So we’re about to ship instruments back to NASA Armstrong to upload for ATom2, our second set of round-the-world flights, taking off in January. You may be wondering what we do in between missions, so here is a little summary of how we’ve been keeping busy between ATom 1 and 2.
First off, as soon as we got the instruments back we thoroughly calibrated them to see if anything had changed in the instrument responses during the mission and to account for losses of particles as they make their way through the inlet and into the different instruments in the rack. This is essential to understanding our data and took over a month to do thoroughly and check that our results were robust against theory. We then had some modifications to make to the instruments, both to improve performance and add new functionality.
We have two Ultra High Sensitivity Aerosol Spectrometers (UHSASs), measuring the size distribution of particles between 60 and 1000nm (sizes that can affect formation of clouds and scatter light directly). We wanted to gain information about the composition of these particles, so we added a thermodenuder to one of the UHSASs. This heats the flow of air to 300C, a temperature at which particles made up of ammonium, nitrate, organics and other volatile material will evaporate, while particles made up of sea salt and other non-volatile species will remain as particles. By comparing the size distribution from the UHSAS with the thermodenuder to the one without, we have an indication of how much sea salt contributes to the particles we see. This work required building and installing the thermodenuder in the UHSAS, and then testing it with particles of different chemical composition to check that the particles that evaporate and those that don’t are what we expect.
One of the Nucleation Mode Aerosol Size Spectrometers (NMASSs -instruments that measure the smallest part of the aerosol size distribution, from 3-60nm) needed a rebuild of large parts of the instrument to make it more robust. We took the whole thing apart, got new parts machined, reinstalled them with improvements to the electronics and plumbing and the tested everything.
This instrument is primarily a back-up incase something happens to the other NMASS, but now that it is more robust, we can run it in a different configuration to get more information at small sizes when everything is working well. On ATom1 we had 5 size channels spanning 3-60nm, identical in both instruments. Now we are shifting the sizes of the second NMASS channels to go in between the first NMASS channels, giving us 10 channels. This required more calibrating and checking.
Everything then had to be put back into our flight rack (to which we made some modification, like installing more cooling fans for when we’re low down in the tropics), and the whole system tested as a unit.
Aside from all this lab work we have been processing and analyzing data from the first mission, and presenting preliminary results. Processing is where we take the raw data (so this would be things like counts of particles, flows through the instruments etc.), and use it to calculate a useful parameter, e.g. concentrations of particles in a given size range, or size distributions. We also remove data from the files from times when we were doing checks on the instruments, like running air through a filter to check there are no leaks, and when we passed through clouds, since cloud particles can shatter on the inlet and show up as large numbers of small particles, which were never actually there.
In analyzing the data, we look at trends in the particles we see. This can be things like spatial variation of different sized particles, what size distributions correlate to things like biomass burning, or dust, that can be determined from other instrument, do the times when we see new particles forming from the gas phase coincide with any specific gas phase species? This is a long process, and we’ve only just scratched the surface, but it’s very exciting to get into the data and see the wealth of information in there. We’ve been able to discuss it with colleagues at NOAA and at a conference of International Global Atmospheric Chemistry, to get input from others in the field and discuss further investigations.
This last week has been spent packing up the instruments, the flight rack and what we need from the lab for the mission. This morning we loaded it all into a truck that’s now on it’s way to NASA Armstrong. Below is a time-lapse of us (this is all the groups from Boulder, CO taking part in ATom) loading the truck in the snow. Part two of the mission is about to begin!
Side note: The photos in this post are all stills from a documentary on the adventures of the ATom mission we’re making with One World Media. I’ll write more about this exciting project soon so check back for that!