Re-evaluation of BioSampler and its improvement for on-line, time-resolved monitoring of environmental coarse aerosol

Abstract

BioSampler is now being widely used for bioaerosol sampling. However, the sampling efficiency in wide size range especially for nanoparticles as well as the size-dependent retention efficiency have not been well evaluated until now. Through literature review, theoretic analysis and experiments, this paper reviews the sampling process, collection mechanism and sampling performance of commercial BioSampler including pressure drop as a function of sampling flow rate, the mass loss rate and temperature of the collection fluid as a function of sampling time, the variation of retention efficiency with time, and the sampling efficiency in wide size range from nanometers to microns. The effects of low pressure and high relative humidity on determination of sampling efficiency in literature were carefully analyzed. To compensate the collection fluid loss and extract the insoluble/dissolved sample for further analysis, Continuous-Extraction BioSampler (CEBS) is proposed. The retention efficiency for particles of different sizes as well as the collection efficiency were determined and found to be identical with commercial BioSampler when no steam was introduced into CEBS. Finally, the combination uses of CEBS and Inductively-Coupled-Plasma Mass Spectrometer (ICP-MS) was developed. Exponentially Modified Gaussian (EMG) Model was derived and verified to describe the temporal concentration of the dissolved component originating from individual soluble droplet. Using internal standard calibration method and EMG fitting of signal curve, the target element amount in individual droplet could be determined accurately. For continuously-collected soluble droplet with duration of minutes, the observed signal curve can be described by EMG model and the fitted value of area varies linearly with the sample amount introduced. This paper not only provides comprehensive performance evaluation of commercial BioSampler, but also demonstrates that the proposed CEBS-ICPMS is capable of monitoring environmental coarse aerosol with time resolution of ~17 min.