Profiler in action!

The inlet of the CRDS automatically moves up and down throughout the night to sample air at two different levels. So far, we have seen lower concentrations of N2O5 at the lower level. This suggests N2O5 is being deposited to the snowpack. This data, coupled with vertical wind speeds, can be used to calculate a flux, or deposition rate, to the snowpack.

New Snow and Cold Temps

Patrick downloading met tower data at -20F. Currently we have low temperatures and a very stable atmosphere. We are not seeing N2O5 because there are high amounts of NO (nitric oxide). When NO is present in the atmosphere it reacts with NO3 (nitrate radical) in the following reaction:

NO + NO3 --> 2NO2

This previous reaction is fast and NO3 does not exist to even form N2O5(NO2+NO3<-->N2O5).

Making Progress

This is a snapshot of the software we use to collect N2O5. The data in the picture shows we are actually seeing N2O5 in the atmosphere. The blue trace decreases as the N2O5 is absorbed by the laser at 662 nanometer wavelength. The blue trace increases during the clean cycle so the cell is ready for the next measurement. It is pretty exciting when you see this modulation occur, because we know we will have data to analyze from this field study.

The profile inlet on the left in the up position and met tower with instruments on the right.

This is a picture of a PhD graduate student near the end of a great and exhausting field study!

The profiler

The profiler is on the gray tripod to the left in the picture. The profiler consists of a long bike chain, two gears and a stepper motor to control the movement of the inlet. The profiler raises and lowers our air sampling inlet to the heights of the met tower instruments. The automated inlet allows us to sample at each level every two minutes. The inlet samples air for the N2O5 instrument, NOx and Ozone.

The inside of the hut and the instruments

The inside of the hut contains all of the instruments that measure NOx (NO + NO2), ozone ( O3) and N2O5.

This is the instrument that measures N2O5. It was developed in our lab by Bill Simpson and other graduate students. It uses a technique called Cavity Ring Down Spectroscopy (CRDS). The instrument has a diode laser at 662 nanometer wavelength(red). The laser light enters the cavity and reflects off the two mirrors; one at each end. The light "rings down" similar to a bell and that time is measured. When there is N2O5 present it absorbs at 662 nanometers and the ringdown time is less. We are able to measure the amount, or mixing ratio, of N2O5 in the atmosphere in pptv (parts per trillion by volume) from the difference in these two ring down times.

Snow at the field site

The hut is now moved out into it's final position the field next to the met tower. We have all of our instruments moved into the hut and they are now collecting data.