Air quality across the National Capital Region (NCR) worsened on Wednesday with the return of “smog situation” and particle pollution crossing “severe plus or emergency” mark across several locations, officials said.

According to the Supreme Court-appointed Environment Pollution (Prevention and Control) Authority (EPCA), Delhi and surrounding regions will see smog – the noxious mixture of pollutant in the air – for the next few days.

On Wednesday around 3 p.m., the major pollutant PM2.5 – or particle in the air with the diameter less than 2.5mm – was at “severe plus or emergency” level across 11 different locations in the NCR, out of 23 active stations.

The PM2.5 was ranged between 419 and 500 units — 16 to 20 times high than the international safe range.

“What we see in Delhi today is smog and not fog. Delhi will see more smog in the coming days and air quality will deteriorate further,” Shambhavi Shukla, a researcher at the Centre for Science and Environment and EPCA member, told IANS.

According to the India Meteorological Department, the mixing height is gradually reducing in the NCR and the temperature is dropping, which combined with low-speed winds will increase air pollution.

Mixing height is where effluents disperse. If the height is low, pollutant gets less space to disperse.

The Central Pollution Control Board said air quality of the national capital at 4 p.m. was recorded “very poor” with PM2.5 recorded at 244 units.

Meanwhile, at 4 p.m. the regions with “severe or severe plus” air quality include Anand Vihar (PM2.5 500 units) in east Delhi, Shadipur (458 units) and Punjabi Bagh (428) in west Delhi, ITO (453) and Lodhi Road (419) in central Delhi, Siri Fort (443) and R.K. Puram (395) in south Delhi, Delhi Technical University (468) in north Delhi, and Noida’s Sector 125 (319) and Ghaziabad’s Vasundhra (440) — both in Uttar Pradesh.

The safe limit for PM2.5 according to the national standards is 60 microgrammes per cubic meters, while the international standards are 25.

Advising people to avoid physical activity outdoors, the System of Air Quality and Weather Forecasting And Research also rated NCR’s air quality as “very poor”, after a five-day breather.

It said the region’s air quality is supposed to drop drastically over the next three days.