NOAA's Global Monitoring Laboratory in Boulder, Colorado is one of the preeminent sources of high quality measurements of the stratosphere. In the Ozone and Water Vapor Group, Electrochemical Concentration Cell Ozonesondes are launched on high altitude balloons to greater than 30km (100,000 feet) to directly measure the Earth's protective Ozone Layer. First flown in Boulder, Colorado in 1967 by Walter Komhyr, these small instruments are vital to the measurement of stratospheric ozone worldwide. Most measurements of atmospheric ozone use light absorption to measure the "Total Column Ozone" value above that location. In contrast, the ECC Ozonesonde is one of the only instruments able to directly measure atmospheric concentrations of ozone as they rise on meteorological balloons to the edge of space.

These instructions follow the 2020 NOAA Ozonesonde Standard Operating Procedure and cover the use of radiosondes using XDATA protocol for additional instruments. Most of the instructions can be followed for other systems, but NOAA uses the SkySonde software package developed in house and available for free on their website. This system allows direct access to the raw data and the receiving equipment is significantly cheaper and more readily available than many other systems.

1- Initial Preparation: The first steps to preparing an ozonesonde is to clean the cell, tubing, and pump block using the step of "High Ozone Conditioning." This step is critical to the proper operation of the ozonesonde. NOAA's baseline observatories currently follow the "high ozone conditioning the DRY cell" method. After cleaning the components, solutions are added for the first time and the sonde is run at several levels of clean "Zero Ozone" and "5uA Ozone" air to verify initial operation of the instrument.

High Ozone Condition the tubing, pump, and a DRY cell. This is the only step that uses the "high ozone cleaning port." Make sure the cell is dry, otherwise it will supersaturate any liquid and significantly delay the remainder of the initial preparation. Run high ozone through the ozonesonde for 30 minutes. This step is critical to the operation of the ozonesonde. Measurements can be upwards of 5-10% low if this step is skipped.

Switch to "Zero Ozone Air" by turning off the lamp and switching to the "Sampling Port" on the test unit.

Use a pressure gauge to verify that the pump can produce at least 8psi of pressure.

Add Cathode and Anode Solutions for the first time.

Remove the cathode tubing from the pump block and use a wrench to remove the cathode cap. Twist with slight upward pressure to remove. Add 3.0cc of cathode solution to the cathode cell. Wait 2 minutes before proceeding to the anode solution.

The cathode cell has a Teflon post in the center of the platinum electrode "clover." When inserting the cathode cap, the tubing must go on this post. This can be somewhat difficult the first couple of times. Be careful to not catch the tubing on the electrode or crush it.

Add 1.5cc of Anode solution to the Anode Cell. The anode solution is supersaturated with potassium iodide and turns yellow as it ages. This is normal. Use separate syringes for changing cathode and anode solutions.

Connect the blue and white cell leads to the test unit. Insert the intake tube in to the Sampling Port and run on "Zero Ozone Air" for 20 minutes. The lamp should be off during this step. After 20 minutes, record the Cell Background Current on the checksheet.

Run on 5uA of Ozone. To do this, turn the lamp on and pull the slide out to the "5uA Spot." This location is unique to each test unit, but should be consistent from test to test.

Measure the response time of the cell from 4.0 - 1.5uA. To do this, prepare the stopwatch and turn the lamp off. Start the stopwatch when the cell current reaches 4.0uA and stop when it reaches 1.5uA. Record this response time on the checksheet. This value is very helpful in identifying malfunctioning ozonesondes, but may be quite long during the initial preparation because the background may still be quite high in some cases.

After 10 minutes of sampling clean zero ozone air, the sonde is ready to be stored until the Mid-Preparation. Short the blue and white cell leads to prevent a buildup of charge in the cell.

Store the intake tube and place the sonde inside of the bag. Store inside of the Styrofoam box and out of sunlight until the next step.

2- Mid Preparation: Approximately a week after the Initial Prep, the solutions are changed out and the sonde is run through a short checkout procedure to make sure that there are no critical issues and that it is operating as intended.

Replace the Cathode and Anode Solutions. Use the syringes to extract the old solution and dispose of it in a waste container. Add 3.0cc of Cathode.

Make sure the cathode tube slides on to the Teflon post inside of the cathode cell and do not damage the platinum electrode.

Replace the 1.5cc of Anode.

Run the sonde on "Zero Ozone Air." After 10 minutes, record the background current on the checksheet.

Turn on the lamp, pull out the slide to the "5uA Spot," and run for 10 minutes on 5uA of ozone.

After 10 minutes, turn off the lamp and time the decay from 4.0uA to 1.5uA. Continue running for 10 minutes on zero ozone air.

Store the sonde until ready for the Day of Flight prep. Short the blue and white cell leads, store the intake tube, and keep the sonde inside of the Styrofoam box.

3- Day-of-Flight Preparation: On the day of the launch, the sonde is once again run through its paces with fresh solutions. Then, "T100 Flowrate Measurements" are taken in order to determine the steady state flowrate of the pump. This timing is the most critical step in the preparation and extra care should be taken during this step in order to maximize accuracy of the measurement.

Start the Day-of-Flight preparation by replacing the 3.0cc cathode and 1.5cc anode solution.

Run sonde for 10 minutes on zero ozone then record the background current on the checksheet.

Run the sonde for 10 minutes on 5uA of ozone and then measure the decay rate from 4.0 - 1.5uA.

Run the sonde on zero ozone for 10 minutes. Record background current on checksheet.

Take 5x "T100 Flowrate Measurements" using a bubble flow meter.

- Place the bubble flow meter tubing on to the exhaust port of the cathode cell.

- You must send bubbles up the graduated cylinder to pre-wet it before taking measurements.

- Send bubbles up until they exit the top without popping.

This is the most important measurement of the checkout procedure!

- Form a single bubble layer. Make sure to release the red bulb before beginning timing.

- Begin your timing when the bubble crosses 0 mL.

- Stop the timing when the bubble crosses 100 mL.

- Record the average of 5x T100 measurements on the checksheet.

- A flowrate correction needs to be calculated to correct for evaporation and the differences in air temperature.

- During the T100 measurements, record the Room Temperature (C), Relative Humidity (%), Pressure (hPa), Test Unit Sample Port Humidity (%), and Pump Temperature (C)

- Sample Humidity depends on the test unit and if there is a drying filter used.

- Pump Temperature can be found using a radiosonde to transmit to SkySonde, or using a USB dongle, the Ozonesonde Viewer software can be used to read pump temperature.

Plug in the USB to XDATA converter (or use a radiosonde transmitting to SkySonde Client) to the V7 ozonesonde circuit board. Open Ozonesonde Viewer. Record the Pump Temperature.

In SkySonde Client, there is a calculator built in to determine the flowrate correction. Enter the Lab Conditions during the T100 measurements, press "Calc Flowrate Corr" and SkySonde will calcluate the Flowrate Correction and populate the corresponding field. Record this value on the checksheet.

Note one final background current on the checksheet and then the sonde is ready to be packaged for flight!

4- Receiving Data / SkySonde Software: It is critical to verify proper operation before releasing the balloon.

Select a new radiosonde for the flight. NOAA currently uses Intermet iMet-1 and iMet-4 radiosondes because they work seamlessly with a vast number of XDATA instruments. The other primary radiosonde in use is the Vaisala RS41 which is not covered here.

There is a "Tab" on the Styrofoam box indicating where the radiosonde should be placed. Prepare double-stick tape and place radiosonde firmly on to the side.

Add a strip of the orange duct tape to either side of the radiosonde. Avoid the foam radisonde "door" so that you can still open it.

There are several flaps to open on the radiosonde. Avoid damaging the fragile sensor boom.

Open up SkySonde Server. SkySonde Server includes a software modem for decoding the signal and can send it across a network to multiple computers recording or monitoring the flight. It will include information about data packets coming in and display a frequency spectrum. Audio can also be turned on or off if needed.

Plug the battery pack in to the plug on the radiosonde. Be careful. This connector is extremely fragile and can easily be ripped off of the circuit board.

Use the slider switch to turn the radiosonde on to the desired frequency. After a couple of seconds, the green LED between the switch and plug will begin flashing and SkySonde Server will begin receiving data. The PTUX circle will flash indicating radiosonde data and the signal should be visible on the frequency spectrum. The signal peaks can be centered inside of the blue shaded area to maximize the signal.

On the ozonesonde circuit board, plug the blue and white cell leads in to their labeled holes. If they are reversed, no ozone data will be measured during the flight. Make sure you are receiving ozone data before releasing the balloon!

Plug the XDATA cable from the radiosonde in to the "RADIOSONDE" port on the circuit board. With one hand squeezing the sides of the casing, slide the shield over the circuit board on the ozonesonde. Do not pinch wires and cables. Using double-stick tape, place the 2x 9V lithium battery pack in to the corner nearest the cells. The warmth from the battery will help keep the solution from freezing. Route the battery cable under the cathode tubing to avoid interfering with the pump piston.

Rotate the ozonesonde so that cables route away from the moving pump block and insert in to the Styrofoam enclosure. Verify the intake tube is exiting the correct slot. Do not tape the intake tube.

You can tape the XDATA cable and power cables in place, but DO NOT tape the intake tube. Verify the intake tube is secure in the ozonesonde pump block, but the tube itself needs to freely slide through the Styrofoam slot as the ozonesonde vibrates and moves around during launch and flight.

Open up SkySonde Client. Client works with Server to display and save the live data. It can also be used to reprocess raw data files if values or settings were entered incorrectly.

The ACQUISITION page includes entry boxes for the Flight Name (usually a two letter station identification followed by sequential flight number), and the Radiosonde number.

The STATION page includes information of the station location, and surface data. There are many default stations saved in the "Default Station Settings" drop down menu. Once a station location is entered, it should not need adjusted unless the software is reinstalled. The Surface Data should be entered as the current pressure, temperature, humidity, and wind data from the launch location at or near launch if available. If there is not a trusted source for this, there is an option for using the first radiosonde packet instead. (When using this, make sure the radiosonde is running before hitting "OK" on SkySonde Client, otherwise the first packet may be incorrect and could cause issues with the geopotential altitude calculation.)

The BALLOON page includes information of the balloon used and also includes a handy payoff weight calculator. Much of this page will not need changed from flight to flight if the instrumentation remains the same.

The OZONE page includes all of the most important checkout information for the ozonesonde. This page also includes a "Flowrate Correction Calculator" on the right side. If you enter the lab information taken during the T100 Flowrate Measurements and press "Calc Flowrate Corr," it will populate the Flowrate Correction box on the left with the correct value.

The OZONE METADATA page includes additional data that historically was only kept on the checkout sheets, but is very helpful for future analysis and corrections. Please fill out this information as well.

There are three additional Tabs if you are flying NOAA's Frost Point Hygrometer, multiple ozonesondes, or a variety of additional instruments. These can be ignored in most cases.

Hit "OK" on SkySonde Client to begin collecting data. Turn on the radiosonde to the desired frequency and center signal in SkySonde Server. The "Radiosonde" portion of SkySonde Client will begin populating once it has received a couple PTU or PTUX packets. Packet reception is indicated in SkySonde Server and at the bottom of SkySonde Client with the flashing colored circles. Typically radiosonde packets are PTUX which includes additional data fields such as Battery Voltage and Internal Temperature. If the radiosonde is placed outside, after a couple of minutes it should also start receiving GPS data in the bottom right portion.

Power instruments on starting from the radiosonde and proceeding down the instrument chain. Plug the ozonesonde battery in and you should hear the motor start and data packets will begin showing up in SkySonde Client. Verify Ozone Cell Current, Battery Voltage, and Pump Temperature. If you are not getting ozone readings, it is possible that the blue and white cell leads are plugged in backwards. If you are still not getting ozone readings and there are local sources of combustion exhaust or volcanoes, it could be the presence of sulfur dioxide. Sulfur dioxide reacts in the opposite manner of ozone and can cause cell current readings of zero. If needed, use the ozone source of the test unit to verify function before releasing. Do not launch an ozonesonde without verifying operation.

Pump temperature is significantly site specific and it is recommended to work with your Principle Investigator on ideal launch pump temperatures. High temperatures cause excess evaporation during the flight, while cold temperatures will end the measurement when the cathode freezes.

Make sure the lid is put on in the correct orientation. There is a corresponding tab and the attachment hook is offset toward the radiosonde. The underside is also cut specifically to give room for the piston to move without interference from the lid. If you hear the pitch of the ozonesonde change when you press down on the lid, double check what is going on.

Use two half-strips of orange duct tape to secure the instrument lid. In the freezing temperatures of the stratosphere, tape separates from the Styrofoam but freezes to itself. Make sure the tape makes complete circuits of the box and press down to make good contact.

You are now ready to fill the balloon, take surface measurements, and launch!

5- Launching the Balloon: The flight train is prepared and the instrument is launched.

Lay out the balloon on a clean surface. (Swept concrete, tarp, or table.) Minimize touching the balloon directly with your hands. Insert the nozzle and secure with string so that it will not slip off of the valve. The balloon neck will need to lift the roughly 2kg payoff weight.

Slowly turn on the helium to begin inflating the balloon.

Prevent the balloon from "rolling" which can cause the neck to twist and pop the balloon off of the valve. Fill the balloon until it lifts the pre-designated "payoff weight."

Tie the balloon shut. Tie a series of overhand knots.

Tie the ends of the string in to a loop and clip it to a secure anchor.

While securely holding the balloon, carefully untie and remove the nozzle. Make sure the anchor is still attached before letting go.

Open and gently "fluff" the parachute.

Tie a loop of string through the top of the parachute and the balloon string.

Choose a payout reel and unwind the string from the axle. It is shipped this way but we want all of the string on the larger spool for launch. There are two "Friction Bars" at the bottom. We loop a "Figure 8" to add a little more friction for the heavier ozonesonde package.

Test the payout reel for proper operation and that it does not "free spool" or "lock up." You may need to adjust the ratchet bar slightly in or out on the gear. The metal is relatively soft and can easily be adjusted to ratchet properly.

Attach the bottom of the parachute to the payout reel. An easy way is to feed the parachute strings under the top bar of the payout reel. Split the strings and wrap around the payout reel.

Trim the excess string that would get caught in the payout reel.

Verify the sonde is functioning well and take pre-flight surface data. Take the ozonesonde to the balloon and tie it on.

Tie the ozonesonde package to the payout reel string. It is easiest to launch with two people. Otherwise, using gloves, hold on to the neck of the balloon and carry the flight package from the payout reel. If you hold it by the "ratchet wheel," it cannot unspool. This is the preferred point of release.

Release the flight package from the payout reel. Avoid damaging the radiosonde sensor boom and do not knock the intake tube loose. It is very sad to do an entire flight measuring only the ozone inside of the Styrofoam box...

After release, verify that data is coming in. You can check any box along the left to see live plots of that field.