Enquiries

Prof James Lee

james.lee@ncas.ac.uk

0190 432 2575

Apply Now
Instrument Support Level 3
Instrument Support Level

Instrument Support Level 3

Manufacturer & Model

Air Quality Design - Bespoke instrument

Daily Facility Charge

Not Applicable

Calendar

Calendar 2:
AQD Fast NOx

AQD Fast NOx

This instrument provides high time resolution (10Hz) and high sensitivity measurements of NO and NO2. The 10 Hz data is suitable for calculation of fluxes using the Eddy Covariance technique. Data is typically captured at 10Hz, however 1 second and 1 minute data is also taken by the data analysis software. Typical detection limits are 15pptv and 20pptv for NO and NO2 respectively for 1 second data. This improves with averaging time such that the ultimate detection limit is 1pptv and 3 pptv for NO and NO2 respectively for hourly averaged data. The instrument is certified to fly on board the NERC ARSF D228 small research aircraft and as a result is capable of making flux measurements from this moving platform using the Eddy Covariance technique.
Approximate spatial resolution is 500m, with a flux footprint ranging from 300 to 2000 metres. Flux data relies on the having concurrent measurements of fast wind vectors (for instance using a sonic anemometer on the ground or turbulence probe on the aircraft). Data analysis for fluxes would require considerable instrument scientist effort

NO measurement is based around the chemiluminescence produced when NO reacts with ozone producing an excited state NO2 molecule.

NO + O3 → NO2* + O2

NO2* + hv → NO2

This emission radiation is detected by a PMT cooled to -20oC by a chiller to reduce dark counts. Most of the chemical interferences that also produce chemiluminescence are taken into account by employing a pre-chamber in the system. This adds oxygen to the gas flow upstream of the main reaction chamber where NO completely reacts with ozone. As most interference reactions are considerably slower than the NO + O3 reaction, the PMT signal when O3 is added to the pre-chamber can be thought of as the instrument zero. A pre-chamber zero is carried out in every measurement cycle (typically 2 minute cycles but these are changeable depending on the specific use). A photolytic NO2 converter (diode based blue light converter (BLC) – Air Quality Design), which selectively converts NO2 to NO, is used to provide measurements of NO2 in a second NO chemiluminescence channel. Data is taken at 10Hz frequency, however averaging to 1second and 1 minute is carried out automatically by the data acquisition software.

The instrument is calibrated using a cylinder of 5 ppm NO in N2 (Air Liquide for aircraft use; BOC for ground use). A small flow (5sccm) is of the calibration gas is added to the sample flow (1000sccm), allowing dilution of the calibration gas to around 25 ppb and calibration at equivalent humidity to ambient air. The calibration cylinder is itself calibrated to an NPL cylinder held in the COZI laboratory in York. NO2 is calibrated using gas phase titration of the NO to NO2 upon addition of a small amount of O3.

For aircraft use, calibrations would be carried out pre-flight, twice in flight (start and end) and post flight. Data will be corrected to affect changing calibrations during the flight. For ground use, calibrations would be carried out every 36-48 hours and data corrected for any changes.

NO and NO2 data is taken at 10Hz time resolution but also averaged to 1 second and 60 seconds by the data analysis software. All three data series would be available (and further averaging on request).

Field Data
  • The instrument produces a range of out files and all are text format.
  • The user can download (but not delete) this data from the instrument but it should be noted that this data will not have been quality controlled.

FAST NOx

Example of 10Hz NO and NO2 data.

 

Archive Data