In the Visual band, the atmosphere on a clear night is good for about 0.2 magnitudes of optical extinction per airmass. At 10 degrees elevation, you are at an airmass of 1/sin(10) = 5.7 so the extinction = 5.7 x 0.2 = +1.1. So, a +5.0 magnitude star will appear as a +6.1 magnitude star etc.