Science Buddies: "Ask an Expert"

My mom downloaded a science project for me "how to monitor atmospheric haze". It's using Forrest M. Mims III atmospheric haze sensor that we can build ourselves using a videocasseste case and various other items. My problem is that aside from the video cassette case and the radio shack green LED #276-022a, there are no specific details on the remaining parts. I have a picture that shows everything that goes in the case, but it doesn't tell me what KIND of resisitor, or operational amplifier, wires, or even how to build it (i.e. weld, superglue, screw in, etc.). My mom and I have tried to find the specifics online, but we haven't had any luck. I will have to do another science project (even though I have already turned my topic in to my teacher) if I don't get specific intructions on what to buy and on how to build this. My mom has spent almost $50, and we though this would be an inexpensive project that would be fun and educational (especially since we live in California where haze seems to be a natural thing lately.) Please, someone tell me where to go for the specifics on this project. If I have to buy a book, then I guess I will have to change my project.

Thanks for your help>

Hi Michael,

What website did you use to get information on the atmospheric haze detector? Let me know and we will probably be able to suggest specific information so you can build your detector.

This sounds like an good idea for a project. Assuming you will be able to complete your detector, what type of experiment were you planning to do?

Donna Hardy

We purchased the idea from http://www.scifair.org/projects/. (Dr. Shawn Carlson's website). I really want to do the experiment, but only if I can build it myself. I have found a haze sensor on ebay, but I would rather put it together myself if possible. My science fair question is how much does haze vary in the atmosphere?

Hi there,

Here is a website that has instructions on how to build a device for measuring haze - it has step by step instructions and figures.

http://haze.concord.org/spbuild.html

Maybe this will help,

Mary

Hi Michael,

The website suggested by Mary appears to have enough detail to complete the project, but please do let us know if you need more information on building the atmospheric haze detector. And please ask questions if you have any questions about designing an experiment.

Donna Hardy

Thank you all for your help, the web site was cool. I think I'll be able to do this project after all. I am excited to get started. "Ask the expert" is a neat place to ask questions, and I am sure I'll be back. Thanks again, and if I have any more problems, I'll let you know.

Hi everyone,

I am doing my 7th grade science project on haze and using the TERC VHS-1 as described in the manual "http://haze.concord.org" that I learned about from my previous post to this website. I got the original idea from one of those science project websites. I really liked building the sunphotometer and collecting all the data, but now I am not sure how to work the formulas very good.

I don't understand the AOT formula very good. First, I don't have a barometer and I couldn't find a chart on the web to measure it for my area (Corona, California). Also, I am not sure I understand how to calculate the data I got from my TERC into the AOT formula. I did get the formula to find the angle of the sun, but I am unsure how to get the air mass. I have been collecting data for 3 weeks, and my project is due next week. Could anyone help me understand the formula's better?

The spreadsheet on this website won't open or download, and I would rather use my calculator for my project (to get a better grade). I guess I need a step by step, but in easier steps, I would like to graph it manually and using my mom's MS software, but I don't understand the formula's or description in the manual well enough. Is there an easier way to analyze the data, or a simpler method/ formula?

My project is due next week and my mom is mad at me because I didn't read the entire manual before starting the project. Help, please! I need to know my location's sea level, (Corona, California), and atmospheric pressure for this area. (Or where I could find this information.)

I have emailed the haze span website moderator for instruction and also the guy from the "Properties Of The U.S. Standard Atmosphere 1976" website for assistance, but I haven't gotten anything back from them yet.

I hope someone can help me.

Here are the formula's and some of the intructions regarding the formula's:

"AOT = (ln ET - ln signal-(0.117 x m) x (p/1013.25))/m

where, ln ET is the ln of the extraterrestrial constant for the TERC VHS-1, ln signal is the ln of the signal measured by the TERC VHS-1, 0.117 is the AOT caused by Rayleigh scattering in the atmosphere at 525 nm, m is the air mass, and p is the atmospheric pressure for your location in millibars. If your barometer indicates inches of mercury instead of millibars, change (p/1013.25) to (p/29.92). If you don't have a barometer, you can use the U.S. Standard Atmosphere to estimate the mean p for your location's elevation above sea level (you can round the value for pressure to the nearest integer value without affecting your AOT results): "

Also, the following pertains to the sun's angle and air mass:

"6. Record the length of the shadow, the date and the exact time of your measurement in your notebook.

7. The tangent of the sun's angle above the horizon is the length of the upper vane divided by the length of the vane's shadow. Use a calculator to find the tangent of the angle.

8. When the tangent is displayed in the calculator's readout, press the cotangent (TAN^-1) key to find the Sun's angle in degrees above the horizon. Enter the angle in the notebook."

I understand the formula for find the angle of the sun: TAN 0= a/b where a is always 25mm (the height of my bracket used to find the angle of the sun) and b is the measurement taken using the shadow method described on the haze website.

Then it gives me another formula to find the air mass: Air mass (m)= 1/SIN 0 . I think that means 1 divided by the number you get from the TAN 0=a/b formula then hit the SIN-1 button on my scientific calculator.



I hope you can help me, I don't want to leave the project half done, and I am really curious about the results.

Thanks,
Michael

Hi there,

Here are a few things to help you get started:

elevation:
Corona, California is 678 ft above sea level (see http://www.usacitiesonline.com/cacountycorona.htm)

atmospheric pressure:
Here are a couple of sites that give you atmospheric pressure and a conversion based on height (barometric formula):

http://hyperphysics.phy-astr.gsu.edu/hb ... n.html#atm
http://hyperphysics.phy-astr.gsu.edu/hb ... or.html#c1

As you will see on the first site standard atmospheric pressure is:
1 atmosphere = 760 mmHg = 29.92 inHg = 14.7 lb/in2 = 101.3 KPa

Then on the second site:
If you enter P0 = 29.92 inHg into the formula on this website and h=678 ft then the resultant atmospheric pressure (Corona, Californa 678 ft above sea level) is 29.22 inHg

You now need to convert this value 29.22 inHg to ___millibars. Use the following conversion 29.22 X 33.8639 = 989.5 millibars

See the following article for conversion factors:
http://www.wrh.noaa.gov/slc/projects/wx ... ersion.pdf

So now you have a value for p (=989.5 millibars)

I recommend that you do this calculation yourself to double check my math and so that you understand how you calculate this value.

I will see wat I can find out about air mass (m) and post any helpful information that I can find.

Good luck and contact us if you need more help.

Mary

Hi again,

Here is a link to an article that explains in detail about relative air mass:

http://www.globe.gov/tctg/airmass.pdf?sectionId=23

Have a look at it as it has some good diagrams showing the different measurements needed to calculate relative air mass. It gives a good explanation of the math you need to do to calculate m.

Please post any further questions you have and good luck!

Mary

Thank you again for helping me...you are life savers (grade savers!) Mom's definately glad that I got the help I needed and I appreciate your quick responses. I know that I'll be using this site again and I'm glad I did this experiment (even though it's been alot of work).
Thanks!

You're very welcome! And congratulations on completing your experiment! Feel free to post again and let us know how it all turns out.

Mary

I am looking for the spreadsheet to calculate the data for the AOT of atmospheric haze. However, the link that to it is broken. ftp://ftp.concord.org/pub/haze/vhs1-download/ I believe that the link should have an http:// instead of ftp in front of it, however the first link does not load, and the second says it no longer exists. Does anyone happen to have this spreadsheet saved onto their computer, or does anyone know where i can find this spreadsheet on the web. My project is due on the 27th of this month and i would really like to have my data analyzed rather soon.
Thanks in advance,
Brett

I can access that ftp directory without a problem. The site is pretty slow, and connectivity seems spotty, so you may have to be patient.

"FTP://" is correct. "FTP" stands for "file transfer protocol." FTP servers are used for transmitting files to be used in secondary applications (like excel) without the sort of processing and interpretation that a web browser does with hypertext (http="hypertext transfer protocol"). Most (but maybe not all) web browsers support FTP downloads in addition to HTTP downloads.

Let us know if you continue to have a problem getting that file. I can upload it to another server if all else fails.

p.s. For reasons unkown, there is an Excel version of that spreadsheet available here:

http://tellus.ssec.wisc.edu/GIFTS/VHS_V1R4.XLS

Maybe someone else had the same problem.

Ok thank you very much for the link. When i would go the link, it would just hang there and nothing would happen, with a white screen. This is most likely due to the fact that i have dial up, but I have the spreadsheet now.

Thanks

Glad I could help. Let us know if you have any questions about that spreadsheet.

Hi again,
Ive been having a big problem with this spreadsheet. Ive entered all of the data that is required such as the latitude, year code, barometric pressure, sunlight voltage, etc. etc. blah blah blah. However, the AOT on many of the measurments becomes negative. All of my other variables seem fine and correct. This is the only thing wrong with it. If anyone would like to see the spreadsheet let me know, i dont know how to make an attachment on this forum though. My project is due Monday and i dont really know what to do here.
PLEASE SOMEONE HELP QUICKLY!!!
Ive been reading, correcting, researching, analyzing, and calculating all day and i really need some help here. Thanks in advance.

Can you post here the values you entered for one of the measurements that yielded a negative AOT?

im am building the haze detector as well and i have used allt he links given to other students but i am planning to measure if temperature affects haze. i was wondering if you would know because i dont want my projects to be a complete flop. i also wanted to know how often you have to measure. i dont have time to measure every 20 mins. i am in school most of the day. i was hoping to measure at only certain times of the day like in the morning, noon, and afternoon. 3 or four times a day. would that work??

ok im doing the atmostpheric haze detector as well and i wanted to measure if temperature affects haze. I need an official topic soo and i don't want my idea to be a flop when it comes to gathering my data. i also wanted to know if you have to measure the haze every 20 mins. like it said. i wanted to measure it 4 times a day but im not sure if doing that will affect the data in a bad way. please help me!

Hi Gabby,
It should be fine to take 4 measurements per day, as long as you take measurements on enough days to get sufficient data to test your hypothesis.

I don't know whether you will be able to measure a correlation between temperature and haze, but it sounds like an interesting experiment. If you are worried that you might not find meaningful results with a comparison of temperature and haze, then perhaps you should collect other meteorological data as well, such as barometric pressure.

Chris

well in a websire i went to it said that some scientists think that increased haze over the northern hemisphere has cause a slight cooling effect because haze scatters some sunlight back into space. if there isn't a dramatic change in haze vs. temperature does that mean that at the scince fair it will be counted against me in some way?

where can i get something to measure barometric pressure?

The easiest way to get barometric pressure data would be to get measurements off of the web. For example, if you go to http://www.noaa.gov and type in your city and state abbreviation in the upper left, you will be sent to page that shows a variety of current meteorological data for your area. You could also buy a barometer if you want to make the measurements yourself.

When they say a "slight cooling effect", they are talking about very small changes happening over a long time and a very large area (the hemisphere). These would probably not be measurable in a short-term science fair project. More likely, if you observe a correlation between haze and temperature, it will relate to shorter term and smaller scale variations that might result from things like the amount of moisture in the atmosphere associated with high pressure or low pressure systems.

one more quick question.
will my data be messed up if i measure in different places? i wanted to measure at the school but christmas break is right around the corner so i thought i would measure it outside my house during the break. good or bad?

I doubt there will be any difference in measurements, unless you live in a place that has very distinct micro-climates, like San Francisco. However, it is always best to be consistent or to account for any necessary inconsistencies. You could take a few measurements at school and at home at a time when conditions aren't changing much to verify whether the measurements at school are similar to measurements at home.

ok well my detector is built and i dont know what to do next... do i just need the voltage or do i need to do that special formula? if all i need is the voltage on my paper should i organize it into columns with date, time, temp, barometric pressure, and the voltage??

i accidently clicked stop watching this topic link. oops so im jst sending another message to make my account jump back in. but same question as before is the voltage measurement, date, time, temp, pressure, and weather condition all i need for my data notebook because i've seen some other topic reply and there talking about a formula or something.

Hi Gabby,
Congrats on building the detector.

As far as I can tell, yes, those are the data you need. Then, to make the data useful, you will need to calibrate your instrument and convert your voltage measurements to standard Aerosol Optical Thickness (AOT) units.
This page explains how to calibrate your instrument:
http://haze.concord.org/calibrate.html
This page gives the equation to convert your measurements to AOT units.
http://haze.concord.org/formula.html

I hope that helps.
Chris

yes it make a little more sense but im having trouble understanding the formula.

AOT= [1n ET - 1n signal - (0.117 x m) x (p/1013.25)]/m

okay i have no idea what 1n signal is or what 1n is in general. i know m is air mass (where to I found out how much that is for my area?)and p/1013.25 is the barometric pressure. and is it necessary that i measure the sun angle?

ok it hink i figured a little more out. 1n ET is the dark signal and 1n signal is the sun signal? but i'm still having trouble figuring out how to get the air mass. and is it necessary that i measure the sun's angle?