Stratospheric Ozone Stratospheric Ozone ExperimentExperiment

Team UNOTeam UNO

Team UNOTeam UNO

Donald SwartDonald Swart Christopher BarberChristopher Barber Michael O’LearyMichael O’Leary Gregg RidlonGregg Ridlon Robert SheffensteinRobert Sheffenstein

UNO AdvisorUNO Advisor Lawrence BlanchardLawrence Blanchard

ObjectivesObjectives

Measure ozone thickness as a Measure ozone thickness as a function of altitude using the function of altitude using the measurable quantities of UV intensitymeasurable quantities of UV intensity

Measure UVB and UVC as it is Measure UVB and UVC as it is transmitted and attenuated through transmitted and attenuated through the stratospherethe stratosphere

BackgroundBackground

What is UltraVoilet radiationWhat is UltraVoilet radiation How does UV help to detect ozone?How does UV help to detect ozone? Absorption cross sectionsAbsorption cross sections Ozone measurementsOzone measurements Beer-Lambert’s LawBeer-Lambert’s Law

Discovery of UVDiscovery of UV Johann W. Ritter in 1801 projected a beam of Johann W. Ritter in 1801 projected a beam of sunlight through the prism, which split the beam sunlight through the prism, which split the beam

into the colors of the spectrum. He them put into the colors of the spectrum. He them put chloride in each color to see the outcome. The chloride in each color to see the outcome. The

red caused a small change while the deep violet red caused a small change while the deep violet darkened the chloride. Ritter placed chloride in darkened the chloride. Ritter placed chloride in the lightless area just beyond the violet and it the lightless area just beyond the violet and it darkened as it were in a smoky fire. The was darkened as it were in a smoky fire. The was

evidence of another wave form just barely higher evidence of another wave form just barely higher than the violet of visible light. It is now known as than the violet of visible light. It is now known as

ultraviolet or UV light.ultraviolet or UV light.

What is UV?What is UV? Ultraviolet (UV) radiation is part of the electromagnetic spectrum from Ultraviolet (UV) radiation is part of the electromagnetic spectrum from

(200nm-400nm) that is emitted by the sun. (200nm-400nm) that is emitted by the sun.

UV rays can be made artificially by passing an electric current through a UV rays can be made artificially by passing an electric current through a gas or vapor, such as mercury vapor.gas or vapor, such as mercury vapor.

UV accounts for approximately 7% of total solar radiationUV accounts for approximately 7% of total solar radiation Wavelengths: Wavelengths:

• UVA - 3200 to 4000 Å UVA - 3200 to 4000 Å • UVB - 2800 to 3200 Å UVB - 2800 to 3200 Å • UVC - 2000 to 2800UVC - 2000 to 2800 Å Å

Determining ozone layer thicknessDetermining ozone layer thickness

Recording altitude dependent Recording altitude dependent intensitiesintensities

Determining relative cloumn density Determining relative cloumn density measurements above the payload measurements above the payload during the accent.during the accent.

Beer-Lambert LawBeer-Lambert Law

Beer-Lambert LawBeer-Lambert Law

In essence, the law states that there is an exponential dependence betweenIn essence, the law states that there is an exponential dependence betweenthe transmission of light through a substance and the concentration of the the transmission of light through a substance and the concentration of the substance, and also between the transmission and the length of material that thesubstance, and also between the transmission and the length of material that the light travels through. Thus if light travels through. Thus if ll and α are known, the concentration of a substance and α are known, the concentration of a substance can be deduced from the amount of light transmitted by it. can be deduced from the amount of light transmitted by it.

The value of the absorption coefficient α varies between different absorbing The value of the absorption coefficient α varies between different absorbing materials and also with wavelength for a particular material. materials and also with wavelength for a particular material.

0

0

(1)

ln ln (2)

(3)162.687 10

I AmeII I AmA DU

I0 is the intensity of the incident light

I1 is the intensity after passing through the material

l is the distance that the light travels through the material (the path length)

A is the concentration of absorbing species in the material is the absorption coefficient of the absorber.

How do we use UV measurement How do we use UV measurement to determine ozone amounts?to determine ozone amounts?

Variation of absorbtion levels due to Variation of absorbtion levels due to different wavelengths of UVdifferent wavelengths of UV

UVA is completely transmitted UVA is completely transmitted through ozonethrough ozone

UVB is partially transmitted through UVB is partially transmitted through ozone.ozone.

UVC is totally auttenuated by ozone.UVC is totally auttenuated by ozone.

Ozone Absorption cont.Ozone Absorption cont.

““Screening” effectScreening” effect

Ozone peak absorption between 250 and 280 nm (2500Å – Ozone peak absorption between 250 and 280 nm (2500Å – 2800Å)2800Å)

Absorption Cross SectionsAbsorption Cross Sections

Elements and compounds absorb Elements and compounds absorb certain wavelengths of light unique certain wavelengths of light unique to eachto each

Ozone (OOzone (O33) absorbs primarily UVB ) absorbs primarily UVB and UVCand UVC

The wavelengths of light (energy) The wavelengths of light (energy) absorbed is referred to as an absorbed is referred to as an absorption cross sectionabsorption cross section

Atmospheric Cross SectionsAtmospheric Cross Sections

Ozone Absorption Cross SectionOzone Absorption Cross Section

Y-axis: absorption cross section in Y-axis: absorption cross section in cmcm22/molecule/molecule

X-axis: light wavelength in nm (10Å)X-axis: light wavelength in nm (10Å) Hartley band 2100Å - 3800ÅHartley band 2100Å - 3800Å Effectively creates a light “screen” that blocks Effectively creates a light “screen” that blocks

light at certain wavelengths better than otherslight at certain wavelengths better than others

Air massAir mass

m=m=sec sec Determined from the prerecorded Determined from the prerecorded

solar zenith angles.solar zenith angles. Expresses the path length Expresses the path length

transversed by solar radiation to transversed by solar radiation to reach the earth’s surface.reach the earth’s surface.

Measuring OzoneMeasuring Ozone

Typical unit of ozone thickness is the Typical unit of ozone thickness is the Dobson Unit (DU)Dobson Unit (DU)

Defined such that 1 DU is .01 mm Defined such that 1 DU is .01 mm thick at STP and has 2.687e16 thick at STP and has 2.687e16 molecules/cmmolecules/cm22

STP is temperature and pressure at STP is temperature and pressure at Earth’s surface (avg.) 101.325 kPa, Earth’s surface (avg.) 101.325 kPa, 298 K298 K

Payload DesignPayload Design

Electrical SystemElectrical System Mechanical SystemMechanical System Detection ArrayDetection Array Power SystemPower System Thermal SystemThermal System

Electrical DesignElectrical DesignThe photodiode signal The photodiode signal

conditioning circuit is conditioning circuit is intended to amplify the intended to amplify the output of the photodiode to a output of the photodiode to a readable analog voltage readable analog voltage signal which is then signal which is then algebraically summed and can algebraically summed and can be measured by the ADC be measured by the ADC included on the BalloonSAT included on the BalloonSAT board. The combined board. The combined summing-amplifier circuit is summing-amplifier circuit is built to operate on a built to operate on a 9Volt 9Volt dual supply power source in dual supply power source in the form of dual 9 Volt the form of dual 9 Volt batteries. Power for the batteries. Power for the payload is controlled by a payload is controlled by a DPDT toggle Master switch, DPDT toggle Master switch, which resides on a discrete which resides on a discrete circuit board with the main circuit board with the main fuses.fuses.

Mechanical DesignMechanical DesignThe payload mechanical design will The payload mechanical design will

be a cube approximately 16.5 cm be a cube approximately 16.5 cm to a side. This size is optimum to a side. This size is optimum allowing sufficient space for allowing sufficient space for electronics as well as the electronics as well as the insulation. A removable construct insulation. A removable construct is used to house the internal is used to house the internal components.components.

A shelf of foam board 10 cm by 12.5 A shelf of foam board 10 cm by 12.5 cm with a 6.25 cm by 5cm hole in cm with a 6.25 cm by 5cm hole in the center will hold the the center will hold the BalloonSAT. A lidless box of BalloonSAT. A lidless box of dimensions 6.25 cm by 6.25 cm dimensions 6.25 cm by 6.25 cm and 6.25 cm tall will house the and 6.25 cm tall will house the batteries and heating element. batteries and heating element. The box will be sized to fit snuggly The box will be sized to fit snuggly into the BalloonSAT shelf in order into the BalloonSAT shelf in order to keep all components close to to keep all components close to the heat source to maximize heat the heat source to maximize heat distribution by conduction and distribution by conduction and radiation.radiation.

Detection ArrayDetection Array

This system’s goal is to This system’s goal is to collect digital data of UV collect digital data of UV intensity in a specific intensity in a specific wavelength range which wavelength range which will then be correlated to will then be correlated to effective ozone coverage. effective ozone coverage. The sensors’ wavelength The sensors’ wavelength range is 2250 Å to 3200 Å range is 2250 Å to 3200 Å with peak sensitivity at with peak sensitivity at 2800 Å. The photodiodes 2800 Å. The photodiodes are arrayed evenly around are arrayed evenly around the payload exterior, one the payload exterior, one per corner.per corner.

Power SystemPower System

Our payload will operate Our payload will operate on four 9V, 1200 mAh on four 9V, 1200 mAh batteries that are batteries that are capable of operating capable of operating in temperatures as in temperatures as low as 233K. Two low as 233K. Two batteries will power batteries will power our opamp circuit, one our opamp circuit, one will power the heater, will power the heater, and a fourth will and a fourth will power the BalloonSAT power the BalloonSAT itself.itself.

Thermal SystemThermal SystemThe temperature control system The temperature control system

will consist of low mass will consist of low mass battery/resistor array that will battery/resistor array that will be activated by the be activated by the BalloonSAT when internal BalloonSAT when internal temperatures reach 283K or temperatures reach 283K or lower.lower.

Heat will be distributed though Heat will be distributed though the payload primarily through the payload primarily through conduction. The heating conduction. The heating array will be placed in array will be placed in immediate contact with power immediate contact with power supply for the BalloonSAT to supply for the BalloonSAT to keep the battery at an keep the battery at an optimum operating optimum operating temperature. A heat sink will temperature. A heat sink will be attached to the heating be attached to the heating elements to distribute the elements to distribute the heat to the BalloonSAT heat to the BalloonSAT components.components.

Sensor CalibrationSensor Calibration

We calibrated our mercury We calibrated our mercury emission at Stennis Space emission at Stennis Space Center using a 1000 watt Center using a 1000 watt quartz-halogen tungsten quartz-halogen tungsten coiled-coil filament lamp coiled-coil filament lamp Standard of Spectral Standard of Spectral Radiance and a .320 m Radiance and a .320 m spectrograph/monochromaspectrograph/monochromator using a diffraction tor using a diffraction grating with 600 grating with 600 grooves/mm blazed at 300 grooves/mm blazed at 300 nm. This standard was nm. This standard was calibrated according to calibrated according to NIST standards to ±2.23%. NIST standards to ±2.23%. Our mercury lamp was Our mercury lamp was calibrated to within ±.25Å.calibrated to within ±.25Å.

Hg Calibration

0.00E+00

1.00E-03

2.00E-03

3.00E-03

4.00E-03

5.00E-03

6.00E-03

7.00E-03

8.00E-03

9.00E-03

1.00E-02

250 260 270 280 290 300 310 320

Wavelength (nm)

Calibration cont.Calibration cont.

Using our calibrated Using our calibrated source we were able source we were able to determine a voltage to determine a voltage change based on our change based on our photodiodes’ exposure photodiodes’ exposure to a known intensity. to a known intensity. The summed intensity The summed intensity of all four photodiodes of all four photodiodes was shown to be was shown to be approximately .374 V approximately .374 V when exposed to when exposed to intensities of ~.008W; intensities of ~.008W; therefore, the average therefore, the average voltage change per voltage change per photodiode is .094 V. photodiode is .094 V.

Data AnalysisData Analysis

In essence we will correlate voltage changes In essence we will correlate voltage changes to changes in the UV intensity that is to changes in the UV intensity that is detected by our photodiodes. This will detected by our photodiodes. This will provide us viable data that will be used in provide us viable data that will be used in eq. 2 to determine the column amount of eq. 2 to determine the column amount of ozone. From that column amount it will be ozone. From that column amount it will be an easy step to determine the thickness of an easy step to determine the thickness of the ozone layer.the ozone layer.

Tracking the changes in UV intensity Tracking the changes in UV intensity through the end of flight will also allow us through the end of flight will also allow us to “map” the ozone density through our to “map” the ozone density through our maximum altitude of 30km.maximum altitude of 30km.

Expected ResultsExpected ResultsThe flight profile will take us up The flight profile will take us up

from 0 to 30km in from 0 to 30km in approximately 90 minutes. As approximately 90 minutes. As we climb in altitude we we climb in altitude we naturally expect to see in naturally expect to see in increase in UV intensity as our increase in UV intensity as our payload rises above greater payload rises above greater amounts of atmosphere. The amounts of atmosphere. The largest change should be seen largest change should be seen at about 15km and increase as at about 15km and increase as we reach our flight peak of we reach our flight peak of 30km.30km.

The curve shown on this graph The curve shown on this graph represents ozone density as a represents ozone density as a function of altitude; using ozone function of altitude; using ozone coverage estimates for the area coverage estimates for the area of 31.78°N and 95.72°W of 31.78°N and 95.72°W provided by NOAA and taken provided by NOAA and taken over the last 3 years during this over the last 3 years during this week we should see week we should see approximately 305 DU of ozone approximately 305 DU of ozone coverage.coverage.