For a naive and non-scientist, it would be obvious that the liquefied petroleum gas (LPG) is a clean fuel. Especially in the cities, it is the most common fuel for domestic cooking. There is also a small fraction of light duty vehicles which run on LPG and has proven to be clean compared to their counter parts - diesel and petrol. Then, why is it that recent studies from national agencies are declaring that LPG is the main culprit to the growing air pollution problems.

Hindustan Times on September 20th, 2010, released a similar note, questioning the results, which are not 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?

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 - ~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.