Implementing detailed nucleation predictions in the Earth system model EC-Earth3.3.4: sulfuric acid–ammonia nucleation

Representing detailed atmospheric aerosol processes in global Earth system models (ESMs) has proven to be challenging from both a computational and a parameterization perspective. The representation of secondary organic aerosol (SOA) formation and new particle formation (NPF) in large ESMs is generally constructed with low detail to save computational costs. The simplification could result in losing the representation of some processes. In this study, we test and evaluate a new approach for improving the description of NPF processes in the ESM EC-Earth3 (ECE3) without significant additional computational burden. The current NPF scheme in EC-Earth3.3.4 is derived from the nucleation of low-volatility organic vapors and sulfuric acid (H2SO4) together with a homogeneous water–H2SO4 nucleation scheme. We expand the existing schemes and introduce a new lookup table approach that incorporates detailed formation rate predictions through molecular modeling of sulfuric acid–ammonia nucleation (H2SO2–NH3). We apply tables of particle formation rates for H2SO2–NH3 nucleation, including dependence on temperature, atmospheric ion production rate, and molecular cluster scavenging sink. The resulting differences between using the H2SO4–NH3 nucleation in ECE3 and the original default ECE3 scheme are evaluated and compared with a focus on changes in the aerosol composition, cloud properties, and radiation balance. From this new nucleation scheme, EC-Earth3's global average aerosol concentrations in the sub-100 nm sizes increased by 12 %–28 %. Aerosol concentrations above 100 nm and the direct radiative effect (in W m−2) showed only minor differences upon changing of the nucleation scheme. However, the radiative effect from clouds affected by aerosols from the new nucleation scheme resulted in a global decrease (cooling effect) by 0.28–1 W m−2. The modeled aerosol concentrations were compared to observed measurements at various stations. In most cases, the new NPF predictions (H2SO2–NH3) performed better at stations where previous underestimations for aerosol concentrations occurred.</p

BVOC–aerosol–climate feedbacks investigated using NorESM

Both higher temperatures and increased CO2 concentrations are (separately) expected to increase the emissions of biogenic volatile organic compounds (BVOCs). This has been proposed to initiate negative climate feedback mechanisms through increased formation of secondary organic aerosol (SOA). More SOA can make the clouds more reflective, which can provide a cooling. Furthermore, the increase in SOA formation has also been proposed to lead to increased aerosol scattering, resulting in an increase in diffuse radiation. This could boost gross primary production (GPP) and further increase BVOC emissions. In this study, we have used the Norwegian Earth System Model (NorESM) to investigate both these feedback mechanisms. Three sets of experiments were set up to quantify the feedback with respect to (1) doubling the CO2, (2) increasing temperatures corresponding to a doubling of CO2 and (3) the combined effect of both doubling CO2 and a warmer climate. For each of these experiments, we ran two simulations, with identical setups, except for the BVOC emissions. One simulation was run with interactive BVOC emissions, allowing the BVOC emissions to respond to changes in CO2 and/or climate. In the other simulation, the BVOC emissions were fixed at present-day conditions, essentially turning the feedback off. The comparison of these two simulations enables us to investigate each step along the feedback as well as estimate their overall relevance for the future climate. We find that the BVOC feedback can have a significant impact on the climate. The annual global BVOC emissions are up to 63&thinsp;% higher when the feedback is turned on compared to when the feedback is turned off, with the largest response when both CO2 and climate are changed. The higher BVOC levels lead to the formation of more SOA mass (max 53&thinsp;%) and result in more particles through increased new particle formation as well as larger particles through increased condensation. The corresponding changes in the cloud properties lead to a −0.43&thinsp;W&thinsp;m−2 stronger net cloud forcing. This effect becomes about 50&thinsp;% stronger when the model is run with reduced anthropogenic aerosol emissions, indicating that the feedback will become even more important as we decrease aerosol and precursor emissions. We do not find a boost in GPP due to increased aerosol scattering on a global scale. Instead, the fate of the GPP seems to be controlled by the BVOC effects on the clouds. However, the higher aerosol scattering associated with the higher BVOC emissions is found to also contribute with a potentially important enhanced negative direct forcing (−0.06&thinsp;W&thinsp;m−2). The global total aerosol forcing associated with the feedback is −0.49&thinsp;W&thinsp;m−2, indicating that it has the potential to offset about 13&thinsp;% of the forcing associated with a doubling of CO2.</p

Process-evaluation of forest aerosol-cloud-climate feedback shows clear evidence from observations and large uncertainty in models

This is the final version. Available on open access from Nature Research via the DOI in this recordData availability: The model data generated in this study have been deposited in the Bolin Center database at59. The SMEAR-II particle number size distribution data is available in the EBAS database at ebas-data.nilu.no. The SMEAR-II OA mass concentration data is available in the EBAS database at ebas-data.nilu.no. The temperature and wind measurement data from SMEAR-II is in the AVAA database at https://smear.avaa.csc.fi. The ATTO station measurement is available in the ATTO data portal at https://www.attodata.org. Source data are provided with this paper.Code availability: The analysis code is available at https://doi.org/10.5281/ZENODO.10401381Natural aerosol feedbacks are expected to become more important in the future, as anthropogenic aerosol emissions decrease due to air quality policy. One such feedback is initiated by the increase in biogenic volatile organic compound (BVOC) emissions with higher temperatures, leading to higher secondary organic aerosol (SOA) production and a cooling of the surface via impacts on cloud radiative properties. Motivated by the considerable spread in feedback strength in Earth System Models (ESMs), we here use two long-term observational datasets from boreal and tropical forests, together with satellite data, for a process-based evaluation of the BVOC-aerosol-cloud feedback in four ESMs. The model evaluation shows that the weakest modelled feedback estimates can likely be excluded, but highlights compensating errors making it difficult to draw conclusions of the strongest estimates. Overall, the method of evaluating along process chains shows promise in pin-pointing sources of uncertainty and constraining modelled aerosol feedbacks

A conceptual framework for understanding juridification of and in education

The legal framing of national education systems has been subject to substantial change in the past decade, especially in Nordic countries. Earlier research has called for better understanding of the implications of these changes which, in turn, points to a need for conceptual development. With an emphasis on legal and education scholarly work, this article explores concepts for further research on juridification in relation to education. This is done through an abductive process of inquiry, in which interpretations of the concept of juridification developed in previous research are explored in relation to changes in Swedish education policy on the area of equal treatment. We distinguish conceptually between juridification of and in education and propose a conceptual framework based on six dimensions of juridification, contributing to a view of policy as both formally regulated and enacted by education actors at different levels. This conceptual framework opens up new directions for further research in different areas and contexts