Did the Metro help reduce air pollution in Delhi?

Deepti Goel of DSE (a dear friend) and Sonam Gupta of Univ of Florida have been doing research on this very important topic.

They share the findings in Mint’s column:

To summarize, preliminary evidence points towards a reduction in the levels of nitrogen dioxide and carbon monoxide. Given that both nitrogen dioxide and carbon monoxide are important vehicular emissions, our initial findings suggest that the Delhi Metro has encouraged people to switch from private to public mode of travel resulting in positive effects on air quality in the city. In the light of our findings and given the existing evidence on the adverse health effects of air pollution, these indirect health benefits should be taken into account when urban policy makers contemplate setting up large scale intra-city transportation systems. We provide a rationale for subsidising these mass transit systems, such as the metro or dedicated bus routes, even when the direct costs do not show a net profit. These public transport systems should be considered seriously for other cities that face similar challenges in terms of vehicular congestion and health costs due to pollution.

The study is based on 2 locations – ITO and Siri Fort:

In our study, we examine the effect of the Delhi Metro on air quality using data obtained from the CPCB on four pollutants—nitrogen dioxide, carbon monoxide, ozone and sulfur dioxide, between 2004 and 2006. This data is collected at two locations in Delhi—ITO, a major traffic intersection in central Delhi, and Siri Fort, a residential locality in South Delhi. We obtained hourly data on temperature, rainfall, wind speed and relative humidity for Delhi from the India Meteorological Department.

In order to establish a causal link between the Delhi Metro and air quality it is important to compare pollution actually observed in the period after the Delhi Metro became operational with its correct “counterfactual”. This counterfactual refers to the level of pollution in the hypothetical scenario where all other factors that affect pollution remain the same as in the post-metro period, and the only difference is that the metro does not exist in the counterfactual. Any difference between the observed pollution in the post-metro period and the pollution in the counterfactual can then be attributed to the Delhi Metro. To do this, we estimate the trend (pattern over time) in pollution using hourly pollution data over a reasonably long time period which includes the date of extension of the Delhi Metro. If we detect a sudden change in the level of pollution at the date of extension of the Delhi Metro, then we attribute this change to the extension of the Delhi Metro.
Between 2004 and 2006, there were six extensions of the Delhi Metro rail network. At each extension, we examine the time trend for each pollutant separately. We identify the localised, short-term effect on pollution that can be attributed to each extension of the Delhi Metro by conducting this analysis separately for pollution data from the ITO (Income Tax Office) and Siri Fort. Our preliminary analysis shows a reduction in the levels of nitrogen dioxide and carbon monoxide at both locations. This reduction varies between 24-29% for nitrogen dioxide and between 26-69% for carbon monoxide. For sulphur dioxide, we find an increase of 90% at ITO, and a decrease ranging between 35-89% for Siri Fort. For ozone, we do not find a uni-directional effect even across extensions at a particular location .
Interesting stuff.
Though, one should also look at the environmental pollution created by metro while constructing it as well.  That would make the exercise even more comprehensive….

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