Model 211 Scrubberless Ozone Monitor™

The World's Most Accurate Ozone Monitor

EPA Federal Equivalent Method (FEM)

Model 211 Scrubberless Ozone Monitor

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


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), and internal data logger. Our data display and graphing software allows continuous display of data which can be saved for offline analysis




Measurement Principle: UV Absorbance at 254 nm; Dual Beam
Federal Equivalent Method (FEM): Yes, 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

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, 0-2.5 V Analog, optional 4-20 mA Analog, optional USB adapter
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