Delhi's air quality 'very poor', drastic decline unlikely till Tuesday

Delhi's air quality was "very poor" on Friday, but drastic decline is likely in next three days as strong winds are expected to blow in region, government's air quality monitoring and forecasting service SAFAR said.

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After a brief relief, national capital's air quality plunged to "very poor" category again because of high humidity due to light rain on Thursday. "Isolated drizzle, cloudy wear and calm winds prevented boundary layer growth and led to accumulation of local emissions (on Thursday)," SAFAR said. 

Delhi experienced "slight secondary particulate formation in early hours (on Friday) but (it) could t multiply much", it said. 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 presence of or factors such as sunlight and moisture.

Examples of secondary particles include sulphates, nitrates, ozone and organic aerosols. An AQI between 201 and 300 is 'poor', 301-400 'very poor' and 401-500 'severe'. An AQI above 500 falls in severe plus category. A change in wind direction to rthwesterly and stubble plume intrusion is expected by vember 9. Though predicted wind direction is favourable for fire plume transport, strong winds, favourable for efficient ventilation, are likely to blow in region in next three days, SAFAR said. 

According to its data, share of stubble burning in Delhi's PM2.5 pollution was just two per cent on Thursday and three per cent on Friday. " surface and boundary-layer winds are from souast and stubble fire contribution was negligible," it said. effective biomass fire count observed on vember 7 was 200. It should be ted that Punjab and Haryana were under a heavy cloud cover; and satellite's capability to detect fires reduces in such a situation, SAFAR said. Smoke from crop residue burning is expected to account for 8 percent of Delhi's PM2.5 concentration on Saturday.

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