Assessment of the impact of improvement measures on air quality: Case study of Delhi

It is well known that the ambient air pollution attributable to road traffic depends on a number of factors such as the quality of fuel used, engine technology, driving conditions, emission control devices, and meteorological conditions. In spite of the efforts to control emissions from road traffic by way of stringent emission norms (such as Euro-Ill and IV) for automobile engines and improved fuel quality, the road traffic emissions form a significant proportion of urban air pollutants. This is primarily due to constant increase in number of motor vehicles and their use in the urban areas. Recognizing this aspect and with a view to provide clean air, the Supreme Court of India has issued an order in a public interest litigation matter, directing that public transport vehicles, namely intracity buses, should be run on compressed natural gas (CNG) in Delhi. The directive of the Supreme Court was implemented but along with it many other actions/measures were also implemented by the concerned authorities. These measures included operation of taxis and auto rickshaws on CNG, scrapping of all commercial vehicles including taxis aged 15 years and above, introduction of Euro-I emission norms for private passenger cars, use of unleaded petrol, and premixing of 2T oil with petrol for two wheeler motor vehicles. The result of the combined efforts is a perceivable change in the ambient air quality for the better. But questions and debates were frequent as to whether the improved quality of air is mainly due to CNG and if so how much is to be attributed to CNG. To answer these questions a detailed study was carried out to quantify the emissions and their reductions due to different measures. This paper presents an account of the study. In this study the quantity of criteria pollutants such as carbon monoxide, nitrogen oxides and particulate matter and hydrocarbons are estimated on the basis of vehicle kilometers traveled by different vehicles in the city during the course of time when the improvement measures were being effected on an incremental basis. The results of the study are discussed and the contribution of each of the measures is estimated. The implemented improvement measures were extremely successful. The improvement was, as made out to be, not simply because of CNG conversion of buses but due to the combined effect of many other steps like improved vehicle technologies and fuel quality, phasing out the old diesel vehicles, conversion of auto rickshaws to CNG, etc. The results are of interest to both the analysts and policy makers in appreciating the impact of each of the measures.