When drizzle worsened Delhi-NCR air quality

Ghaziabad: 4 Nov, 2019 (Times of India)

SAFAR data showed contribution of farm fires to Delhi’s PM 2.5 concentration had fallen to 17% after touching 44% on Friday.

NEW DELHI: As the heavens opened up on Saturday, little did people know that its effect would be the exact opposite of what they were for hoping for. While the showers did bring down pollution levels briefly, by evening, it had started to rise — owing to the increased moisture content in the air.

By midnight, as temperatures dropped, a shallow layer of fog had enveloped the city and by Sunday morning, it had brought down the boundary layer (mixing height) to around 50-100 metres, effectively trapping pollutants close to the ground. 


Governments at the Centre and in Delhi, Haryana, Punjab and UP need to start behaving as if they recognise that the NCR is facing a monumental public health emergency. This is no time for blame games or cornering credit for what few positive measures have been taken. Even concerted action by all governments may not be enough to deal with the crisis in the short to medium term, but anything less would be criminal neglect of their duty and a complete abdication of leadership. Let’s also not argue about which source of pollution deserves priority action. Every source, minor or major, needs urgent tackling. Central and state governments should jointly commit to a 5-year plan with annual targets of AQI reduction to less than 100 by 2025, and below 50 soon after. Breathing this toxic air is imperiling all of us, particularly children, even if we can ensure we won’t have to do so in future. The damage already done will continue to extract its toll in the years to come, so every extra day of inhaling this poison is one day too many. As citizens and victims, we need to pitch in – through efforts such as car pooling and maximising use of public transport. We need to treat these tasks as if our lives depend on them – because they do.

SAFAR, a forecasting body under the Union ministry of earth sciences, said the increase in secondary particle formation (a mechanism when PM 2.5 starts to multiply rapidly) was triggered due to the light rain on Saturday, which increased the air-holding capacity. “A good spell of rain improves air quality but Saturday night’s drizzle in calm wind conditions acted as catalyst towards increasing the air-holding capacity, triggering secondary particle formation. In absence of sufficient solar radiation, the boundary layer continued to be very low (50-100m) even during daytime, arresting pollutants firmly,” SAFAR said.

“It is a unique condition because such process is a characteristic of colder foggy period between December and January. The secondary particle theory is validated by the SAFAR model, as share of PM2.5 increased immensely to above 75% (normal is 50%), meaning most of the particles in air are PM2.5 and less of the coarser PM 10,” it added.

Visibility fell to its lowest around 8am on Sunday, with Safdarjung observatory recording visibility down to 200 metres. IMD said such a situation is generally seen when temperatures are low. “The western disturbance influencing the region was weak, which in turn brought only light rain and drizzle activity. Pollutants did not settle due to this and instead, made the air heavy with moisture,” said Kuldeep Srivastava, scientist at IMD.

Srivastava said that wind speeds had reached 15 km/hr on Sunday, helping dispersal of pollutants towards the evening, a trend likely to continue on Monday. According to him, northwesterly winds are still influencing the region.

SAFAR data showed contribution of farm fires to Delhi’s PM 2.5 concentration had fallen to 17% after touching 44% on Friday. Its contribution will remain around 14% over the next 48 hours.