Buy a quality mask from the US. Pollution in Kathmandu is outrageous. You will literally see thick fog of pollution in front of you. Public transportation in Kathmandu is like going to a war. Be prepared ! Also, 40 days after 15 years doesn't seem adequate time for me. It will pass so quick that you will wonder what the heck I did on those 40 days! Treat your 20 rupees as 5 rupees. Take some time to visit Pashupatinath. Whatever is your reasons to visit Nepal, one thing is certain: You will enjoy your visit no matter what the pollution is, no matter the country is poor, no matter the politics is bad and no matter whatever !

Mother tongue and mother land are the givers of happiness - Rig Veda.