Effect of high relative humidity on performance of pdr-100 nephelometric aerosol monitor for sampling ambient particulate within a controlled environmental chamber
Samimi, B., Jalocon, A., Quintana, J., Bufalino, C. and Delfino, R.
2002 American Industrial Hygiene Conference, AIHce PDCs - San Diego, June 1 - 2, paper 83
Samimi, B., Jalocon, A., Quintana, J., Bufalino, C. and Delfino, R., (2002), "Effect of high relative humidity on performance of pdr-100 nephelometric aerosol monitor for sampling ambient particulate within a controlled environmental chamber", American Industrial Hygiene Conference, AIHce PDCs - San Diego, June 1 - 2, paper 83.
Abstract:
Extraordinary high levels of airborne particulate have been reported during high RH by investigators using various pDR nephelometric samplers for ambient sampling. This study was conducted to evaluate the effect of high RH on pDR performance by comparing two co-located groups of pDRs under varied RH. Experiments were conducted within a walk-in chamber. The chamber was programmed to simulate typical summer 24-hour variations of RH and temperature with RH reaching saturation levels during nights. One group of pDRs including two passive, one active and one heated active operated inside the chamber. A 2nd combination of pDRs, excluding the heated active, were placed inside a heated field chamber within which RH was reduced. The field chamber was placed inside the walk-in chamber. Both chambers were continuously purged with outdoors air. Sampling runs were conducted for 24 hours while monitoring temperature and RH within both chambers. Statistical tests were applied to the results. Passive pDRs under high RH showed, up to several folds, higher concentrations compared to the co-located passive pDRs within the dry field chamber whereas there was no significant difference between the same two samplers during moderate RH levels. A strong positive correlation between the RH and the passive pDR outputs was observed. The active pDRs under high RH also showed higher outputs than those within the dry field chamber. However, the continuous flow of air over the instrument's optic system seemed to somewhat reduce the interfering effect of high humidity. The MIE heated pDRs outputs were also higher than those of active pDRs inside the dry field chamber. Our heated field chamber, however, showed good potential for use as a RH shelter for ambient air sampling when encountering high RH. Factors responsible seem to be growth of hygroscopic particles, increase in surface refractive index and condensation of water vapor.
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