scholarly journals Halogen activation via interactions with environmental ice and snow in the polar lower troposphere and other regions

2012 ◽  
Vol 12 (14) ◽  
pp. 6237-6271 ◽  
Author(s):  
J. P. D. Abbatt ◽  
J. L. Thomas ◽  
K. Abrahamsson ◽  
C. Boxe ◽  
A. Granfors ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Regional Scale ◽  
Lower Troposphere ◽  
Current State ◽  
Field Evidence ◽  
Halogen Chemistry ◽  
Activation Mechanisms ◽  
Global Impacts ◽  
Rapid Pace ◽  
Halogen Activation

Abstract. The role of ice in the formation of chemically active halogens in the environment requires a full understanding because of its role in atmospheric chemistry, including controlling the regional atmospheric oxidizing capacity in specific situations. In particular, ice and snow are important for facilitating multiphase oxidative chemistry and as media upon which marine algae live. This paper reviews the nature of environmental ice substrates that participate in halogen chemistry, describes the reactions that occur on such substrates, presents the field evidence for ice-mediated halogen activation, summarizes our best understanding of ice-halogen activation mechanisms, and describes the current state of modeling these processes at different scales. Given the rapid pace of developments in the field, this paper largely addresses advances made in the past five years, with emphasis given to the polar boundary layer. The integrative nature of this field is highlighted in the presentation of work from the molecular to the regional scale, with a focus on understanding fundamental processes. This is essential for developing realistic parameterizations and descriptions of these processes for inclusion in larger scale models that are used to determine their regional and global impacts.

scholarly journals Halogen activation via interactions with environmental ice and snow

2012 ◽  
Vol 12 (4) ◽  
pp. 8677-8769
Author(s):  
J. P. D. Abbatt ◽  
J. L. Thomas ◽  
K. Abrahamsson ◽  
C. Boxe ◽  
A. Granfors ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Regional Scale ◽  
Multiphase Reactions ◽  
Current State ◽  
Field Evidence ◽  
Halogen Chemistry ◽  
Activation Mechanisms ◽  
Global Impacts ◽  
Rapid Pace ◽  
Halogen Activation

Abstract. The role of ice in the formation of chemically active halogens in the environment requires a full understanding because of its role in atmospheric chemistry, including controlling the oxidizing capacity of the atmosphere. In particular, ice and snow are important for facilitating multiphase oxidative chemistry and as media upon which marine algae live. This paper reviews the nature of environmental ice substrates that participate in halogen chemistry, describes the multiphase reactions that occur on such substrates, presents the field evidence for ice-mediated halogen activation, summarizes our best understanding of ice-halogen activation mechanisms, and describes the current state of modeling these processes at different scales. Given the rapid pace of developments in the field, this paper largely addresses advances made in the past five years, with emphasis given to the polar boundary layer. The integrative nature of this field is highlighted in the presentation of work from the molecular to the regional scale, with a focus on understanding fundamental processes. This is essential for developing realistic parameterizations and descriptions of these processes for inclusion in larger scale models that are used to determine their regional and global impacts.

scholarly journals Tropospheric Ozone Assessment Report: Present-day tropospheric ozone distribution and trends relevant to vegetation

Elem Sci Anth ◽  
2018 ◽  
Vol 6 ◽  
Author(s):  
Gina Mills ◽  
Håkan Pleijel ◽  
Christopher S. Malley ◽  
Baerbel Sinha ◽  
Owen R. Cooper ◽  
...  
Keyword(s):  
Tropospheric Ozone ◽  
Regional Scale ◽  
Mean Values ◽  
Assessment Report ◽  
North West ◽  
Northern India ◽  
Current State ◽  
Field Evidence ◽  
The Usa ◽  
The Republic

This Tropospheric Ozone Assessment Report (TOAR) on the current state of knowledge of ozone metrics of relevance to vegetation (TOAR-Vegetation) reports on present-day global distribution of ozone at over 3300 vegetated sites and the long-term trends at nearly 1200 sites. TOAR-Vegetation focusses on three metrics over vegetation-relevant time-periods across major world climatic zones: M12, the mean ozone during 08:00–19:59; AOT40, the accumulation of hourly mean ozone values over 40 ppb during daylight hours, and W126 with stronger weighting to higher hourly mean values, accumulated during 08:00–19:59. Although the density of measurement stations is highly variable across regions, in general, the highest ozone values (mean, 2010–14) are in mid-latitudes of the northern hemisphere, including southern USA, the Mediterranean basin, northern India, north, north-west and east China, the Republic of Korea and Japan. The lowest metric values reported are in Australia, New Zealand, southern parts of South America and some northern parts of Europe, Canada and the USA. Regional-scale assessments showed, for example, significantly higher AOT40 and W126 values in East Asia (EAS) than Europe (EUR) in wheat growing areas (p < 0.05), but not in rice growing areas. In NAM, the dominant trend during 1995–2014 was a significant decrease in ozone, whilst in EUR it was no change and in EAS it was a significant increase. TOAR-Vegetation provides recommendations to facilitate a more complete global assessment of ozone impacts on vegetation in the future, including: an increase in monitoring of ozone and collation of field evidence of the damaging effects on vegetation; an investigation of the effects on peri-urban agriculture and in mountain/upland areas; inclusion of additional pollutant, meteorological and inlet height data in the TOAR dataset; where not already in existence, establishing new region-specific thresholds for vegetation damage and an innovative integration of observations and modelling including stomatal uptake of the pollutant.

scholarly journals Sensitivity of stomatal conductance to soil moisture: implications for tropospheric ozone

2017 ◽  
Author(s):  
Alessandro Anav ◽  
Chiara Proietti ◽  
Laurent Menut ◽  
Stefano Carnicelli ◽  
Alessandra De Marco ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Stomatal Conductance ◽  
Soil Water ◽  
Water Uptake ◽  
Atmospheric Chemistry ◽  
Water Availability ◽  
Dry Deposition ◽  
Lower Troposphere ◽  
Lower Atmosphere ◽  
Water Limitation

Abstract. Soil moisture and water stress play a pivotal role in regulating stomatal behaviour of plants; however, in the last decade, the role of water availability was often neglected in atmospheric chemistry modelling studies as well as in integrated risk assessments, despite through stomata plants remove a large amount of atmospheric compounds from the lower troposphere. The main aim of this study is to evaluate the effect of soil water limitation on stomatal conductance and assess the resulting changes in atmospheric chemistry testing various hypotheses of water uptake by plants in the rooting zone; following the main assumption that roots maximize water uptake, i.e. they adsorb water at different soil depths depending on the water availability, we improve the dry deposition scheme within the chemistry transport model CHIMERE. Results highlight how dry deposition significantly declines when soil moisture is used to regulate the stomatal opening, mainly in the semi-arid environments: in particular, over Europe the amount of ozone removed by dry deposition in one year without considering any soil water limitation to stomatal conductance is about 8.5 Tg O3, while using a dynamic layer that ensures plants to maximize the water uptake from soil, we found a reduction of about 10 % in the amount of ozone removed by dry deposition (~ 7.7 Tg O3). Despite dry deposition occurs from top of canopy to ground level, it affects the concentration of gases remaining into the lower atmosphere with a significant impact on ozone concentration (up to 4 ppb) extending from the surface to the upper troposphere (up to 650 hPa). Our results shed light on the importance of improving the parameterizations of processes occurring at plant level (i.e. from the soil to the canopy) as they have significant implications on concentration of gases in the lower troposphere.

scholarly journals Multi-model study of mercury dispersion in the atmosphere: Vertical distribution of mercury species

2016 ◽  
Author(s):  
Johannes Bieser ◽  
Franz Slemr ◽  
Jesse Ambrose ◽  
Carl Brenninkmeijer ◽  
Steve Brooks ◽  
...  
Keyword(s):  
Vertical Distribution ◽  
Atmospheric Chemistry ◽  
Lower Troposphere ◽  
Elemental Mercury ◽  
Mercury Species ◽  
Substantial Impact ◽  
Model Studies ◽  
Model Study ◽  
The Impact ◽  
The Vertical Distribution

Abstract. Atmospheric chemistry and transport of mercury play a key role in the global mercury cycle. However, there are still considerable knowledge gaps concerning the fate of mercury in the atmosphere. This is the second part of a model inter-comparison study investigating the impact of atmospheric chemistry and emissions on mercury in the atmosphere. While the first study focused on ground based observations of mercury concentration and deposition, here we investigate the vertical distribution and speciation of mercury from the planetary boundary layer to the lower stratosphere. So far, there have been few model studies investigating the vertical distribution of mercury, mostly focusing on single aircraft campaigns. Here, we present a first comprehensive analysis based on various aircraft observations in Europe, North America, and on inter-continental flights. The investigated models proved to be able to reproduce the distribution of total and elemental mercury concentrations in the troposphere including inter-hemispheric trends. One key aspect of the study is the investigation of mercury oxidation in the troposphere. We found that different chemistry schemes were better at reproducing observed oxidized mercury (RM) patterns depending on altitude. High RM concentrations in the upper troposphere could be reproduced with oxidation by bromine while elevated concentrations in the lower troposphere were better reproduced by OH and ozone chemistry. However, the results were not always conclusive as the physical and chemical parametrizations in the chemistry transport models also proved to have a substantial impact on model results.

scholarly journals Dynamics and composition of the Asian summer monsoon anticyclone

2017 ◽  
Author(s):  
Klaus-Dirk Gottschaldt ◽  
Hans Schlager ◽  
Robert Baumann ◽  
Duy S. Cai ◽  
Veronika Eyring ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Atmospheric Chemistry ◽  
Asian Summer Monsoon ◽  
Monsoon Season ◽  
Lower Troposphere ◽  
Equatorial Region ◽  
Ozone Production ◽  
Trace Gas ◽  
Asian Summer ◽  
Southern Fringe

Abstract. This study places HALO research aircraft observations in the upper-tropospheric Asian summer monsoon anticyclone (ASMA) obtained during the Earth System Model Validation (ESMVal) campaign in September 2012 into the context of regional, intra-annual variability by hindcasts with the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. The simulations demonstrate that tropospheric trace gas profiles in the monsoon season are distinct from the rest of the year. Air uplifted from the lower troposphere to the tropopause layer dominates the eastern part of the ASMA’s interior, while the western part is characterised by subsidence down to the mid-troposphere. Soluble compounds are being washed out when uplifted by convection in the eastern part, where lightning simultaneously replenishes reactive nitrogen in the upper troposphere. Net photochemical ozone production is significantly enhanced in the ASMA, contrasted by an ozone depleting regime in the mid-troposphere and more neutral conditions in autumn and winter. An analysis of multiple monsoon seasons in the simulation shows that stratospherically influenced tropopause layer air is regularly entrained at the eastern ASMA flank, and then transported in the southern fringe around the interior region. Observed and simulated tracer-tracer relations reflect photochemical O3 production, as well as in-mixing from the lower troposphere and the tropopause layer. The simulation additionally shows entrainment of clean air from the equatorial region by northerly winds at the western ASMA flank. Although the in situ measurements were performed towards the end of summer, the main ingredients needed for their interpretation are present throughout the monsoon season. A transition between two dynamical modes of the ASMA took place during the HALO ESMVal campaign. Transport barriers of the original anticyclone are overcome effectively when it splits up. Air from the fringe is stirred into the interiors of the new anticyclones and vice versa. Instabilities of this and other types occur quite frequently. Our study emphasises their paramountcy for the trace gas composition of the ASMA and its outflow into regions around the world.

scholarly journals The global impacts of COVID-19 lockdowns on urban air pollution

Elem Sci Anth ◽  
2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Georgios I. Gkatzelis ◽  
Jessica B. Gilman ◽  
Steven S. Brown ◽  
Henk Eskes ◽  
A. Rita Gomes ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Urban Air Pollution ◽  
Future Research ◽  
Specific Method ◽  
Data Sets ◽  
Atmospheric Pollutant ◽  
Government Interventions ◽  
Pollutant Concentrations ◽  
Global Impacts ◽  
The Government

The coronavirus-19 (COVID-19) pandemic led to government interventions to limit the spread of the disease which are unprecedented in recent history; for example, stay at home orders led to sudden decreases in atmospheric emissions from the transportation sector. In this review article, the current understanding of the influence of emission reductions on atmospheric pollutant concentrations and air quality is summarized for nitrogen dioxide (NO2), particulate matter (PM2.5), ozone (O3), ammonia, sulfur dioxide, black carbon, volatile organic compounds, and carbon monoxide (CO). In the first 7 months following the onset of the pandemic, more than 200 papers were accepted by peer-reviewed journals utilizing observations from ground-based and satellite instruments. Only about one-third of this literature incorporates a specific method for meteorological correction or normalization for comparing data from the lockdown period with prior reference observations despite the importance of doing so on the interpretation of results. We use the government stringency index (SI) as an indicator for the severity of lockdown measures and show how key air pollutants change as the SI increases. The observed decrease of NO2 with increasing SI is in general agreement with emission inventories that account for the lockdown. Other compounds such as O3, PM2.5, and CO are also broadly covered. Due to the importance of atmospheric chemistry on O3 and PM2.5 concentrations, their responses may not be linear with respect to primary pollutants. At most sites, we found O3 increased, whereas PM2.5 decreased slightly, with increasing SI. Changes of other compounds are found to be understudied. We highlight future research needs for utilizing the emerging data sets as a preview of a future state of the atmosphere in a world with targeted permanent reductions of emissions. Finally, we emphasize the need to account for the effects of meteorology, emission trends, and atmospheric chemistry when determining the lockdown effects on pollutant concentrations.

Surface-Promoted Redox Reactions Occurs Spontaneously on Solvating Salt Surfaces

2021 ◽  
Author(s):  
Xiangrui Kong ◽  
Ivan Gladich ◽  
Dimitri Castarede ◽  
Erik Thomson ◽  
Anthony Boucly ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Photoelectron Spectroscopy ◽  
Ambient Pressure ◽  
Species Abundance ◽  
Ammonium Oxidation ◽  
Gas Uptake ◽  
Sulfate Reducing ◽  
Interfacial Processes ◽  
Key Species ◽  
Halogen Chemistry

<p>Gas-particle interfaces play essential roles in the atmosphere and directly influence many atmospheric processes, including gas uptake, halogen chemistry, ozone depletion, and heterogeneous ice nucleation. However, because interfacial processes take place on molecular scales, classical bulk thermodynamic theories are often insufficient to describe interfaces. Also, interfacial processes are challenging to characterize and are often overlooked in current atmospheric chemistry.</p><p>For this study, ambient pressure X-ray photoelectron spectroscopy (APXPS) experiments were performed. A surface-promoted sulfate-reducing ammonium oxidation reaction is discovered to spontaneously take place on common inorganic aerosol surfaces undergoing solvation. Several key intermediate species including, S<sup>0</sup>, HS<sup>-</sup>, HONO, and NH<sub>3(aq)</sub> are identified as reaction components associated with the solvation process. Depth profiles of relative species abundance show the surface propensity of key species. The species assignments and depth profile features are supported by classical and first-principle molecular dynamics calculations. A detailed mechanism is proposed to describe the processes that lead to unexpected products during salt solvation. This discovery reveals novel chemistry that is uniquely linked to a solvating surface and has great potential to illuminate current puzzles within heterogeneous chemistry. Lastly, natural salts sampled from saline lakes and playas are examined for this behavior, and provide further evidence of the important roles this surface-promoted redox mechanism may play in nature.</p>

scholarly journals On the impact of future climate change on tropopause folds and tropospheric ozone

2019 ◽  
Vol 19 (22) ◽  
pp. 14387-14401 ◽  
Author(s):  
Dimitris Akritidis ◽  
Andrea Pozzer ◽  
Prodromos Zanis
Keyword(s):  
Atmospheric Chemistry ◽  
Tropospheric Ozone ◽  
Eastern Mediterranean ◽  
Stratospheric Ozone ◽  
Lower Troposphere ◽  
Future Climate Change ◽  
Identification Algorithm ◽  
The Future ◽  
Projected Changes ◽  
The Impact

Abstract. Using a transient simulation for the period 1960–2100 with the state-of-the-art ECHAM5/MESSy Atmospheric Chemistry (EMAC) global model and a tropopause fold identification algorithm, we explore the future projected changes in tropopause folds, stratosphere-to-troposphere transport (STT) of ozone, and tropospheric ozone under the RCP6.0 scenario. Statistically significant changes in tropopause fold frequencies from 1970–1999 to 2070–2099 are identified in both hemispheres, regionally exceeding 3 %, and are associated with the projected changes in the position and intensity of the subtropical jet streams. A strengthening of ozone STT is projected for the future in both hemispheres, with an induced increase in transported stratospheric ozone tracer throughout the whole troposphere, reaching up to 10 nmol mol−1 in the upper troposphere, 8 nmol mol−1 in the middle troposphere, and 3 nmol mol−1 near the surface. Notably, the regions exhibiting the largest changes of ozone STT at 400 hPa coincide with those with the highest fold frequency changes, highlighting the role of the tropopause folding mechanism in STT processes under a changing climate. For both the eastern Mediterranean and Middle East (EMME) and Afghanistan (AFG) regions, which are known as hotspots of fold activity and ozone STT during the summer period, the year-to-year variability of middle-tropospheric ozone with stratospheric origin is largely explained by the short-term variations in ozone at 150 hPa and tropopause fold frequency. Finally, ozone in the lower troposphere is projected to decrease under the RCP6.0 scenario during MAM (March, April, and May) and JJA (June, July, and August) in the Northern Hemisphere and during DJF (December, January, and February) in the Southern Hemisphere, due to the decline of ozone precursor emissions and the enhanced ozone loss from higher water vapour abundances, while in the rest of the troposphere ozone shows a remarkable increase owing mainly to the STT strengthening and the stratospheric ozone recovery.

scholarly journals e-HRM in a Cloud Environment

2019 ◽  
Vol 10 (4) ◽  
pp. 16-40
Author(s):  
Robert-Christian Ziebell ◽  
Jose Albors-Garrigos ◽  
Klaus-Peter Schoeneberg ◽  
Maria Rosario Perello Marin
Keyword(s):  
Technology Implementation ◽  
Cloud Environment ◽  
Resources Management ◽  
Functional Changes ◽  
Current State ◽  
Use Of Technology ◽  
Rapid Pace ◽  
Different Dimensions ◽  
State Of Research ◽  
Technical Basis

As the digitization of HR processes in companies continues to increase, at the same time, the underlying technical basis is also developing at a rapid pace. Electronic human resources (e-HRM) solutions are used to map a variety of HR processes. However, the introduction of such systems has various consequences, which are not only technical but also imply organizational and functional changes within the organization. Additionally, the cloud environment contributes to enhancing e-HRM capabilities and introduces new factors in its adoption. A systematic review of the available literature on the different dimensions of electronic resources management was conducted to assess the current state of research in this field. This review includes topics such as the evolution of e-HRM, its practical application, use of technology, implementation as well as HR analytics. By identifying and reviewing articles under e-HRM, IT technology, and HR journals, it was possible to identify relevant controversial themes and gaps as well as limitations.

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