Heat wave leads to deadly ozone pollution in Delhi: CSE analysis

Delhi has witnessed significant ozone build-up this summer, shows a latest analysis done by the Centre for Science and Environment (CSE). A study of the real-time air quality data available from the key monitoring locations of the Delhi Pollution Control Committee (DPCC) for the period January to early June 2014, shows rapid build-up of ozone and more frequent violation of standards this summer.

CSE experts say warmer temperatures and the extreme heat waves are threatening to increase the frequency of days with unhealthy levels of ozone—with serious public health consequences.

Read more on ozone pollution

• Deadly ozone

Ground-level ozone is not directly emitted by any source. This is formed when oxides of nitrogen (NOX) and a range of volatile gases—primarily from vehicles and other sources—are exposed to each other in sunlight. Warm and stagnant air increases the formation of ozone, which is known to be extremely hazardous for human health.

According to Anumita Roychowdhury, executive director, research and advocacy and head of CSE’s air pollution programme: “Ozone is the new generation public health threat and a difficult challenge. It must be curbed at the early stages with stringent controls on nitrogen oxide (NOx) and toxic and volatile gases, the major ingredients of ozone recipe.”

What CSE found

CSE has analysed ozone data from the automatic monitoring stations of the DPCC located in R K Puram, Civil Lines, Mandir Marg and Punjabi Bagh—all residential areas—as well as the IGI airport, a heavy traffic and peripheral location. This exposes worrying trends in the city. Though there is a variation in trends across months, there is a clear trend towards newer heights. The key highlights are:

• Heat wave worsens ozone pollution: While ozone levels are rising steadily with the onset of summer, it doubled up very quickly as soon as the heat wave hit Delhi in the first week of June this year. The average temperature has increased rapidly from 35°C on June 1, to more than 44°C on June 6. As a result, the ozone level shot up by 87 per cent in Civil Lines, 171 per cent in Punjabi Bagh, 315 per cent at Mandir Marg and 82 per cent at IGI airport, within a week. The average ozone level of all locations was 73 microgramme per cubic metre on June 1 that doubled beyond the standards by June 5 (see Delhi summer ozone factsheet on CSE website).
• More frequent violation of ozone standards as the temperature rises this summer: CSE has tracked daily ozone since January 2014. This shows that frequency of days violating ozone standards has increased with the onset of summer. For instance, in R K Puram, while 22.5 per cent of the days in January and 39.2 per cent days in February have exceeded the standards, as much as 87 per cent of days in March, 80 per cent in April and 64.5 per cent in May have exceeded the safe limit of eight-hour average of 100 microgram per cubic metre. In Civil Lines, a pollution hot spot, about 48 per cent of the days in January and 60.7 per cent in February had exceeded the standards, but this increased to 86.6 per cent in April and all 12 days analysed (100 per cent) for May. In Mandir Marg, 83.3 per cent of days in April and 83.8 per cent in May have violated the standards. In the high traffic area of IGI airport at the periphery of Delhi, the month of May has been particularly bad with 93.5 per cent days exceeding the standard. This trend could have been worse if the city had not experienced intermittent rains with cooling effect this summer.
• Peak ozone levels are very high: While the number of days violating the ozone standards has increased during summer, the daily peaks have also hit dizzying heights. On several occasions and locations, very high peak levels have been noted, close to 2.5 to three times the standards. This is of serious concern as even short duration exposure to high ozone levels can cause great harm. This is one of the reasons why ozone standards are set for eight hours average as well as one hour average.

Why should we worry about ozone?

Ozone is an extremely harmful gas—particularly for those involved in outdoor activities. Just a few hours of exposure to it can trigger serious health problems, especially among those who are already suffering from respiratory and asthmatic problems. Ozone worsens symptoms of asthma, leads to lung function impairment and damages lung tissues. Chest pain, coughing, nausea, headaches and chest congestion are common symptoms. It can even worsen heart disease, bronchitis and emphysema. It increases emergency hospital visits and admissions related to respiratory diseases.

Scientists inform that ozone is a powerful oxidiser, which means it can damage cells in a process akin to rusting. Children and the elderly are at special risk. International studies have also found a strong association between ozone and daily premature death counts; deaths related to ozone exposure are more likely among people with pre-existing diseases.

Ozone that gets created in the polluted environment of a city can drift, depending on the wind direction, and move towards cleaner environs in the rural periphery. Here, it can begin to accumulate as it has less chances of reacting with other pollutants. It builds up faster at the outskirts of cities and can damage crops.

What do other governments do?

Ozone is included in the daily smog and health alert programmes in countries such as Mexico, the US and China. In Mexico City, the elderly, children and those suffering from respiratory and cardiac problems are advised to stay indoors when levels of ozone go up. The US-based National Research Council, part of the National Academies of Science, has recommended that local health authorities should keep the harmful effects of ozone in mind when advising people to stay indoors on polluted days. A study carried out in the US by scientists led by the University of Southern California and reported in Lancet, has found that in high-ozone areas the relative risk of developing asthma in children playing three or more sports was more compared to children playing no sports. Outdoor heavy exercise is not recommended as with every breath taken in, by athletes in particular, 10 to 20 times as much air, and thus pollutants, as sedentary people do.

What should Delhi do?

“Delhi needs to act immediately to protect public health,” says Roychowdhury. “Explosive increase in vehicle numbers, especially diesel vehicles that spew much higher levels of NOx and volatile organic compounds, can only worsen the deadly recipe needed for formation of ozone in the city with hot and extreme climate.”

• The city government must prevent this trend by making serious efforts to control NOx and volatile organic compounds that largely come from vehicles. Reduce numbers of vehicles, especially diesel vehicles. For instance, diesel cars emit three times more NOx than petrol cars and NOx is the main catalyst that triggers reaction among gases to form ozone.
• The city government must introduce a daily health alert system to inform the sensitive population (children, elderly and those suffering from respiratory and cardiac problems) about the high daily levels and enforce emergency pollution control measures such as reducing traffic volume, allowing only clean fuel and vehicles and scaling up public transport, walking and cycling in the city.