NOXious trail | Centre for Science and Environment

NOXious trail

Over the last few weeks we were inundated with queries from the media. The air quality data produced by the apex air quality monitoring body in the country - the Central Pollution Control Board (CPCB) shows NOx levels in Delhi rising dramatically. Why? We were equally curious - has CPCB explained the reasons? According to media reports, the CPCB is blaming the CNG programme in Delhi for the rise in NOx levels.

We checked with CPCB whether any study was conducted to establish the basis of their claim. CPCB said no. This was a mere hypotheses based on what is generally known about the potential of CNG vehicles to emit high Nox, if NOT maintained properly. Such a glib explanation spurred us to get to the basics - what is the pattern in NOx levels in the city. We scanned the time series data for seven monitoring stations in the city. And we were in for a few surprises:

dot.gif (88 bytes)The average annual NOx levels have begun to surpass the standards in one station in Delhi - the busy traffic intersection of ITO, and that too since 1997. During 1997 and 2001, the levels have hovered between 59 microgramme per cum to 63 microgramme per cum, as against the annual average standard of 60 microgramme per cum. During the last two years -- 2002 and 2003, the annual average levels are comparatively higher - 74 and 94 microgramme per cum, respectively.

dot.gif (88 bytes)A detailed traffic survey conducted by the Transportation Research and Injury Prevention Programme of the Indian Institute of Technology, Delhi, show that among five major traffic intersections surveyed in Delhi during 2002, the ITO intersection had much higher traffic volumes and density during different peak times of the day. Two-wheelers and cars together dominated the traffic volume, from 53 per cent to 70 per cent. The heavy-duty commercial vehicles including buses formed 5 to 14 per cent.

dot.gif (88 bytes)Is the rise in NOx levels similar to the ITO trend in the other six monitoring sites in Delhi? No. In all other sites during 1997 - 2002, the lowest average level reported was 19.4 microgramme per cum, while the highest average reported was around 39 microgramme per cum, but never above the standard.

dot.gif (88 bytes)CPCB data also shows that other Indian cities, including Kolkata and Pune, have crossed the NOx standards consistently over the last couple of years. There are more questions still. But at least the pattern is clear to us.  Though the NOx levels are low, it is possible to detect a steady rise over time. But after one careless remark - that the increase in NOx in Delhi could be due to the CNG programme - the authorities once again are lulled into complacency.

And that makes us angry. Why is NOx increasing and how do we deal with it? NOx may prove extremely difficult to control in the future. The word of caution going around globally is that unlike other air pollutants, which follow the simple processes of emission, concentration, dispersion and deposition, nitrogen oxides have a more complex life cycle. NOx also triggers formation of more harmful pollutants, such as ozone. The mention of ozone opens up yet another Pandora's box. Ozone has not as yet been assessed adequately and in Delhi is only monitored in the high-traffic ITO intersection, which records very low levels. Naturally, high levels of NOx will first trigger ozone, but later, react with this pollutant to mop it up.

Therefore ozone monitoring should be expanded immediately to include more representative areas of the city. For most effective results, both hydrocarbons and NOx will have to be controlled effectively, and simultaneously, to prevent an ozone catastrophe.

But what gripped our attention is the 'inadvertent' leak -- a recent monitoring at a downwind residential site in Delhi has exposed high ozone concentrations, which CPCB has not yet made public.

Our air quality regulators refuse to acknowledge the looming air pollution challenge. While particulate levels are still high, NOx has begun to rise, too. But there is still no policy recognition of the dire consequences of the city getting caught in the crippling grip of the NOx-PM trade off. The problem of NOx emissions is linked with improved technology. All new technology solutions to particulate, carbon monoxide and hydrocarbon emissions today are traded for higher NOx emissions. Engineering and technological solutions to reduce one only increases the other. The trend in Delhi only reconfirms what the industrialised North has already witnessed. For instance, while the US has seen a dramatic decline in PM, CO and HC emissions between 1970 and 2000, NOx emissions have increased by 20 per cent during the same time. This has spurred the US to move towards the most stringent fuel-neutral emissions standards of this decade.

It is therefore baffling why our regulators show such complete lack of insight into Delhi's experience. NOx level rise in Delhi coincides with the implementation of the CNG programme, higher penetration of new diesel vehicles, and much deeper penetration of four-stroke two-wheelers. Unstable NOx emissions from poorly maintained CNG fleet are suspect.

The phenomenal spurt in diesel vehicles sales over the last four years are also suspect, as they are legally allowed to emit higher NOx than petrol vehicles. Four stroke engines that form nearly 80 per cent of the new two-wheeler sales in the city are also expected to have higher NOx levels than two-stroke engines. Where is the blueprint for action to monitor the impact of these developments and design a NOx control strategy?

Instead of being so eloquent with superficial judgments on the local air quality situation, the regulators need to spruce up their monitoring capacity to be able to track changes and act on them. NOx and particulates are a serious challenge today. Include their measurements in the vehicle inspection programme for the in-use fleet, even as new standards are tightened. There is no reason why CNG vehicles cannot maintain their low emitting characteristics with disciplined, preventive maintenance.

Regulators also shy away from engaging in debates on why any fuel should be allowed the leniency to emit more NOx and PM, as is done in the case of diesel vehicles, which also give them a competitive edge in the market? They are content with inheriting the inconsistency of the European standards that are still not fuel-neutral. Similarly, the government refuses to separate out the hydrocarbon and NOx emissions standards
for two-wheelers. Combined standards allow both two- and four-stroke vehicles a generous margin to emit more hydrocarbon and NOx, respectively. Make separate and stringent hydrocarbon and NOx emission standards for all two-wheelers to settle the trade-off between two-stroke and four-stroke.

Raising alarm is easier than finding solutions. Let us be clear -- achieving the very low levels of NOx, PM and toxins - which all categories of vehicles will need to meet in the future - presents a very serious challenge to air quality regulators and the vehicle industry. Acknowledge it and act on it, but don't just look for a whipping boy.

-- Anumita Roychowdhury

Right To Clean Air Campaign



  • Air pollution is the fifth largest killer and seventh biggest illness burden in India as estimated by the Global Burden of Disease (GBD) report. The speed at which urban air pollution is growing across our cities is alarming. Severe particulate pollution and newer pollutants like nitrogen oxides, ozone and air toxics are worsening the public health challenge. Vehicles are a special challenge as these are the fastest growing sources of air pollution.

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