Size-resolved aerosol chemistry on Whistler Mountain, Canada with a high-resolution aerosol mass spectrometer during INTEX-B Y. Sun1, Q. Zhang1, A. M. Macdonald2, K. Hayden2, S. M. Li2, J. Liggio2, P. S. K. Liu2, K. G. Anlauf2, W. R. Leaitch2, A. Steffen2, M. Cubison3, D. R. Worsnop4, A. van Donkelaar5, and R. V. Martin5,* 1Atmospheric Sciences Research Center (ASRC), University at Albany, State University of New York, 251 Fuller Road, Albany, NY 12203, USA 2Environment Canada, Toronto, Canada 3University of Colorado-Boulder, Colorado, USA 4Aerodyne Research Inc., Massachusetts, USA 5Dalhousie University, Halifax, Canada *also at: Harvard-Smithsonian Center for Astrophysics, Massachusetts, USA
Abstract. An Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer
(HR-ToF-AMS) was deployed at the peak of Whistler Mountain (2182 m above sea
level), British Columbia, from 19 April to 16 May 2006, as part of the
Intercontinental Chemical Transport Experiment Phase B (INTEX-B) campaign.
The mass concentrations and size distributions of non-refractory submicron
particle (NR-PM1) species (i.e., sulfate, nitrate, ammonium, chloride,
and organics) were measured in situ at 10-min time resolution. The HR-ToF-AMS
results agreed well with collocated measurements. The average concentration
of non-refractory submicron particulate matter (NR-PM1; 1.9 μg m−3)
is similar to those observed at other remote, high elevation sites
in North America. Episodes of enhanced aerosol loadings were observed, due
to influences of regional and trans-Pacific transport of air pollution.
Organics and sulfate were the dominant species, on average accounting for
55% and 30%, respectively, of the NR-PM1 mass. The average size
distributions of sulfate and ammonium both showed an accumulation mode
peaking at ~500 nm in vacuum aerodynamic diameter (Dva) while
those of organic aerosol (OA) and nitrate peaked at ~300 nm. The size
differences suggested that sulfate and OA were mostly present in external
mixtures from different source origins. We also quantitatively determined
the elemental composition of OA using the high resolution mass spectra.
Overall, OA at Whistler Peak was highly oxygenated, with an average
organic-mass-to-organic-carbon ratio (OM/OC) of 2.28±0.23 and an atomic
ratio of oxygen-to-carbon (O/C) of 0.83±0.17. The nominal formula for
OA was C1H1.66N0.03O0.83 for the entire study. Two
significant trans-Pacific dust events originated from Asia were observed at
Whistler Peak during this study. While both events were characterized with
significant enhancements of coarse mode particles and mineral contents, the
composition and characteristics of NR-PM1 were significantly different
between them. One trans-Pacific event occurred on 15 May 2006, during which
ammonium sulfate contributed >90% of the total NR-PM1 mass. This
event was followed by a high OA episode likely associated with regional
emissions. In total, three enhanced regional OA events, each of which lasted
2–3 days, were observed during this study. In contrast to the two dust
events, the regional OA events were generally characterized with higher
OA/sulfate ratio, less oxidized OA, and lower OM/OC ratio.
Citation: Sun, Y., Zhang, Q., Macdonald, A. M., Hayden, K., Li, S. M., Liggio, J., Liu, P. S. K., Anlauf, K. G., Leaitch, W. R., Steffen, A., Cubison, M., Worsnop, D. R., van Donkelaar, A., and Martin, R. V.: Size-resolved aerosol chemistry on Whistler Mountain, Canada with a high-resolution aerosol mass spectrometer during INTEX-B, Atmos. Chem. Phys., 9, 3095-3111, doi:10.5194/acp-9-3095-2009, 2009.