A Re-Evaluation of Sulfur Budgets, Lifetimes, and Scavenging Ratios for Eastern North America

Lifetimes, scavenging ratios, andbudgets describe the cycling of atmosphericconstituents and are often used in formulating airpollution control strategies. Most previous studiesof sulfur lifetimes, budgets, and scavenging ratioshave been based on limited observational data or datafrom highly simplified models. The Regional AcidDeposition Model (RADM2.61) shows some skill inpredicting atmospheric mixing ratios of acidicmaterials and other related trace constituents andacid deposition patterns in North America, and so,analysis of its established, theoretical, databaseserves as a counterpoint to previous studies of sulfurbudgets, lifetimes, and scavenging ratios. The annualbudget shows that the net transport (outflow minusinflow) of sulfur compounds out of eastern NorthAmerica is equal to the total deposition within thedomain. Of the total deposition, 63% is from wetdeposition and 37% is from dry deposition. Theannual average lifetime of sulfur dioxide (38 hours),estimated by the turnover time, is limited by aqueousconversion, while that for sulfate aerosols (54 hours)is limited by their removal in precipitation. Theannual average lifetime of sulfur in this domain isslightly more than three days. Episodic lifetimes andbudgets, based on particular synoptic situations, showlarge variations around the annual values. Episodicprecipitation scavenging ratios exhibit similarvariability and are used to offer explanations ofseveral potential biases found in the wet sulfurdeposition amounts as predicted by the EMEP sulfurtransport model and other published results.     

What if negative emission technologies fail at scale? Implications of the Paris Agreement for big emitting nations

A cumulative emissions approach is increasingly used to inform mitigation policy. However, there are different interpretations of what ‘2°C’ implies. Here it is argued that cost-optimization models, commonly used to inform policy, typically underplay the urgency of 2°C mitigation. The alignment within many scenarios of optimistic assumptions on negative emissions technologies (NETs), with implausibly early peak emission dates and incremental short-term mitigation, delivers outcomes commensurate with 2°C commitments. In contrast, considering equity and socio-technical barriers to change, suggests a more challenging short-term agenda. To understand these different interpretations, short-term CO₂ trends of the largest CO₂ emitters, are assessed in relation to a constrained CO₂ budget, coupled with a ‘what if’ assumption that negative emissions technologies fail at scale. The outcomes raise profound questions around high-level framings of mitigation policy. The article concludes that applying even weak equity criteria, challenges the feasibility of maintaining a 50% chance of avoiding 2°C without urgent mitigation efforts in the short-term. This highlights a need for greater engagement with: (1) the equity dimension of the Paris Agreement, (2) the sensitivity of constrained carbon budgets to short-term trends and (3) the climate risks for society posed by an almost ubiquitous inclusion of NETs within 2°C scenarios.

POLICY RELEVANCE

Since the Paris meeting, there is increased awareness that most policy ‘solutions’ commensurate with 2°C include widespread deployment of negative emissions technologies (NETs). Yet much less is understood about that option’s feasibility, compared with near-term efforts to curb energy demand. Moreover, the many different ways in which key information is synthesized for policy makers, clouds the ability of policy makers to make informed decisions. This article presents an alternative approach to consider what the Paris Agreement implies, if NETs are unable to deliver more carbon sinks than sources. It illustrates the scale of the climate challenge for policy makers, particularly if the Agreement’s aim to address ‘equity’ is accounted for. Here it is argued that much more attention needs to be paid to what CO₂ reductions can be achieved in the short-term, rather than taking a risk that could render the Paris Agreement’s policy goals unachievable.     

Low-carbon transition risks for India’s financial system

As the low-carbon transition accelerates, loans to and investments in carbon-intensive assets, firms and sectors are at risk of not generating the anticipated returns, with implications for individual financial institutions as well as financial markets more broadly. However, research on this topic has largely been focused on high- and upper-middle income economies to date. In this paper, we explore the salience of this issue in India – one of the world’s largest emitters and economies – by asking: (1) how extensive is financial-sector exposure to transition risks? And: (2) are finance professionals and financial institutions taking sufficient action to manage those transition risks? Our findings reveal that India’s financial sector is much more heavily exposed to low-carbon transition risks than standard borrowing classifications might suggest. For example, our granular assessment of individual loans and bonds finds that three-fifths of lending to the ‘mining’ sector is for oil and gas extraction, while one-fifth of ‘manufacturing’ debt is for petroleum refining and related industries. We also find that electricity production – by far the largest source of emissions – accounts for 5.2% of outstanding credit, but that only 17.5% of this lending is to pureplay renewables. Yet our survey of India’s largest financial institutions suggests that there have been limited efforts to identify, measure or manage low-carbon transition risks. Fewer than half of the 154 finance professionals surveyed were familiar with environmental issues including climate change mitigation and adaption, greenhouse gas emissions or transition risks. Only four of the ten major financial institutions surveyed collect information on ESG risks, and these firms do not systematically incorporate that data into business continuity planning, internal capital adequacy assessment processes, credit risk assessments, enterprise risk management frameworks or loan product pricing. Given extensive financial-sector exposure to low-carbon transition risks coupled with the absence of bottom-up action to manage those risks, our findings suggest that financiers, regulators and policymakers in emerging and developing economies should be acting swiftly to ensure an orderly transition to net-zero.     

Some observations on the chemical weathering of the Dartmoor granite

The majority of geomorphological papers about Dartmoor have been essentially speculative, particularly when discussing weathering processes and the evolution of the Dartmoor landscape. In contrast, this article presents a synthesis of several experimental investigations aimed at studying the chemical weathering of Dartmoor granite through the systematic analysis of soil and water samples. This involved the computation of a geochemical budget to determine the amount of erosion in the catchment, as well as more detailed mineralogical investigations within a soil profile. The annual output of solutes due to weathering was 116 kg ha^?1 a^?1 of which the majority was silica (93 kg ha^?1 a^?1). From an examination of the soil mineralogy, it was calculated that these solutes were derived from the dissolution of approximately 200 kg ha^?1 a^?1 plagioclase, 90 kg ha^?1 a^?1 biotite, and 40 kg ha^?1 a^?1 orthoclase. As well as the weathering of granite, there was also the production of kaolinite (150 kg ha^?1 a^?1) and gibbsite (0.02 kg ha^?1 a^?1). Analysis of the soil water chemistry confirmed that kaolinite was the stable mineral phase in the regolith, although in areas where interflow was the dominant mode of water movement, the solute composition was in equilibrium with both kaolinite and gibbsite. Examination of the clay mineralogy confirmed these results. The microtexture of quartz grains was examined by the scanning electron microscope as another means of investigating the hydrochemical environment in the soil. Silica was found precipitated on all the grains examined but the maximum amount occurred in the Bs horizon. This evidence showed that, firstly, the dissolution of aluminosilicate minerals is greater than that calculated by the chemical budget and, secondly, that models of granite weathering must take localized weathering in the soil profile into account. The final part of the paper highlights the limitations of calculating denudation rates for an entire catchment and stresses the need to consider weathering as a highly localized phenomenon, particularly where there are high volumes of interflow at hill crest sites. Observations on granite decomposition in the future should be quantitative in approach and be related to the local site conditions.     

Contributions of H2S to the atmospheric sulfur cycle

H₂S is a most important biogenic sulfur compound with regard to the atmospheric sulfur cycle. Our present knowledge of the spatial and temporal distribution of this trace gas is rather incomplete owing to unreliable analytical methods. Therefore, a new method for the analysis of H₂S in the g-range was applied. This paper deals with the results of ground- and aircraft measurements of H₂S in unpolluted air over swamps and tidal flats. Based on the measured vertical distributions a removal coefficient of 2.3×10^–5 sec^–1 and an average lifetime of 12 hours were calculated. Some conclusions of the contribution of H₂S to the atmospheric sulfur budget are added.     

An evaluation of lightning and corona discharge on thunderstorm air and precipitation chemistry

This study synthesizes literature to provide a best estimate for the integrated effect of cloud-to-ground lightning, intracloud lightning, and corona discharge on air and precipitation chemistry for an idealized thunderstorm. The cloud volume concentration of NO (the predominant chemical species produced by lightning), assuming all flashes occurred simultaneously in an undiluted, idealized storm volume of 1.5×10³ km³, is approximately 0.8 ppbv at STP. Uncertainties are discussed, and assumptions used in this estimate are evaluated and compared to the literature for consistency. Also, NO production values (an average of field, theoretical, and laboratory observations) are used to scale theoretical estimates of other chemical species produced by lightning that can be scavenged by precipitation. The maximum concentrations of these pollutants in rain water are estimated by assuming complete removal of these select, acid rain related species and found to be insignificant.     

The distribution of light nonmethane hydrocarbons over the mid-Atlantic: Results of the Polarstern cruise ANT VII/1

During the cruise ANT VII/1 (September/October 1988) of the German research vessel Polarstern the latitudinal distributions of several nonmethane hydrocarbons were measured over the Atlantic between 45°N and 30°S by in-situ gas chromatography.On the average, the highest mixing ratios of ethane, propane, i- and n-butane, ethene and acetylene were observed in the Northern Hemisphere around 40° N and just north of the intertropical convergence zone, respectively. South of the equator, a bulge in the mixing ratios of ethane and acetylene was observed indicating aged biomass burning emissions. This observation coincided with enhanced tropospheric ozone found in this region at this season. On the average ethane and acetylene mixing ratios were around 500 and 100 ppt, respectively, whereas the levels of the other NMHC were in the range of some ppt up to 100 ppt.compared with the results of the cruise ANT V/5 (March/April, 1987), the ethane mixing ratios in September/October proved to be a factor of 3 lower in the Northern Hemisphere and a factor of 2 higher in the Southern Hemisphere, probably due to seasonal effects. Possible causes are the higher OH radical concentrations in summer, which result in a faster removal of ethane or stronger emission from biomass burning which also peaks in the dry season.The relative pattern of the hydrocarbons just north of the ITCZ was very similar for both measurement series. In this region, the NMHC were advected by long-range transport from the continent, whereas generally the ocean itself acts as a major NMHC source. This is supported by the results of a balance calculation between oceanic emissions and atmospheric removal rates.     

In-channel woody vegetation controls on sedimentary processes and the sedimentary record within alluvial environments: a modern example of an anabranch of the River Loire, France

A multidisciplinary approach was used to analyse the role of pioneer trees (Populus nigra) on bar formation in the modern fluvial system of the River Loire (France). Data were collected on seven plots located on a secondary channel, chosen for their vegetation cover and their sedimentary context. Physical features of vegetation, topographical evolution, sediment grain size and flow velocity were investigated during and after floods between 2001 and 2003. Woody vegetation responds morphologically to fast‐flowing waters and sediment deposition. These adaptations influence the role played by trees on local sedimentary processes. Some morphological types of trees exert a strong influence during flood events by deflecting, reducing or increasing the flow energy. As a consequence, the evolution of bedforms, distribution of sediment grain size and slopes are controlled by the flood type, the morphological context (i.e. high‐ or low‐energy zones), the morphology of the vegetated bar and the characteristics of vegetation. Conceptual models are proposed to account for local processes and evolution of tree groves. The first model, which describes the behaviour of groves during a single flood, underlines the sediment deposition downstream of the trees and the trapping of bedload sediments. During the falling stage of the flood, the reorientation of current streams, constrained by both local bed topography and woody vegetation, induces transverse sediment fluxes. For these water levels, the control exerted by trees on small‐scale sedimentary processes becomes significant. The second model shows the evolution of vegetation bands over several flood events. In particular, it describes the influence of vegetation on the fixing and reworking of bedload sediments during the falling limb of the hydrograph. The coalescence of vegetation‐induced bedforms and the resulting morphological changes increase the deflection power of the vegetated bar, inducing the deposition of finer sediments.     

The effect of beech stemflow on spatial patterns of soil solution chemistry and seepage fluxes in a mixed beech/oak stand

Stemflow of beech (Fagus sylvatica L.) represents a significant input of water and elements to the soil and might influence the spatial patterns and the rate of seepage fluxes at the stand scale. We investigated the soil solution chemistry at different depths and distances from the stem and the element fluxes with stemflow, throughfall and seepage in proximal and distal stem areas of a 130‐year‐old beech/oak forest in Steigerwald (northern Bavaria, Germany). The proximal stem area (in total 286 m² ha⁻¹) was defined as a 1 m², 60 cm deep cylinder around the beech stem. Seepage fluxes were calculated by a soil hydrological model for 1996 using measured soil matrix potentials and tree xylem flow data for calibration. Stemflow represented 6·6% of the annual soil water input. With the exception of H⁺ fluxes, less than 10% of the total element fluxes with throughfall and stemflow reached the soil via stemflow. The volume‐weighted concentrations of H⁺, K⁺ and SO₄²⁻ in stemflow were higher than those in throughfall, while other elements had similar concentrations. Soil solution K⁺ concentrations decreased with stem distance, but the Na⁺, Mg²⁺, Cl⁻ and SO₄²⁻ concentrations increased. Gradients for other elements were not statistically significant. Stemflow had a strong influence on the spatial patterns of element fluxes with seepage. The water fluxes through the soil of the proximal stem areas at a depth of 60 cm contributed 13·5% to the total seepage at the stand scale. Proximal to the stems about 20% of total seepage for K⁺, Mn²⁺, Alⁿ⁺, dissolved organic N and dissolved organic C were concentrated, but only 8–10% for Na⁺, Mg²⁺ and Ca²⁺. The loss of acid‐neutralizing capacity calculated from the flux balance was about four times higher proximal to the stems compared with distal areas, indicating high rates of soil acidification proximal to the stems. Our results confirm the concept of a microsite around beech stems, characterized by high element and water fluxes in comparison with distal stem areas. Calculations of seepage fluxes and element budgets in beech stands have to consider the spatial heterogeneity of fluxes induced by stemflow. Copyright © 2000 John Wiley & Sons, Ltd.