Change Padding of Third Column

Hey guys,
I have a three column portfolio an I am trying to change the top padding of each column individually, so the pics are more randomly distributed accross the page.

I managed to change the padding of the first column with this:

.no_margin.av_one_third.first {
padding-top: 120px;
}

but I cant address the second and the third column in the same way.. (trying to put .second and .third instead of .first)

this is my project site:

http://ernst-inc.com/mark-braun/

thanks for your help!
Mark