Science Buddies: "Ask an Expert"

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?

ET is the "Extraterrestrial constant" which is determined for your instrument by using the calibration procedure. Yes, I do think you need to measure the sun's angle as a part of the calibration procedure, and to determine the air mass, m.

Here is an explantion of how you calculate the air mass term, m.
http://hop.concord.org/lph/lph.concepts.html

"ln ET" is sometimes written as "ln(ET)", which in plain english is "the natural logarithm of ET". If you need more help with that, I would suggest making a post in the mathematics forum, where they will give you a very thorough explanation.

well today i went to a physics teacher and he gave me the average air mass so i might use that because i dont think i can measure the suns angle. and the ET, i dont realy understand all that well. its the constant of the monitor? is that the reading when i put a dark object over the hole that the sunlight goes through?

Gabby, there is no generic "average" air mass of the type that is needed for this equation. This air mass in the equation is normalized to 1 atmosphere thickness, so it will depend on the time of year, time of day, and latitude. More info is provided on those web pages that are linked in previous posts.

Yes, you can think of ET as a constant of the monitor. Here are three ways to calculate the value:
http://hop.concord.org/lph/lph.concepts ... chor967681

Hi,
I have now purchased everything I need for the project including one extra "op. amp" and an extra LED. I got these because "going forward" section suggested that I could measure some other wavelength using these extra components. Now, I am wondering where can I get instructions for adding these components into the haze monitor .... How do I get to measure another wavelength of light ? My project is due on first week of February.

Any suggestions/pointers would be much appreciated .
Thank you.

Hi,
I have now purchased everything I need for the project including one extra "op. amp" and an extra LED. I got these because "going forward" section suggested that I could measure some other wavelength using these extra components. Now, I am wondering where can I get instructions for adding these components into the haze monitor .... How do I get to measure another wavelength of light ? My project is due on first week of February.

Any suggestions/pointers would be much appreciated .
Thank you.

[quote="nxg"]Hi,
I have now purchased everything I need for the project including one extra "op. amp" and an extra LED. I got these because "going forward" section suggested that I could measure some other wavelength using these extra components. Now, I am wondering where can I get instructions for adding these components into the haze monitor .... How do I get to measure another wavelength of light ? My project is due on first week of February.

Any suggestions/pointers would be much appreciated .
Thank you.
[/quote]

I am very sorry, While trying to delete my first post [ which I could not finally] -- I ended up posting it thrice. Seems like there is no way to delete it.

Thanks.

I am unable to figure out where the 4 terminals are [referred to in step 4 of "Prepare the switch".
Please help ASAP.

Thanks.

Finally, I have built the first version of it and I think it is working. But would love to add another LED and op amp to add a new feature but I need help.
Can someone please point me to the right direction ?

Thanks,
nxg

Sorry - I'm not adept at electronics. I'll see if I can find somebody to help.

HELP!!!! i have all the sun angles now but i dont know where to go from there. what equation do i need for air mass because i need to air mass to find the 1n ET. my project will be late but i have just been stuck on this one thing and if there is an equation is there a place where i can just enter my data and it automatically give me the air mass.???

well while im here let me tell you how and where i got the angle of the sun. http://www.susdesign.com/sunangle. soooooo how do i get the air mass with the angle? all the places i went to want the pole height and shadow length and then put that in a formula and BAM you got your air mass. pleeeze im desperate![/url]

"The air mass m for each of your measurements is 1 divided by the sine of the Sun's angle."

http://hop.concord.org/lph/lph.concepts.html

The xls speadsheet refers to some year code, the year code for 2007 is not provided. Can someone please provide me that and let me know what is it ?

Thanks,
nxg

The year code for 2007 should be 2557. In this case, it is the number of days elapsed between 1/1/2000 and 1/1/2007.