Transport of very short-lived substances from the Indian Ocean to the stratosphere through the Asian monsoon

Anthropogenic halogenated substances cause the ozone hole above Antarctica through catalytic ozone destruction and depletion of the stratospheric ozone layer, which shields the Earth from harmful ultraviolet radiation. Their emissions were regulated through the Montreal Protocol in 1989. Since the beginning of the 21st century, the amount of chlorine and bromine in the stratosphere from long-lived ozone depleting substances (ODS) has been decreasing and stratospheric ozone has started to increase slowly. Under these circumstances the importance of natural halogenated substances for atmospheric composition and chemistry will increase in the future. Trace-gases with atmospheric lifetimes of less than half a year belong to the so-called very short-lived substances(VSLS). The most important bromine containing VSLS bromoform (CHBr3, 17 days lifetime) and dibromomethane (CH2Br2, 150 days) from marine sources currently contribute about 25% to the observed stratospheric bromine loading. In addition, the short-lived VSLS methyl iodide (CH3I, 3.5 days) contributes to stratospheric iodine levels. Sulfur containing compounds, such as dimethylsulfide (DMS, 1 day), also influence stratospheric ozone. Sulfur supplies the stratospheric aerosol layer, which amplifies heterogeneous chemical ozone depleting reactions under high chlorine levels. DMS is a potential source of sulfur to the stratosphere. VSLS are naturally produced in the oceans by phytoplankton, macro algae, and photochemistry. They are primarily transported to the stratosphere with deep convection in the tropics and mainly enter the stratosphere over the Pacific warm pool in boreal winter and the Asian monsoon region in boreal summer. Major uncertainties still exist with respect to the oceanic emissions of halogenated VSLS from the Indian Ocean and their stratospheric entrainment through the Asian monsoon circulation. This thesis investigates the emissions of VSLS from the Indian Ocean and their transport to the stratosphere with novel combinations of data and modeling

Transport von sehr kurzlebigen Substanzen vom Indischen Ozean in die Stratosphäre durch den asiatischen Monsun

Anthropogenic halogenated substances cause the ozone hole above Antarctica through catalytic ozone destruction and depletion of the stratospheric ozone layer, which shields the Earth from harmful ultraviolet radiation. Their emissions were regulated through the Montreal Protocol in 1989. Since the beginning of the 21st century, the amount of chlorine and bromine in the stratosphere from long-lived ozone depleting substances (ODS) has been decreasing and stratospheric ozone has started to increase slowly. Under these circumstances the importance of natural halogenated substances for atmospheric composition and chemistry will increase in the future. Trace-gases with atmospheric lifetimes of less than half a year belong to the so-called very short-lived substances(VSLS). The most important bromine containing VSLS bromoform (CHBr3, 17 days lifetime) and dibromomethane (CH2Br2, 150 days) from marine sources currently contribute about 25% to the observed stratospheric bromine loading. In addition, the short-lived VSLS methyl iodide (CH3I, 3.5 days) contributes to stratospheric iodine levels. Sulfur containing compounds, such as dimethylsulfide (DMS, 1 day), also influence stratospheric ozone. Sulfur supplies the stratospheric aerosol layer, which amplifies heterogeneous chemical ozone depleting reactions under high chlorine levels. DMS is a potential source of sulfur to the stratosphere. VSLS are naturally produced in the oceans by phytoplankton, macro algae, and photochemistry. They are primarily transported to the stratosphere with deep convection in the tropics and mainly enter the stratosphere over the Pacific warm pool in boreal winter and the Asian monsoon region in boreal summer. Major uncertainties still exist with respect to the oceanic emissions of halogenated VSLS from the Indian Ocean and their stratospheric entrainment through the Asian monsoon circulation. This thesis investigates the emissions of VSLS from the Indian Ocean and their transport to the stratosphere with novel combinations of data and modeling.Anthropogene halogenierte Substanzen verursachen das Ozonloch über der Antarktis durch katalytische Ozonzerstörung und einen Schwund der stratosphärischen Ozonschicht,welche die Erde vor schadhafter ultravioletter Strahlung schützt. Seit 1989 reguliert das Montrealer Protokoll die Emissionen von langlebigen halogenierten Fluorchlorkohlenwasserstoffen. Seit dem Beginn des 21. Jahrhundert sinkt die atmosphärische Konzentration von Chlor und Brom aus den langlebigen anthropogenen Substanzen und das stratosphärische Ozon nimmt langsam wieder zu. Unter diesen Voraussetzungen wird die Bedeutung natürlicher halogenhaltiger Substanzen, vor allem sehr kurzlebiger Substanzen (engl. very short-lives substances, VSLS) mit atmosphärischen Lebenszeiten kürzer als ein halbes Jahr, für die Zusammensetzung und Chemie der Atmosphäre in der Zukunft zunehmen. Momentan beträgt der Beitrag von VSLS zum stratosphärischen Brom etwa 25%. Die beiden wichtigsten bromierten VSLS sind Bromoform (CHBr3, 17 Tage Lebenszeit) und Dibrommethan (CH2Br2, 150 Tage). Weiterhin wird ein stratosphärischer Eintrag von Methyliodid (CH3I, 3,5 Tage) und schwefelhaltigem Dimethylsulfid (DMS, 1 Tag) vermutet. Schwefel verstärkt die heterogene chemische Ozonzerstörung bei hohem Chlorgehalt in der Stratosphäre. VSLS werden im Ozean auf natürlichem Wege von Phytoplankton, Makroalgen und durch chemische Reaktionen produziert. Sie werden in tropischen Gebieten mit hochreichender Konvektion in die Stratosphäre eingetragen, hauptsächlich über dem tropischen Westpazifik im borealen Winter und der asiatischen Monsunzirkulation im borealen Sommer. Die Unsicherheiten bezüglich der VSLS-Emissionen aus dem Indischen Ozean und des Transportes durch den asiatischen Monsun in die Stratosphäre sind groß. Diese Arbeit untersucht erstmalig VSLS Emissionen aus dem Indischen Ozean und ihren Transport in die Stratosphäre mit einer neuartigen Kombination aus Daten und Modellierung

Meteorological constraints on oceanic halocarbons above the Peruvian Upwelling

During a cruise of R/V METEOR in December 2012 the oceanic sources and emissions of various halogenated trace gases and their mixing ratios in the marine atmospheric boundary layer (MABL) were investigated above the Peruvian upwelling. This study presents novel observations of the three very short lived substances (VSLSs) – bromoform, dibromomethane and methyl iodide – together with high-resolution meteorological measurements, Lagrangian transport and source–loss calculations. Oceanic emissions of bromoform and dibromomethane were relatively low compared to other upwelling regions, while those for methyl iodide were very high. Radiosonde launches during the cruise revealed a low, stable MABL and a distinct trade inversion above acting as strong barriers for convection and vertical transport of trace gases in this region. Observed atmospheric VSLS abundances, sea surface temperature, relative humidity and MABL height correlated well during the cruise. We used a simple source–loss estimate to quantify the contribution of oceanic emissions along the cruise track to the observed atmospheric concentrations. This analysis showed that averaged, instantaneous emissions could not support the observed atmospheric mixing ratios of VSLSs and that the marine background abundances below the trade inversion were significantly influenced by advection of regional sources. Adding to this background, the observed maximum emissions of halocarbons in the coastal upwelling could explain the high atmospheric VSLS concentrations in combination with their accumulation under the distinct MABL and trade inversions. Stronger emissions along the nearshore coastline likely added to the elevated abundances under the steady atmospheric conditions. This study underscores the importance of oceanic upwelling and trade wind systems on the atmospheric distribution of marine VSLS emissions

Importance of seasonally resolved oceanic emissions for bromoform delivery from the tropical Indian Ocean and west Pacific to the stratosphere

Oceanic very short-lived substances (VSLSs), such as bromoform (CHBr3), contribute to stratospheric halogen loading and, thus, to ozone depletion. However, the amount, timing, and region of bromine delivery to the stratosphere through one of the main entrance gates, the Indian summer monsoon circulation, are still uncertain. In this study, we created two bromoform emission inventories with monthly resolution for the tropical Indian Ocean and west Pacific based on new in situ bromoform measurements and novel ocean biogeochemistry modeling. The mass transport and atmospheric mixing ratios of bromoform were modeled for the year 2014 with the particle dispersion model FLEXPART driven by ERA-Interim reanalysis. We compare results between two emission scenarios: (1) monthly averaged and (2) annually averaged emissions. Both simulations reproduce the atmospheric distribution of bromoform from ship- and aircraft-based observations in the boundary layer and upper troposphere above the Indian Ocean reasonably well. Using monthly resolved emissions, the main oceanic source regions for the stratosphere include the Arabian Sea and Bay of Bengal in boreal summer and the tropical west Pacific Ocean in boreal winter. The main stratospheric injection in boreal summer occurs over the southern tip of India associated with the high local oceanic sources and strong convection of the summer monsoon. In boreal winter more bromoform is entrained over the west Pacific than over the Indian Ocean. The annually averaged stratospheric injection of bromoform is in the same range whether using monthly averaged or annually averaged emissions in our Lagrangian calculations. However, monthly averaged emissions result in the highest mixing ratios within the Asian monsoon anticyclone in boreal summer and above the central Indian Ocean in boreal winter, while annually averaged emissions display a maximum above the west Indian Ocean in boreal spring. In the Asian summer monsoon anticyclone bromoform atmospheric mixing ratios vary by up to 50% between using monthly averaged and annually averaged oceanic emissions. Our results underline that the seasonal and regional stratospheric bromine injection from the tropical Indian Ocean and west Pacific critically depend on the seasonality and spatial distribution of the VSLS emissions

Quantification of CH4 coal mining emissions in Upper Silesia by passive airborne remote sensing observations with the Methane Airborne MAPper (MAMAP) instrument during the CO2 and Methane (CoMet) campaign

Methane (CH4) is the second most important anthropogenic greenhouse gas, whose atmospheric concentration is modulated by human-induced activities, and it has a larger global warming potential than carbon dioxide (CO2). Because of its short atmospheric lifetime relative to that of CO2, the reduction of the atmospheric abundance of CH4 is an attractive target for short-term climate mitigation strategies. However, reducing the atmospheric CH4 concentration requires a reduction of its emissions and, therefore, knowledge of its sources. For this reason, the CO2 and Methane (CoMet) campaign in May and June 2018 assessed emissions of one of the largest CH4 emission hot spots in Europe, the Upper Silesian Coal Basin (USCB) in southern Poland, using top-down approaches and inventory data. In this study, we will focus on CH4 column anomalies retrieved from spectral radiance observations, which were acquired by the 1D nadir-looking passive remote sensing Methane Airborne MAPper (MAMAP) instrument, using the weighting-function-modified differential optical absorption spectroscopy (WFM-DOAS) method. The column anomalies, combined with wind lidar measurements, are inverted to cross-sectional fluxes using a mass balance approach. With the help of these fluxes, reported emissions of small clusters of coal mine ventilation shafts are then assessed. The MAMAP CH4 column observations enable an accurate assignment of observed fluxes to small clusters of ventilation shafts. CH4 fluxes are estimated for four clusters with a total of 23 ventilation shafts, which are responsible for about 40 % of the total CH4 mining emissions in the target area. The observations were made during several overflights on different days. The final average CH4 fluxes for the single clusters (or sub-clusters) range from about 1 to 9 t CH4 h−1 at the time of the campaign. The fluxes observed at one cluster during different overflights vary by as much as 50 % of the average value. Associated errors (1σ) are usually between 15 % and 59 % of the average flux, depending mainly on the prevailing wind conditions, the number of flight tracks, and the magnitude of the flux itself. Comparison to known hourly emissions, where available, shows good agreement within the uncertainties. If only emissions reported annually are available for comparison with the observations, caution is advised due to possible fluctuations in emissions during a year or even within hours. To measure emissions even more precisely and to break them down further for allocation to individual shafts in a complex source region such as the USCB, imaging remote sensing instruments are recommended

The Lagrangian Atmospheric Radionuclide Transport Model (ARTM) — Sensitivity studies and evaluation using airborne measurements of power plant emissions

The Atmospheric Radionuclide Transport Model (ARTM) operates at the meso-γ-scale and simulates the dispersion of radionuclides originating from nuclear facilities under routine operation within the planetary boundary layer. This study presents the extension and validation of this Lagrangian particle dispersion model and consists of three parts: i) a sensitivity study that aims to assess the impact of key input parameters on the simulation results; ii) the evaluation of the mixing properties of five different turbulence models using the well-mixed criterion; and iii) a comparison of model results to airborne observations of carbon dioxide (CO2) emissions from a power plant and the evaluation of related uncertainties. In the sensitivity study, we analyse the effects of stability class, roughness length, zero-plane displacement factor and source height on the three-dimensional plume extent as well as the distance between source and maximum concentration at the ground. The results show that the stability class is the most sensitive input parameter as expected. The five turbulence models are the default turbulence models of ARTM 2.8.0 and ARTM 3.0.0, one alternative built-in turbulence model of ARTM and two further turbulence models implemented for this study. The well-mixed condition tests showed that all five turbulence models are able to preserve an initially well-mixed atmospheric boundary layer reasonably well. The models deviate only 6% from the expected uniform concentration below 80% of the mixing layer height except for the default turbulence model of ARTM 3.0.0 with deviations by up to 18%, respectively. CO2 observations along a flight path in the vicinity of the lignite power plant Bełchatów, Poland measured by the DLR Cessna aircraft during the CoMet campaign in 2018 allow to evaluate the model performance for the different turbulence models under unstable boundary layer conditions