Suchergebnisse

Intro -- 1 Einleitung und Aufgabenstellung -- 2 Brennverfahren bei Ottomotoren mit Benzin-Direkteinspritzung -- 2.1 Fremdgezündeter Betriebsmodus -- 2.1.1 Betriebsarten -- 2.1.2 Abgasnachbehandlung -- 2.2 Kontrollierte Selbstzündung -- 2.2.1 Grundlagen des Brennverfahrens - Verbrennung höherer Kohlenwasserstoffe -- 2.2.2 Praktische Umsetzung der kontrollierten Selbstzündung -- 3 Stickoxidemissionen -- 4 Abgasrückführung -- 4.1 Wirkmechanismen -- 4.2 AGR und geschichtete Benzin-Direkteinspritzung -- 4.3 AGR und kontrollierte Selbstzündung -- 4.3.1 Interne AGR als Maßnahme zur Einleitung der Selbstzündung -- 4.3.2 Auswirkungen der externen AGR auf das Brennverfahren -- 5 Versuchsträger und Messtechnik -- 5.1 Basisaggregat und Prüfstandsaufbau -- 5.2 Prinzip und Realisierung der Abgasschichtung -- 5.3 Sondermesstechnik -- 5.3.1 Gasentnahme-Technik -- 5.3.2 Hochgeschwindigkeitsvisualisierung -- 5.3.3 3-D Visualisierung -- 6 Numerisches Modell -- 6.1 Berechnungsgitter und -parameter -- 6.2 Spraymodelle -- 6.3 Fortschrittsvariablenmodell -- 7 Ergebnisse mit strahlgeführter Benzin-Direkteinspritzung -- 7.1 Voruntersuchungen -- 7.2 Homogene Abgasrückführung -- 7.3 Geschichtete Abgasrückführung -- 8 Ergebnisse mit kontrollierter Selbstzündung -- 8.1 Einfluss der Ventilsteuerzeiten -- 8.1.1 Variation der Einlasssteuerzeiten -- 8.1.2 Variation der Auslasssteuerzeiten -- 8.2 Einfluss des Zündzeitpunktes -- 8.3 Variation der Einspritzparameter -- 8.3.1 Variation des Einspritzbeginns -- 8.3.2 Variation des Einspritzdruckes -- 8.4 Untersuchungen zur kontrollierten Selbstzündung mit Aufladung -- 8.5 Homogene Abgasrückführung -- 8.6 Geschichtete Abgasrückführung -- 8.7 Bewertung der geschichteten externen Abgasrückführung -- 9 Zusammenfassung.

Nitrogen oxides, released from fossil fuel use and other combustion processes, affect air quality and climate. From the mid-1990s onward, nitrogen dioxide (NO2) has been monitored from space, and since 2004 with relatively high spatial resolution by the Ozone Monitoring Instrument. Strong upward NO2 trends have been observed over South and East Asia and the Middle East, in particular over major cities. We show, however, that a combination of air quality control and political factors, including economical crisis and armed conflict, has drastically altered the emission landscape of nitrogen oxides in the Middle East. Large changes, including trend reversals, have occurred since about 2010 that could not have been predicted and therefore are at odds with emission scenarios used in projections of air pollution and climate change in the early 21st century.

Nitrous oxide (N2O) is important to Earth's climate because it is a strong absorber of radiation and an important ozone depletion agent. Increasing anthropogenic nitrogen input into the marine environment, especially to coastal waters, has led to increasing N2O
emissions. Identifying the nitrogen compounds that serve as substrates for N2O production in coastal waters reveals important pathways and helps us understand their control by environmental factors. In this study, sediments were collected from a long-term fertilization site in Great
Sippewissett Marsh, Falmouth, Massachusetts. The 15N tracer incubation time course experiments were conducted and analyzed for potential N2O production and consumption rates. The two nitrogen substrates of N2O production, ammonium and nitrate, correspond to
the two production pathways, nitrification and denitrification, respectively. When measurable nitrate was present, despite ambient high ammonium concentrations, denitrification was the major N2O production pathway. When nitrate was absent, ammonium became the dominant substrate
for N2O production, via nitrification and coupled nitrification-denitrification. Net N2O consumption was enhanced under low oxygen and nitrate conditions. N2O production and consumption rates increased with increasing levels of nitrogen fertilization in long-term
experimental plots. These results indicate that increasing anthropogenic nitrogen input to salt marshes can stimulate sedimentary N2O production via both nitrification and denitrification, whereas episodic oxygen depletion results in net N2O consumption.

We use 23 atmospheric chemistry transport models to calculate current and future (2030) deposition of reactive nitrogen (NOy, NHx) and sulfate (SOx) to land and ocean surfaces. The models are driven by three emission scenarios: (1) current air quality legislation (CLE); (2) an optimistic case of the maximum emissions reductions currently technologically feasible (MFR); and (3) the contrasting pessimistic IPCC SRES A2 scenario. An extensive evaluation of the present-day deposition using nearly all information on wet deposition available worldwide shows a good agreement with observations in Europe and North America, where 60–70% of the model-calculated wet deposition rates agree to within ±50% with quality-controlled measurements. Models systematically overestimate NHx deposition in South Asia, and underestimate NOy deposition in East Asia. We show that there are substantial differences among models for the removal mechanisms of NOy, NHx, and SOx, leading to ±1 σ variance in total deposition fluxes of about 30% in the anthropogenic emissions regions, and up to a factor of 2 outside. In all cases the mean model constructed from the ensemble calculations is among the best when comparing to measurements. Currently, 36–51% of all NOy, NHx, and SOx is deposited over the ocean, and 50–80% of the fraction of deposition on land falls on natural (nonagricultural) vegetation. Currently, 11% of the world's natural vegetation receives nitrogen deposition in excess of the "critical load" threshold of 1000 mg(N) m−2 yr−1. The regions most affected are the United States (20% of vegetation), western Europe (30%), eastern Europe (80%), South Asia (60%), East Asia (40%), southeast Asia (30%), and Japan (50%). Future deposition fluxes are mainly driven by changes in emissions, and less importantly by changes in atmospheric chemistry and climate. The global fraction of vegetation exposed to nitrogen loads in excess of 1000 mg(N) m−2 yr−1 increases globally to 17% for CLE and 25% for A2. In MFR, the reductions in NOy are offset by further increases for NHx deposition. The regions most affected by exceedingly high nitrogen loads for CLE and A2 are Europe and Asia, but also parts of Africa.

While shipping has long been recognised as a very carbon-efficient transport medium, there is an increasing focus on its broader environmental consequences. The International Maritime Organisation is responsible for the regulation of ship emissions arising from fuel combustion. Their current regulations are, however, much less strict than those applying to land-based transport within the European Union. Five different groups of pollutant emission from ship smokestacks are addressed in this paper: sulphur oxides, nitrogen oxides, particulate matter, organic matter and metals. The reduction of sulphur oxide emissions into the atmosphere using scrubber technology adds another dimension to the discussion, as this approach results in focused discharge of some pollutants to the surface water. A scoping calculation shows that an open-loop scrubber on a medium-sized ship could discharge more copper and zinc daily to the surface water than the ship's antifouling paint. The use of antifouling paint in the European Union is subject to a prior risk assessment, but scrubber discharges are not subject to any such risk assessment. This situation presents a problem from the perspective of the Marine Strategy Framework Directive, as environmental monitoring programmes in some coastal areas of the Baltic Sea have shown that levels of both copper and zinc exceed environmental quality standards. To fulfil the Marine Strategy Framework Directive requirements and achieve Good Environmental Status, having knowledge of the magnitude of different anthropogenic pressures is important. Metal inputs from open-loop scrubbers have been largely neglected until now: some metals have the potential to serve as tracers for monitoring scrubber discharges.

Is nitrogen oxides emissions spatially correlated in a Chinese context? What is the relationship between nitrogen oxides emission levels and fast-growing economy/urbanization? More importantly, what environmental preservation and economic developing policies should China's central and local governments take to mitigate the overall nitrogen oxides emissions and prevent severe air pollution at the provincial level in specific locations and their neighboring areas? The present study aims to tackle these issues. This is the first research that simultaneously studies the nexus between nitrogen oxides emissions and economic development/urbanization, with the application of a spatial panel data technique. Our empirical findings suggest that spatial dependence of nitrogen oxides emissions distribution exists at the provincial level. Through the investigation of the existence of an environmental Kuznets curve (EKC) embedded within the Stochastic Impacts by Regression on Population, Affluence, and Technology (STIRPAT) framework, we conclude something interesting: an inverse N-shaped EKC describes both the income-nitrogen oxides nexus and the urbanization-nitrogen oxides nexus. Some well-directed policy advice is provided to reduce nitrogen oxides in the future. Moreover, these results contribute to the literature on development and pollution.