Instrument Support Level 3
Air Quality Design Inc, High Performance, 2 Channel NOx Monitor
AQD High Sensitivity NOx Monitor
This instrument built by Air Quality Design inc. is designed to be deployed in situations where a high degree of sensitivity and a low limit of detection are required for NO and NO2 selectively – down to ~1 pptv for NO and ~4 pptv for NO2. The instrument can run 24 hours unattended with automatic calibration carried out systematically and consistently on a daily basis. The instrument is built into a single rack/flight case assembly allowing for easy rapid deployment and for the instrument to be powered on within 5 minutes of being sited. The data computer runs a custom DAQfactory interface for the instrument providing simple button based control, graphical read-out of current signals, and graphical read-out of time series. Data is logged constantly automatically in 24 hour block files in CSV format.
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 -30°C by peltier coolers 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. A photolytic NO2 converter (diode based blue light converter (BLC) – Droplet Measurement Technologies) is used to provide sequential measurements of NO2 (2.5 minutes each for a 5 minute data cycle).
The instrument is calibrated using a cylinder of 5 ppm NO in N2 (BOC, UK). 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. This is done before the cylinder is shipped to Cape Verde. NO2 is calibrated using gas phase titration of the NO to NO2 upon addition of a small amount of O3. Calibrations are carried out every 37 hours and the data is corrected to reflect any changes in the calibration.
Data is provided at 1 minute, 5 minute and 1 hour averages of 1hz 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.
- Data is provided in NetCDF files following the AMOF data standard
- Files contain no more than 24hr of data.
- Instrument name is
- The data product(s) associated with this instrument:
- Example data file