How to organise a field mission ?

Moving a laboratory for a fortnight is certainly not the easiest exercise you can do. This is what Sarah Albertin, a second year PhD thesis student, has done by installing an atmospheric measurement laboratory in the Arve valley, in Chamonix.

Before going on holiday, it is convenient to prepare a list of objects not to be forgotten, a check list. Sarah has been preparing this list since January. She knew she couldn’t forget anything but above all she knew she would only have a short time window to carry her measurements. This study focuses on particles pollution events during winter imputable to local emissions coupled with poor dispersion caused by surface temperature inversions. Understanding the physical and chemical processes driving such strong pollution events is a crucial subject today for cities located in mountain/polar regions.

For Sarah, the key word for field missions is adaptation. This starts with the decision of the location. The study of the oxidation mechanisms and aerosol formation in urban environments in winter, her research topic, initially targeted the town of Fairbanks, Alaska. As the health situation prevented her to travel to this location, it was necessary to find a comparable site from a meteorological and chemical point of view, hence the choice of the Arve Valley.

But how to go from a laboratory in Grenoble to an ex nihilo installation in Chamonix ?

For her mission, Sarah had to install three platforms : an air sampling plateform for gas and particles collection, an instrumental plateform and a chemistry laboratory. Atmospheric pollutants will be captured by outdoor collectors and analysed by indoor equipment with some analyses requiring a chemical stage. The rule, although obvious but often difficult to apply, is to always think about the limits and needs of each step.

On the instrumental part, the devices impose a stable temperature close to 20°C : the repeatability of the measurements is at stake. However, it is necessary to be able to connect these analysers to the external sampling platform. In addition, each device must be supplied with electricity and gas bottles. These gases are used to calibrate the instruments, i.e. to set the reference values.

There is no such thing as an ideal collection location. The location of the sampling site must meet the criteria of scientific studies while maintaining accessibility for handling and an electrical power supply. A compromise must always be found between these two points.

Finally, and certainly the most surprising, is the installation of a chemistry laboratory. These laboratories are often aseptic places on the one hand - no contamination should alter the samples - and chemically hazardous on the other hand. Handling then requires personal protective equipment (coat, gloves, glasses) as well as a laminar flow hood that does not contaminate the samples. These laboratories require a lot of small equipment such as pipettes, glassware and chemicals. A particular point of attention concerns the purified water that allows the dishes to be washed and the molecules to be extracted : no less than 200 litres were required.

With the equipment loaded, the field mission can then begin in earnest. Installing the 2 collection devices and testing the 5 analysers before the measurement campaign already takes 6 days. Fortunately, the toolbox had been designed to repair the defective instruments directly. Everything is ready ! Well almost... a south wind decided to disturb the data by bringing Saharan sand. So once again, we had to adapt and wait for a return of the study conditions.

As you will have understood, a mission cannot be improvised. It certainly requires a great deal of preparation but also an important knowledge of the equipment to be able to respond to any change. Certain risks can be limited though. Working on a study site adapted to the mission plays an essential role, hence the importance of a network of stations made available by the CNRS such as Le Clos de l’Ours chalet in Chamonix.