Role of Meteorology in Delhi's Air Pollution Problems

An article January 8th, 2010, in India Today reads "Blame air pollution for Capital's blanket of fog". This is true is some ways, for example, the low lying emissions do increase in Winter in Delhi, due to the extra heating and use of biomass (or anything people get their hands on). However, this phenomena has more to do with the meteorology typical to these latitudes.

This working paper is now published as a journal article in EMAS in May, 2012.

It is given that the air pollution can only be controlled at the source and the limiting factor is most often the balance sheet of costs and associated benefits (like health). However, in some cases, the possible reductions in emissions are a direct function of the geographical location and prevalent meteorological conditions. For example, in cities like Los Angeles or Ulaanbaatar, which form a valley terrain, irrespective of the wind patterns, the emissions tend to stay in the area longer and contribute more to the local air pollution problems. On the other hand, in cities like Bangkok, Beijing, Delhi, Dhaka, and Manila, with flat terrains, the meteorology tends to have higher impact on either dispersing or retaining the air pollution. The Beijing EPB considers the recent heavy snow fall is good for their blue-sky program, because the snow and rain precipitates most of the pollution.

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.


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.

********
Other articles linked to Air Pollution in Delhi under SIM-air Working Paper series

1. AQM in Delhi: Then, Now, & Next
2. Photochemistry of Air Pollution in Delhi
3. Monitoring & Mapping Air Pollution
4. Impact of Metro System on Air Pollution in Delhi