Instrument - Thermal dissociation laser induced fluoresence
Thermal dissociation laser induced fluoresence
What is being measured:
Nitrogen dioxide (NO2), Peroxynitrates (PNs), Alkyl nitrates (ANs), and particulate nitrates (apANs)
Data recording software:
Data analysis software:
Raw data time resolution:
Analysis data averaging:
90 parts per trillion (ppt) 10 s−1, S/N ratio = 2 on a background of 1 ppb NO2 and 30 ppt 10 s−1 on a background of 100 ppt NO2
Sensitivity to temperature (and correction method, if applicable):
Sensitivity to relative humidity (and correction method, if applicable):
Inquire with PI
Sample preparation method:
Sample residence time (chamber to instrument) (seconds):
Length of tubing (cm):
Instrument flow rate:
Tubing inner diameter:
Heated stainless steel and Quartz
Chemical identification method:
NO2 laser induced fluorescence following thermal dissociation of nitrooxy compounds. See reference for more information.
Data analysis method:
Thermal dissociation operates at 200°C for compounds of the form RO2NO2 (and N2O5), 400°C for compounds of the form RONO2, including both alkyl nitrates and hydroxyalkyl nitrates, and finally, 650°C for HNO3. The concentration of a class of compounds is determined by the difference between two detection channels. Particulate nitrates are obtained as a difference between total ANs and ANs after filtering.
A background is measured and the direct NO2 calibration is applied. The background consists of chamber scatter and any NO2 reaching the detection cell from desorption within the flow system.
We calibrate at 150‐min intervals using an NO2 standard (5.85 ppm in N2, Scott Specialty Gas) diluted to 1–10 ppb in zero air. We use a low‐volume regulator that we fully dump and flush prior to calibrating. We also regularly cross‐calibrate our NO2 gas standards of 5, 10, and 50 ppm (Scott Specialty Gases). The calibration mixture is injected (overflow) at the second PFA tee in the inlet. This ensures that the calibration gas mixture passes though the same flow path and otherwise mimics, as best we can, the flow when sampling ambient air. We use separate tubing for the pure zero air and the NO2 mixture to ensure the zero determinations are not compromised by residual NO2 in the tubing. A three‐way stainless steel valve is located prior to the PFA tee where the calibration gas is injected in order to insure that the calibration line is isolated from the inlet during ambient sampling and zero checks. We also conduct standard addition calibrations regularly and apply a correction to the calibration based on measured ambient water concentrations (<5%) since water is an efficient quencher of the NO2 excited state [Thornton et al., 2000].
Calibration drift estimate:
Uncertainty estimation method:
Estimate of NO2 calibration bottle accuracy is 5 percent, estimated accuracy of PNs and ANs differences is 15 percent
Potential interference from: NO oxidation, NO2 reduction, NO2 complexation. Please see Day et al., (2002) for more information. In summary, the effects of the three major classes of interferences on our measurements are all <5%. We estimate the error due to oxidation of NO in most environments to cause errors of <1%.
Link to supplemental information: