Measuring Ozone - NWS Bismarck

Hello and thanks for joining me for another video for the Bismarck Weather

Education Center

Today we'll be learning about measuring ozone, but first why do we care about

this trace gas in our atmosphere.

Well as you may know the Sun emits radiation at many different wavelengths

some those wavelengths are harmful UV rays, if these UV rays made it down to the


life as we know it would not exist however with an ozone layer high in the


most of these harmful UV rays are absorbed this absorption also calls the

ozone layer to heat up

and plays a key role in the temperature structure of our atmosphere that's right

Hooray ozone. now that we know why ozone is important

why do we need to measure it most all research on ozone is done by NOAA

and NASA research ranges from how the ozone layer interacts with the rest of

the atmosphere

to most importantly how ozone concentrations are changing so how do we


ozone satellites with all the satellite in orbit nasa can map the entire ozone

layer around the earth

however satellite ozone measurements do fall short when keeping ozone records

Satellites have relatively short life cycles and each satellite has its own

measuring bias

which means its satellite gives different answers second satellite


only go back so far but where satellites fail

surface observations succeed the purple stars represent 15 locations around the

world that give regular ozone measurements

some locations date back to as long ago as the 1920s

the site bismarck dates back to 1962

machines taking measurements at these locations rarely if ever get changed out

so there's little to no bias in the data this is the machine

we measure ozone with the Dobson ozone spectrophotometer

or Dobson for short the Dobson was invented back in 1924 by Gordon Dobson

and besides a few electronic upgrades the machine has changed very little since

here the Bismarck office the Dobson gets its own building

which is located behind the main office the building is climate-controlled

and has a rotating and retractable roof so direct solar radiation or sunlight at

different times a day can reach the Dobson

so how does the Dobson work lets walk through a measurement

solar radiation enters a tube that reflects down into the machine

from there sunlight bounces off another mirror and goes back through

a lense and Prism light reflects off a mirror

and goes back through the prism from there the light is separated into a

spectrum at known wavelengths

this spectrum enters a wedge with slits

that allows only certain wavelengths that are affected by ozone molecules


a chopper wheel inside the Dobson acts to segment the wavelengths so they can be

measured individually

after going through another series of lenses prisims and mirrors

the segmented wavelengths are sent into a photomultiplier tube

which measures the difference between the wavelengths this difference allows

us to know

the thickness of ozone in a column of atmosphere the units are measured

in Dobson units

and a typical measurement when brought to standard temperature and pressure

only comes to about an eighth of an inch this means that if we took all the ozone from the


to the edge of the atmosphere and brought it down to the surface the amount of ozone

would only be as thick as two pennies

that is all the ozone it takes to protect life on Earth for more on ozone


and measurement you can visit NOAA's Earth System Research Laboratory website

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