First, a PSP is extremely sensitive to thermal imbalance issues, so that its offset needs correction. See http://www.sciencedirect.com/science/article/pii/S0038092X08001813
Then, you need other sources of data, since you need to compare your measurements to what the surface radiation would be without aerosols. There is an abundance of publications on this topic. See e.g. https://www.researchgate.net/publication/249312655_Aerosol_properties_and_radiative_forcing_over_Kanpur_during_severe_aerosol_loading_conditions
You also need a measurement of aerosol optical characteristics from satellite remote sensing or (better) by a ground-based sunphotometer.
Article Aerosol properties and radiative forcing over Kanpur during ...