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Model 205 Dual Beam Ozone Monitor

EPA-certified Federal Equivalent Method (FEM) dual-beam UV absorption at 254 nm with two detection cells to improve precision, baseline stability, and response time. Lightweight with low power consumption and a quiet, long-life internal air pump. For research and monitoring applications where high precision and/or fast response are required.

  • 0-250 ppm measurement range with 1.0 ppb precision
  • Dual beam for heightened precision and fast measurements
  • 2-second measurement frequency (fastest available on the market)
  • Approved by the EPA as a FEM: EQOA-0410-190


  • Makes use of two detection cells to improve precision, baseline stability, and response time
  • UV light intensity measurements Io (ozone-scrubbed air) and I (unscrubbed air) are made simultaneously
  • Fastest UV-based ozone monitor on the market, while still retaining the small size, weight, and power requirements of our popular Model 202 Ozone Monitor
  • Desirable for aircraft and balloon measurements where high spatial resolution is needed
  • For 10-s averaging, a precision of 1.0 ppb is achieved.  Alternatively, one can choose to average more points internally to obtain even better precision
  • Flash card memory and a long-life, quiet internal air sampling pump are now standard on the instrument
  • Rackmount configuration available as an optional upgrade

Schematic Diagram


Photo of Model 205 with Rackmount Enclosure

  • Ozone measured 0-250 ppm by UV absorption at 254 nm, dual beam
  • Quiet long-life internal air pump (now standard)
  • Low power consumption (~8 watt)
  • Internal data logger (EEPROM), logs 16,383 lines of data
  • Real-time clock
  • Both serial and user-scalable analog voltage outputs (4-20 mA current output optional)
  • Flash card memory (SD card) for virtually unlimited, portable data storage
  • Three 0-2.5 VDC analog inputs for logging other measurements, such as external temperature, pressure, and humidity
  • Convenient user interface to microprocessor, including calibration parameters (gain and zero)
  • Selectable measurement time of 2 s or data averaging times of 10 s, 1 min, 5 min and 1 hr (custom averaging times available)
  • DewLine™ for elimination of any water vapor interference, a unique feature of 2B Tech instruments
  • Dual beam feature allows for heightened precision and improved baseline stability for applications where high spatial resolution is required.
  • Model 205 Dual Beam Ozone Monitor
  • 1.25A power adapter
  • serial port cable (9PinF-9PinF)
  • External ozone scrubber
  • Hex ball driver (7/64″)
  • SD card reader
  • USB flash drive preloaded with operation manual and other useful documentation
  • NIST-traceable calibration certificate
  • External lithium-ion battery available (not included with standard purchase)
  • External particle filter
  • Cold-weather upgrade  (-20 to 50°C) (temporarily unavailable)
  • High-altitude upgrade (25km)
  • 4-20mA analog out upgrade
  • GPS upgrade
  • Bluetooth upgrade for wireless data transmission
  • Lower-power option
  • Extra-long-life pump
  • Serial-to-USB converter (not included with standard purchase
  • Rack-mount configuration upgrade available
  • Emission Rates of Volatile Organic Compounds from Humans, N. Wang, L. Ernle, G. Bekö, P. Wargocki and J. Williams, Environmental Science & Technology (2022), doi: 10.1021, acs.est.1c08764.  ACS Link
  • Cold Air Outbreaks Promote New Particle Formation Off the U.S. East Coast, A.F. Corral, Y. Choi, E. Crosbie, H. Dadashazar, J.P. DiGangi, G.S. Diskin, M. Fenn, D.B. Harper, S. Kirschler, H. Liu, R.H. Moore, J.B. Nowak, A.J. Scarino, S. Seaman, T. Shingler, M.A. Shook, K.L. Thornhill, C. Voigt, B. Zhang, L.D. Ziemba and A. Sorooshian, Geophysical Research Letters (2022) 49, 5, e2021GL096073.  AGU Link
  • Ozone Exposure and Prothrombosis: Mechanistic Insights from a Randomized Controlled Exposure Trial, Y. Niu, H. Li, W. Wang, C. Wang, C. Liu, X. Du, Q. Zhang, J. Li, S. Shi, X. Meng, R. Chen and H. Kan, Journal of Hazardous Materials (2022) 429, 128322.  ScienceDirect
  • Long Island Enhanced Aerosol Event during 2018 LISTOS: Association with Heatwave and Marine Influences, J. Zhang, J. Mak, Z. Wei, C. Cao, M. Ninneman, J. Marto and J.J. Schwab, Environmental Pollution (2021) 270, 116299.  Science Direct
  • Winter Ozone Pollution in Utah’s Uinta Basin is Attenuating, M.L. Mansfield and S.N. Lyman, Atmosphere (2021) 12, 4.   MDPI Link


Spec Sheet
Measurement Principle UV Absorption at 254 nm; Dual Beam
Federal Equivalent Method (FEM) Yes, 0-500 ppb for 10-40°C: EQOA-0410-190
Linear Dynamic Range 0 to 250 ppm
Resolution 0.1 ppb
Precision (1σ rms noise) Greater of 1.0 ppb or 2% of reading for 10-s average
Accuracy Greater of 1.0 ppb or 2% of reading
Limit of Detection (2σ) 2.0 ppb for 10-s average
NIST-Traceable Calibration Yes
Measurement Interval 2 s (Data averaging options: 10 s, 1 min, 5 min, 1 hr)
Flow Rate (nominal) ~1.8 Liter/min
Flow Rate Requirement >1.2 L/min
Baseline Drift < 1 ppb/day
< 3 ppb/year
Sensitivity Drift < 1%/day
< 3%/year
Measurement Time, Frequency 2 s, 0.5 Hz
Response Time, 100% of Step Change 4 s, 2 points
Measurement and Averaging Times 2 s, 10 s, 1 min, 5 min, 1 hr
Ozone Units ppb, pphm, ppm, µg m-3, mg m-3
Pressure Units mbar, torr
Temperature Units °C, K
T and P Corrected Yes
Operating Temperature Range 0 to 50°C standard; optional -20 to 50°C with low temperature modifications (pump and lamp heater cold-weather package)
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
12 V dc or 120/240 V ac, nominally 650 mA at 12 V, ~8 watt (~7 watt with cell heater unplugged)
Size 3.7H x 8.5W x 11.8L inches (9.5 x 21.5 x 30 cm)
Weight 5.8 lb (2.6 kg); 3.1 lb (1.4 kg) without instrument case
Internal Data Logger Capacity 16,383 lines (2-s fast measurement mode = 9.1 hr; 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 > 2 GB (> 5-year capacity for 10-s averaging mode)
Analog Inputs for Internal Logging of Other Instruments 3 Analog Inputs, 0-2.5 V; For example, could log external T, P, and RH
Data Outputs RS232, 0-2.5 V Analog, LCD Display (Optional 4-20 mA Current; request quote)
Data Transfer Baud Rates 2400, 4800, 19200
Output Ranges User-Defined Scaling Factor in Menu
DewLine™ Yes
Quiet, Long-Life Internal Air Pump Yes
Flow Meter Yes
Options Battery; External Particle Filter; Serial-to-USB Adapter; GPS (for 10-s data mode and above); Bluetooth; 4-20 mA Current Output; Cold-Weather Package, -20 to 50° C (pump, lamp heater); High-Altitude Upgrade 0-25 km (pressure sensor); Extra-Long-Life, Low-Temperature Internal Air Pump; Low-Power Option; Rack-Mount Case Configuration


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Case Studies

Case Studies for this product are coming soon!
"I have been a regular customer of 2B Tech since the launch of the company. We've purchased many 202s and one 205 and have gained invaluable insight from John Birks' team as to how best operate their systems in Antarctica. Their product range has improved remarkably over the years and their customer service has always been first class."
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