| 1. |
- Andersson, Camilla, et al.
(författare)
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Achievements and experiences from science–policy interaction in the field of air pollution : Synthesising 20 years of research and outreach,thinking about future needs
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- For 20 years, the Swedish Environmental Protection Agency together with the MISTRA research foundation have funded five air pollution research programmes with focus on producing knowledge that supports policy and emission control in national and international arenas. The research has been multidisciplinary and has included research on emissions, atmospheric transport and transformation processes, human health effects, ecosystem effects, and emission control strategies. Research has also been conducted on the interaction between air pollution and climate change.Over these years, the link between the research programmes and the development of emission control strategies and policies in Sweden, the EU, and the UNECE Air Convention has been of high importance. This report presents how the research programmes have created societal benefits through support for the development of air pollution policies and emission control measures. The report also identifies future research needs to ensure continued progress towards even better air quality for future generations.
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| 2. |
- Bardakov, Roman, et al.
(författare)
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A Novel Framework to Study Trace Gas Transport in Deep Convective Clouds
- 2020
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Ingår i: Journal of Advances in Modeling Earth Systems. - 1942-2466. ; 12:5
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Tidskriftsartikel (refereegranskat)abstract
- Deep convective clouds reach the upper troposphere (8-15 km height). In addition to moisture and aerosol particles, they can bring aerosol precursor gases and other reactive trace gases from the planetary boundary layer to the cloud top. In this paper, we present a method to estimate trace gas transport based on the analysis of individual air parcel trajectories. Large eddy simulation of an idealized deep convective cloud was used to provide realistic environmental input to a parcel model. For a buoyant parcel, we found that the trace gas transport approximately follows one out of three scenarios, determined by a combination of the equilibrium vapor pressure (containing information about water-solubility and pure component saturation vapor pressure) and the enthalpy of vaporization. In one extreme, the trace gas will eventually be completely removed by precipitation. In the other extreme, there is almost no vapor condensation on hydrometeors and most of the gas is transported to the top of the cloud. The scenario in between these two extremes is also characterized by strong gas condensation, but a small fraction of the trace gas may still be transported aloft. This approach confirms previously suggested patterns of inert trace gas behavior in deep convective clouds, agrees with observational data, and allows estimating transport in analytically simple and computationally efficient way compared to explicit cloud-resolving model calculations.
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| 3. |
- Bardakov, Roman, 1992-, et al.
(författare)
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The Role of Convective Up- and Downdrafts in the Transport of Trace Gases in the Amazon
- 2022
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Ingår i: Journal of Geophysical Research - Atmospheres. - : American Geophysical Union (AGU). - 2169-897X .- 2169-8996. ; 127:18
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Tidskriftsartikel (refereegranskat)abstract
- Deep convective clouds can redistribute gaseous species and particulate matter among different layers of the troposphere with important implications for atmospheric chemistry and climate. The large number of atmospheric trace gases of different volatility makes it challenging to predict their partitioning between hydrometeors and gas phase inside highly dynamic deep convective clouds. In this study, we use an ensemble of 51,200 trajectories simulated with a cloud-resolving model to characterize up- and downdrafts within Amazonian deep convective clouds. We also estimate the transport of a set of hypothetical non-reactive gases of different volatility, within the up- and downdrafts. We find that convective air parcels originating from the boundary layer (i.e., originating at 0.5 km altitude), can transport up to 25% of an intermediate volatility gas species (e.g., methyl hydrogen peroxide) and up to 60% of high volatility gas species (e.g., n-butane) to the cloud outflow above 10 km through the mean convective updraft. At the same time, the same type of gases can be transported to the boundary layer from the middle troposphere (i.e., originating at 5 km) within the mean convective downdraft with an efficiency close to 100%. Low volatility gases (e.g., nitric acid) are not efficiently transported, neither by the updrafts nor downdrafts, if the gas is assumed to be fully retained in a droplet upon freezing. The derived properties of the mean up- and downdraft can be used in future studies for investigating convective transport of a larger set of reactive trace gases.
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| 4. |
- Bardakov, Roman, 1992-
(författare)
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Transport and chemical processing of trace gases in deep convective clouds
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Deep convective clouds can efficiently transport trace gases from the planetary boundary layer to the upper troposphere. Once there, some gases will contribute to new particle formation and growth, eventually producing aerosols that are large enough to influence cloud properties, the radiative budget of the Earth, and climate. The magnitude and exact pathways of the convective transport of many organic and inorganic compounds are, however, still unclear. This dissertation presents a framework to study vertical transport of gas mixtures by deep convective clouds. The method consists of a chemical box model that is driven by cloud air parcel trajectory data generated by large-eddy simulation. This combination allows us to examine detailed gas-cloud interactions as well as complex systems of gas-phase chemical reactions. A large ensemble of simulated cloud trajectories was used to identify and characterize convective up- and downdrafts in the Amazon region. The analysis showed that air parcels starting close to the surface (at 0.5 km) experienced a substantially larger probability of reaching the upper troposphere (above 10 km) than parcels starting at the top of the boundary layer. Furthermore, the framework was used to estimate the vertical transport of isoprene, isoprene oxidation products, ammonia, and several non-reactive trace gases. We found that a typical Amazonian deep convective cloud can transport around 30% of the boundary layer isoprene to the cloud outflow if the efficiency of the gas uptake on ice is high and there is no lightning within the cloud. If the efficiency of gas uptake on ice is low and lightning within the cloud is extensive, all isoprene will be oxidized. Several low-volatility isoprene oxidation products will then have relatively high concentrations in the outflow, which potentially could lead to new particle formation and growth. Another result was that up to 10% of the boundary layer ammonia can reach the cloud outflow, where it in some environments can nucleate synergistically with nitric and sulfuric acid. A key uncertainty in our estimates is the efficiency of gas uptake by ice particles.
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| 5. |
- Bardakov, Roman, et al.
(författare)
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Transport and chemistry of isoprene and its oxidation products in deep convective clouds
- 2021
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Ingår i: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 73:1, s. 1-21
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Tidskriftsartikel (refereegranskat)abstract
- Deep convective clouds can transport trace gases from the planetary boundary layer into the upper troposphere where subsequent chemistry may impact aerosol particle formation and growth. In this modelling study, we investigate processes that affect isoprene and its oxidation products injected into the upper troposphere by an isolated deep convective cloud in the Amazon. We run a photochemical box model with coupled cloud microphysics along hundreds of individual air parcel trajectories sampled from a cloud-resolving model simulation of a convective event. The box model simulates gas-phase chemical reactions, gas scavenging by liquid and ice hydrometeors, and turbulent dilution inside a deep convective cloud. The results illustrate the potential importance of gas uptake to anvil ice in regulating the intensity of the isoprene oxidation and associated low volatility organic vapour concentrations in the outflow. Isoprene transport and fate also depends on the abundance of lightning-generated nitrogen oxide radicals (NOx = NO + NO2). If gas uptake on ice is efficient and lightning activity is low, around 30% of the boundary layer isoprene will survive to the cloud outflow after approximately one hour of transport, while all the low volatile oxidation products will be scavenged by the cloud hydrometeors. If lightning NOx is abundant and gas uptake by ice is inefficient, then all isoprene will be oxidised during transport or in the immediate outflow region, while several low volatility isoprene oxidation products will have elevated concentrations in the cloud outflow. Reducing uncertainties associated with the uptake of vapours on ice hydrometeors, especially HO2 and oxygenated organics, is essential to improve predictions of isoprene and its oxidation products in deep convective outflows and their potential contribution to new particle formation and growth.
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| 6. |
- Baró Pérez, Alejandro, 1991-
(författare)
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Aerosol impacts on subtropical low-level clouds: a satellite and modelling perspective
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Complex interactions between aerosols, clouds, and radiation impact Earth's climate. However, several aspects of these interactions remain uncertain, which has led to extensive research over the last decades. This thesis explores some unresolved aspects by focusing on subtropical low-level stratocumulus (Sc) clouds, which have a significant cooling effect on climate. The clouds are also sensitive to varying aerosol conditions, which can influence their formation, properties, and lifetime. Clouds over the South East Atlantic have been studied in detail, using both numerical modeling and satellite observations, to shed light on the interactions between aerosols, clouds, and radiation. This geographical region displays a large and semi-permanent Sc cloud deck and is also subjected to meteorological conditions that bring large amounts of light-absorbing aerosols from biomass fires over the African continent. The biomass-burning plumes also bring enhanced levels of moisture, and the individual influence of the aerosols and the moisture on the low-level cloud properties have been investigated.The analysis of satellite retrievals showed a radiative impact (sensitive to aerosol composition and aerosol optical depth) of moist aerosol layers in the free troposphere over the South East Atlantic; however, it was not possible to observe a clear influence of these humid aerosol layers on the underlying low-level clouds. Aerosol-radiation interactions were implemented in a large eddy simulation (LES) code that was used to model stratocumulus to cumulus transitions (SCT) in weather situations where moist absorbing aerosol layers were in contact with low-level clouds and mixed into the marine boundary layer (MBL). In these simulations, the heating by the absorbing aerosol within the MBL affected the persistence of the Sc clouds by accelerating the SCT, especially during daylight and broken cloud conditions. However, the humidity accompanying the absorbing aerosol was also found to be important -- it reduced the deepening of the MBL when located above the Sc deck and delayed the SCT when in contact with clouds. Furthermore, the additional moisture resulted in a radiative cooling effect that was comparable to the radiative cooling effect caused by the aerosol itself. The simulated SCTs were found to be mostly driven by increased sea surface temperatures, regardless of aerosol conditions. This result was different compared to two other LES models where the SCT was driven by drizzle under the same low aerosol conditions. On a larger scale, it was found that an explicit description of aerosol-cloud interactions in a climate model led to smaller differences between the simulated and mean observed values of the shortwave cloud radiative effect compared to when a non-interactive parameterization was used.
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| 7. |
- Baró Pérez, Alejandro, et al.
(författare)
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Comparing the simulated influence of biomass burning plumes on low-level clouds over the southeastern Atlantic under varying smoke conditions
- 2024
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Ingår i: Atmospheric Chemistry And Physics. - 1680-7316 .- 1680-7324. ; 24:8, s. 4591-4610
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Tidskriftsartikel (refereegranskat)abstract
- Biomass burning plumes are frequently transported over the southeast Atlantic (SEA) stratocumulus deck during the southern African fire season (June-October). The plumes bring large amounts of absorbing aerosols and enhanced moisture, which can trigger a rich set of aerosol-cloud-radiation interactions with climatic consequences that are still poorly understood. We use large-eddy simulation (LES) to explore and disentangle the individual impacts of aerosols and moisture on the underlying stratocumulus clouds, the marine boundary layer (MBL) evolution, and the stratocumulus-to-cumulus transition (SCT) for three different meteorological situations over the southeast Atlantic during August 2017. For all three cases, our LES shows that the SCT is driven by increased sea surface temperatures and cloud-top entrainment as the air is advected towards the Equator. In the LES model, aerosol indirect effects, including impacts on drizzle production, have a small influence on the modeled cloud evolution and SCT, even when aerosol concentrations are lowered to background concentrations. In contrast, local semi-direct effects, i.e., aerosol absorption of solar radiation in the MBL, cause a reduction in cloud cover that can lead to a speed-up of the SCT, in particular during the daytime and during broken cloud conditions, especially in highly polluted situations. The largest impact on the radiative budget comes from aerosol impacts on cloud albedo: the plume with absorbing aerosols produces a total average 3 d of simulations. We find that the moisture accompanying the aerosol plume produces an additional cooling effect that is about as large as the total aerosol radiative effect. Overall, there is still a large uncertainty associated with the radiative and cloud evolution effects of biomass burning aerosols. A comparison between different models in a common framework, combined with constraints from in situ observations, could help to reduce the uncertainty.
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| 8. |
- Baró Pérez, Alejandro, et al.
(författare)
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Impact of smoke and non-smoke aerosols on radiation and low-level clouds over the southeast Atlantic from co-located satellite observations
- 2021
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 21:8, s. 6053-6077
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Tidskriftsartikel (refereegranskat)abstract
- Data derived from instruments on board the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and CloudSat satellites as well as meteorological parameters from reanalysis are used to explore situations when moist aerosol layers overlie stratocumulus clouds over the southeast Atlantic during the biomass burning season (June to October). To separate and quantify the impacts of aerosol loading, aerosol type, and humidity on the radiative fluxes (including cloud top cooling), the data are split into different levels of aerosol and moisture loadings. The aerosol classification available from the CALIPSO products is used to compare and contrast situations with pristine air, with smoke, and with other (non-smoke) types of aerosols. A substantial number of cases with non-smoke aerosols above clouds are found to occur under similar meteorological conditions to the smoke cases. In contrast, the meteorology is substantially different for the pristine situations, making a direct comparison with the aerosol cases ambiguous. The moisture content is enhanced within the aerosol layers, but the relative humidity does not always increase monotonously with increasing optical depth. Shortwave (SW) heating rates within the moist aerosol plumes increase with increasing aerosol loading and are higher in the smoke cases compared to the non-smoke cases. However, there is no clear correlation between moisture changes and SW absorption. Cloud top cooling rates do not show a clear correlation with moisture within the overlying aerosol layers due to the strong variability of the cooling rates caused by other meteorological factors (most notably cloud top temperature). No clear influence of aerosol type or loading on cloud top cooling rates is detected. Further, there is no correlation between aerosol loading and the thermodynamic structure of the atmosphere nor the cloud top height.
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| 9. |
- Braun, Christoph, et al.
(författare)
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Controls on Subtropical Cloud Reflectivity during a Waterbelt Scenario for the Cryogenian Glaciations
- 2022
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Ingår i: Journal of Climate. - 0894-8755 .- 1520-0442. ; 35:21, s. 3457-3476
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Tidskriftsartikel (refereegranskat)abstract
- Waterbelt climate states with an ice-free tropical ocean provide a straightforward explanation for the survival of advanced marine species during the Cryogenian glaciations (720–635 million years ago). Previous work revealed that stable waterbelt states require the presence of highly reflective low-level mixed-phase clouds with a high abundance of supercooled liquid in the subtropics. However, the high uncertainty associated with representing mixed-phase clouds in coarse-scale general circulation models (GCMs) that parameterize atmospheric convection has prohibited assessment of whether waterbelt states are a robust feature of Earth’s climate. Here we investigate whether resolving convective-scale motion at length scales of hectometers helps us to assess the plausibility of a waterbelt scenario. First, we show that substantial differences in cloud reflectivity among GCMs do not arise from the resolved atmospheric circulation. Second, we conduct a hierarchy of simulations using the Icosahedral Nonhydrostatic (ICON) modeling framework, ranging from coarse-scale GCM simulations with parameterized convection to large-eddy simulations that explicitly resolve atmospheric convective-scale motions. Our hierarchy of simulations supports the existence of highly reflective subtropical clouds if we apply moderate ice nucleating particle (INP) concentrations. Third, we test the sensitivity of cloud reflectivity to the INP concentration. In the presence of high but justifiable INP concentrations, cloud reflectivity is strongly reduced. Hence, the existence of stable waterbelt states is controlled by the abundance of INPs. We conclude that explicitly resolving convection can help to constrain Cryogenian cloud reflectivity, but limited knowledge concerning Cryogenian aerosol conditions hampers strong constraints. Thus, waterbelt states remain an uncertain feature of Earth’s climate.
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| 10. |
- Bulatovic, Ines
(författare)
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Investigating aerosol effects on stratocumulus clouds through large-eddy simulation
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Clouds have a large impact on Earth’s radiative budget by reflecting, absorbing and re-emitting radiation. They thus play a critical role in the climate system. Nevertheless, cloud radiative effects in a changing climate are highly uncertain. Atmospheric aerosol particles are another factor affecting Earth’s climate but the magnitude of their influence is also associated with high uncertainty. Therefore, an accurate representation of aerosol-cloud interactions in models is critical for having confidence in future climate projections. This thesis investigates aerosol impacts on cloud microphysical and radiative properties through numerical modelling, more specifically large-eddy simulation (LES). Moreover, the thesis investigates how the simulated cloud response to changes in the aerosol population depends on the model description of different processes. Mixed-phase stratocumulus (MPS) clouds are especially problematic to simulate for models on all scales. These clouds consist of a mixture of supercooled water and ice in the same volume and are therefore potentially thermodynamically unstable. MPS clouds over the central (north of 80° N) Arctic Ocean are particularly sensitive to aerosol changes due to the relatively clean atmospheric conditions in this region. At the same time, the clouds also have an important impact on the Arctic surface radiative budget. Therefore, this thesis mostly focuses on Arctic MPS clouds.Simulations of a typical subtropical marine stratocumulus cloud showed that the aerosol-cloud forcing depends on the model treatment for calculating the cloud droplet number concentration (CDNC). The simulated change in the top of the atmosphere shortwave radiation due to increased aerosol number concentrations was almost three times as large when the CDNC was prescribed compared to when the CDNC was prognostic. Simulations of a central Arctic summertime low-level MPS cloud confirmed that the chemical composition and the size of aerosol particles both can play an important role in determining the efficiency of an aerosol to act as cloud condensation nuclei - and thus influence cloud properties. However, the hygroscopicity of the aerosol particle was only important if the particles were small in size (i.e., if they correspond to the Aitken mode size) or if they were close to hydrophobic. Further, it was also found that Aitken mode particles can significantly change microphysical and radiative properties of central Arctic MPS if the concentration of larger particles (i.e., corresponding to the accumulation mode) is less than approximately 10-20 cm-3. One of the most recent research expeditions in the central Arctic (in the summer of 2018) was characterized by a high occurrence of multiple cloud layers. Namely, the boundary layer structure consisted of two MPS, one located close to the surface and one at the top of the boundary layer. Large-eddy simulations of an observed case with this particular cloud structure showed that the two-layer boundary-layer clouds are persistent unless the aerosol number concentrations are low (< 5 cm-3) or the wind speed is high (≥ 8.5 m s-1). In the model, low aerosol numbers led to a dissipation of the upper cloud layer while the lower cloud layer dissipated if the wind speed was strong. Changes in the optical thickness and cloud emissivity of each individual cloud layer of the two-layer cloud structure were found to substantially impact the surface radiative fluxes.
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