A single-particle characterization of a mobile Versatile Aerosol Concentration Enrichment System for exposure studies.
BACKGROUND
An Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) was used to investigate the size and chemical composition of fine concentrated ambient particles (CAPs) in the size range 0.2-2.6 microm produced by a Versatile Aerosol Concentration Enrichment System (VACES) contained within the Mobile Ambient Particle Concentrator Exposure Laboratory (MAPCEL). The data were collected during a study of human exposure to CAPs, in Edinburgh (UK), in February-March 2004. The air flow prior to, and post, concentration in the VACES was sampled in turn into the ATOFMS, which provides simultaneous size and positive and negative mass spectral data on individual fine particles.


RESULTS
The particle size distribution was unaltered by the concentrator over the size range 0.2-2.6 microm, with an average enrichment factor during this study of approximately 5 (after dilution of the final air stream). The mass spectra from single particles were objectively grouped into 20 clusters using the multivariate K-means algorithm and then further grouped manually, according to similarity in composition and time sequence, into 8 main clusters. The particle ensemble was dominated by pure and reacted sea salt and other coarse inorganic dusts (as a consequence of the prevailing maritime-source climatology during the study), with relatively minor contributions from carbonaceous and secondary material. Very minor variations in particle composition were noted pre- and post-particle concentration, but overall there was no evidence of any significant change in particle composition.


CONCLUSIONS
These results confirm, via single particle analysis, the preservation of the size distribution and chemical composition of fine ambient PM in the size range 0.2-2.6 microm after passage through the VACES concentration instrumentation.
Freney
Evelyn J
EJ
School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JJ, UK. e.j.freney@sms.ed.ac.uk
Heal
Mathew R
MR
Donovan
Robert J
RJ
Mills
Nicholas L
NL
Donaldson
Kenneth
K
Newby
David E
DE
Fokkens
Paul H B
PH
Cassee
Flemming R
FR