Ozone is most effective at absorbing radiation at the 250 nm wavelength. In fact, it is 100 times more efficient at 250 nm than it is at 350 nm. After ozone absorbs this shortwave radiation, it reradiates it at generally longer wavelengths which initially goes in all directions. Some is reabsorbed by other atmospheric constituents, some makes it to Earth's surface, and some returns to space. The net effect, however, is an increase in temperature in the upper stratosphere.
Many factors affect the amount of uv radiation that reaches Earth's surface.
The sun's angle from the vertical or solar zenith angle, is determined by the latitude, time of year, and time of day. In the Northern Hemisphere, the sun shines directly overhead at noon at the Tropic of Cancer on the first day of summer, at the equator on the first day of spring and autumn, and directly overhead at the Tropic of Capricorn on the first day of the winter. As a point moves farther from the latitude where the sun shines directly overhead, the radiation must travel a longer path through the atmosphere to reach the point. With a longer path length, there is an increased opportunity for the incoming radiation to be absorbed or reflected back into space by atmospheric constituents. During winter, as you approach the pole, the solar zenith angle increases, and the length of the day decreases.