Zero rain at fault for spell of ‘poor’ air quality in city

The lack of rain in Delhi since the last week of February is also impacting the city’s pollution levels, with the air quality largely in the ‘poor’ category during the 45-day long dry spell, data from the Central Pollution Control Board (CPCB) shows.

The first two weeks of April so far have seen Delhi record an air quality index (AQI) of over 200 (classified as ‘poor’) each day. The Capital also recorded 19 ‘poor’ air days in March and just 12 ‘moderate’ days —where the AQI was between 101 and 200. While the average AQI for March this year was 217, a tad lower than 223 in the month last year, the air in April so far has been worse off.

Delhi has recorded an average AQI of 250 in April so far, against 199 in the corresponding period last year, data shows.

The city last received rain on February 27 this year.

Dust remains Delhi’s major pollutant at the moment, but experts warned that the concentration of ground-level ozone — a highly reactive gas formed in the presence of sunlight from combustion sources like vehicles and power plants — is starting to shoot up.

On Thursday, Delhi recorded a 24-hour average AQI of 279 at 4pm, a slight dip from 286 on Wednesday, placing it in the higher end of the ‘poor’ category on both days.

An AQI between 51 and 100 is ‘satisfactory’, 101 and 200 is ‘moderate’, 201 to 300 is ‘poor’ and 301 to 400 is ‘very poor’.

Safar, a forecasting body under central government, said the present pollution levels were primarily due to dust from west Rajasthan, with coarser PM10 particles comprising of around 70% of the total particulate matter.

“Winds from the west are likely to increase dust intrusion,” Safar said on Thursday.

Data shows that Delhi has failed to record a ‘satisfactory’ air day this year since February 27, when the AQI was 92, thanks to light rain across the city.

With 29.7mm of rain, Delhi recorded its cleanest February since the AQI was launched in April 2016, as the average AQI for the month clocked in at 225. The previous lowest AQI for February was 241, recorded in 2020.

In stark contrast, this March recorded no rainfall days, with an average AQI of 227.

Met officials also concurred that the pollution spike over the last two weeks could be down to dry and dusty westerly winds, bringing dust in from Rajasthan. “We are seeing a rise in mercury largely down to clear skies and westerly winds from Rajasthan, which in turn is also bringing dust,” said an official of the India Meteorological Department.

But most pollution is likely due to local sources, experts said, stressing that other primary sources of bad air include industries, vehicles and power plants.

A 2018 source apportionment study by The Energy and Resources Institute (TERI) showed that the contribution of dust in PM2.5 concentration in summer was 38%, followed by industries (22%) and the transport sector (17%).

The Delhi government has also taken note of the pollution levels in summer and earlier this week launched a 14-point Summer Action Plan to this effect.

The plan includes a one-month long campaign against open burning in the Capital that started from April 12, while an anti-dust drive will begin from April 15.

The Commission for Air Quality Management (CAQM), a central government body, also held a review on dust pollution on April 7, where Delhi’s three civic bodies informed the panel that of the 18,540km roads in Delhi, at least 5,085km will be covered under daily mechanical sweeping.

Tanushree Ganguly, programme lead at the Council on Energy, Environment and Water (CEEW) said multiple studies have shown that summer pollution is largely driven by dust, adding that biomass burning and vehicular emissions are prominent sources.

“We are halfway through April and have already witnessed 10 ‘poor’ air quality days, compared to just three in the same period last year if the average of DPCC, CPCB and Safar taken was considered. Poor air quality during the summer months reinforces the message that air pollution in Delhi is not a winter-only problem, and needs attention and concerted action throughout the year. Delhi Pollution Control Committee, Delhi Development Authority and Delhi’s municipalities should address sources like waste burning, construction activities and dust from unpaved roads,” says Ganguly.

Anumita Roychowdhury, executive director, research and advocacy at the Centre for Science and Environment (CSE) says controlling dust pollution remains a challenge in terms of intervention strategies, but suggests Delhi to carry out infrastructural changes by tackling its unpaved roads and unpaved footpaths.

“These need to be paved and we need vegetative barriers, while also trying to meet the per-capita green area requirements as per the Master Plan,” she said, stressing that ozone and other gases are largely produced due to emissions coming from vehicles, industries and other combustion sources.