CCL4 = carbon tetrachloride

The following are the known natural sources of CCL4 emission

1. Volcanoes (but in extremely trace amounts - order 1 part per billion) - according to Schwander etal 2004 Journal of Geophysical Research - world wide emissions would be about 3 +/- 1 tonnes per year (insignificant)

2.  Mine gas and mineral leakage (I don't believe anyone is detecting CCL4 emission associated with increases in fracking tho this might not be checked for)

3. The arctic ocean (and ocean bottom) - warming may accelerate release of these stored deposits.

4. Some forms of marine algae emit CCL4

5.  There is an atmospheric chemistry process that involves Chlorine and Methane that can make CCL4 (at very low rates)

So its possilble that the now observed excess is due to a combination of these natural sources.  Personally I doubt this.

I believe the most likely culprit are the following two "black market" sources:

a) insecticide production

b) solvents for various electronic components

Prior to the Montreal Protocol, the biggest source of CCL4 emission was the dry cleaning industry.

CCL4 = carbon tetrachloride

The following are the known natural sources of CCL4 emission

1. Volcanoes (but in extremely trace amounts - order 1 part per billion) - according to Schwander etal 2004 Journal of Geophysical Research - world wide emissions would be about 3 +/- 1 tonnes per year (insignificant)

2.  Mine gas and mineral leakage (I don't believe anyone is detecting CCL4 emission associated with increases in fracking tho this might not be checked for)

3. The arctic ocean (and ocean bottom) - warming may accelerate release of these stored deposits.

4. Some forms of marine algae emit CCL4

5.  There is an atmospheric chemistry process that involves Chlorine and Methane that can make CCL4 (at very low rates)

So its possilble that the now observed excess is due to a combination of these natural sources.  Personally I doubt this.

I believe the most likely culprit are the following two "black market" sources:

a) insecticide production

b) solvents for various electronic components

Prior to the Montreal Protocol, the biggest source of CCL4 emission was the dry cleaning industry.

Besides, the research shows that N2O contributes substantially to ozone layer depletion. Accordingly to NOAA, N2O is now the largest man-made ODS and is expected to remain the largest throughout the 21st century. See more detail at (http://rstb.royalsocietypublishing.org/content/367/1593/1256.full.pdf.

Thanks goes to Dr. Bothun for giving valuable information.