http://en.wikipedia.org/wiki/Phippsburg,_Maine


https://apps.carleton.edu/curricular/geol/ Location: Minnesota
Advisor to the study below:
Bereket Haileab
Professor of Geology, Geology
Office: Mudd Hall 162
Phone: 507 222 5746
Email: bhaileab@carleton.edu
https://apps.carleton.edu/profiles/bhaileab/

"Fluoride 0 mg/L
Chloride 0,8269 mg/L
Bromide 0 mg/L
Nitrite 0 mg/L
Nitrate 0,5302 mg/L
Phosphate 0 mg/L
Sulfate 0,6654 mg/L"
Root, Ellen; Jones, Whit; Schwarz, Bessie; Gibbons, Jack
Rainwater Chemistry Across the United States, November 22, 2004
http://www.people.carleton.edu/~bhaileab/environmentalgeology/RainWater.pdf
Location of the sample: page 18
Content of the sample: page 21

Method:
"Anion Concentrations
We analyzed our samples for seven anions using the Ion Chromatograph (For a sample readout from the Ion Chromatograph, see Figure 3 in Appendix). Of the seven nations we analyzed for, fluoride and bromide were not present in any of the samples (see Figure 4)." page 8

This means it was not looked for other substances except those declared for. The reason of this way of research is the research interest. If the focus of the research interest is looking for causes of forest dying it will look into the biology of the forests and how it could be effected by common human influence. There is no thought on a possible conspiracy or secret circumstances for whatever reason. At least, this will be the case of some college students probably - and at that time. And of course, if you don't know what to look for, the research gets even more expensive until you know what is all in the air. It is a little bit like with the electromagnetic frequency spectrum which is also huge.