The air quality in the national capital slipped to "very poor" category on Friday with Air Quality Index at 301 as at 7 am, according to Central Pollution Control Board.
A thin layer of dust and smog engulfed the city after spells of rainfall and thundershowers earlier this week brought a brief improvement.
An AQI between zero and 50 is considered "good", 51 and 100 "satisfactory", 101 and 200 "moderate", 201 and 300 "poor", 301 and 400 "very poor", 401 and 450 "severe" and above 450 "severe-plus".
Alipur, Anand Vihar, Ashok Vihar, Mathura Road, DTU, Dwarka Sector-8, Jahangirpuri, and Okhla were some of the most polluted areas in the city with AQI above 301.
Mundka and Wazirabad recorded even higher levels of pollution with AQI above 400.
| Station | AQI |
| Alipur | 352 |
| Anand Vihar | 362 |
| Ashok Vihar | 328 |
| Bawana | 289 |
| Burari Crossing | 243 |
| CRRI Mathura Road | 344 |
| DTU | 365 |
| Dr Karni Singh Shooting Range | 290 |
| Dwarks Sector-8 | 338 |
| IGI Airport (T3) | 240 |
| IBHAS, Dilshad Garden | 334 |
| ITO | 218 |
| Jahangirpuri | 353 |
| Jawahar Lal Nehru Stadium | 260 |
| Lodhi Road | 247 |
| Dhyan Chand Stadium | 249 |
| Mandir Marg | 241 |
| Mundka | 406 |
| NSIT Dwarka | 355 |
| Najafgarh | 271 |
| Narela | 311 |
| Nehru Nagar | 264 |
| New Moti Bagh | - |
| North Campus, DU | 324 |
| Okhla Phase-2 | 322 |
| Patparganj | 321 |
| Punjabi Bagh | 311 |
| Pusa, DPCC | 261 |
| Pusa, IMD | 259 |
| RK Puram | 265 |
| Rohini | 338 |
| Shadipur | 326 |
| Siri Fort | 355 |
| Sonia Vihar | 302 |
| Sri Aurobindo Marg | 213 |
| Vivek Vihar | 324 |
| Wazirpur | 419 |
The adjacent NCR cities also logged poor air quality with Gurugram reoprting an AQI of 294, Faridabad 288, Ghaziabad 283, Greater Noida 256, and Noida 289.
The city experienced high levels of pollution with layer of dust on the horizon on Thursday following overnight dust storms. The poor air quality reduced visibility.
According to India Meteoroligcal Department, dust from northern Pakistan advected towards Delhi-NCR across Punjab and Haryana, driven by strong westerly winds over the two states.
On Wednesday, visibility at the Indira Gandhi International Airport dropped from 4,500 metres to 1,200 metres between 10 a.m. and 11:30 pm.
Doctors have advised Delhi residents to exercise caution as the dust can cause long-term damage. The particulate matter can lodge deep in the lungs, potentially causing progressive lung diseases, a Lok Nayak Hospital (LNJP) doctor told PTI.