City’s air qual­ity im­proves to ‘very poor’ af­ter 7 days

Hindustan Times (Gurugram) - - Metro - HT Cor­re­spon­dent htre­porters@hin­dus­tan­ n

NEWDELHI:The Na­tional Cap­i­tal’s air qual­ity im­proved a lit­tle on Tues­day, go­ing back to its preDi­wali lev­els. The air qual­ity in Delhi had been hov­er­ing in the ‘se­vere’ cat­e­gory in the last seven days, putting peo­ple of the Cap­i­tal at ma­jor health risk.

Weather ex­perts said that Del­hi­ites will now be able to breathe in ‘very poor’ air for some time now, con­sid­ered nor­mal for this time of the year.

The av­er­age AQI dropped to 308 on Tues­day from 460 on Mon­day. The level of par­tic­u­late mat­ter, which had hit the ‘se­vere+’ zone, also dropped to ‘se­vere’ lev­els in the past 24 hours.

The last time Delhi wit­nessed such pro­longed spells of se­vere air qual­ity was in November 2016 when the city faced its worst smog in 17 years. Last November too, the AQI re­mained 401+ on a scale of 500 for seven straight days. But the sever­ity then was higher with pol­lu­tion peak­ing at 497 on the AQI. This year, the high­est so far has been 486.

Ex­perts said that weather con­di­tions, which started turn­ing in Delhi’s favour from Sun­day, helped bring the im­prove­ments.

Pol­lu­tion lev­els first en­tered the ‘se­vere’ zone on November 7. The AQI hit its peak of 486 on November 9. There­after it started im­prov­ing. The re­lief, how­ever, was short lived as the air turned foul again from Satur­day af­ter­noon. This time the AQI touched 460. But since Sun­day it has started im­prov­ing again.

“The air qual­ity has im­proved to what it was be­fore Di­wali. Such qual­ity of air was last en­coun­tered just two days be­fore Di­wali. The AQI was 306 on Oc­to­ber 17,” said D Saha head of the air qual­ity lab­o­ra­tory of Cen­tral Pol­lu­tion Con­trol Board.

The level of par­tic­u­late mat­ter – PM10 and PM2.5 – have al­most halved from what it was on Sun­day af­ter­noon.

Sev­eral fac­tors helped in the clean­ing up the air. The plum­met­ing mer­cury con­densed the mois­ture in the air to dew which got de­posited on the sur­face, grass and leaves, in the early morn­ing hours. Some pol­lu­tants were re­moved in this way as they stuck to wa­ter droplets.

When the sun’s rays pen­e­trated, they heated up the at­mos­phere which in turn in­creased the mix­ing height al­low­ing the pol­lu­tants to dis­perse at a faster rate.

“The chang­ing wind pat­tern has helped in the process too. While high al­ti­tude winds that usu­ally bring in pol­lu­tants from out­side have calmed down, the sur­face level winds that help to flush out lo­cal pol­lu­tants are gath­er­ing speed,” said Gur­fan Beig, project di­rec­tor of SAFAR, which op­er­ates un­der the min­istry of earth sci­ences.

The ve­loc­ity of wind that had dropped to 2km/hr on Satur­day shot up to 7km/hr on Tues­day.


n The av­er­age AQI dropped to 308 on Tues­day from 460 on Mon­day.

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