Example of PILS coupled with Ion Chromatographs for Online Measurements of PM2.5 inorganic aerosol composition
Hints on running 15 lpm Pils
Heater control box:
Left hand readout is to control heater temperature. Can be changed.
Right hand readout reads temperature at tip of steam injector. This is readout only.
Fine tuning the steam temperature:
The goal is to heat just high enough until you get a constant steam jet but not too high that you have superheated steam.
( If your steam temperature is too high, you reduce your super saturation and may risk activation of small particles- i.e., The lower the steam temperature the higher the super saturation to activate the small particles. ) Also, the lower the temperature the less you heat the aerosol sample.
Steam liquid flow rate should be between 1.4 and 1.6 ml/min for most cases. In aircraft where very low RH conditions can be encountered the steam liquid flow rate should be slightly higher, 1.7 ml/min.
The technique we have used to set an appropriate temperature for the heater (left controller), is to start near 100C. Remove the 2inch diameter stainless steel cone containing the steam jet so that the steam jet can be observed. The goal is to achieve a temperature just above that at which the steam flow transitions from “spitting” to a steady steam jet with no liquid water. Spitting can be detected by a change in sound or by feel (holding your hand about 2 inches from the jet). Note, wide variation (±20°C) for the heater T can occur and is not of concern. It is due to placement of the thermocouple in the steam generating coil). The most important aspect is that the steam issuing from the steam injection tip (1/16 inch tube) is not composed of many liquid drops and not overly hot. The temperature indicated on the Tip controller should be used mainly as an indicator that everything is operational. For example, if it falls below 80°C or so, steam is not being generated. A typical Tip temperature during PILS operation is between 90 and 110°C
Heater Coil / Steam injector :
After first hours of initial use, all fittings should be retightened. This should also be checked periodically.
Important: Steam jet must be centered along axis of Pils. This should be checked if any fittings have been retightened or turned.
The impacted liquid-sample is wicked-away by a small strip of stainless steal mesh which lines the outside of the impactor cavity. This should be replaced after periods of continuous use to avoid clogging (e.g., 1 month of continuous operation) by insoluble material in the aerosol. See notes on installing wicking mesh.
The Pils instrument is very sensitive and can deliver quantitative results.
Best results are obtained with:
1. The best IC calibration possible: Calibrations should be performed to bracket expected atmospheric concentrations. Lower limits depend strongly on your DI-water baseline.
2. Clean water : The sample is both collected and transported in the DI water (which also contains lithium). Clean water is incredibly important.
3. Good Backgrounds : On startup, it is normally necessary for the Pils to run for a few hours until surfaces have been washed from contamination. If backgrounds are still too high (especially for NH4+), it may require the operator to wash impactor surfaces. BUT first make sure it is not contaminated water.
March 7, 2003
Installation of stainless steel wicking mesh.
Method to install stainless wickiing mesh . (Note, you can leave the impaction plate attached to the PILS body to do this, however it is easier if the complete lexan impaction plate assembly is removed). Wetting the grove in which the wicking material fits can ease installation.
Once you get the hang of this, it is fairly easy to do.