Delhi air 'very poor' again due to high humidity

New Delhi : After a brief relief, the national capital's air quality plunged to the "very poor" category again on Thursday because of high humidity following light rain, officials said.

Delhi had been breathing relatively less polluted air for three days after a bright sun and improved wind speed pulled the city out of the grip of a dense haze that had been lingering over it since October 29. But the increased humidity on Thursday proved harmful.

On Sunday, too, a drizzle resulted in an increase in humidity, triggering a massive pollution spike. Weather experts said high humidity and slower winds hamper dispersion of pollutants and lead to the formation of more harmful secondary particles.

Secondary particles are products of complicated atmospheric reactions between primary particles, such as particulate matter, sulphur dioxide and nitrogen dioxide directly emitted by stubble burning and vehicles, in the presence of other factors such as sunlight and moisture.

Examples of secondary particles include sulphates, nitrates, ozone and organic aerosols.

Delhi's overall air quality index read 309 at 4pm and 320 at 7 pm on Thursday.