Air Pollution during Delhi Winters - How Bad is it?

  • 16/12/2010

For multiple reasons, the winters are the worst in Delhi, India - harsh winters, limited air movement, and restraining meteorological conditions worsen the already topped out air pollution problem. Access the real time air quality monitoring data from nine stations in Delhi here, operated by the Central Pollution Control Board and Delhi Pollution Control Committee. An article from January 8th, 2010, in India Today reads "Blame air pollution for Capital's blanket of fog". This is very true. For example, the low lying emissions do increase during the Delhi Winters, such as extra heating that is required and use of biomass (or anything people get their hands on). In addition to that, this phenomena has more to do with the meteorology typical to these latitudes.

The Center for Science and Environment (CSE) in Delhi, India, organized a gathering of air pollution experts to review the pollution problems and here is what they have to say

  • Not only are the tiny particles choking us, nitrogen dioxide levels have worsened; daily peaks of carbon monoxide are unacceptable, ozone pollution has persisted through the winter months. This has emerged from the official public information system on daily air pollution and monitoring. Some of these pollutants come predominantly from vehicles.
  • This cocktail of toxic gases and particles is alarming in a city already experiencing severe respiratory health problems. These underlying diseases make people more vulnerable to the toxic air.
  • Second generation reforms will have to scale up public transport, cycling and walking, reduce traffic volume and get the cleanest vehicles quickly. Daily smog alert should target to reduce daily dose of toxins.

More @ CSE, December 13th, 2010.

In the SIM 25-2009 working paper, "Photochemistry of Air Pollution in Delhi, India: A Monitoring Based Analysis", the monitoring data from the Indian Tax Office (ITO) station in Delhi, India, is analyzed to explain the observed trends in the criteria pollutants, PM2.5, NOx, CO, and Ozone. The photochemical formation of Ozone, including the seasonal and diurnal cycles, influence of NOx-VOC chemistry and policy implications of further controls is discussed in this paper.

Figures below present the correlation between the observed monthly 24-hr averages over the period of 2006-09. The measurements for the summer months are separated.

In this regards, a study of air movement over urban areas can help us better understand the movement of pollutants and their respective impact on pollution planning. The role of meteorology as a diffusing or non-diffusing agent, is studied using 20 year meteorological fields over Delhi, India and its impact on air pollution dispersion. See the animation of the dispersion patterns by clicking the image below.

See the detailed report "Role of Meteorology on Urban Air Pollution Dispersion".

Some figures from the report are presented below.

1. Mixing heights effect the observed air pollution levels in Winter months - lower the mixing heights, mathematically, higher the concentrations that we daily observe.

2. Average mixing heights in 2008 over Delhi, India

3. Variation of monthly average tracer concentrations compared to the annual average concentration for the Delhi emission domain. A clear conclusion is that irrespective of the constant emissions over each month, the observed concentrations are invariably 40% to 80% higher in the winter months (November, December, and January) and 10% to 60% lower in the summer months (May, June, and July) when compared to the annual average tracer concentrations. See a comparison to the measured pollution below.

4. PM2.5 monitoring data from the ITO monitoring station in Delhi, India

A back trajectory analysis was also conducted to assess the influence of emission sources outside Delhi. See the full report.

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