Raining trouble: Why Delhi may be set for another spike in pollution on Nov 15
Experts warned that a single day of light rain, triggered by a western disturbance, might help to bring down pollution levels temporarily. But, in the long run, it may do more harm than good.delhi Updated: Nov 12, 2017 11:47 IST
Pollution levels in Delhi may have declined in the last 48 hours, but the respite would only last four to five days, weather experts have said.
Instead, Delhi may be set for another spike in pollution levels soon after a drizzle that is expected to hit the city on November 15.
On Saturday, Delhi registered an average of 403 on air quality index (AQI), which was significantly lower than the 486 recorded on Thursday — the peak AQI of this season. On Friday, it had dropped to 468. The pollution levels were declining steadily till Saturday morning, but a cloud cover in the afternoon played spoilsport.
“One of the primary reasons behind this was the accumulation of clouds. As the clouds cut off the sun’s rays, the temperature dipped. This slowed the process of dispersal further. Winds were also calm. Pollution from local sources started accumulating once again,” said a senior official of the Met department.
SAFAR, a pollution monitoring agency under the Union government, has forecasted that the levels of both PM10 and PM2.5 would improve again on Sunday and further drop on Monday.
Experts warned that a single day of light rain, triggered by a western disturbance, might help to bring down pollution levels temporarily. But, in the long run, it may do more harm than good.
The rain would also ensure that moisture level in the air goes up. This moisture would trap pollutants, triggering fresh smog-like conditions on November 16 and 17. The weather office, however, did not specify the intensity of this smog.
“We don’t know to what levels the pollution will spike to. But, we expect it would be milder than the present spell,” said Gurfan Beig, project director at SAFAR.
He said that once the western disturbance withdraws and the rain fades, the level of moisture is going to increase in Delhi’s air. “There would be a dip in the mercury level too. This may result in the increase in pollution levels once again.”
Scientists said that fog and aerosol hazes likely amplify each other and forms a vicious cycle.
“While on one hand, aerosol — a kind of pollutant — serves as ‘seed’ that make it easier for fog to form, on the other hand the moisture droplets in the fog acts like small ‘chemical factories’ that help gaseous pollutants to graduate into haze causing aerosols,” said SN Tripathi, coordinator of the Centre for Environmental Science & Engineering at IIT Kanpur.
Even though the levels of both PM10 and PM2.5 had been steadily declining since Friday and had come out of the “emergency” zone by around 11am on Saturday, it started shooting up again later in the day.
The level of PM10 which had dropped to 453 ug/m3 around 12 noon, shot up to 533 ug/m3 around 7pm. PM10 values above 500 denote emergency levels.
The level of PM2.5 which had dropped to 298 ug/m3 around 11am, shot up to 339 ug/m3 around 7pm. PM2.5 values above 300 denote emergency levels.