Wednesday, November 24, 2010

Is LPG Bad for the Air Quality in Indian Cities?

For a naive and non-scientist, it would be obvious that the liquefied petroleum gas (LPG) is a clean fuel, where ever it is burnt. Especially in the cities, it is the most common fuel for domestic cooking - it is expected to burn cleanly and the flames are free of the soot or other aerosols, which are immediately visible when burning coal or any form of biomass. There is also a small fraction of light duty vehicles (for examples, small cars and 3-wheelers) which run on LPG and was proven to be clean compared to their counter parts - diesel and petrol. Then, why is it that recent studies from national agencies declaring that LPG is the main culprit to the growing air pollution problems in the cities like Delhi, Pune, and Mumbai?

Hindustan Times on September 20th, 2010, released a similar note, questioning the results, which are not in the public domain, but being presented at international scientific conferences. The article reports
An IOC presentation at a seminar organised by diesel vehicle manufacturers said that half of PM 2.5 in residential areas of Delhi was because of combustion of domestic LPG. In industrial areas, it was as high as 61 per cent and at traffic junctions 40.5 per cent.

Is this even logically possible?
  • How can a clean burning LPG contribute to ~40% of the air pollution being observed in the city?
  • What is the fraction of LPG usage in Delhi compared to petrol or diesel or CNG to give 40-60 percent contributions to PM2.5, the most harmful of the pollutants?
Lets look at some numbers. The daily PM2.5 concentrations in Delhi average around 80-120 micro-gm/m3, at least twice the WHO health standards. If 40 percent of the outdoor air pollution is coming from domestic LPG combustion, then what is this contributing to the indoor air pollution in the urban houses? Are these results suggesting that the urban houses in Delhi are very hazardous because of the LPG combustion?

Is LPG not a clean fuel anymore?

Similar results were presented for Mumbai at the Better Air Quality Conference in Singapore in November, 2010, by NEERI - nearly 13 to 34 percent of PM2.5 pollution in Mumbai is due to LPG combustion?

Link to the presentation by NEERI.

How can once a clean fuel and most used domestic fuel be that deadly?

What is the science behind these numbers?

The CPCB study, which Environment Minister Jairam Ramesh has decided not to put in public domain, is likely to be the basis for India’s future auto fuel policy.

If these results are good enough to be presented at international conferences, why is this report not public?

Similarly, this is the kind of false interpretation of the results, which leads to think that we can put a vacuum cleaner in the air and suck up all the bad parts of the air and make it all better for us to breath.

What is source apportionment?
A number of source apportionment studies are conducted across the globe and a number of them are on-going. Technically, this is the most sound approach to pinpoint the contributions of various sources to the local air pollution. However, the methodology does have some limitations which can be rectified with proper planning and local resource information.

In short, this methodology starts with the sampling of pollution (what we breathe and what we monitor) on to a filter, followed by chemical analysis of the sample to identify the mass of various metals, ions, and carbon compounds. The individually masses are then statistically matched with source profiles (also sampled and analyzed similar to the air samples, but sampled as close to the source as possible). The last part is called Receptor Modeling; the end result of which is the apportionment of sources for the air sample monitoring.

Of course, the source profiles are wrongly selected or erroneous during their establishment, the results will be illogical or hard to support the real world observations (like above).

These links above also present a library of source apportionment studies conducted in various parts of the world (courtesy of the Dr. Judith Chow and Dr. John Watson @ Desert Research Institute)

No comments: