| 1. |
- Artaxo, Paulo, et al.
(författare)
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Tropical and Boreal Forest – Atmosphere Interactions : A Review
- 2022
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Ingår i: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 74:1, s. 24-163
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Forskningsöversikt (refereegranskat)abstract
- This review presents how the boreal and the tropical forests affect the atmosphere, its chemical composition, its function, and further how that affects the climate and, in return, the ecosystems through feedback processes. Observations from key tower sites standing out due to their long-term comprehensive observations: The Amazon Tall Tower Observatory in Central Amazonia, the Zotino Tall Tower Observatory in Siberia, and the Station to Measure Ecosystem-Atmosphere Relations at Hyytiäla in Finland. The review is complemented by short-term observations from networks and large experiments.The review discusses atmospheric chemistry observations, aerosol formation and processing, physiochemical aerosol, and cloud condensation nuclei properties and finds surprising similarities and important differences in the two ecosystems. The aerosol concentrations and chemistry are similar, particularly concerning the main chemical components, both dominated by an organic fraction, while the boreal ecosystem has generally higher concentrations of inorganics, due to higher influence of long-range transported air pollution. The emissions of biogenic volatile organic compounds are dominated by isoprene and monoterpene in the tropical and boreal regions, respectively, being the main precursors of the organic aerosol fraction.Observations and modeling studies show that climate change and deforestation affect the ecosystems such that the carbon and hydrological cycles in Amazonia are changing to carbon neutrality and affect precipitation downwind. In Africa, the tropical forests are so far maintaining their carbon sink.It is urgent to better understand the interaction between these major ecosystems, the atmosphere, and climate, which calls for more observation sites, providing long-term data on water, carbon, and other biogeochemical cycles. This is essential in finding a sustainable balance between forest preservation and reforestation versus a potential increase in food production and biofuels, which are critical in maintaining ecosystem services and global climate stability. Reducing global warming and deforestation is vital for tropical forests.
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| 2. |
- Dusek, Ulrike, et al.
(författare)
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Enhanced organic mass fraction and decreased hygroscopicity of cloud condensation nuclei (CCN) during new particle formation events
- 2010
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Ingår i: Geophysical Research Letters. - 1944-8007. ; 37
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Tidskriftsartikel (refereegranskat)abstract
- In a forested near-urban location in central Germany, the CCN efficiency of particles smaller than 100 nm decreases significantly during periods of new particle formation. This results in an increase of average activation diameters, ranging from 5 to 8% at supersaturations of 0.33% and 0.74%, respectively. At the same time, the organic mass fraction in the sub-100-nm size range increases from approximately 2/3 to 3/4. This provides evidence that secondary organic aerosol (SOA) components are involved in the growth of new particles to larger sizes, and that the reduced CCN efficiency of small particles is caused by the low hygroscopicity of the condensing material. The observed dependence of particle hygroscopicity (k) on chemical composition can be parameterized as a function of organic and inorganic mass fractions (forg, finorg) determined by aerosol mass spectrometry: k = korg forg + kinorg finorg. The obtained value of korg ~ 0.1 is characteristic for SOA, and kinorg ~ 0.7 is consistent with the observed mix of ammonium, sulfate and nitrate ions.
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| 3. |
- Gramlich, Yvette, 1993-
(författare)
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Chemical composition of Arctic aerosols and their link to clouds
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Arctic is a place particularly vulnerable to climate change, warming at an accelerated rate compared to the rest of the Earth. In this remote environment, the atmosphere, the ocean, the ice, and the land are all interlinked and are shaping a very complex system. This is why the interplay between aerosols and clouds and their role in the warming Arctic is still not fully understood.To address this issue, a better understanding of the sources, properties, and fate of aerosol particles in the Arctic is needed. By means of in situ observations of aerosols and clouds at the Zeppelin Observatory on Svalbard, this thesis aims to shed light on aerosol-cloud interactions in the Arctic. These measurements were conducted within the framework of the one-year long Ny-Ålesund Aerosol Cloud Experiment (2019-2020). A special focus of this thesis is on the chemical composition of aerosol particles from a molecular-level perspective, where measurements from a filter inlet for gases and aerosols coupled to a chemical ionization mass spectrometer were used.To identify the properties of the aerosol particles serving as cloud condensation nuclei (CCN) or ice nucleating particles (INP), cloud droplets and ice crystals were sampled with a ground-based counterflow virtual impactor inlet. The measured particles are called cloud residuals. The observations show that the cloud residuals have sizes in the Aitken and accumulation mode (as small as 10 nm in diameter). The chemical composition of these cloud residuals followed largely the expected annual cycle of aerosol particles in the Arctic, suggesting that most of the aerosol particles can act as CCN or INP in the Arctic. Anthropogenic signatures were present in the cloud residuals in the winter and spring, whereas in the summer a large contribution from methanesulfonic acid (MSA) was present, indicating natural source regions.The thesis also investigated how the oxidation products of dimethyl sulfide, MSA, sulfuric acid, and hydroperoxymethyl thioformate (HPMTF) are related to each other in the gaseous and particulate phase. HPMTF was observed to be present mainly in the gas phase, where it followed the gas phase signal of MSA in the summer. However, it was not present in significant amounts in the particle phase. In the presence of clouds, the gas phase levels of HPMTF decreased, indicating the uptake by cloud droplets.Another source of aerosol particles investigated are those from biomass burning (BB) emissions. The BB aerosol showed a largely similar molecular-level chemical composition of the organic aerosol compared to the rest of the year; however, a clear change to a largely organic dominated bulk aerosol composition was observed. Back trajectories suggested mainly Eastern Europe and Siberia as the source regions for the BB events. Using BB tracer compounds in combination with the back trajectories suggested that agricultural fires from Eastern Europe have a larger impact on the Arctic aerosol population, where mass and number enhancements compared to times not influenced by BB were found to reach up to one order of magnitude.The results from this thesis show that aerosol particles from natural emissions are an important source for Arctic aerosol particles. Especially, emissions from marine biological activity are relevant for the growth of aerosol particles to sizes in the CCN active regime in the summer.
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| 4. |
- Porada, Philipp, et al.
(författare)
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Estimating global nitrous oxide emissions by lichens and bryophytes with a process-based productivity model
- 2017
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 14:6, s. 1593-1602
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Tidskriftsartikel (refereegranskat)abstract
- Nitrous oxide is a strong greenhouse gas and atmospheric ozone-depleting agent which is largely emitted by soils. Recently, lichens and bryophytes have also been shown to release significant amounts of nitrous oxide. This finding relies on ecosystem-scale estimates of net primary productivity of lichens and bryophytes, which are converted to nitrous oxide emissions by empirical relationships between productivity and respiration, as well as between respiration and nitrous oxide release. Here we obtain an alternative estimate of nitrous oxide emissions which is based on a global process-based non-vascular vegetation model of lichens and bryophytes. The model quantifies photosynthesis and respiration of lichens and bryophytes directly as a function of environmental conditions, such as light and temperature. Nitrous oxide emissions are then derived from simulated respiration assuming a fixed relationship between the two fluxes. This approach yields a global estimate of 0.27 (0.19-0.35) (TgN(2)O) year(-1) released by lichens and bryophytes. This is lower than previous estimates but corresponds to about 50% of the atmospheric deposition of nitrous oxide into the oceans or 25% of the atmospheric deposition on land. Uncertainty in our simulated estimate results from large variation in emission rates due to both physiological differences between species and spatial heterogeneity of climatic conditions. To constrain our predictions, combined online gas exchange measurements of respiration and nitrous oxide emissions may be helpful.
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| 5. |
- Schmale, Julia, et al.
(författare)
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Long-term cloud condensation nuclei number concentration, particle number size distribution and chemical composition measurements at regionally representative observatories
- 2018
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 18:4, s. 2853-2881
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Tidskriftsartikel (refereegranskat)abstract
- Aerosol-cloud interactions (ACI) constitute the single largest uncertainty in anthropogenic radiative forcing. To reduce the uncertainties and gain more confidence in the simulation of ACI, models need to be evaluated against observations, in particular against measurements of cloud condensation nuclei (CCN). Here we present a data set - ready to be used for model validation - of long-term observations of CCN number concentrations, particle number size distributions and chemical composition from 12 sites on 3 continents. Studied environments include coastal background, rural background, alpine sites, remote forests and an urban surrounding. Expectedly, CCN characteristics are highly variable across site categories. However, they also vary within them, most strongly in the coastal background group, where CCN number concentrations can vary by up to a factor of 30 within one season. In terms of particle activation behaviour, most continental stations exhibit very similar activation ratios (relative to particles 20nm) across the range of 0.1 to 1.0% supersaturation. At the coastal sites the transition from particles being CCN inactive to becoming CCN active occurs over a wider range of the supersaturation spectrum. Several stations show strong seasonal cycles of CCN number concentrations and particle number size distributions, e.g. at Barrow (Arctic haze in spring), at the alpine stations (stronger influence of polluted boundary layer air masses in summer), the rain forest (wet and dry season) or Finokalia (wildfire influence in autumn). The rural background and urban sites exhibit relatively little variability throughout the year, while short-term variability can be high especially at the urban site. The average hygroscopicity parameter, calculated from the chemical composition of submicron particles was highest at the coastal site of Mace Head (0.6) and lowest at the rain forest station ATTO (0.2-0.3). We performed closure studies based on -Köhler theory to predict CCN number concentrations. The ratio of predicted to measured CCN concentrations is between 0.87 and 1.4 for five different types of . The temporal variability is also well captured, with Pearson correlation coefficients exceeding 0.87. Information on CCN number concentrations at many locations is important to better characterise ACI and their radiative forcing. But long-term comprehensive aerosol particle characterisations are labour intensive and costly. Hence, we recommend operating migrating-CCNCs to conduct collocated CCN number concentration and particle number size distribution measurements at individual locations throughout one year at least to derive a seasonally resolved hygroscopicity parameter. This way, CCN number concentrations can only be calculated based on continued particle number size distribution information and greater spatial coverage of long-term measurements can be achieved.
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