Comparison of the different approaches to calculate kW
To demonstrate the implications of different approaches modelling kWm values, we plotted CO2 curves of four different authors in Figure 6. At low wind speeds (<3 m s-1] the model of McGillis et al. (2001, denoted as M01) gives highest values, whereas Liss & Merlivat (1986, denoted as LM86) and Wanninkhof & McGillis (1999, denoted as WM99) show lowest values. The model of Wanninkhof (1992, denoted as W92) gives medium values. At low wind speed (3 m s-1< u > 8 m s- 1] highest values are calculated with W92. Other models give lower values (factor about 1.75]. At moderate wind conditions (8 m s-1< u > 14 m s-1) W92 still modulate highest values whereas LM86
deviate strongly from all other models and gives lowest values. Both cubic models (WM99 and MG01) return median values. At strong wind conditions (u > 14 m s-1] the linear model differ VHOC: State of the art towards low values compared to the W92 whereas the cubic models differ towards high values compared to the W92.
Notes on calculations of air mixing ratios
Although part-per-notation is not a SI-unit (international system of units), parts per trillion (ppt) is commonly used in atmospheric chemistry. Another drawback of the part-per-notation is disaccords due to the different meanings in short and long scales for numbers: for most languages in continental Europe billion has the value of 1012 and trillion of 1018. English language-speaking countries however using short scale notation with billion = 109 and trillion of 1012. Consequently ppt for instance stands for 1 · 10-12.
Though part-per-notation do have some strong advantages to express air concentrations: in contrast to the metric units (e.g. ng · m-3), ppt is not influenced by temperature, pressure or molecular weight. This has a crucial benefit, since gas mole fractions of different atmospheric layers are directly comparable.
Beside ppt, pptv (part per trillion by volume) are present in the literature too as a unit for gas mole fraction. However both units are identical for the purposes in atmospheric chemistry. Since mole and volume fraction are identical for ideal gases (and practically identical for most gases) pptv can be calculated under standard temperature and pressure (STP = 1013.25 mbar and 273.15 K) using the following.
Working with Trace Elements
VHOCs occur as trace elements in the atmospheric and marine environment. Common concentrations rage at pmol · L-1-level for water samples and pptv for air samples. To illustrate this concentration range, Wikipedia gives the following figure: Parts per trillion “is equivalent to one drop of water diluted into 20, two-meter-deep Olympic-size swimming pools (50,000 m3)”. Hence working with trace elements requires very careful handling to avoid pollution of the sample or the analytical cycle. Desorption of pollutants and adsorption of analytes from/towards materials must be considered as a challenging problem. Materials and cleaning procedures should be adapted with regards to their interfering potential. Borosilicate glassware and stainless steel are preferable to plastic material. In order to maintain high analytical precision, the analytical cycle must be absolutely gastight towards the atmosphere.
The low environmental concentrations pose a challenge for the detection: usually air- and water concentrations are below the detection limit; including the most sensitive methods. Direct injection of water samples onto the capillary column was tried (Grob and Habich 1983) but emerged as unsuitable for halocarbon measurements. For detection, the analytes needed to be preconcentrated: in a first step, the analytes are separate from the medium. Then, in a second step the concentrated analytes are chromatographically separated and finally measured by a specific detector.
The following paragraphs give a review on different techniques necessary for halocarbon measurements. For a better understanding, theory is explained succinctly for techniques and apparatus. Finally the implemented methods are described.
Halocarbons can be extracted from a liquid medium by a liquid solvent (e.g. pentane). Originally introduced by Eklund et al. (1978) this technique was frequently used until the nineties of the last century (e.g. by Abrahamsson and Klick 1990). Even though the extraction procedure is simple, the method has some crucial technical drawbacks: the separation of the two phases can be interfered in organic rich water by the formation of emulsions. Furthermore it is often necessary to insert high volumes of solvent for high extraction efficiency. This however disagrees with the aimed preconcentration of the analytes.
In this method an inert gas (nitrogen, helium, argon) is used to separate analytes from a liquid medium. The technique was described by Swinnerton et al. (1962) for the first time. Since then, this technique became the main technique used for the determination of halocarbons.
The gaseous-liquid extraction is differentiated into two groups: In the static headspace extraction a water sample is given into a gas tight container. An adequate headspace is left and replaced by an inert gas. The container is shaken until equilibrium between the water phase and the headspace is reached. This equilibrium depends on the temperature, the partial pressure and the salinity and is describes by the Henry’s Law (see 2.5.1). The Henry’s Law constant determine the precision of the method: low gas-to-liquid concentration ratios causes low gas phase concentrations and therefore accuracy can be limited. Larger headspace volume might solve this problem (King et al. 2000). Static headspace techniques had been developed for incubation experiments (Itoh et al. 1997; Manley and de la Cuesta 1997; Amachi et al. 2001) and for environmental samples (Drewer et al. 2008; Jakubowska et al. 2009).
Table of contents :
Table of Contents
List of Figures
List of Tables
1.1 Thesis Goals
2 VHOC: State of the art
2.1 Chemical properties
2.2.1 Biological sources
2.2.2 Natural, nonbiological formation of VHOCs
2.2.3 Anthropogenic sources
2.3 Lifetimes in the Troposphere
2.4 VHOC contribution to reactive stratospheric halogens
2.5 Air-Sea Exchange
2.5.1 Henry’s law constants
2.5.2 Transfer velocity
2.5.3 Notes on calculations of air mixing ratios
3 Methods and Development of the Analytical System
3.1 Working with Trace Elements
3.2 Sampling Devices
3.3.1 Solid-Liquid extraction
3.3.2 Liquid-Liquid extraction
3.3.3 Gaseous-Liquid extraction
3.4 Purge gas desiccation
3.5 Preconcentration of the analytes and injection
3.6 Separation and Detection
3.7 Limit of Detection
3.8 Implemented GC-ECD-System
3.8.1 Sampling device
3.8.3 Retention times and identification of the compounds
3.8.5 Summary of the PAT-GC-ECD parameters
3.9 Protocols for maintaining the system
4 Distribution of Volatile Halogenated Organic Compounds in the Iberian Peninsula Upwelling System
4.2.1 Study Area
4.2.2 Physical variables and pigment analysis
4.2.3 Analysis of volatiles
4.2.4 Data analysis
4.3.1 Upwelling during the campaign and sampling strategy
4.3.2 Spatial distribution of selected VHOCs
4.3.3 SST as grouping variable
4.3.4 Relationship Between the Compounds
4.3.5 Vertical distribution of VHOCs compared to environmental parameters .
4.3.6 Temporal and tide factors in the upper layers
4.4.1 Comparison to other studies
4.4.2 On the different origin of VHOCs
4.4.3 Evidence for phytoplanctonic production of VHOCs
4.4.4 Near shore production: main source for brominated compounds in the upwelling?
5 Annual distribution of reactive halocarbons in a tide influenced estuary: Exchange fluxes between ocean and atmosphere
5.2.1 Sampling area
5.2.2 Sampling strategy
5.2.3 Methods for physical, chemical and biological variables
5.2.4 VHOC measurements
5.3.1 Meteorological variables
5.3.2 Environmental data describing seasonality at ASTAN and ESTACADE point
5.3.3 Environmental data describing seasonality along a salinity gradient in the Bay of Morlaix
5.3.4 Seasonality of VHOC surface concentrations
5.3.5 Formation of halocarbons during a diurnal tidal cycle
5.3.6 Possible input of halocarbons by a sewage treatment plant at Morlaix
5.4.1 Comparison to other costal measurements
5.4.2 Temporal trends
5.4.3 Biogenic sources
5.4.4 Different sources along the gradient
5.4.5 Sea-air Fluxes
6 Physiological function of VHOCs for macroalgae
6.3 Material and Methods
6.3.1 Algal material and elicitation procedures.
6.3.2 Conditioning procedure in the laboratory
6.3.3 Transient transplantation in the field
6.3.4 Aldehydes and volatile halogenated organic compounds (VHOCs) measurements
6.3.5 RNA extraction and RT-qPCR
6.4.1 Wild and laboratory-grown algae display different defense responses
6.4.2 Effect of transient transplantation
6.4.3 Development of a conditioning procedure in the laboratory
6.4.4 The conditioning procedure down-regulated the oligoguluronates-induced release of VOCs
7 Conclusions and perspectives