Wind directions changed by Tuesday noon, creating an outlet for the toxic air over the Delhi-NCR region and thereby improving the air quality to "very poor," from "severe" in the morning and "emergency" a day before.

Coarser and highly dangerous PM2.5 or particles with diameter less than 2.5 mm continue to dominate the pollution factor in Delhi, and are still at least four times higher than the national standards and nine times the international standards.

PM2.5 levels are expected to spike, bringing the regions's air quality back to "emergency" for two days -- November 8 and 9 -- if Delhi bursts even 50 per cent of firecrackers that it did on last year's Diwali, warns System of Air Quality and Weather Forecasting And Research (SAFAR).

The Air Quality Index (AQI) of Delhi at 2 p.m. was 360, while at 12 noon it was 385, considered "very poor", against 403 or "severe" at 9 a.m. On Monday, air quality across NCR had worsened to "severe-plus" or "emergency" levels due to north-westerly winds that brought stubble smoke from Punjab and Haryana, while the high moisture levels trapped the local and external pollutants in Delhi.

"The lower winds changed to dry and comparatively warm westerly on Tuesday, due to which the pollutants were not trapped tightly and were dispersed easily by noon," said Mahesh Palawat, Director of private weather forecaster Skymet.

According to India Meteorologcial Department (IMD), morning temperatures are likely to drop by one to two degrees on Wednesday, when Diwali will be celebrated, and a day after, which is likely to be another factor adding to the pollution.

Warning that the Diwali day is expected to be polluted, weather analysts say that while currently the polluting north-westerly winds are blowing higher at 5,000 meters, bringing a temporary relif to the region, the particles will start settling down, adding to pollution on Diwali.

"Delhi's fate depends on meteorologcial factors and the firecrackers. If temperature drops or lower winds change to north-westerly, it may get polluted," Shambahvi Shukla, researcher with the Centre for Science and Environment said. She added that currently the ventilation index, which depends on wind speed and mixing height, is higher due to which air quality has improved.

At 2 p.m., the average particle pollutants across 35 regions of Delhi was 215 microgrammes per cubic meters, falling under the "very poor" category, against 257 or "severe" category at 9 a.m.

The PM2.5 levels across 47 areas of NCR were 208 units.

The safe limit for PM2.5 is 60 units by national standards and 25 units by international standards.

--IANS

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