EDUCATION: URBANMAAP

Aerosols Study: Recording Measurements

Two students should conduct the following activities simultaneously. Repeat the training activities several times to ensure that your team is well trained. Have each team member take the training skill test at the conclusion of these activities.

1. Connect the digital voltmeter to the output jacks of your sunphotometer. Be sure to put the red lead in the red jack and the black lead in the black jack.



2. Turn the voltmeter on



3. Select the DC volts setting (this is the first setting on the voltmeters). Do not use the AC volts setting.



4. Record the time. Time should be reported with an error of no more than a minute, so you should set your watch against a reliable standard. Official United States time can be found on the web at http://www.time.gov. Time is required because analysis of your measurements requires knowledge of the exact position of the sun, which depends on location and time.



5. Switch the sun photometer on. Your voltmeter should give a reading of about 13 or 14 mV. This is the dark current reading. Record the dark current reading. (Note: if your digital voltmeter is on and connected to your sun photometer but the photometer is turned off, you will get unpredictable voltage readings on the voltmeter. This is normal for these devices. When you turn your sunphotometer on, then the reading should produce a stable reading in the indicated range.)



6. Face the sun and point the sunphotometer at the sun. Use the spot marked on the rear alignment bracket as an approximate guide to align the sun. The voltage should increase dramatically to more than 1 V.



7. Adjust the pointing until you see the maximum voltage in your digital voltmeter. This value is the sun-lit current that you will enter on your data form. Record the sun-lit value. (Note: the voltage you read will vary due to small "jiggles" when you point the sun photometer and to real fluctuations in the atmosphere itself. Do not try to average the voltmeter readings. It is important to be consistent about recording only the maximum voltage you obtain during a few seconds of measurement time. Adjusting your sun photometer to obtain the maximum voltage quickly requires some practice. The entire measurement process should not take more than 15 or 20 seconds.)



8. Record the sky condition. Sunphotometer measurements can only be made when the sun is not obscured by clouds. (Note: whenever you try to determine the sky conditions you must never look directly at the sun. Radiation from the sun can seriously damage your eyes!)



9. Record the dark reading and each sun-lit reading onto your data collection sheet Sunphotometer Data Collection.



10. When you are done making measurements, switch the sunphotometer off and turn the voltmeter off. Disconnect the voltmeter.



11. After you have completed making your measurements for the day, collect all the data sheets that students have been recording measurements on to and record your school's daily data on the electronic data form located at http://icp.giss.nasa.gov/education/urbanmaap/aerosols_form.html and be sure to enter your location and instrument number.

Remember, the best times to make your measurements are from 7 to 9 a.m. and from 5 to 7 p.m. when the air mass is changing the fastest.

Taking Care of Your Sunphotometer

Your sunphotometer is a simple and rugged device with no easily breakable parts. However, you must take care of it in order to make accurate measurements. Here are some things you should and should do to make sure that your sunphotometer performs reliably.

Sunphotometer DOs

• DO protect your sunphotometer from dirt and dust by storing it in the sealable plastic bag when you are not using it.
• DO keep your sun photometer switched off when you are not using it. If you accidentally leave your sunphotometer turned on for hours or days when you are not using it, you should let us know about it and we will guide you through what to do.

Sunphotometer DON'Ts

• DO NOT drop your sunphotometer.
• DO NOT expose your sunphotometer to extremely hot or cold temperatures or leave it sitting in the sun.
• DO NOT modify the electronics inside your sun photometer in any way.
• DO NOT enlarge the aperture through which the sunlight enters your photometer. You might be tempted to do this to make it a little easier to point your instrument at the sun. However, the interpretation of your measurements is based on the size of this hole. If you change it, your measurements will be useless.

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