Instrument Support Level 3
Air Quality Design Inc, High Performance, 2 Channel NOx monitor
COZI: AQD High Sensitivity NOx Monitor
This high sensitivity NOx instrument is for laboratory based calibrations of NO standards. It is permanently in the COZI lab at the University of York, along with an NPL 1ppm NO in N2 calibration standard (which the WMO GAW recommended standard). The calibration standard is diluted with zero air (from an Ecophysics PAG003) to provide NO mixing ratios from 1 – 10ppbv.
The entire system is available in York for calibrations/checks of a user’s own NO calibration cylinder. Also available is an O3 source for titration of the NO to NO2 , providing a calibration source for NO2 . The laboratory has space for a user’s own NOx instrument which would be operated alongside the COZI instrument (measuring calibration standards or ambient air).
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 -20°C 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. A photolytic NO2 converter (diode based blue light converter (BLC) – Droplet Measurement Technologies) is used to provide sequential measurements of NO2 (30 seconds each).
The calibration standard is 1ppm NO in nitrogen from the National Physical Laboratory (NPL), UK. This is the recommended calibration standard for NO for the World Meteorological Office (WMO), Global Atmospheric Watch (GAW) program.
The dilution unit (Environics Inc 6100), consists of 10000sccm and 100sccm thermal mass flow controllers, calibrated early by the manufacturer.
Data provided will be an assessment of the NO content of the user’s own calibration cylinder. This will include the raw data of the calibration so the user can assess the statistics of the measurements. If ambient data is taken then a time series of NO and NO2 from the COZI instrument will be provided.
Data from instruments that are part of a laboratory do not archive their data to CEDA and so do not have to conform to any AMOF standard.
Data can be provided for the period of time that the user has accessed the facility.