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Model 405 nm NO2/NO/NOx Monitor

FEM-approved NO2 monitor that uses the technique of direct absorption of 405 nm light by NO2 molecules. The Model 405 nm also measures NO by conversion to NO2 using ozone. The instrument provides a total measurement of NOx as the sum of NO and NO2.

  • 0-10 ppm for NO2, 0-2 ppm for NO and NOx with a precision of < 1 ppb
  • EPA certified (FEM) for NO2 compliance monitoring (EQNA-0217-243)
  • Extremely selective – No species found in ambient air has significant absorbance at the 405 nm wavelength


  • Highly selective direct measurement of NO2 by absorbance at 405 nm (FEM EQNA-0217-243)
  • Wavelength of 405 nm chosen becuase no other species found in ambient air has significant absorbance at that wavelength
  • Nitric oxide (NO) is measured by conversion to NO2 using the reaction of NO with ozone
  • Patented folded cell design achieves a path length of ~2 m, enabling a detection limit of <1 ppb
  • Ideal for applications that require precise and accurate measurement of NO and NO2, such as air quality monitoring both outdoors and indoors
  • Portable and relatively low power, making it particularly well suited for field deployments


See 2B Tech’s published paper and patent on the folded cell design:

Atmospheric Measurement Techniques paper

Patent on Folded Tubular Photometer

  • Measurement of NO2 over the range 0-10 ppm; measurement of NO over the range 0-2 ppm
  • Federal Equivalent Method (FEM) for NO2 over the ranges 0-500 ppb and 20-30°C (EQNA-0217-243)
  • Measurement frequency of once every five seconds, with selectable averaging times of 1 min, 5 min, and 1 hour
  • Three measurement modes: NO2 only; NO only; or NO, NO2, and NOx
  • SD card for virtually unlimited, portable data logging
  • Power consumption: ~16 watts after warmup
  • Long-Life pump (~15,000 hours)
  • DewLine for elimination of any water vapor interference, a unique feature of 2B Tech instruments
  • Model 405 nm NO2/NO/NOx nm Monitor
  • 5A power adapter
  • Serial port cable (9PinF-9PinF)
  • External (zero) Nafion assembly
  • SD card and SD card reader
  • USB flash drive preloaded with operation manual and other useful documentation
  • Extra LED assembly
  • NIST-traceable calibration certificate
  • Bluetooth upgrade for wireless data transmission
  • USB output (in place of RS232)
  • Touchscreen available upon request
  • Side panels with mounting ears for easy installation into instrument rack (available upon request)
  • Current Challenges in Visibility Improvement in Sichuan Basin, G. Zhao, M. Hu, Z. Zhang, L. Tang, D. Shang, J. Ren, X. Meng, Y. Zhang, M. Feng, Y. Luo, S. Yang, Q. Tan, D. Song, S. Guo, Z. Wu, L. Zeng, Y. Zhang and S. Xie, Geophysical Research Letters (2022) 49, 12. AGU Link


  • Assessment of Traffic-Related Air Pollution (TRAP) at Two Near-Road Schools and Residence in El Paso, Texas, USA, A. Rangel, A.U. Raysoni, M.C. Chavez, S. Jeon, J. Aguilera, L.D. Whigham and W.-W. Li, Atmospheric Pollution Research (2022) 13, 101304. ScienceDirect


  • Observations of Gas-Phase Products from the Nitrate Radical-Initiated Oxidation of Four Monoterpenes, M. Dam, D.C. Draper, A. Marsavin, J.L. Fry and J.N. Smith, Atmospheric Chemistry and Physics (2022) 22, 13, 9017-9031. ACP Link


  • Characterizing the Aging of Alphasense NO2 Sensors in Long-Term Field Deployments, J. Li, A. Hauryliuk, C. Malings, S.R. Eilenberg, R. Subramanian and A.A. Presto, ACS Sensors (2021) 6, 2952-2959. ACS Link


  • Confining Single-Atom Pd on g-C3N4 with Carbon Vacancies Towards Enhanced Photocatalytic NO Conversion, G. Liu, Y. Huang, H. Lv, H. Wang, Y. Zeng, M. Yuan, Q. Meng and C. Wang, Applied Catalysis B: Environmental (2021) 284, 119683. ScienceDirect


Spec Sheet
  • US EPA Federal Equivalent Method (FEM) for NO2 (0-500 ppb, 20-30°C)
  • CE
Principle of Measurement Direct absorbance of NO2 at 405 nm
Measurement Modes NO2 only; NO only; NO2, NO and NOx
Linear Dynamic Range 0-10,000 ppb (0-10 ppm) for NO2; 0-2,000 ppb (0-2 ppm) for NO
(FEM approved for 0-500 ppb NO2 for 20-30°C)
Resolution 0.1 ppb
Precision (1σ rms noise) < 0.5 ppb or 0.5% of reading (with adaptive filter1)
Accuracy Greater of 2 ppb or 2% of reading
Limit of Detection (2σ) < 1 ppb (with adaptive filter1)
Flow Rate (nominal) 1.5 Liter/min
Flow Rate Requirement Minimum: 1.4 Liter/min; Maximum: 1.6 Liter/min
Response Time, 100% of Step Change 10 s for 5-s averaging
20 s with adaptive filter1
Measurement Frequency 0.2 Hz (once every 5 s)
Averaging Times 5 s, 1 min, 5 min, 1 hr
SD Card Logger Capacity Minimum 2 GB (> 2-year capacity for 5-s measurement mode)
Internal Data Logger Capacity 8,192 data lines (5-s avg = 0.47 days; 1-min avg = 5.7 days; 5-min avg = 1.0 mo; 1-hr avg = 0.94 yr)
Concentration Units ppb, ppm, pphm
Pressure Units mbar
Temperature Units °C
T and P Corrected Yes
Operating Temperature Range 10 to 50°C (FEM approved for 20-30°C for NO2)
Power Requirement;
Supplied by 5-amp 110/220 VAC Power Pack (provided) or Battery
11-14 V dc or 120/240 V ac, 1.4 A at 12 V, 17 watt
Max: 2.9 A at 12 V, 35 watt (warmup)
Size Rackmount: 17″ w x 14.5″ d x 5.5″ h (43 x 37 x 14 cm)
Weight 18.6 lb (8.4 kg)
Data Outputs LCD; RS232; SD card; 0-2.5 V Analog Outputs for NO and for NO2
Data Transfer Baud Rates 2400, 4800, 19200
Output Ranges User-Defined Scaling Factor in Menu
DewLine™ Yes
Long-Life Pump Yes: 15,000 hr, 1.7 yr of continuous operation
Flow Meter Yes
Options Bluetooth for wireless data transmission; USB output (in place of RS232); touchscreen; side panels with mounting ears for easy installation into instrument rack


1An adaptive filter may be selected from the menu, making signal averaging similar to competing NOx monitors. Specifications above are for default parameters: Change Difference = 40 ppb, Change Percent = 10%, Short Filter = 4 pts (20 s), Long Filter = 36 pts (3 min). Adaptive filter parameters may be adjusted by the user.


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"We purchased a 2B ozone monitor in 2005 and an NO monitor in 2007. Although we have had limited need for customer service our experiences when needed have been uniformly good. And the product is working well for us."
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