*snipped*
what effect would the oxygen present in the trunk have to do with diluting that condition?
IMHO, regarding conditions for decomposition we're dealing w/ 3 environments:
1) internal to the body covering
2) internal to the plastic bag(s)
c) internal to the trunk
Greatly simplifying things we can assume the barriers between each of these is somewhat effective, but, not 100%, therefore, no one is perfectly 'sealed' from either of the other two. The presence of the stain is one means of suggesting this is a reasonable assumption to make...not perfect (owing to possible tear of a sealed bag during a lift outta the trunk), but, let's go with it for now, shall we? Let's say things are 'enclosed' not to imply 'sealed'.
The highest degree of decomposition that generates chloroform under 'normal' circumstances even when the body isn't enclosed is during the rapid, early phase of the delicate internal organs, gut, etc. This takes place inside the covering of the skin, etc. which is, to a large extent, anaerobic. So...even under 'normal' circumstances in the very early stages of decomp we get chloroform...tada.
In this case, the body being inside a plastic bag further ensures...perhaps even extends...the time in which the decomposition is taking place w/o excess oxygen because under 'normal' circumstances when the skin is breached oxygen becomes available to (a) allow chloroform to escape and (b) *advertiser censored* the generation of chloroform because oxygen is now present during decomposition. To a lesser extent having an overall effect, chloroform is 'heavier' than air...so it displaces air from the bottom of the trunk first. As the trunk 'filled' with chloroform and other decomp gases the air would have been slowly displaced from the trunk through any leaks around the trunk lid seal. This would, albeit only slightly, reduce the amount of oxygen available for decomposition, hence, reducing chloroform generation. IMHO, 6/16-6/18 there's not so much off-gassing going on, but, by ~6/19...it is becoming tremendous, esp. if the body was disturbed 6/18 during the shovel shuffle.
So....oxygen available in the trunk have an effect? Sure...a little, but, not much owing to the plastic bag, IMHO.
Also, if some of the chloroform was a result of the natural decomp situation, and additional chloroform was present in any cleaning chemicals used on the carpet, could that make for an unusually high amount
I'm gonna take exception to the use of "unusually high amount" because there is no such thing as a usual amount in this situation...we just don't know what to expect under these circumstances. Nothing to compare it to other than a trunk w/o a HDE taking place in it. THAT is what is giving us the comment that there was an high amount of chloroform in Casey's Pontiac...there shouldn't be a dead body in the damn car...therefore there usually shouldn't be any/much chloroform in there.
With that outta the way...the short answer is sure...yes...if chloroform-containing solvents were used to clean the carpet it would show up as exacerbating the chloroform level in the trunk that was already present from the HDE.
(if there is still a consensus that certain carpet or car cleaning chemicals do have chloroform as a component)?
Not a consensus...it is a certainty. I'm sure you can find'em if you search for'em. BTW...chloroform also can be found in some commercial-grade pesticides (since you didn't mention). FYI.
If the trunk was aired out for several hours, but solvents were used to clean it or perhaps mask the odor, that might make for the higher concentration, would it not?
Only if the solvent contained chloroform.
HTH.