Measuring snow absorption

Lab Note #22
Jun 02, 2014
One of the other measurements Maria has been performing in the lab is measurements of the amount of ultra-violet (UV) light that is absorbed by impurities (such as black carbon and dust) in the snow.  This is a way of getting a good quantitative number on the absorption of UV light by the dusty layer I mentioned in my previous post.  By absorbing UV light, this dusty layer reduces the chemistry going on in the snow that recycles reactive nitrogen back to the atmosphere.

Below is a photo similar to what I showed you back in January - these are filters that contain all of the insoluble impurities from the snow, after we melted the snow and passed the melt water through the filters last winter in Utah.



We then measure the amount of UV light absorbed by the filters using what we call an integrating sphere spectrophotometer (ISSW), which is shown below.




Maria places each filter sample in the apparatus as shown below.

 

There is an "integrating sphere" above and below the filter, which basically means that the only source of light absorption is by the impurities on the filter itself.

A very stable slight source shown below is connected to the ISSW via a fiber optic cable.



The amount of light transmitted through the filter is measured by the spectrometer shown below, which is recorded on a laptop computer via a USB connection.

 

The amount of absorption of UV light is measured at each 1 cm depth increment in each snowpit.  This data will be fed into our snow chemistry model, where we will calculate the recycling rate of reactive nitrogen in the snow.

Maria is now at a 10-day meeting in DC, attending the highly-competitive AMS Summer Policy Colloquium.  She will follow that trip with a trip to Utah for a science meeting about the field-campaign.  There all of the scientists, including Maria, will present their preliminary results.  When she returns, she will get back to the final portion of the project, the computer model calculations.

We have hired an undergraduate student to work with us on this project this summer.  She will be helping Maria in the lab, and with the computer model calculations.  We will introduce you all to her when she arrives!

Thanks again for your support!
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