CSE says ozone pollution has increased in Delhi this summer because of heatwave

Extreme weather events like unprecedented heat waves can worsen the health risk when air pollution is already high in the city, says the new analysis 

  • CSE tracks ozone data in the April to June 2019 period – finds Delhi-NCR has had more days with average ozone levels over the national air quality limits than in previous summer
  • Ozone has emerged as a dominant pollutant along with particulate matter on at least 28 days during summer of 2019 as opposed to only 17 days in 2018 summer.
  • In several residential and commercial locations including Siri Fort and Najafgarh, number of days on which ozone levels crossed the limit were very high – 53-92 per cent of the days. In NCR, Faridabad and Ghaziabad experience the biggest spikes
  • Ozone is a deadly gas -- even short duration exposure can worsen respiratory conditions and asthma and leadto emergency hospital admission
  • Ozone is not directly emitted from any source, but is formed from reaction between gases in the air under the influence of sunlight and high temperature
  • Controlling emissions from vehicles and industry is the solution 

New Delhi, June 19, 2019: Centre for Science and Environment (CSE) has tracked the daily ozone data released by the Central Pollution Control Board (CPCB) for Delhi and the National Capital Region (NCR) for the period April 1-June15, 2019. Its analysis shows that this summer, when the capital witnessed searing temperatures, average ozone levels exceeded the prescribed standard on 16 per cent of the days overall – as compared to 5 per cent of the days during the same period in 2018. The eight-hour average standard for ozone exposure is 100 microgramper cubic metre (cu m). 

In several residential and industrial locations, the number of days crossing the limit was very high – ranging from 53 to 92 per cent of the days. 

Says CSE executive director (research and advocacy) AnumitaRoychowdhury: “This is a matter of serious concern as ozone is a highly reactive gas and can have immediate adverse effect on those suffering from asthma and respiratory conditions.”  

“There is a special reason for tracking ozone during summer”, Roychowdhury adds.“This is mainly because ozone is not directly emitted from any source. Other gases such as nitrogen oxide and volatile organic compounds that are emitted from combustion sources like vehicles, industry or power plants, react in the air under the influence of sunlight and temperature to form ozone. Summer months, with their high sunshine and high ambient temperatures, increase our vulnerability to ozone impacts. It seems the intense heatwave experienced this summer may have influenced this trend in the region,which is already suffering from severe air pollution.” 

The CSE analysis of available data found the following trends in ozone pollution in Delhi-NCR: 

This summer, more days have violated the daily standards
During the entire period of April to June 15, overall 16 per cent of days have exceeded the eight-hour average standard of 100 microgramper cum. This is much higher than the 5 per cent of days violating the standards during the same period in 2018. It may be noted that ozone is a highly reactive gas that merits short duration standard of only one hour to eight hours average, as opposed to 24-hour average for other pollutants. For 2018, data is available from 31 monitoring stations in Delhi; in 2019,there is data from 36 stations (sporadic for three stations). 

According to daily Air Quality Index, ozone is emerging as dominant pollutant
It is shocking to note that according to the Air Quality Index which the CPCB releases every day, ozone -- along with particulate matter – has been the dominant pollutant of the day on 28 days between April 1 and June 15, 2019. During the same period in 2018, ozone was the dominant pollutant along with particulate matter on only 17 days. Says Roychowdhury: “If this trend continues and worsens, the Graded Response Action Plan will also have to initiate action to address the precursor gases that form ozone -- NOx, hydrocarbonsetc-- and crack down on vehicles and industry.” 

Ozone is high in the NCR towns
The analysis has exposed that among the key NCR towns, Faridabad has experienced the highest share of days – 80 per cent -- when ozone crossed the eight-hourly standards. This has been followed by Ghaziabad with 67 per cent and Gurugramwith 21 per cent of days. Noida shows much less impactwith only 1 per cent of the days exceeding the standards.  

Peak levels remain high during Delhi’s summer
The highest concentration in 2019 went up to 122 microgramper cum, which is 1.22 times higher than the eight-hour average standard. During 2018, it had gone up to 106 microgramper cum which is 1.1 times higher than the standard. 

Monthly variation is stark in Delhi
There is also a distinct monthly variation. In the month of May 2019, close to 20 per cent of the days exceeded the standards compared to 3 per cent in May 2018. Similarly, while during June 2018 not a single day had violated the ozone standard, 27 per cent of the days in June 2019 crossed the limit. Only April 2018 had comparatively higher share of days violating standards (10 per cent) compared to 7 per cent during April 2019. 

Deadly hotspots in Delhi
While the average level in Delhi has exceeded the standard on 16 per cent of days this summer, the share of days exceeding the standard in several residential and industrial locations have been significantly higher. Prominent residential areas show more exceedance: Siri Fort (76 per cent of the days in the period under analysis), Sri Aurobindo Marg (87 per cent), R K Puram (53 per cent), JLN Stadium (71 per cent), Dwarka Sector 8 (68 per cent) and Rohini(63 per cent). The industrial and institutional areas are in an equally bad situation: Bawana (78 per cent of the days in the period under analysis), Jahangirpuri (67 per cent), Najafgarh (92 per cent), and Narela (80 per cent). This is bad news as it indicates increased and extended exposure for people living in these areas almost on a daily basis.  

Locations with low levels
The city’s average could have been worse if some locations did not have low levels. In locations like Aya Nagar, Karni Singh Shooting Range, IGI airport, Lodhi Road, Mandir Marg, Pusa Road, Patparganj, North Campus, ITO and AnandVihar less than 5 per cent of the days have experienced exceedance. This is a complex atmospheric chemistry and needs investigation, point out CSE researchers. Experts explain that sometimes in highly polluted locations that may generate ozone,levels can dip due to further reaction with gases like NOx. Ozone also drifts to other places and builds up in low polluted areas. 

Says Roychowdhury: “Even as Delhi is battling serious particulate pollution, newer rogues are beginning to raise their ugly heads to add to the health risk. The number of days exceeding or crossing the standard have certainly gone up this summer. It can be a serious health crisis if the short duration levels begin to increase hereafter.” 

As the Air Quality Index is also beginning to show ozone as a dominant pollutant, this will require strong action to cut down gaseous emissions from combustion sources – vehicles and industry. The new source assessment studies of 2018 have already implicated vehicles as the highest source of NOx (which is a key culprit in the ozone recipe) -- according to the SAFAR study of 2018, vehicles in Delhi are responsible for 62.5 per cent and industry 24.4 per cent of the total NOx load from all sources. The Teri-ARAI study of 2018 had found vehicles responsible for 81 per cent. NOx mainly catalyses reaction between gases in the air. 

Ozone is a unique problem that is dependent on emissions of gases from different sources as well as on the atmospheric conditions. Clearly, the combination of high gaseous emissions and intense summer conditions with severe heat waves can aggravate this problem. 

Delhi requires immediate steps to:

  • Keep real world emissions from vehicles low and phase in electric mobility.
  • Scale up – massively -- convenient, affordable and reliable public transport systems.
  • Initiate more pedestrian- and cycling-friendly, compact and accessible development.
  • Introduce city-wide parking management and pricing and low emissions zones to restrain use of personal vehicles.
  • Aggressively control industrial emissions. 

Says Roychowdhury: “We cannot afford to let this problem grow to worsen the health emergency.”

For interviews, more details etc, please contact Sukanya Nair of The CSE Media Resource Centre, sukanya.nair@cseindia.org / 8816818864.