Favourable wind speed keeps pollution levels in check in Delhi

The national capital's air quality improved marginally on Monday despite a significant increase in stubble burning in neighbouring states as favourable wind speed helped disperse pollutants. However, the winds are expected to become calm October 23 onwards, resulting in further deterioration of air quality to the "very poor" category.

Pollution levels in Delhi dipped on Monday by around 10 points at air quality index (AQI), according to data from the Central Pollution Control Board. Delhi's AQI stood at 249 on Monday as against 258 on Sunday evening. Currently, the wind direction is prominently northwesterly, according to the India Meteorological Department.

Westerly and northwesterly winds bring dust from western regions and smoke caused by burning of crop residue in neighbouring Punjab and Haryana to Delhi-NCR. Barring Siri Fort with AQI 363, Dwarka Sector eight (326) and Jahangirpuri (302), all monitoring stations in Delhi recorded air quality in the "poor" category.

An AQI between 0 and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', and 401 and 500 'severe'. Kuldeep Srivastava, a senior IMD scientist, said winds clocking 22-25 kilometers per hour helped disperse pollutants on Monday and subdued the effect of stubble burning in neighbouring states.

The Ministry of Earth Sciences' air quality forecast and research service, SAFAR, said, "The overall air quality of Delhi is in the poor category. The leading factor keeping AQI  in check is faster surface winds." The System of Air Quality and Weather Forecasting and Research (SAFAR) said a gradual increase in stubble burning incidents in Haryana, Punjab and nearby border regions has been noticed.

"Though the circulation pattern (boundary layer wind direction is northwesterly) is supportive for efficient biomass plume transport to Delhi, the high wind speed in Delhi is helping disperse pollutants," it said. SAFAR said Delhi's air quality is expected to deteriorate slightly on Tuesday, but will still remain in the 'poor' category.

"Further deterioration to 'very poor' is expected anytime thereafter as there is a high probability of winds becoming calm October 23 onwards," it said. A fresh western disturbance is approaching the northern region on October 23, but it will be weak and may not have a major impact on pollution levels in the city, Srivastava said.

SAFAR said the calm anticyclonic conditions are expected to restrengthen by the first week of November and associated sinking motion will make the atmosphere very stable with calm surface winds. "Both will lead to stagnant weather conditions which favours rapid fine particulate matter formation and accumulation of pollutants," it said.

According to data available on SAFAR's website, the share of smoke from stubble burning to Delhi's PM2.5 concentration was 12 per cent on Monday. It is likely to increase to 14 per cent on Tuesday. Data available from the pollution control boards of Punjab and Haryana shows 4,530 incidents of farm fires since the harvesting of paddy crop started around September 25. Last year, the farm-fire count till October 20 was 4,263.

The period between October 15 and November 15 is considered critical as maximum number of stubble burning incidents take place in this span in Punjab and adjoining states and is one of the main reasons for the alarming spike in pollution in Delhi-NCR. Despite a ban on stubble burning in Punjab and Haryana, farmers continue to defy it amid lack of financial incentives.

State governments are providing 50 to 80 per cent subsidy to farmers and cooperative societies to buy modern farm equipment for in-situ management of paddy straw and running a massive awareness campaign against stubble burning. The Delhi government repeatedly attributed the increase in pollution in the winter to rampant stubble burning in neighbouring states.

"Air quality in Delhi has been good or moderate for the last seven to eight months, but they (pollution levels) have starkly gone up now... Clearly, the sudden spike in pollution is a result of smoke coming from outside," Chief Minister Arvind Kejriwal had said earlier. The Delhi government has also tied up with Washington University and set up a centre near India Gate to collect data, with the help of which it will be able to tell the degree of air pollution due to specific sources from April next year.

(This story has not been edited by Devdiscourse staff and is auto-generated from a syndicated feed.)