E-BAM developed for rapid field deployment and variable data intervals.

4. History of Beta Technology • Over 2,000 BAM-1020 units deployed. • Over 200 E-BAM units deployed.

5. Theory of Operation • Beta rays are measured through clean filter tape. • Air containing particulate is sampled and deposited on the filter tape. • Beta rays are measured through dirty filter tape. • The difference between the two measurements is proportional to the mass concentration.

6. Beta Gauge Advantages • Time proven, stable technology: beta gauges have been in use for over 60 years. • Beta attenuation technique is simple, easy to use, and requires less maintenance than other methods. • Fewer site trips required, ideal for remote deployment. • Met One beta gauges are manufactured and supported from the United States.

7. Beta Gauge Advantages • Seasonal and geographical correction factors are not needed. • It is not necessary to calibrate the beta measurement system in the field. • BAMs provide excellent agreement with gravimetric reference standards when properly maintained and operated. • Beta technology is virtually unaffected by the chemical composition of the sampled particulate.

8. Beta Gauge Safety • The BAM-1020 and E-BAM each contain a small amount of 14C, a naturally occurring radioactive isotope of carbon. • Activity level of the 60 mCi 14C source is similar to a commercial smoke detector, and is licensed with the NRC under the same provisions. • Sources with activity under 100 mCi require no special government licensing to own. • Met One Instruments has an “Exempt Distribution License” from the US-NRC to distribute the beta sources.

9. Beta Gauge Safety • Users are not required to take any specific precautions when handling the beta gauge. • USA customers do not require licensing to own a Met One beta gauge. • The end user will never need to remove, replace, or handle the beta source. • The unit may be returned to the factory for disposal at the end if its service life, although this is not required.

10. BAM-1020

11. BAM-1020 Advantages • Continuously samples and measures ambient air for particulate matter. • Designed to predict the mass concentration measured by manual gravimetric samplers with the highest accuracy. • Does not require the use of correction factors

12. BAM-1020 Advantages • 60 day continuous operation between filter tape changes. • Designed for long term operation at a fixed installation. • Powerful integrated 6 channel data logger compatible with a wide array of meteorological sensors. • Best accuracy of all beta models.

13. US-EPA Equivalent Method • Met One BAM-1020 is the ONLY US-EPA designated beta gauge currently manufactured. • EQPM-0798-122 • Equivalency for PM10 measurement

14. Simplicity – Flow System • The BAM-1020 airflow system consists of a few simple components: • Inlet/Nozzle • Temp/RH/BP sensors • Debris filter • Mass flow sensor • Flow controller • Pump (external)

15. Simplicity – Measurement System • The BAM-1020 measurement system consists of a few simple components: • Carbon 14 Beta source • Filter tape support • Photomultiplier tube detector • Preamp circuitry

16. Critical Checks • The flow system should be calibrated or verified on a regular basis. • A leak check is performed with every flow calibration. • The nozzle sealing surface and support vane may need to be cleaned more frequently in humid environments.

17. Critical Checks • The nozzle seal against the filter tape is important for proper airflow regulation. • The nozzle and support vane need to be cleaned at least as often as the filter tape is changed.

18. BAM-1020 Calibration • Calibration occurs once at the factory against a transfer standard in a smoke room chamber. • There are no environmental correction factors that need to be employed. • Zero and Span are checked once per hour during operation. No changes are made however.

19. BAM Comparison to EPA Reference for PM10

20. BAM Comparison to EPA Reference for PM2.5

21. BAM-1020 ETV Fresno PM2.5

22. E-BAM

23. E-BAM Advantages • Rapid deployment, portable unit. • DC operation for batteries or solar arrays. • All weather construction. • Easy set up: may be mounted on tripod or existing structure. • Compatible with optional wind sensors for smoke tracking. • Instrument operating temperature between -30° and +40° C.

24. E-BAM Advantages • “As needed” filter tape advance. One roll of tape may last up to a year depending on concentration levels. • Real-time data capability due to simultaneous sampling and measurement. • Concentration can be calculated on a 5, 15, 30, or 60 minute basis. Higher time resolution than the BAM-1020 is possible. • Up to 200 days of data storage, depending on data storage rate.

25. E-BAM Advantages • Lower cost and less parts. • AirSys satellite communications available for remote data retrieval. • Replaceable integral air pump.

26. Typical E-BAM Field Deployment

27. Just to be fair…

28. Mass Calculation

29. Mass Calculation • DEFINITIONS: • I0– beta measurement across clean filter • I – beta ray measurement across dirty filter •  – calibration coefficient (m2/g) • x – mass density on filter tape (g/m2) • A – dust spot deposition area on filter tape (m2 ) • V – sampled volume (m3) • C – particulate matter concentration (g/m3)

30. How Performance is Measured • Accuracy • Percentage deviation from 24-hour gravimetric Reference Standard • Beta technology has superior 24 hour accuracy compared to other methods. • Precision • Repeatability of a single measurement. • Stability

31. Measurement Challenges • Environmental conditions can play a role in the accuracy of beta attenuation measurements. The two main factors are: • Air temperature • Relative humidity and moisture.

32. Measurement Challenges • Temperature: • The BAM-1020 must be in a temperature controlled environment. • The temperature of the air flow in the E-BAM is measured and automatically compensated.

33. Measurement Challenges • Humidity: • Moisture accumulation on the sample spot may be measures as mass. • BAM-1020 and E-BAM use smart heater technology to lower the RH of incoming air. • Mild heat and hourly spot changes virtually preclude effects on VOCs. • Either unit may be operated at ambient conditions if desired.

34. What’s Next in Beta Technology • Detector sensitivity and noise improvements. • New pump options for E-BAM. • Advances temperature correction algorithms. • Advanced filter tape materials. • Less affect on concentration measurement. • Tests ongoing to improve nozzle leaks with thinner material. • Studies underway for maximum concentration levels.

35. Conclusion • Met One Instruments is constantly testing and experimenting to improve the beta gauge product line. • BAM-1020 exhibits documented superior performance to other beta gauges. • We welcome suggestions for future improvements.

36. Contacts • Applications/Sales: David Gobeli, Ph.D. • Science: Herbert Schloesser, Ph.D. • Service: Mike Putnam, Service Mgr. • www.metone.com • (541) 471-7111