Air

COVID-19 flattens peak-hour pollution

The flat rates of peak-hour pollution due to the lockdown proves why strong action is needed to reduce traffic volumes and cut tailpipe emissions to near zero

 
By Anumita Roychowdhury, Avikal Somvanshi
Published: Monday 30 March 2020
A deserted Rajpath in New Delhi on March 25. Photo: Vikas Choudhary / CSE
A deserted Rajpath in New Delhi on March 25. Photo: Vikas Choudhary / CSE A deserted Rajpath in New Delhi on March 25. Photo: Vikas Choudhary / CSE

As vehicles go off the road after the country-wide lockdown in the wake of the novel coronavirus disease (COVID-19) outbreak, the typical two humps of daily pollution coinciding with morning and evening traffic peak-hours have nearly flattened out in India's big cities.

As cities slow down to fight the pandemic, daily average levels of particulate matter of size less than 2.5 micron (PM2.5) and nitrogen dioxide (NO2) have reduced sharply from the pre-lockdown days by close to more than half in Delhi and the towns of the national capital region (NCR).

A similar trend is evident in other big cities including Mumbai, Kolkata, Bengaluru, Hyderabad and Chennai. But the impact of this overall declining trend is dramatic on daily peak-hour pollution.

This is evident from the new analysis carried out by the Centre for Science and Environment that has assessed hourly trend in PM2.5 and NO2 levels during the day before and after the lockdown and also on the day of the Janata curfew.

This brings out the pronounced effect of traffic on hourly pollution trends. With traffic minimised, hourly trends have plummeted, reducing daily exposures to toxic vehicular pollution.

While overall daily levels of PM2.5 and NO2 concentrations have fallen significantly — by up to 60 per cent in several cities during the lockdown days, the hourly change is also dramatic. Hourly NO2 levels that are strongly associated with vehicles, have dropped more sharply.

Hourly PM2.5 levels that are also influenced by other pollution sources have reduced substantially. For comparison, the average of March 18-19, 2020, have been taken as regular days and the average of March 25-26 as lockdown days. Janata curfew was on March 22, 2020. Real-time data has been sourced from the website of the Central Pollution Control Board.

Normally, on regular days, peak hour pollution during morning and evening traffic hours inflates like a balloon. But after the lockdown and imposition of curfew, the peak hour PM2.5 concentrations have dropped by 57 per cent in Delhi, 69 per cent in Gurugram, 62 per cent in Faridabad and Noida, and 64 per cent in Ghaziabad.

Similarly, peak hour NO2 concentration has dropped sharply — by 64 per cent in Delhi, 66 per cent in Gurugram, 40 per cent in Faridabad, 79 per cent in Noida, and 75 per cent in Ghaziabad.

From studies done by SAFAR and TERI-ARAI in 2018, it is known that vehicles contribute about 40 per cent of the total particulate load in Delhi. According to SAFAR, vehicles contribute about 62.5 per cent of the NOx load and according to TERI-ARAI, 81.3 per cent of NOx load.

The overall impact during the lockdown is hugely substantial. Comparatively, the effect is somewhat lesser on Janata curfew day in Delhi and NCR. This could be due to the shorter duration of Janata curfew (14 hours) that had also shifted the peak hours beyond the curfew hours. It is also reported that people had rushed out for panic buying on that day. But this experience is different in other cities.

What about other cities?

Other cities including Kolkata, Mumbai, Bengaluru, Hyderabad and Chennai also witnessed a drastic drop in peak hour pollution and also daily average levels with some variation. Mumbai was the first one to lockdown and shows a sharper drop. Kolkata has witnessed a higher drop on Janata curfew day, compared to the subsequent lockdown days.

Overall, peak hour NO2 levels during locked-down days show a sharper drop than PM2.5 in all these cities as well. In Kolkata, peak hour PM2.5 reduced by 46 per cent and NO2 by 74 per cent on a lockdown day. Similarly, in Mumbai, it is 52 per cent and 85 per cent respectively; in Bengaluru, it is 42 per cent and 76 per cent respectively; in Hyderabad, 32 per cent and 72 per cent respectively and in Chennai, it is 46 per cent vs 44 per cent. 

The take away

Emergency response to the pandemic has induced this change in air quality and hourly concentrations. This does not make a case for crisis-led change. But this experience shows that the measures adopted to fight the new health crisis have somewhat tamed the health risk associated with the ongoing air pollution crisis to give a short breather. This change has been possible due to massive community-wide lifestyle adjustments to practice social distancing.

This proves why we need strong action to reduce traffic volume and phase in a near zero emissions mandate. This crisis-induced change must force us to find and sustain long-term solutions to reduce our vulnerability to toxic risk.

City-wise trends in hourly pollution and peak hour pollution at a glance

Delhi: Hourly trend in PM2.5 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on a lockdown day by about 57 per cent compared to a regular day
  • Daily peak has declined on a Janata curfew day by about 24 per cent compared to a regular day

Note: Average of 37 stations

Delhi: Hourly trend in NO2 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on lockdown day by about 64 per cent compared to a regular day
  • Daily peak has declined on Janata curfew day by about 62 per cent compared to a regular day

Note: Average of 37 stations

Gurugram: Hourly trend in PM2.5 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on a lockdown day has reduced by about 69 per cent compared to a regular day
  • Daily peak has declined on a Janata Curfew day by about 7 per cent compared to a regular day

Note: Average of three stations

Gurugram: Hourly trend in NO2 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on a lockdown day by about 66 per cent compared to a regular day
  • Daily peak has declined on a Janata Curfew day by about 32 per cent compared to a regular day

Note: Average of three stations

Faridabad: Hourly trend in PM2.5 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on a lockdown day has reduced by about 62 per cent compared to a regular day
  • Daily peak has declined on a Janata Curfew day by about 10 per cent compared to a regular day

Note: PM2.5 - average of four stations; NO2 – average of three stations

Faridabad: Hourly trend in NO2 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on a lockdown day by about 40 per cent compared to a regular day
  • Daily peak has declined on a Janata Curfew day by about 19 per cent compared to a regular day

Note: PM2.5 - average of four stations; NO2 – average of three stations

Noida: Hourly trend in PM2.5 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on a lockdown day has reduced by about 62 per cent compared to a regular day
  • Daily peak has declined on a Janata Curfew day by about 36 per cent compared to a regular day

Note: Average of four stations

Noida: Hourly trend in NO2 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on a lockdown day by about 79 per cent compared to a regular day
  • Daily peak has declined on a Janata Curfew day by about 74 per cent compared to a regular day

Note: Average of four stations

Ghaziabad: Hourly trend in PM2.5 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on a lockdown day has reduced by about 64 per cent compared to a regular day
  • Daily peak has declined on a Janata Curfew day by about 7 per cent compared to a regular day

Note: Average of four stations

Ghaziabad: Hourly trend in NO2 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on a lockdown day by about 75 per cent compared to a regular day
  • Daily peak has declined on a Janata Curfew day by about 63 per cent compared to a regular day

Note: Average of four stations

Mumbai: Hourly trend in PM2.5 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on a lockdown day by about 52 per cent compared to a regular day
  • Daily peak has declined on a Janata curfew day by about 65 per cent compared to a regular day

Mumbai: Hourly trend in NO2 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on lockdown day by about 85 per cent compared to a regular day
  • Daily peak has declined on Janata curfew day by about 83 per cent compared to a regular day

Kolkata: Hourly trend in PM2.5 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on a lockdown day by about 46 per cent compared to a regular day
  • Daily peak has declined on a Janata curfew day by about 82 per cent compared to a regular day

Note: Average of 7 stations

Kolkata: Hourly trend in NO2 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on lockdown day by about 74 per cent compared to a regular day
  • Daily peak has declined on Janata curfew day by about 80 per cent compared to a regular day

 

Note: Average of 7 stations

Chennai: Hourly trend in PM2.5 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on lockdown day by about 46 per cent compared to a regular day
  • Daily peak has declined on Janata curfew day by about 37 per cent compared to a regular day

Chennai: Hourly trend in NO2 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on lockdown day by about 44 per cent compared to a regular day
  • Daily peak has declined on Janata curfew day by about 41 per cent compared to a regular day

 

Hyderabad: Hourly trend in PM2.5 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on lockdown day by about 32 per cent compared to a regular day
  • Daily peak has declined on Janata curfew day by about 11 per cent compared to a regular day

Hyderabad: Hourly trend in NO2 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on lockdown day by about 72 per cent compared to a regular day
  • Daily peak has declined on Janata curfew day by about 60 per cent compared to a regular day

 

Bengaluru: Hourly trend in PM2.5 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on lockdown day by about 42 per cent compared to a regular day
  • Daily peak has declined on Janata curfew day by about 13 per cent compared to a regular day

Bengaluru: Hourly trend in NO2 levels on a regular day, after lockdown and as on Janata curfew day

  • Daily peak has declined on lockdown day by about 76 per cent compared to a regular day
  • Daily peak has declined on Janata curfew day by about 43 per cent compared to a regular day

 

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