What is User Development Fee and why User Development Fee is charged? What is PSF and why PSF is charged? What are the charges/fees levied to passengers by private airports / JVS for development / upgradation of airports?

Greenfield airports like Hyderabad and Bangalore are levying User Development Fee (UDF) from embarking passengers to fund viability gap of these airports. DIAL and MIAL have also been authorised by the Government to levy UDF from embarking passengers at Delhi and Mumbai airports to fund modernization of Delhi and Mumbai airports.