Air quality over the national capital crossed the 500 mark on November 3. Delhi’s Air Quality Index (AQI) is now in the ‘hazardous’ category, which is harmful to people’s health.

At 5 am, a thick layer of smog enveloped the national capital and the AQI soared to 507, taking PM2.5 levels in Delhi-NCR over 65 times the limit prescribed by the WHO, according to data from the IQAir website.

Delhi is now the second most polluted city in the world, according to IQAir data. AQI levels rose from 327 to 507 in 12 hours in the national capital.

Aditya, a resident of Delhi told ANI, “It is very difficult to breathe…this is not the time to go out and exercise…”

Weather stations have been recorded at Alipur, Anand Vihar, Ashok Vihar, Bawana, Burari, IGI Airport, Dwarka, Jahangirpuri, Mundka, Narela, Patparganj, Rohini, Mandir Marg, Nehru Nagar, RK Puram, DITE Okhla, Najafgarh and other stations of weather monitoring “hazardous” air quality, according to Central Pollution Control Board (CPCB) data.

Particulate matter (PM2.5) pollution is a concern when levels in the air are unhealthy. Breathing unhealthy levels of PM2.5 can increase the risk of health problems such as heart disease, asthma and low birth weight.

Delhi’s IQA remained “very poor” at 321 on November 2. A day before, the IQA in the national capital was recorded at 359. Several areas in Delhi experienced firecrackers blast including Lajpat Nagar, Kalkaji, Chhatarpur, Jaunapur, East of Kailash, Saket, Rohini, Dwarka, Punjabi Bagh, Vikas Puri, Dilshad Garden and Burari.

After Diwali on October 31, Delhi’s AQI on November 1 was recorded to be around 14 times the limit recommended by the World Health Organization (WHO).

The concentration of PM2.5, a major pollutant, in Delhi at 8 am was measured at 209.3 micrograms per cubic metre, according to data from the Central Pollution Control Board (CPCB). WHO guidelines specify a permissible limit of 15 micrograms per cubic meter over a 24-hour period.

An AQI, which is a ratio of air quality in a region, is considered “poor” between 200-300, “very poor” at 301 and 400, severe at 401 and 450, and above 450 is “severe-plus” and can cause harmful health problems to residents.