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Book ; Online: Impacts of marine organic emissions on low level stratiform clouds – a large eddy simulator study

Prank, Marje / Tonttila, Juha / Ahola, Jaakko / Kokkola, Harri / Kühn, Thomas / Romakkaniemi, Sami / Raatikainen, Tomi

eISSN: 1680-7324

2022

Abstract: The goal of this study is to investigate the role of organic aerosols emitted with sea spray or formed from marine gas phase emissions of volatile organic compounds (VOCs) in influencing the stability of stratiform marine clouds. We aim at pointing out ... ...

Abstract	The goal of this study is to investigate the role of organic aerosols emitted with sea spray or formed from marine gas phase emissions of volatile organic compounds (VOCs) in influencing the stability of stratiform marine clouds. We aim at pointing out the processes and drivers that could be relevant in larger scale and should thus be considered in global climate models. We employ large eddy simulator that includes a detailed description of aerosols, cloud droplets and rain drops together with different model parameterizations for emission of sea salt, primary organic aerosol and VOCs from sea surface, and oxidation of the emitted VOCs and partitioning of the resulting semi-volatile organic species between vapor and aerosol phases. As a case study, we apply the model to simulate the conditions of the DYCOMS-II observational campaign characterized by low level stratocumulus clouds transitioning from closed cells to drizzling open cell structure. We find that the inclusion of online sea spray emissions can both extend and shorten the lifetime of the cloud layer based on the parameterization employed. Fine sea spray provides extra cloud condensation nuclei (CCN) and delays the onset of drizzle as the collision-coalescence process is slowed down due to smaller cloud droplet mean size. From the same emissions, the coarse mode has an opposite effect due to giant CCN (GCCN) speeding up the drizzle formation through the enhanced collision-coalescence processes. The balance between two process depends on the model parameterization employed. Compared to differences between different sea spray parameterizations, the sensitivity of the clouds to the variations in organic fraction of sea spray and hygroscopicity of the emitted fine aerosols is relatively limited. However, our results show that it is important to account for the size dependence of the sea spray organic fraction as attributing organic emissions to coarse mode noticeably reduces the GCCN effect. In addition, including the secondary aerosol formation from VOCs can potentially have a noticeable impact, but only when emitting the highest observed fluxes of monoterpenes. This impact is also highly sensitive on the size distribution of the background aerosol population. SOA production from isoprene is visible only if aqueous phase SOA production pathways are included in the model, and even then, the effect is lower than from monoterpenes.
Subject code	551
Language	English
Publishing date	2022-04-26
Publishing country	de
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Impacts of marine organic emissions on low-level stratiform clouds – a large eddy simulator study

Prank, Marje / Tonttila, Juha / Ahola, Jaakko / Kokkola, Harri / Kühn, Thomas / Romakkaniemi, Sami / Raatikainen, Tomi

eISSN: 1680-7324

2022

Abstract	The goal of this study is to investigate the role of organic aerosols emitted with sea spray or formed from marine gas phase emissions of volatile organic compounds (VOCs) in influencing the stability of stratiform marine clouds. We aim to point out the processes and drivers that could be relevant for global climate and should thus be considered in large-scale models. We employ a large eddy simulator coupled with an aerosol–cloud microphysical model together with different parameterizations for emission of sea salt, primary organic aerosol, and VOCs from sea surface and formation of secondary organic aerosol (SOA), to simulate the conditions of the second Dynamics and Chemistry of Marine Stratocumulus observational campaign characterized by low-level stratocumulus clouds transitioning from closed cells to drizzling open cell structure. We find that the inclusion of sea spray emissions can both extend and shorten the transitioning timescale between closed and open cells based on the parameterization employed. Fine sea spray provides extra cloud condensation nuclei (CCN) and delays the onset of drizzle as the collision–coalescence process is slowed down due to smaller cloud droplet mean size. The coarse mode has an opposite effect due to giant CCN (GCCN) speeding up the drizzle formation through the enhanced collision–coalescence processes. The balance between two processes depends on the model parameterization employed. Compared to differences between different sea spray parameterizations, the sensitivity of the clouds to the variations in organic fraction of sea spray and hygroscopicity of the emitted particles is relatively limited. However, our results show that it is important to account for the size dependence of the sea spray organic fraction as attributing organic emissions to coarse mode noticeably reduces the GCCN effect. In addition, including the secondary organic aerosol formation from VOCs can potentially have a noticeable impact, but only when emitting the highest observed fluxes of monoterpenes. ...
Subject code	551
Language	English
Publishing date	2022-08-30
Publishing country	de
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Using a coupled LES aerosol-radiation model to investigate the importance of aerosol-boundary layer feedback in a Beijing haze episode.

Slater, Jessica / Tonttila, Juha / McFiggans, Gordon / Coe, Hugh / Romakkaniemi, Sami / Sun, Yele / Xu, Weiqi / Fu, Pingqing / Wang, Zifa

Faraday discussions

2021 Volume 226, Page(s) 173–190

Abstract: Haze episodes, characterised by extremely high aerosol concentrations and a reduction in visibility to less than 10 km, are a frequent occurrence in wintertime Beijing, despite policy interventions leading to an overall improvement in average annual air ... ...

Abstract	Haze episodes, characterised by extremely high aerosol concentrations and a reduction in visibility to less than 10 km, are a frequent occurrence in wintertime Beijing, despite policy interventions leading to an overall improvement in average annual air quality. The main drivers in the onset of haze episodes in wintertime Beijing are changing synoptic conditions, however, aerosol-radiation interactions and their feedback on boundary layer meteorology are thought to play an essential role in the intensity and longevity of haze episodes. In this study we use a coupled LES aerosol-radiation model (UCLALES-SALSA), which we have recently configured for the urban environment of Beijing. The model's high resolution and control over meteorological and aerosol conditions as well as atmospheric processes means we can directly elucidate and quantify the importance of specific aspects of the aerosol-radiation-meteorology feedback in the cumulative stage of Beijing haze. The main results presented here show (a) synoptic scale meteorology has a larger impact on boundary layer suppression than high aerosol concentrations and (b) unlike previous results obtained using regional models or observationally driven analyses, there is no threshold value at which the aerosol-radiation-meteorology feedback has a significant effect on PBL height. Rather, our work shows that for the aerosol composition in this case study, the role of the feedback effect in reducing PBL height increases under shallow boundary layer conditions and with increasing pollution loading in an almost linear fashion. This lack of a threshold found for our case study has important policy implications since interventions based on such a value will not result in large reductions associated with turning off the feedback process. Furthermore, this work directly shows that although the right synoptic changes are a prerequisite for pollution episodes in Beijing, local and regional emissions drive increases in aerosol load that are sufficient to initiate the aerosol feedback loop. This further drives suppression of the boundary layer top and promotes stagnation of air and increased stability, which can be self-sustaining. This results in higher surface aerosol concentrations for extended periods of time, with severe consequences for human health [Lv et al., Atmos. Environ., 2016, 124, 98-108; Wang et al., Atmos. Chem. Phys., 2019, 19(10), 6949-6967].
Language	English
Publishing date	2021-01-07
Publishing country	England
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ISSN	1364-5498
ISSN (online)	1364-5498
DOI	10.1039/d0fd00085j
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Book ; Online: The effect of marine ice nucleating particles on mixed-phase clouds

Raatikainen, Tomi / Prank, Marje / Ahola, Jaakko / Kokkola, Harri / Tonttila, Juha / Romakkaniemi, Sami

eISSN: 1680-7324

2021

Abstract: Shallow marine mixed-phase clouds are important for the radiative balance, but modelling their formation and dynamics is challenging. These clouds depend on boundary layer turbulence and cloud top radiative cooling, which is related to the cloud phase. ... ...

Abstract	Shallow marine mixed-phase clouds are important for the radiative balance, but modelling their formation and dynamics is challenging. These clouds depend on boundary layer turbulence and cloud top radiative cooling, which is related to the cloud phase. The fraction of frozen droplets depends on the availability of suitable ice nucleating particles (INPs), which initiate droplet freezing. While desert dust is the dominating INP type in most regions, remote boundary layer clouds are dependent on local marine INP emissions, which are often related to biogenic sources including phytoplankton. Here we use high resolution large eddy simulations to examine the potential effects of marine emissions on boundary layer INP concentrations and their effects on clouds. Surface emissions have a direct effect on INP concentration in a typical well-mixed boundary layer whereas a steep inversion can block the import of background INPs from the free troposphere. The importance of the marine source depends on the background INP concentration, so that marine emissions become dominant with low background concentrations. For the INP budget it is also important to account for INP recycling. Finally, with the high-resolution model we show how ice nucleation hotspots and high INPs concentrations are focused on updraught regions. Our results show that marine INP emissions contribute directly to the boundary layer INP budget and therefore have an influence on mixed-phase clouds.
Subject code	551
Language	English
Publishing date	2021-07-12
Publishing country	de
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Using a coupled LES-aerosol radiation model to investigate urban haze

Slater, Jessica / Tonttila, Juha / McFiggans, Gordon / Romakkaniemi, Sami / Kühn, Thomas / Coe, Hugh

eISSN: 1680-7324

Sensitivity to aerosol loading and meteorological conditions

2020

Abstract: The aerosol-radiation-meteorological feedback loop is the process by which aerosols interact with solar radiation to influence boundary layer meteorology. Through this feedback, aerosols cause cooling of the surface, resulting in reduced buoyant ... ...

Abstract	The aerosol-radiation-meteorological feedback loop is the process by which aerosols interact with solar radiation to influence boundary layer meteorology. Through this feedback, aerosols cause cooling of the surface, resulting in reduced buoyant turbulence, enhanced atmospheric stratification and suppressed boundary layer growth. These changes in meteorology result in the accumulation of aerosols in a shallow boundary layer, which can enhance the extent of aerosol-radiation interactions. The feedback effect is thought to be important during periods of high aerosol concentrations, for example during urban haze. However, direct quantification and isolation of the factors and processes affecting the feedback loop has thus far been limited to observations and low resolution modelling studies. The coupled LES-aerosol model, UCLALES-SALSA, allows for direct interpretation on the sensitivity of boundary layer dynamics to aerosol perturbations. In this work, UCLALES-SALSA has for the first time been explicitly set up to model the urban environment, including addition of an anthropogenic heat flux and treatment of heat storage terms, to examine the sensitivity of meteorology to the newly coupled aerosol-radiation scheme. We find that: a) Sensitivity of boundary layer dynamics in the model to initial meteorological conditions is extremely high, b) Simulations with high aerosol loading (220 μg/m 3 ) compared to low aerosol loading (55 μg/m 3 ) cause overall surface cooling and a reduction in sensible heat flux, turbulent kinetic energy and planetary boundary layer height for all three days examined and c) Initial meteorological conditions impact the vertical distribution of aerosols throughout the day.
Subject code	551
Language	English
Publishing date	2020-03-31
Publishing country	de
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Technical note

Nordling, Kalle / Keskinen, Jukka-Pekka / Romakkaniemi, Sami / Kokkola, Harri / Räisänen, Petri / Lipponen, Antti / Partanen, Antti-Ilari / Ahola, Jaakko / Tonttila, Juha / Alper, Muzaffer Ege / Korhonen, Hannele / Raatikainen, Tomi

eISSN:

Emulation of a large-eddy simulator for stratocumulus clouds in a general circulation model

2023

Abstract: Here we present for the first time a proof of concept for an emulation-based method that uses a large-eddy simulations (LES) to present sub-grid cloud processes in a general circulation model (GCM). We focus on two key variables affecting the properties ... ...

Abstract	Here we present for the first time a proof of concept for an emulation-based method that uses a large-eddy simulations (LES) to present sub-grid cloud processes in a general circulation model (GCM). We focus on two key variables affecting the properties of shallow marine clouds: updraft velocity and precipitation formation. The LES is able to describe these processes with high resolution accounting for the realistic variability in cloud properties. We show that the selected emulation method is 5 able to represent the LES outcome with relatively good accuracy and that the updraft velocity and precipitation emulators can be coupled with the GCM practically without increasing the computational costs. We also show that the emulators influence the climate simulated by the GCM, but do not consistently improve or worsen the agreement with observations on cloud related properties. Although especially the updraft velocity at cloud base is better captured. A more quantitative evaluation of the emulator impacts against observations would, however, have required model re-tuning, which is a significant task and thus could 10 not be included in this proof-of-concept study. All in all, the approach introduced here is a promising candidate for representing detailed cloud and aerosol related sub-grid processes in GCMs. Further development work together with increasing computing capacity can be expected to improve the accuracy and the applicability of the approach in climate simulations.
Subject code	551
Language	English
Publishing date	2023-05-31
Publishing country	de
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Comparing the simulated influence of biomass burning plumes on low-level clouds over the southeastern Atlantic under varying smoke conditions

Baró Pérez, Alejandro / Diamond, Michael S. / Bender, Frida A.-M. / Devasthale, Abhay / Schwarz, Matthias / Savre, Julien / Tonttila, Juha / Kokkola, Harri / Lee, Hyunho / Painemal, David / Ekman, Annica M. L.

eISSN:

2023

Abstract: Biomass burning plumes are frequently transported over the Southeast Atlantic stratocumulus deck during the southern African fire season (June–October). The plumes bring large amounts of absorbing aerosols as well as enhanced moisture, which can trigger ... ...

Abstract	Biomass burning plumes are frequently transported over the Southeast Atlantic stratocumulus deck during the southern African fire season (June–October). The plumes bring large amounts of absorbing aerosols as well as 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, causes a reduction in cloud cover that can lead to a speed-up of the SCT, in particular during 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 net radiative cooling effect between -4 and -9 W m -2 over the three days 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.
Subject code	551
Language	English
Publishing date	2023-10-16
Publishing country	de
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: UCLALES–SALSA v1.0

Tonttila, Juha / Maalick, Zubair / Raatikainen, Tomi / Kokkola, Harri / Kühn, Thomas / Romakkaniemi, Sami

eISSN: 1991-9603

a large-eddy model with interactive sectional microphysics for aerosol, clouds and precipitation

2018

Abstract: Challenges in understanding the aerosol–cloud interactions and their impacts on global climate highlight the need for improved knowledge of the underlying physical processes and feedbacks as well as their interactions with cloud and boundary layer ... ...

Abstract	Challenges in understanding the aerosol–cloud interactions and their impacts on global climate highlight the need for improved knowledge of the underlying physical processes and feedbacks as well as their interactions with cloud and boundary layer dynamics. To pursue this goal, increasingly sophisticated cloud-scale models are needed to complement the limited supply of observations of the interactions between aerosols and clouds. For this purpose, a new large-eddy simulation (LES) model, coupled with an interactive sectional description for aerosols and clouds, is introduced. The new model builds and extends upon the well-characterized UCLA Large-Eddy Simulation Code (UCLALES) and the Sectional Aerosol module for Large-Scale Applications (SALSA), hereafter denoted as UCLALES-SALSA. Novel strategies for the aerosol, cloud and precipitation bin discretisation are presented. These enable tracking the effects of cloud processing and wet scavenging on the aerosol size distribution as accurately as possible, while keeping the computational cost of the model as low as possible. The model is tested with two different simulation set-ups: a marine stratocumulus case in the DYCOMS-II campaign and another case focusing on the formation and evolution of a nocturnal radiation fog. It is shown that, in both cases, the size-resolved interactions between aerosols and clouds have a critical influence on the dynamics of the boundary layer. The results demonstrate the importance of accurately representing the wet scavenging of aerosol in the model. Specifically, in a case with marine stratocumulus, precipitation and the subsequent removal of cloud activating particles lead to thinning of the cloud deck and the formation of a decoupled boundary layer structure. In radiation fog, the growth and sedimentation of droplets strongly affect their radiative properties, which in turn drive new droplet formation. The size-resolved diagnostics provided by the model enable investigations of these issues with high detail. It is also shown that the results remain consistent with UCLALES (without SALSA) in cases where the dominating physical processes remain well represented by both models.
Subject code	551
Language	English
Publishing date	2018-09-27
Publishing country	de
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Significance of the organic aerosol driven climate feedback in the boreal area.

Yli-Juuti, Taina / Mielonen, Tero / Heikkinen, Liine / Arola, Antti / Ehn, Mikael / Isokääntä, Sini / Keskinen, Helmi-Marja / Kulmala, Markku / Laakso, Anton / Lipponen, Antti / Luoma, Krista / Mikkonen, Santtu / Nieminen, Tuomo / Paasonen, Pauli / Petäjä, Tuukka / Romakkaniemi, Sami / Tonttila, Juha / Kokkola, Harri / Virtanen, Annele

Nature communications

2021 Volume 12, Issue 1, Page(s) 5637

Abstract: Aerosol particles cool the climate by scattering solar radiation and by acting as cloud condensation nuclei. Higher temperatures resulting from increased greenhouse gas levels have been suggested to lead to increased biogenic secondary organic aerosol ... ...

Abstract	Aerosol particles cool the climate by scattering solar radiation and by acting as cloud condensation nuclei. Higher temperatures resulting from increased greenhouse gas levels have been suggested to lead to increased biogenic secondary organic aerosol and cloud condensation nuclei concentrations creating a negative climate feedback mechanism. Here, we present direct observations on this feedback mechanism utilizing collocated long term aerosol chemical composition measurements and remote sensing observations on aerosol and cloud properties. Summer time organic aerosol loadings showed a clear increase with temperature, with simultaneous increase in cloud condensation nuclei concentration in a boreal forest environment. Remote sensing observations revealed a change in cloud properties with an increase in cloud reflectivity in concert with increasing organic aerosol loadings in the area. The results provide direct observational evidence on the significance of this negative climate feedback mechanism.
Language	English
Publishing date	2021-09-24
Publishing country	England
Document type	Journal Article ; Research Support, U.S. Gov't, Non-P.H.S. ; Research Support, Non-U.S. Gov't
ZDB-ID	2553671-0
ISSN	2041-1723 ; 2041-1723
ISSN (online)	2041-1723
ISSN	2041-1723
DOI	10.1038/s41467-021-25850-7
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Book ; Online: Implementation of the sectional aerosol module SALSA2.0 into the PALM model system 6.0

Kurppa, Mona / Hellsten, Antti / Roldin, Pontus / Kokkola, Harri / Tonttila, Juha / Auvinen, Mikko / Kent, Christoph / Kumar, Prashant / Maronga, Björn / Järvi, Leena

eISSN: 1991-9603

model development and first evaluation

2019

Abstract: Urban pedestrian-level air quality is a result of an interplay between turbulent dispersion conditions, background concentrations, and heterogeneous local emissions of air pollutants and their transformation processes. Still, the complexity of these ... ...

Abstract	Urban pedestrian-level air quality is a result of an interplay between turbulent dispersion conditions, background concentrations, and heterogeneous local emissions of air pollutants and their transformation processes. Still, the complexity of these interactions cannot be resolved by the commonly used air quality models. By embedding the sectional aerosol module SALSA2.0 into the large-eddy simulation model PALM, a novel, high-resolution, urban aerosol modelling framework has been developed. The first model evaluation study on the vertical variation of aerosol number concentration and size distribution in a simple street canyon without vegetation in Cambridge, UK, shows good agreement with measurements, with simulated values mainly within a factor of 2 of observations. Dispersion conditions and local emissions govern the pedestrian-level aerosol number concentrations. Out of different aerosol processes, dry deposition is shown to decrease the total number concentration by over 20 %, while condensation and dissolutional increase the total mass by over 10 %. Following the model development, the application of PALM can be extended to local- and neighbourhood-scale air pollution and aerosol studies that require a detailed solution of the ambient flow field.
Subject code	910
Language	English
Publishing date	2019-04-11
Publishing country	de
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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