| 1. |
- Ekman, Annica M. L., et al.
(author)
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Sub-micrometer aerosol particles in the upper troposphere/lowermost stratosphere as measured by CARIBIC and modeled using the MIT-CAM3 global climate model
- 2012
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. D11202-
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Journal article (peer-reviewed)abstract
- In this study, we compare modeled (MIT-CAM3) and observed (CARIBIC) sub-micrometer nucleation (N4-12, 4 <= d <= 12 nm) and Aitken mode (N-12, d > 12 nm) particle number concentrations in the upper troposphere and lowermost stratosphere (UT/LMS). Modeled and observed global median N4-12 and N-12 agree fairly well (within a factor of two) indicating that the relatively simplified binary H2SO4-H2O nucleation parameterization applied in the model produces reasonable results in the UT/LMS. However, a comparison of the spatiotemporal distribution of sub-micrometer particles displays a number of discrepancies between MIT-CAM3 and CARIBIC data: N4-12 is underestimated by the model in the tropics and overestimated in the extra-topics. N-12 is in general overestimated by the model, in particular in the tropics and during summer months. The modeled seasonal variability of N4-12 is in poor agreement with CARIBIC data whereas it agrees rather well for N-12. Modeled particle frequency distributions are in general narrower than the observed ones. The model biases indicate an insufficient diffusive mixing in MIT-CAM3 and a too large vertical transport of carbonaceous aerosols. The overestimated transport is most likely caused by the constant supersaturation threshold applied in the model for the activation of particles into cloud droplets. The annually constant SO2 emissions in the model may also partly explain the poor representation of the N4-12 seasonal cycle. Comparing the MIT-CAM3 with CARIBIC data, it is also clear that care has to be taken regarding the representativeness of the measurement data and the time frequency of the model output.
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| 2. |
- Karl, Matthias, et al.
(author)
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Marine nanogels as a source of atmospheric nanoparticles in the high Arctic
- 2013
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In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 40:14, s. 3738-3743
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Journal article (peer-reviewed)abstract
- The high Arctic (north of 80 degrees N) in summer is a region characterized by clean air and low abundances of preexisting particles. Marine colloidal nanogels i.e., assembled dissolved organic carbohydrate polymer networks have recently been confirmed to be present in both airborne particles and cloud water over the Arctic pack ice area. A novel route to atmospheric nanoparticles that appears to be operative in the high Arctic is suggested. It involves the injection of marine granular nanogels into the air from evaporating fog and cloud droplets, and is supported by observational and theoretical evidence obtained from a case study. Statistical analysis of the aerosol size distribution data recorded in the years 1991, 1996, 2001, and 2008 classified 75nanoparticle eventscovering 17% of the observed time periodas nanogel-type events, characterized by the spontaneous appearance of several distinct size bands below 200nm diameter.
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