| 1. |
- Carlsson, Philip T. M., et al.
(author)
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Neutral Sulfuric Acid-Water Clustering Rates : Bridging the Gap between Molecular Simulation and Experiment
- 2020
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In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 11:10, s. 4239-4244
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Journal article (peer-reviewed)abstract
- The role of sulfuric acid during atmospheric new particle formation is an ongoing topic of discussion. In this work, we provide quantitative experimental constraints for quantum chemically calculated evaporation rates for the smallest H2SO4-H2O clusters, characterizing the mechanism governing nucleation on a kinetic, single-molecule level. We compare experimental particle size distributions resulting from a highly supersaturated homogeneous H2SO4 gas phase with the results from kinetic simulations employing quantum chemically derived decomposition rates of electrically neutral H2SO4 molecular clusters up to the pentamer at a large range of relative humidities. By using high H2SO4 concentrations, we circumvent the uncertainties concerning contaminants and competing reactions present in studies at atmospheric conditions. We show good agreement between molecular simulation and experimental measurements and provide the first evaluation of theoretical predictions of the stabilization provided by water molecules.
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| 2. |
- Clusius, Petri, et al.
(author)
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Atmospherically Relevant Chemistry and Aerosol box model - ARCA box (version 1.2)
- 2022
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In: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 15:18, s. 7257-7286
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Journal article (peer-reviewed)abstract
- We introduce the Atmospherically Relevant Chemistry and Aerosol box model ARCA box (v.1.2.2). It is a zero-dimensional process model with a focus on atmospheric chemistry and submicron aerosol processes, including cluster formation. A novel feature in the model is its comprehensive graphical user interface, allowing for detailed configuration and documentation of the simulation settings, flexible model input, and output visualization. Additionally, the graphical interface contains tools for module customization and input data acquisition. These properties - customizability, ease of implementation and repeatability - make ARCA an invaluable tool for any atmospheric scientist who needs a view on the complex atmospheric aerosol processes. ARCA is based on previous models (MALTE-BOX, ADiC and ADCHEM), but the code has been fully rewritten and reviewed. The gas-phase chemistry module incorporates the Master Chemical Mechanism (MCMv3.3.1) and Peroxy Radical Autoxidation Mechanism (PRAM) but can use any compatible chemistry scheme. ARCA's aerosol module couples the ACDC (Atmospheric Cluster Dynamics Code) in its particle formation module, and the discrete particle size representation includes the fully stationary and fixed-grid moving average methods. ARCA calculates the gas-particle partitioning of low-volatility organic vapours for any number of compounds included in the chemistry, as well as the Brownian coagulation of the particles. The model has parametrizations for vapour and particle wall losses but accepts user-supplied time- and size-resolved input. ARCA is written in Fortran and Python (user interface and supplementary tools), can be installed on any of the three major operating systems and is licensed under GPLv3.
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| 3. |
- Kontkanen, Jenni, et al.
(author)
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What controls the observed size-dependency of the growth rates of sub-10 nm atmospheric particles?
- 2022
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In: Environmental Science. - : Royal Society of Chemistry (RSC). - 2634-3606. ; :2, s. 449-468
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Journal article (peer-reviewed)abstract
- The formation and growth of atmospheric particles involving sulfuric acid and organic vapors is estimated to have significant climate effects. To accurately represent this process in large-scale models, the correct interpretation of the observations on particle growth, especially below 10 nm, is essential. Here, we disentangle the factors governing the growth of sub-10 nm particles in the presence of sulfuric acid and organic vapors, using molecular-resolution cluster population simulations and chamber experiments. We find that observed particle growth rates are determined by the combined effects of (1) the concentrations and evaporation rates of the condensing vapors, (2) particle population dynamics, and (3) stochastic fluctuations, characteristic to initial nucleation. This leads to a different size-dependency of growth rate in the presence of sulfuric acid and/or organic vapors at different concentrations. Specifically, the activation type behavior, resulting in growth rate increasing with the particle size, is observed only at certain vapor concentrations. In our model simulations, cluster-cluster collisions enhance growth rate at high vapor concentrations and their importance is dictated by the cluster evaporation rates, which demonstrates the need for accurate evaporation rate data. Finally, we show that at sizes below ∼2.5-3.5 nm, stochastic effects can importantly contribute to particle population growth. Overall, our results suggest that interpreting particle growth observations with approaches neglecting population dynamics and stochastics, such as with single particle growth models, can lead to the wrong conclusions on the properties of condensing vapors and particle growth mechanisms.
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| 4. |
- Lagergren, Fredrik, et al.
(author)
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Kilometre-scale simulations over Fennoscandia reveal a large loss of tundra due to climate warming
- 2024
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In: Biogeosciences. - 1726-4170 .- 1726-4189. ; 21:5, s. 1093-1116
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Journal article (peer-reviewed)abstract
- The Fennoscandian boreal and mountain regions harbour a wide range of vegetation types, from boreal forest to high alpine tundra and barren soils. The area is facing a rise in air temperature above the global average and changes in temperature and precipitation patterns. This is expected to alter the Fennoscandian vegetation composition and change the conditions for areal land use such as forestry, tourism and reindeer husbandry. In this study we used a unique high-resolution (3 km) climate scenario with considerable warming resulting from strongly increasing carbon dioxide emissions to investigate how climate change can alter the vegetation composition, biodiversity and availability of suitable reindeer forage. Using a dynamical vegetation model, including a new implementation of potential reindeer grazing, resulted in simulated vegetation maps of unprecedented high resolution for such a long time period and spatial extent. The results were evaluated at the local scale using vegetation inventories and for the whole area against satellite-based vegetation maps. A deeper analysis of vegetation shifts related to statistics of threatened species was performed in six “hotspot” areas containing records of rare and threatened species. In this high-emission scenario, the simulations show dramatic shifts in the vegetation composition, accelerating at the end of the century. Alarmingly, the results suggest the southern mountain alpine region in Sweden will be completely covered by forests at the end of the 21st century, making preservation of many rare and threatened species impossible. In the northern alpine regions, most vegetation types will persist but shift to higher elevations with reduced areal extent, endangering vulnerable species. Simulated potential for reindeer grazing indicates latitudinal differences, with higher potential in the south in the current climate. In the future these differences will diminish, as the potentials will increase in the north, especially for the summer grazing grounds. These combined results suggest significant shifts in vegetation composition over the present century for this scenario, with large implications for nature conservation, reindeer husbandry and forestry.
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| 5. |
- Olenius, Tinja, et al.
(author)
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Modeling of exhaust gas cleaning by acid pollutant conversion to aerosol particles
- 2021
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In: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 290
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Journal article (peer-reviewed)abstract
- Sulfur and nitrogen oxides (SOx and NOx) are harmful pollutants emitted into the atmosphere by industry and transport sectors. In addition to being hazardous gases, SOx and NOx form sulfuric and nitric acids which contribute to the formation of airborne particulate matter through nucleation and condensation, hence magnifying the environmental impact of these species. In this work, we build a modeling framework for utilizing this phenomenon for low-temperature exhaust gas cleaning. It has been reported that ammonia gas can be used to facilitate particle formation from the aforementioned acids, and thus remove these gaseous pollutants by converting them into ammonium sulfate and nitrate particles. Here we provide comprehensive modeling tools for applying this idea to exhaust gas cleaning by combining detailed models for nucleation, gas-particle mass exchange and particle population dynamics. We demonstrate how these models can be used to find advantageous operating conditions for a cleaning unit. In particular, the full model is computationally cheap and enables optimization of the particle formation efficiency and particle growth, hence ensuring sufficient conversion of gaseous pollutants into collectable particulate matter. This constitutes a ground for future engineering tools for designing next-generation sustainable exhaust gas cleaners.
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| 6. |
- Olenius, Tinja, et al.
(author)
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Role of gas–molecular cluster–aerosol dynamics in atmospheric new-particle formation
- 2022
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 12:1
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Journal article (peer-reviewed)abstract
- New-particle formation from vapors through molecular cluster formation is a central process affecting atmospheric aerosol and cloud condensation nuclei numbers, and a significant source of uncertainty in assessments of aerosol radiative forcing. While advances in experimental and computational methods provide improved assessments of particle formation rates from different species, the standard approach to implement these data in aerosol models rests on highly simplifying assumptions concerning gas–cluster–aerosol dynamics. To quantify the effects of the simplifications, we develop an open-source tool for explicitly simulating the dynamics of the complete particle size spectrum from vapor molecules and molecular clusters to larger aerosols for multi-compound new-particle formation. We demonstrate that the simplified treatment is a reasonable approximation for particle formation from weakly clustering chemical compounds, but results in overprediction of particle numbers and of the contribution of new-particle formation to cloud condensation nuclei for strongly clustering, low-concentration trace gases. The new explicit approach circumvents these issues, thus enabling robust model–measurement comparisons, improved assessment of the importance of different particle formation agents, and construction of optimal simplifications for large-scale models.
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| 7. |
- Schlesinger, Daniel, 1982-, et al.
(author)
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Molecular perspective on water vapor accommodation into ice and its dependence on temperature
- 2020
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In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 124:51, s. 10879-10889
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Journal article (peer-reviewed)abstract
- © 2020 American Chemical Society. Accommodation of vapor-phase water molecules into ice crystal surfaces is a fundamental process controlling atmospheric ice crystal growth. Experimental studies investigating the accommodation process with various techniques report widely spread values of the water accommodation coefficient on ice, αice, and the results on its potential temperature dependence are inconclusive. We run molecular dynamics simulations of molecules condensing onto the basal plane of ice Ih using the TIP4P/Ice empirical force field and characterize the accommodated state from this molecular perspective, utilizing the interaction energy, the tetrahedrality order parameter, and the distance below the instantaneous interface as criteria. Changes of the order parameter turn out to be a suitable measure to distinguish between the surface and bulk states of a molecule condensing onto the disordered interface. In light of the findings from the molecular dynamics, we discuss and re-analyze a recent experimental data set on αice obtained with an environmental molecular beam (EMB) setup [Kong, X.; et al. J. Phys. Chem. A 2014, 118 (22), 3973-3979] using kinetic molecular flux modeling, aiming at a more comprehensive picture of the accommodation process from a molecular perspective. These results indicate that the experimental observations indeed cannot be explained by evaporation alone. At the same time, our results raise the issue of rapidly growing relaxation times upon decreasing temperature, challenging future experimental efforts to cover relevant time scales. Finally, we discuss the relevance of the water accommodation coefficient on ice in the context of atmospheric cloud particle growth processes.
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| 8. |
- Shcherbacheva, Anna, et al.
(author)
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Identification of molecular cluster evaporation rates, cluster formation enthalpies and entropies by Monte Carlo method
- 2020
-
In: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 20:24, s. 15867-15906
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Journal article (peer-reviewed)abstract
- We address the problem of identifying the evaporation rates for neutral molecular clusters from synthetic (computer-simulated) cluster concentrations. We applied Bayesian parameter estimation using a Markov chain Monte Carlo (MCMC) algorithm to determine cluster evaporation/fragmentation rates from synthetic cluster distributions generated by the Atmospheric Cluster Dynamics Code (ACDC) and based on gas kinetic collision rate coefficients and evaporation rates obtained using quantum chemical calculations and detailed balances. The studied system consisted of electrically neutral sulfuric acid and ammonia clusters with up to five of each type of molecules. We then treated the concentrations generated by ACDC as synthetic experimental data. With the assumption that the collision rates are known, we tested two approaches for estimating the evaporation rates from these data. First, we studied a scenario where time-dependent cluster distributions are measured at a single temperature before the system reaches a steady state. In the second scenario, only steady-state cluster distributions are measured but at several temperatures. Additionally, in the latter case, the evaporation rates were represented in terms of cluster formation enthalpies and entropies. This reparame-terization reduced the number of unknown parameters, since several evaporation rates depend on the same cluster formation enthalpy and entropy values. We also estimated the evap- oration rates using previously published synthetic steady-state cluster concentration data at one temperature and compared our two cases to this setting. Both the time-dependent and the two-temperature steady-state concentration data allowed us to estimate the evaporation rates with less variance than in the steady-state single-temperature case. We show that temperature-dependent steady-state data outperform single-temperature time-dependent data for parameter estimation, even if only two temperatures are used. We can thus conclude that for experimentally determining evaporation rates, cluster distribution measurements at several temperatures are recommended over time-dependent measurements at one temperature.
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