Model 211 Scrubberless Ozone Monitor™
The World's Most Accurate Ozone Monitor
EPA Federal Equivalent Method (FEM)
The new Model 211 Scrubberless Ozone Monitor uses the proven ultraviolet (UV) absorption method in combination with our patented (US Patent No. 8,395,776 B2) gas-phase scrubber technology to measure ozone virtually free of interferences. The instrument is ideally suited for measurements of ozone in heavily polluted air where interference is likely from particulates, mercury, or VOCs. The Model 211 combines the stability of our proven dual beam ozone monitors with our selective scrubber technology to provide accurate ozone measurements in the most polluted air. The enhanced optical path length of 30 cm provides a precision of better than 0.5 ppb for 10-second measurements, and the instrument can output new ozone measurements as often as every 2 seconds. The Model 211 now comes with SD flash card memory as a standard feature. The Model 211 Scrubberless Ozone Monitor has been designated by the EPA as a Federal Equivalent Method (FEM): EQOA–0514–215
Theory
Ozone monitors based on UV absorbance measure ozone by comparing the transmission of light through a detection cell. Light intensity measurements are made with ozone present (I) and with ozone removed (Io), and the ozone concentration is calculated using the Beer-Lambert Law. Conventional ozone monitors remove ozone for the Io measurement by passing the sample air flow through a solid scrubber (e.g., hopcalite or a series of metal oxide screens). Ideally, the solid-phase scrubber would destroy ozone but pass mercury and other UV-absorbing compounds. In that case, the values of I and Io would be reduced by the same amount, and the interfering compounds would not affect the ozone measurement. In practice, however, mercury and aromatic compounds such as benzene, toluene, xylenes, phenols, etc. either adsorb or react at the solid-phase scrubber surface. As a result, conventional ozone monitors may report erroneously high ozone values by up to a few ppb on highly polluted days and possibly cause a region to be out of compliance with the EPA's ozone standard. The 2B Tech Model 211 Ozone Monitor removes interferences from all UV-absorbing compounds and mercury by using nitric oxide (NO) in a GPT (gas phase titration) reaction in place of a solid-phase scrubber according to the well known reaction: NO + O3 → NO2 + O2
The animation above illustrates the principle of a gas-phase NO scrubber for a single-beam instrument. A small amount (~5 ppm) of nitric oxide (NO; blue) is pulsed into the air flow every 2 seconds to destroy the ozone and produce nitrogen dioxide (NO2; green) which doesn't absorb the UV light. When ozone (red) is present the signal at the photodiode is reduced due to ozone absorbing the UV light. When ozone is destroyed by the NO, the signal increases. The difference in measured light intensities is proportional to the ozone concentration. Because the potentially interfering species (benzene, toluene, xylenes, aldehydes, mercury, etc.; colored yellow) are always present and not modulated by NO, they do not contribute to the signal difference and thus do not interfere with the ozone measurement.
Like our Model 205 Ozone Monitor, the Model 211 is actually dual beam, with a measurement of the transmission of UV light through ozone-depleted air being made simultaneously with a measurement of UV light passing through unscrubbed air, thus increasing the precision and baseline stability of the instrument.
Nitric oxide can be added directly from a compressed gas cylinder or by photolysis of nitrous oxide (N2O) provided from a liquid N2O cartridge (either a 16-gram cartridge for 8 hr of operation for portable applications; or an 8-gram cartridge for 4 hr operation), half-sized cylinder (8 mo of operation) or full-sized cylinder (2 yr operation). The use of N2O as a source gas eliminates the need for maintaining cylinders of toxic NO gas. Nitrous oxide is a relatively non toxic gas sold as a consumer product as "Whippit" cartridges for making whipped cream. The same method for producing NO from N2O is used in our Model 408 Nitric Oxide Calibration Source.
The Model 211 allows remote instrument operation via RS-232, choice of averaging time (2 s to 1 hr), analog voltage output (0-2.5 V), optional analog current output (4-20 mA), SD flash memory card, and internal data logger. Our data display and graphing software allows continuous display of data which can be saved for offline analysis
Like our Model 205 Ozone Monitor, the Model 211 is actually dual beam, with a measurement of the transmission of UV light through ozone-depleted air being made simultaneously with a measurement of UV light passing through unscrubbed air, thus increasing the precision and baseline stability of the instrument.
Nitric oxide can be added directly from a compressed gas cylinder or by photolysis of nitrous oxide (N2O) provided from a liquid N2O cartridge (either a 16-gram cartridge for 8 hr of operation for portable applications; or an 8-gram cartridge for 4 hr operation), half-sized cylinder (8 mo of operation) or full-sized cylinder (2 yr operation). The use of N2O as a source gas eliminates the need for maintaining cylinders of toxic NO gas. Nitrous oxide is a relatively non toxic gas sold as a consumer product as "Whippit" cartridges for making whipped cream. The same method for producing NO from N2O is used in our Model 408 Nitric Oxide Calibration Source.
The Model 211 allows remote instrument operation via RS-232, choice of averaging time (2 s to 1 hr), analog voltage output (0-2.5 V), optional analog current output (4-20 mA), SD flash memory card, and internal data logger. Our data display and graphing software allows continuous display of data which can be saved for offline analysis
Features
- Interference-free measurement of ambient ozone
- DewLine™ for elimination of water vapor interference, a unique feature of 2B Tech instruments
- Inexpensive, simple, and robust instrument design in a 19” rack mount enclosure
- Internal data logger
- SD flash memory for virtually unlimited portable data storage
- Dual beam, long path (30 cm) optical bench with high precision (< 0.5 ppb)
- NIST-traceable calibration (calibration suggested annually)
- Internal long-life sample pump (20,000 hours)
- EPA Federal Equivalent Method (FEM) for compliance monitoring (EQOA–0514–215)
- Candidate to become a new EPA Federal Reference Method (FRM)
- Convenient user interface, including remote operation via RS-232 communication
- Internal NO generator from non-toxic, non-corrosive nitrous oxide (N2O)
- Portable N2O Source (provided) can use "Whippit"-type cartridges (use either 16-gram cartridge for 8 hours of operation, or 8-gram cartridge for 4 hours of operation)
- Very low NO concentration used in comparison to ozone monitors based on NO chemiluminescence
Options
- Battery
- External particle filter
- Lamp heater for outdoor operation in extreme environments
- Bluetooth wireless data transmission
- 4-20 mA analog current output
- External serial-to-USB adapter
- High-altitude upgrade allows operation up to ~25 km (pressure sensor)
Recent Publications and Presentations Evaluating the Model 211
- W. M. Ollison, W. Crow and C. W. Spicer (2013) Journal of the Air and Waste Management Association 63, 855-863, "Field testing of new-technology ambient air ozone monitors."
- T. Johnson, J. Capel and W. Ollison (2014) Journal of the Air and Waste Management Association 64, 360-371, "Measurement of microenvironmental ozone concentrations in Durham, North Carolina, using a 2B Technologies 205 Federal Equivalent Method monitor and interference-free 2B Technologies 211 monitor."
- Russell Long (2015) "Evaluation and Proposal of a New Federal Reference Method for Ozone: Nitric Oxide Chemiluminescence," Briefing for NACAA, Office of Research and Development, National Exposure Research Laboratory, Environmental Protection Agency, January 14, 2015.
- John Birks, Peter Andersen, Craig Williford and Andrew Turnipseed (2015) "2B Tech Model 211 Scrubberless Ozone Monitor for Interference-Free Measurements," Air Monitoring Conference, Region 4, Environmental Protection Agency, Chattanooga, Tennessee, March 18, 2015.
Application Note
This Application Note gives one example of the use of the Model 211 in research; in this case it was used in a study of wintertime air quality in Utah. The 211's ability to measure ozone without interferences from VOCs made it uniquely suited to this study. Please see the short write-up linked below to learn more.
Specifications
| Measurement Principle | UV Absorbance at 254 nm; Dual Beam |
| Federal Equivalent Method (FEM) | Yes, 0-500 ppb for 20-30°C: EQOA–0514–215 |
| Ozone Scrubber Technology | Gas-phase scrubber using NO, provided directly or by photolysis of N2O (supplied by either compressed gas cylinder or portable liquid N2O cartridge) |
| Linear Dynamic Range | 0-2,000 ppb (0-2 ppm) |
| Resolution | 0.1 ppb |
| Precision (1σ rms noise) | Greater of 0.5 ppb or 1% of reading for 10-s average |
| Accuracy | Greater of 1.0 ppb or 2% of reading |
| Limit of Detection (2σ) | 1.0 ppb for 10-s average |
| NIST-Traceable Calibration | Yes |
| Flow Rate (nominal) | ~2 Liter/min |
| Flow Rate Requirement | >1.2 L/min |
| Baseline Drift | < 1 ppb/day < 3 ppb/year |
| Sensitivity Drift | < 0.5%/day < 3%/year |
| Response Time, 100% of Step Change | 20 s for 10-s averaging; 4 s for 2-s measurement |
| Measurement and Averaging Times | 2 s, 10 s, 1 min, 5 min, 1 hr |
| Internal Data Logger Capacity | 16,383 lines (10-s avg. = 1.9 days; 1-min avg = 11 days; 5-min avg = 1.9 mo; 1-hr avg = 1.9 yr) |
| SD Card Logger Capacity | Minimum 2 GB (> 5-year capacity for 10-s measurement mode) |
| Ozone Units | ppb, ppm, pphm, µg m-3, mg m-3 |
| Pressure Units | mbar, torr |
| Temperature Units | °C, K |
| T and P Corrected | Yes |
| Operating Temperature Range | 10 to 50 °C |
| Operating Altitude Range | ~0-13.5 km (150-1,013 mbar) standard; optional ~0-25 km (30-1,013 mbar) with upgraded pressure sensor |
| Power Requirement; Supplied by Battery or 110/220 VAC Power Pack |
11-14 V dc or 120/240 V ac, 1 A at 12 V, 12 watt |
| Size | Rackmount: 17" w x 14.5" d x 5.5" h (43 x 37 x 14 cm) |
| Weight | 14.7 lb (6.7 kg) |
| Data Outputs | RS232, SD data card, LCD, 0-2.5 V Analog, optional 4-20 mA Analog |
| Data Transfer Baud Rates | 2400, 4800, 19200 |
| Output Ranges | User-Defined Scaling Factor in Menu |
| DewLine™ | Yes |
| Long-Life Pump | Yes, 20,000 hr |
| Flow Meter | Yes |
| Options | Battery; External Particle Filter; Bluetooth; External Serial-to-USB Adapter; 4-20 mA Current Output; Lamp Heater; High-Altitude Upgrade (pressure sensor) |
System Includes
- Model 211 Scrubberless Ozone Monitor
- AC Power Adapter (100-240 VAC to 12 VDC) with Country-Specific Plug
- Zeroing Cartridge
- Portable N2O Source (use with either 8-g or 16-g N2O cartridges for 4 hr or 8 hr of continuous operation)
- SD Card and Card Reader
- Operation Manual on USB Stick
- Calibration Data and NIST-Traceable Calibration Certificate
- Instrument Birth Certificate
- One-Year Warranty
Confused about which ozone monitor best suits your application?
- Decision Tree: This will help you decide which ozone monitor is best for your application.
- Comparison: See a table that compares the specifications of all of our ozone monitors.
- Applications: The most suitable ozone monitors for different applications are discussed here.