What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?

(N/A) Delhi was categorized as the fourth most polluted city in the world. The burning of fossil fuels significantly contributed to air pollution in Delhi.
Various steps were taken to improve the air quality in Delhi:
$1$. Introduction of $CNG$ (Compressed Natural Gas): By the order of the Supreme Court of India,$CNG$-powered vehicles were introduced by the end of $2006$ to reduce pollution levels. $CNG$ is a cleaner fuel that produces very few unburnt particles.
$2$. Phasing out of old vehicles.
$3$. Use of unleaded petrol.
$4$. Use of low-sulphur petrol and diesel.
$5$. Use of catalytic converters in vehicles.
$6$. Application of stringent pollution-level norms for vehicles.
$7$. Implementation of Bharat Stage $II$ (equivalent to Euro $II$ norms) in major Indian cities.
Yes,the introduction of $CNG$-powered vehicles has improved Delhi's air quality,leading to a substantial fall in the levels of $CO_2$ and $SO_2$. However,the problem of suspended particulate matter $(SPM)$ and respiratory suspended particulate matter $(RSPM)$ still persists.