Monday, November 10, 2014

Science: Aerosols

I am in Antarctica to help with the Automatic Weather Station project (which I will post about soon), but there are many other interesting bits of science happening here. Today I got a chance to visit the instrument shack of the "2ODIAC (2-season Ozone Depletion and Interaction with Aerosols Campaign)" study. The aim of their study is to understand how aerosols behave in a natural and largely undisturbed environment. Aerosols are tiny particles in the air, hundreds of time smaller than the thickness of a human hair. To carry out this study they have to sample the air very rapidly and measure the number of particles in the air, their size and composition. I went for a trip to the 2ODIAC field site with the lead investigator, Dr. Lars Kalnajs. It took us about 45 minutes by snow mobile to reach the site, which is located on sea ice 21km (13 miles) north-west of McMurdo Station.

Lars next to the 2OIDAC instrument shack. On many occasions team members stay the night at the field site to monitor the instrument. The large white mountain in the background is a volcano called Mt. Erebus and is over 3000m (11,000ft) tall. 

The nine instruments/items with numbers are listed below. Lars is making sure that uncontaminated outside air, which contains aerosols, is being sampled correctly.
2ODIAC Instruments
  1.  Aerosol size sensor; tells us how many aerosols exist and how big they are.
  2. Ultra High Sensitivity Aerosol Spectrometer. It measures the sizes of small aerosols very quickly. The spectra can tell you the type of particle encountered
  3. Particle Into Liquid Sampler - catches aerosol particles and puts them in a vial of water, which we can analyze later.
  4. Aerosol Mass Spectrometer (AMS). The AMS measures both the size of particles and what each particle is made of.   It is a very expensive and complicated instrument. 
  5. Computer - logs and stores data from all instruments as well as transmitting it to McMurdo. 
  6. NO, NO2, NOx Analyzer - Measures pollution gasses, which tell us when the air we are sampling is not clean.
  7. Ozone Analyzer - measures a gas called ozone which reacts with aerosol particles.
  8. Condensation Particle Counter - turn aerosol particles into cloud droplets, that we can then count, which gives us the total number of particles, even the extremely small paricles that we can't measure until we grow them to cloud droplet size.
  9. Weather station data - records temperature, humidity and wind speed outside the instrument shack

The 2ODIAC study will continue through the Southern Hemisphere summer (when there is 24hrs/day sunlight). However, the science team will be back near the end of winter when temperatures are much colder and sunlight is minimal in order to see how aerosols behave under these different conditions - hence "2-season" in the name of the study.

Lars checks the generators that power all the instruments. To be a field scientist you have to understand all aspect of your instrumentation, from power, to field location, to sampling methods through to understanding the data being collected.

We really are on sea ice! While Lars tended to instruments I dug a snow pit to look at the snow and sea ice. I stood my leatherman tool vertically against the snowpit wall. There is about 30cm (1 ft) of snow, in three layers. Most of the snow appeared in October. The dark ice at the bottom of the picture is sea ice - it is first year ice and still tasted a bit salty when I chipped a piece and ate it. As sea water freezes it rejects the salt back into the ocean.

We encountered this young fellow lazing on the snow mobile track. This photo was taken with a +1000mm lens; we keep our distance so as to not disturb the wildlife.

When traveling on sea ice you have to make sure the ice is safe. When cracks appear we need to test whether they have refrozen enough to support the weight of a snow mobile and rider. Lars is drilling into the ice across the profile of a crack to see how thick it is. You might be able to see a "caution!" marking black flag behind Lars.

Maybe this seal was suggesting we take a different route

(Thanks to Lars for explaining all the instruments and to my co-worker Lee for taking meetings solo so I could take this tour.)


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