Shallow fog in the morning mixed with the pollutants lead to smog.
The national capital and its surroundings continued to suffer toxic air quality today morning with only a slight improvement from "emergency" to "severe" category.
The Air Quality Index (AQI) of Delhi at 9 a.m. was recorded 403, on a scale of 0 to 500. The AQI on Monday at the same time was 415, which had gradually worsened to 435 by evening.
According to the India Meteorological Department, the shallow fog in the morning mixed with the pollutants that lead to smog.
On Tuesday, there was a slight drop in moisture, which was good for dispersion of pollutants.
The pollution monitoring agencies said that the extra load of pollutants coming from stubble burning from neighbouring states also registered a slight drop, leading to slight improvement -- though still in the danger zone.
"The condition is expected to prevail till Diwali," said the System of Air Quality and Weather Forecasting and Research (SAFAR)
However, it might improve if no additional emission from firecrackers add to Delhi's air, it added.
The average volume of particle pollutant PM2.5 , or particles with a diametre less than 2.5 mm, was 257 microgrammes per cubic meters, considered "severe".
The safe limit of PM2.5 and PM10 is under-60 and 100 units, as per national standards. The international standards are 25 units for PM2.5 and 50 units for PM10.