Note: I cannot verify its accuracy and authenticity.
Also, the Department of Environment has setup two stations in the valley to monitor air quality. The real-time data is put up here.
Anyway, analyzing these data as done here (8 months ago) could help form a better though primitive picture.
Still, the shortest and probably the most accurate answer would be: almost all of the major places in Kathmandu. The valley is choking. And so are we.ANSWERS： Most of the places, as KMC is extending road, there is dust pollution every where . Some notable places could be , Balkhu, Kalimati, Kalanaki, SamakhusiANSWERS： Bouddha, Jorpati, Chabahil, Kalimati, Kalanki, Jamal.ANSWERS： Thanks for A2A
Balkhu, Kaliamati, Kalanaki, Mitrapark, Chabhil.