Composition of weed flora in spring cereals in Finland

vokKirjasto Aj-kKevätviljapeltojen rikkakasvit ja niiden runsau

Application of several activity coefficient models to water-organic-electrolyte aerosols of atmospheric interest

In this work, existing and modified activity coefficient models are examined in order to assess their capabilities to describe the properties of aqueous solution droplets relevant in the atmosphere. Five different water-organic-electrolyte activity coefficient models were first selected from the literature. Only one of these models included organics and electrolytes which are common in atmospheric aerosol particles. In the other models, organic species were solvents such as alcohols, and important atmospheric ions like NH₄⁺ could be missing. The predictions of these models were compared to experimental activity and solubility data in aqueous single electrolyte solutions with 31 different electrolytes. <P style='line-height: 20px;'> Based on the deviations from experimental data and on the capabilities of the models, four predictive models were selected for fitting of new parameters for binary and ternary solutions of common atmospheric electrolytes and organics. New electrolytes (H⁺, NH₄⁺, Na⁺, Cl^-, NO₃^- and SO₄^2-) and organics (dicarboxylic and some hydroxy acids) were added and some modifications were made to the models if it was found useful. All new and most of the existing parameters were fitted to experimental single electrolyte data as well as data for aqueous organics and aqueous organic-electrolyte solutions. Unfortunately, there are very few data available for organic activities in binary solutions and for organic and electrolyte activities in aqueous organic-electrolyte solutions. This reduces model capabilities in predicting solubilities. <P style='line-height: 20px;'> After the parameters were fitted, deviations from measurement data were calculated for all fitted models, and for different data types. These deviations and the calculated property values were compared with those from other non-electrolyte and organic-electrolyte models found in the literature. Finally, hygroscopic growth factors were calculated for four 100 nm organic-electrolyte particles and these predictions were compared to experimental data and to predictions from other models. <P style='line-height: 20px;'> All of the newly fitted models show good agreement with experimental water activity data in binary and ternary solutions. One of the models is for activities of non-electrolytes only, but the other three models show quite small deviations from measured electrolyte activities. Because there were not enough experimental data for organic and electrolyte activities, some models show bigger deviation for mutual deliquescence relative humidities of organic-electrolyte particles, but calculated growth factors for liquid droplets are quite close to the experimental data. Even in cases with somewhat bigger deviations, the results can be considered satisfactory, because they were calculated based mainly on the predictive properties of the models

The role of surfactants in Köhler theory reconsidered

International audienceAtmospheric aerosol particles typically consist of inorganic salts and organic material. The inorganic compounds as well as their hygroscopic properties are well defined, but the effect of organic compounds on cloud droplet activation is still poorly characterized. The focus of the present study is in the organic compounds that are surface active i.e. they concentrate on droplet surface and decrease droplet surface tension. Gibbsian surface thermodynamics were used to find out how partitioning in binary and ternary aqueous solutions affects the droplet surface tension and the droplet bulk concentration in droplets large enough to act as cloud condensation nuclei. Sodium dodecyl sulfate was used as a model compound together with sodium chloride to find out the effect the correct evaluation of surfactant partitioning has on the solute effect (Raoult effect). While the partitioning is known to lead to higher surface tension compared to a case in which partitioning is neglected, the present results show that the partitioning also alters the solute effect, and that the change is large enough to further increase the critical supersaturation and hence decrease the droplet activation. The fraction of surfactant partitioned to droplet surface increases with decreasing droplet size, which suggests that surfactants might enhance the activation of larger particles relatively more thus leading to less dense clouds. Cis-pinonic acid-ammonium sulfate aqueous solution was studied in order to relate the partitioning to more realistic atmospheric situation and to find out the combined effects of dissolution and partitioning behaviour. The results show that correct partitioning consideration alters the shape of the Köhler curve when compared to a situation in which the partitioning is neglected either completely or in the Raoult effect

The role of surfactants in Köhler theory reconsidered

International audienceAtmospheric aerosol particles typically consist of inorganic salts and organic material. The inorganic compounds as well as their hygroscopic properties are well defined, but the effect of organic compounds on cloud droplet activation is still poorly characterized. The focus of the present study is the organic compounds that are surface active i.e. tend to concentrate on droplet surface and decrease the surface tension. Gibbsian surface thermodynamics was used to find out how partitioning between droplet surface and the bulk of the droplet affects the surface tension and the surfactant bulk concentration in droplets large enough to act as cloud condensation nuclei. Sodium dodecyl sulfate (SDS) was used together with sodium chloride to investigate the effect of surfactant partitioning on the Raoult effect (solute effect). While accounting for the surface to bulk partitioning is known to lead to lowered bulk surfactant concentration and thereby to increased surface tension compared to a case in which the partitioning is neglected, the present results show that the partitioning also alters the Raoult effect, and that the change is large enough to further increase the critical supersaturation and hence decrease cloud droplet activation. The fraction of surfactant partitioned to droplet surface increases with decreasing droplet size, which suggests that surfactants might enhance the activation of larger particles relatively more thus leading to less dense clouds. Cis-pinonic acid-ammonium sulfate aqueous solutions were studied in order to study the partitioning with compounds found in the atmosphere and to find out the combined effects of dissolution and partitioning behavior. The results show that the partitioning consideration presented in this paper alters the shape of the Köhler curve when compared to calculations in which the partitioning is neglected either completely or in the Raoult effect. In addition, critical supersaturation was measured for SDS particles with dry radii of 25-60nm using a static parallel plate Cloud Condensation Nucleus Counter. The experimentally determined critical supersaturations agree very well with theoretical calculations taking the surface to bulk partitioning fully into account and are much higher than those calculated neglecting the partitioning

2-Iodo-imidazolium receptor binds oxoanions via charge-assisted halogen bonding.

A detailed (1)H-NMR study of the anion binding properties of the 2-iodo-imidazolium receptor 1 in DMSO allows to fully attribute the observed affinities to strong charge-assisted C-IX(-) halogen bonding (XB). Stronger binding was observed for oxoanions over halides. Phosphate, in particular, binds to 1 with an association constant of ca. 10(3) M(-1), which is particularly high for a single X-bond. A remarkably short C-IO(-) contact is observed in the structure of the salt 1·H(2)PO(4)(-)

Global warming will affect the maximum potential abundance of boreal plant species

Forecasting the impact of future global warming on biodiversity requires understanding how temperature limits the distribution of species. Here we rely on Liebig's Law of Minimum to estimate the effect of temperature on the maximum potential abundance that a species can attain at a certain location. We develop 95%‐quantile regressions to model the influence of effective temperature sum on the maximum potential abundance of 25 common understory plant species of Finland, along 868 nationwide plots sampled in 1985. Fifteen of these species showed a significant response to temperature sum that was consistent in temperature‐only models and in all‐predictors models, which also included cumulative precipitation, soil texture, soil fertility, tree species and stand maturity as predictors. For species with significant and consistent responses to temperature, we forecasted potential shifts in abundance for the period 2041–2070 under the IPCC A1B emission scenario using temperature‐only models. We predict major potential changes in abundance and average northward distribution shifts of 6–8 km yr−1. Our results emphasize inter‐specific differences in the impact of global warming on the understory layer of boreal forests. Species in all functional groups from dwarf shrubs, herbs and grasses to bryophytes and lichens showed significant responses to temperature, while temperature did not limit the abundance of 10 species. We discuss the interest of modelling the ‘maximum potential abundance’ to deal with the uncertainty in the predictions of realized abundances associated to the effect of environmental factors not accounted for and to dispersal limitations of species, among others. We believe this concept has a promising and unexplored potential to forecast the impact of specific drivers of global change under future scenarios.202

UCLALES–SALSA v1.0: a large-eddy model with interactive sectional microphysics for aerosol, clouds and precipitation

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

Ammonium nitrate evaporation and nitric acid condensation in DMT CCN counters

The effect of inorganic semivolatile aerosol compounds on the cloud condensation nucleus (CCN) activity of aerosol particles was studied by using a computational model for a DMT-CCN counter, a cloud parcel model for condensation kinetics and experiments to quantify the modelled results. Concentrations of water vapour and semivolatiles as well as aerosol trajectories in the CCN column were calculated by a computational fluid dynamics model. These trajectories and vapour concentrations were then used as an input for the cloud parcel model to simulate mass transfer kinetics of water and semivolatiles between aerosol particles and the gas phase. Two different questions were studied: (1) how big a fraction of semivolatiles is evaporated from particles after entering but before particle activation in the DMT-CCN counter? (2) How much can the CCN activity be increased due to condensation of semivolatiles prior to the maximum water supersaturation in the case of high semivolatile concentration in the gas phase? Both experimental and modelling results show that the evaporation of ammonia and nitric acid from ammonium nitrate particles causes a 10 to 15 nm decrease to the critical particle size in supersaturations between 0.1% and 0.7%. On the other hand, the modelling results also show that condensation of nitric acid or similar vapour can increase the CCN activity of nonvolatile aerosol particles, but a very high gas phase concentration (as compared to typical ambient conditions) would be needed. Overall, it is more likely that the CCN activity of semivolatile aerosol is underestimated than overestimated in the measurements conducted in ambient conditions

1,3-Bis(bromo­meth­yl)-2-nitro­benzene

In the title compound, C8H7Br2NO2, an inter­mediate for the synthesis of macrocycles, the NO2 group makes a dihedral angle of 65.07 (19)° with the arene ring, and the bromo­methyl substituents adopt a trans conformation about the ring such that the mol­ecule closely approximates C2 symmetry

Modelling mixed-phase clouds with the large-eddy model UCLALES-SALSA

The large-eddy model UCLALES-SALSA, with an exceptionally detailed aerosol description for both aerosol number and chemical composition, has been extended for ice and mixed-phase clouds. Comparison to a previous mixed-phase cloud model intercomparison study confirmed the accuracy of newly implemented ice microphysics. A further simulation with a heterogeneous ice nucleation scheme, in which ice-nucleating particles (INPs) are also a prognostic variable, captured the typical layered structure of Arctic mid-altitude mixed-phase cloud: a liquid layer near cloud top and ice within and below the liquid layer. In addition, the simulation showed a realistic freezing rate of droplets within the vertical cloud structure. The represented detailed sectional ice microphysics with prognostic aerosols is crucially important in reproducing mixed-phase clouds