Verklaring studentendecaan moet zwart op wit

Een studente aan de Hogeschool Inholland in Den Haag vocht haar negatieve bsa aan bij het College. Ze had weliswaar slechts dertig van de veertig benodigde studiepunten gehaald, maar voerde aan dat dit het gevolg was van bijzondere persoonlijke omstandigheden. Die waren volgens de studente niet meegewogen in het besluit van de examencommissie.

Volgens de hogeschool was de studentendecaan wel om informatie gevraagd, maar had die alleen een mondelinge toelichting gegeven aan de examencommissie. Dat zou aan het computersysteem van de studentendecanen te wijten zijn.

Maar het CBHO vindt dat zo’n toelichting, met het oog op de rechtsbescherming van de student, altijd op schrift moet staan. De hogeschool moet nu opnieuw een besluit nemen. Of de studente alsnog mag doorstuderen is nog niet bekend.

Methane is thought to be 23 to 25 times more effective in trapping heat than carbon dioxide, while the warming potential of nitrous oxide – commonly known as laughing gas – is even 298 times higher than that of carbon dioxide. Although the warming potential of these molecules is fairly well documented, the contributions they make to climate change are not. This may well change however thanks to a technique dr. Petra Kroon-van Loon has developed to accurately measure such emissions. She defended her PhD dissertation on this subject last Tuesday at the faculty of Applied Sciences.

A much-used technique to measure the emissions straight from one of the important sources, namely pasture lands, involves placing boxes on the pasture land, covering about half a square meter. Within these little chambers the increase of the gasses is measured over a certain period of time. 

The problem with this technique is that the variation within a particular field is often much too high to allow for representative sampling. “It sounds trivial, but simply the fact that if cattle pooped somewhere or not can lead to variations in concentrations of up to a factor 100”, says Kroon-van Loon’s PhD supervisor, climate researcher professor Harm Jonker.

Kroon-van Loon, who works for the Dutch energy research institute ECN, used a completely different approach to measure the emissions. She used a technique known as spectrometry to measure the concentration of the gasses in the air three meters above the pasture land. Owing to wind and turbulence, a measurement taken from this position is much more representative of the entire field.

But the fact that the wind causes the gas molecules to move continuously also has a disadvantage. The researchers want to determine the net amount of gas that moves up from the ground towards the atmosphere. Yet what they measure is molecules that move up at one moment and down at another. Consequently, they had to use an extra trick: prior to each concentration measurement, Kroon-van Loon used an anemometer to measure the three-dimensional wind flow at the same spot. An anemometer measures wind speed based on the time of flight of sonic pulses between pairs of transducers.

Based on her work and that of colleagues from Wageningen University, Kroon-van Loon, who was unable to comment before Delta went to press, concludes that the standard numbers for emissions of methane and nitrous oxide from different ecosystems that are currently employed for policymaking are underestimated. This is one of her PhD propositions.

Her PhD supervisor, prof. Jonker, believes however that it is still too early to say whether emissions have thus far been underestimated: “We have a technique now that works for a whole pasture. We have to find out if it works for agricultural land in general. The work is now really getting started.”

The professor sees great potential for this kind of research. “If you know more about the processes that give rise to methane and nitrous oxide, you can do a lot to prevent emissions”, he says. “It is known, for instance, that if it rains shortly after manure has been put on the land, this results in an enormous production of laughing gas. Perhaps it’s possible to prevent these emissions by fertilizing underground, although this is not my field of expertise. But surely there must be possible solutions. In the end, what you want to do is to monitor the effects of such actions accurately.” 

Petra S. Kroon-van Loon, ‘Eddy covariance observations of methane and nitrous oxide emissions’, 8 June 2010, PhD supervisor Professor Harm Jonker