"To reach the surface" means to move from a lower position or level to a higher one, such as going from underwater to above water or emerging from underground. Full definition
The small ash particles decrease the amount of sunlight reaching the surface of the earth and lower average global temperatures. (scientificamerican.com)
Experts said certain types of aerosol emissions cause a strange cooling effect to the climate by blocking solar radiation from reaching the surface of our planet. (techtimes.com)
Smaller satellites burn up completely before reaching the surface. (businessinsider.com)