> In 1995 I went to downtown LA. The air looked like your picture of the Red Fort. In LA at the time I could not see more than 2/3 of a mile.

Delhi and LA have similar problems in that they are both at the foothills of a mountain range (in Delhi it's the Aravali mountains). This makes it much more difficult for the pollution to dissipate once it's there, because the mountains obstruct wind and airflow. LA has been making efforts for decades to reduce emissions, but the payoff has been incredibly slow for this reason.

Of course, Delhi is a much larger and densely populated city - the Delhi metro area has almost the same population as the entire state of Texas - and it's also nowhere near as wealthy as LA. All three of those factors make it much harder to address pollution directly and much slower for the benefits to actually start manifesting.