How do we collect particles

We are finally in the place we wanted to be after two weeks of waiting. We had a great trip from Manaus, no problems with anything falling from the truck and we only had some bad rain for the last 5 km on the mud road, but when we arrived at the site it stopped. Now it was time to set up our instruments; I’m in charge of an optical particle counter (I’ll explain what it does exactly in another entry) and Johannes is in charge of an aerosol mass spectrometer; there are plenty of other instruments which I hope I can get the people in charge of them to write a little about them, or I’ll explain to the best of my knowledge the way they work and what they measure.

Johannes explained what are we doing in the rain forest and what do we want to measure, now I’ll explain how do we get the particles we want to measure, we need to collect the particles some how if not all the fancy instruments we have are useless, here is where the high towers you’ve seen in other pictures come into play. Why don’t we just collect the particles at ground level? Because we will not be measuring the particles we want to measure. We will be collecting dust from our shoes, the cigarette smoke from our fellow friends taking a break, or the particles from the only car that passes by once a day to bring people to the site, so as you can imagine our samples will be contaminated, the data will be useless. We want the particles from the rain forest, so to collect them with the least amount of “foreign particles” we take them 10 meters and 40 meters above the ground. However, we cannot just put a hose, tie it to the tower and measure, remember we want to measure the aerosols not the water vapor in the air. If you’ve been to the rain forest you can remember it is very humid, we need to get rid of all the water vapor in the air. To do these we literally dry the particles before they go into the instruments by making them pass through “marbles” made out of very absorbing material. We also need to heat up the tubes. In a hot sunny day the temperature on top of the trees is higher than at the ground, so the pumps from the instruments will be sucking hot humid air from the top and as the temperature decreases on the way down water droplets will form, and we don’t want water, besides sticking to the tubes and not letting all the particles go through it will ruin the pumps from the instruments.

In summary, we collect particles by sucking air from 10 or 40 meters above the ground making them go through a heated tube, then we dry them and finally they get distributed to the different instruments.