| 1. |
- Friedman, Beth, et al.
(author)
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Subarctic atmospheric aerosol composition: 1. Ambient aerosol characterization
- 2009
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In: Journal of Geophysical Research. - 2156-2202. ; 114
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Journal article (peer-reviewed)abstract
- Subarctic aerosol was sampled during July 2007 at the Abisko Research Station Stordalen field site operated by the Royal Swedish Academy of Sciences. Located in northern Sweden at 68 degrees latitude and 385 m above sea level (m asl), this site is classified as a semicontinuous permafrost mire. Number density, size distribution, cloud condensation nucleus properties, and chemical composition of the ambient aerosol were determined. Back trajectories showed that three distinct air masses were present over Stordalen during the sampling period. Aerosol properties changed and correlated with air mass origin to the south, northeast, or west, suggesting that particle source and transport were important factors. We observe that Arctic aerosol is not compositionally unlike that found in the free troposphere at midlatitudes. Internal mixtures of sulfates and organics, many on insoluble biomass burning and/or elemental carbon cores, dominate the number density of particles from similar to 200-to 2000-nm aerodynamic diameter. Mineral dust that had interacted with gas-phase species was observed in all air masses. Sea salt, due to the uptake of nitrate species and loss of chlorine, was the aerosol type that most varied chemically with air mass.
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| 2. |
- Kammermann, Lukas, et al.
(author)
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Subarctic atmospheric aerosol composition: 3. Measured and modeled properties of cloud condensation nuclei
- 2010
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In: Journal of Geophysical Research. - 2156-2202. ; 115
-
Journal article (peer-reviewed)abstract
- Aerosol particles can modify cloud properties by acting as cloud condensation nuclei (CCN). Predicting CCN properties is still a challenge and not properly incorporated in current climate models. Atmospheric particle number size distributions, hygroscopic growth factors, and polydisperse CCN number concentrations were measured at the remote subarctic Stordalen mire, 200 km north of the Arctic Circle in northern Sweden. The CCN number concentration was highly variable, largely driven by variations in the total number of sufficiently large particles, though the variability of chemical composition was increasingly important for decreasing supersaturation. The hygroscopicity of particles measured by a hygroscopicity tandem differential mobility analyzer (HTDMA) was in agreement with large critical diameters observed for CCN activation (kappa approximate to 0.07-0.21 for D = 50-200 nm). Size distribution and time- and size-resolved HTDMA data were used to predict CCN number concentrations. Agreement of predictions with measured CCN within +/- 11% was achieved using parameterized Kohler theory and assuming a surface tension of pure water. The sensitivity of CCN predictions to various simplifying assumptions was further explored: We found that (1) ignoring particle mixing state did not affect CCN predictions, (2) averaging the HTDMA data in time with retaining the size dependence did not introduce a substantial bias, while individual predictions became more uncertain, and (3) predictions involving the hygroscopicity parameter recommended in literature for continental sites (kappa approximate to 0.3 +/- 0.1) resulted in a significant prediction bias. Future modeling studies should therefore at least aim at using averaged, size-resolved, site-specific hygroscopicity or chemical composition data for predictions of CCN number concentrations.
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