Union Environment Minister Harsh Vardhan directed agencies to be on "maximum" alert and take all measures to contain sources of dust as Delhi's air quality remained "severe" for the third day today . Referring to an India Meteorological Department (IMD) data, the ministry said the dusty condition will remain for the next two days. It said the Task Force under the Graded Response Action Plan (GRAP) met with the Central Pollution Control Board (CPCB) and recommended that construction activity-related enforcement measures under the Graded Response Action Plan (GRAP) be brought into operation immediately. The ministry said air quality of Delhi and NCR, which worsened on June 12-13 due to the incoming dust from Rajasthan, has shown a slight improvement today, with PM10 declining to 759 \u00b5g\/m3 at 4 pm from a peak of 823 \u00b5g\/m3 at 5 pm yesterday. "In view of the seriousness of the situation, Union Environment Minister Harsh Vardhan has directed agencies concerned to be on maximum alert and to ensure all necessary measures to contain sources of dust and to check garbage burning. "He also appealed to the people to avoid unnecessary exposure, given the prevailing situation," an official statement said today. Delhi's air quality remained \u201csevere\u201d for the third day, prompting authorities to issue warning to people to avoid staying outdoors for long and suspend construction activities, according to the Central Pollution Control Board (CPCB). The 24-hour average concentration (rolling) of PM10 was 1,400 microgramme per cubic metre (ug\/m3), more than three times above the severe level, said Gufran Beig, a scientist at the Centre-run System of Air Quality and Weather Forecasting and Research institute (SAFAR). The severe level begins at 430 ug "The pollution caused due to dust storm was expected to settle but the wind speed reduced yesterday, causing the dust that entered Delhi to get trapped in the atmosphere leading to prolonging of pollution," Beig said. According to the CPCB, the air quality index (AQI) - a measurement of the concentration of toxic particulate matter in the air - at several places in Delhi remained over 500. The PM10 level (presence of particles with diameter less than 10mm) was at 756 in Delhi-NCR and 785 in Delhi, leading to hazy conditions. The PM2.5 level (presence of particles with diameter less than 2.5 mm) worsened and became severe from very poor level in the past 24 hours in Delhi-NCR at 268 and Delhi at 277. "The Task Force held a meeting with the construction agencies, municipal corporations and local bodies in the neighbouring cities of Delhi to ensure effective action on the ground. "According to IMD, dusty conditions in Delhi and NCR are likely to continue over the next two days," the ministry said.