24-hr ambient and residential aerosol characterization using automated piezoelectric cascade impactors
Marcham, C., Johnson, D., Esmen, N., Clinkenbeard, R. and Lynch, R.
2002 American Industrial Hygiene Conference, AIHce PDCs - San Diego, June 1 - 2
Marcham, C., Johnson, D., Esmen, N., Clinkenbeard, R. and Lynch, R., (2002), "24-hr ambient and residential aerosol characterization using automated piezoelectric cascade impactors", American Industrial Hygiene Conference, AIHce PDCs - San Diego, June 1 - 2.
Abstract:
C. Marcham, D. Johnson, N. Esmen, R. Clinkenbeard, R. Lynch, The University of Oklahoma, Oklahoma City, OK
Quartz crystal microbalance (QCM) piezoelectric cascade impactors have been used with some success in characterizing atmospheric aerosol concentrations and particle size distributions. These devices are extremely sensitive, with mass detection limits in the nanogram range, as measured using the frequency shift in a greased piezoelectric crystal used as the impaction surface of each stage. Use of paired crystals in each stage minimizes the potential influence of air temperature and relative humidity. The commercially available model of this instrument must be manually operated and so is poorly suited to 24-hr sampling applications. We modified two commercial instruments by adding relays and programmable digital controllers, and used these instruments to measure aerosol concentrations and size distributions indoors and outdoors at residences. An EPA reference PM2.5 ambient air sampler was operated simultaneously with the outdoor QCM sampler. Stage overloading and mass decoupling were not found to be a problem for sample durations of up to 8 minutes per hour for 24 hours. Stage frequency drift was random for properly matched sensing and reference crystals with a variation of approximately +2 Hz (+3 ng) for an 8-minute sample duration. Sudden ambient temperature changes appeared to influence QCM readings in a transient manner. PM2.5 concentrations estimated from the QCM results were similar to those measured by the reference sampler. The difference between the estimation of PM2.5 concentration by systematic and random sampling within each hour was not statistically significant. The measurement and operational data that relates our field measurement experiences suggest that although QCM might be used as a field instrument, it is not problem-free. However, the more cumbersome and to some extent more problem prone field operation of QCM notwithstanding, its ability to estimate the ultra fine fraction of the atmospheric aerosol may be an important asset that should be seriously considered.
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