Its seems fog/smog is already very heavy earlier this year than usual. DEL hast Cat IIIb in place nicely, allowing landing for low vis consistently, but traffic backs up due to spacing requirements. I monitored the METAR for DEL/VIDP last week in preparation and looked at flight radar to see what was going on. Luckily the day I was flying had better visibility:

http://www.aviationweather.gov/metar...ate=0&hours=36

Sadly the diversion airports (ATQ & LKO) used during fog congestion at DEL didn't get the Cat IIIb upgrade this year in time, instead the works in progess forced them to loose existing Cat II clearance and are now no longer available as diversion airports