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Temperature-dependent accumulation mode particle and cloud nuclei concentrations from biogenic sources during WACS 2010

by L. Ahlm, K. M. Shakya, L. M. Russell, J. C. Schroder, J. P S Wong, S. J. Sjostedt, K. L. Hayden, J. Liggio, J. J B Wentzell, H. A. Wiebe, C. Mihele, W. R. Leaitch, A. M. MacDonald show all authors
Atmospheric Chemistry and Physics ()
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Abstract

Submicron aerosol particles collected simultane- ously at the mountain peak (2182 m a.s.l.) and at a forested mid-mountain site (1300 m a.s.l.) on Whistler Mountain, British Columbia, Canada, during June and July 2010 were analyzed by Fourier transform infrared (FTIR) spectroscopy for quantification of organic functional groups. Positive ma- trix factorization (PMF) was applied to the FTIR spectra. Three PMF factors associated with (1) combustion, (2) bio- genics, and (3) vegetative detritus were identified at both sites. The biogenic factor was correlated with both temper- ature and several volatile organic compounds (VOCs). The combustion factor dominated the submicron particle mass during the beginning of the campaign, when the tempera- ture was lower and advection was from the Vancouver area, but as the temperature started to rise in early July, the bio- genic factor came to dominate as a result of increased emis- sions of biogenic VOCs, and thereby increased formation of secondary organic aerosol (SOA). On average, the biogenic factor represented 69 % and 49 % of the submicron organic particle mass at Whistler Peak and at the mid-mountain site, respectively. The lower fraction at the mid-mountain site was a result of more vegetative detritus there, and also higher in- fluence from local combustion sources. The biogenic factor was strongly correlated ( r ∼ 0 . 9) to number concentration of particles with diameter ( D p )> 100 nm, whereas the combustion factor was better corre- lated to number concentration of particles with D p < 100 nm ( r ∼ 0 . 4). The number concentration of cloud condensation nuclei (CCN) was correlated ( r ∼ 0 . 7) to the biogenic fac- tor for supersaturations ( S ) of 0.2 % or higher, which indi- cates that particle condensational growth from biogenic va- pors was an important factor in controlling the CCN concen- tration for clouds where S ≥ 0 . 2 %. Both the number concen- tration of particles with D p > 100 nm and numbers of CCN for S ≥ 0 . 2 % were correlated to temperature. Considering the biogenic influence, these results indicate that temperature was a primary factor controlling these CCN concentrations at 0.2 % supersaturation.

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