The solar irradiance for infrared radiation at a solar altitude of 25 degrees can be calculated using the following formula: [ \text{Solar Irradiance} = \frac{\cos(\alpha)}{\cos(90^\circ - \alpha)} \times I_0 ] Where: (\alpha) is the solar altitude (given as 25 degrees). (I_0) is the total irradiance at the top of the atmosphere (given as 1350 W/m). Let's plug in the values: [ \text{Solar Irradiance} = \frac{\cos(25\circ)}{\cos(90\circ - 25^\circ)} \times 1350 , \text{W/m} ] First, calculate the cosine values: [ \cos(25^\circ) \approx 0.9063 ] [ \cos(90^\circ - 25^\circ) = \cos(65^\circ) \approx 0.4226 ] Now compute the solar irradiance: [ \text{Solar Irradiance} \approx \frac{0.9063}{0.4226} \times 1350 , \text{W/m} ] [ \text{Solar Irradiance} \approx 2900 , \text{W/m} ] Therefore, the solar irradiance for infrared radiation at the horizontal level on the Earth's surface with a solar altitude of 25 degrees is approximately 2900 W/m12