The Guardian, a highly reputable newspaper, seems to use "on/in" interchangeable after "impact".
Sentences 1 and 2 are mine, and I want to know if my reasoning for the usage of on/in after "impact" has any merit. I want to follow through on this "reasoning" consistently, and not write "on" one time and "in" another time. This is just for the use of "impact", not in general.
Ngram shows "impact on reducing" is more often used than "impact in reducing".
- The program's impact on reducing benefits . . .
Example: . . . family doctors can also have a dramatic impact on reducing emissions in the NHS . . . – The Guardian
- The program's impact in reducing benefits . . .
Example: . . . such a scheme could also have an impact in reducing the climate footprint of the global plastics . . . – The Guardian
The following is my understanding/reasoning:
We say impact on noun/noun phrase – the impact [of something] on the reduction of carbon emission.
We say impact in verb+ing – the impact [of something] in reducing carbon emission.
Note: I have looked at questions from ELU and ELL on the usage of "impact on/in". There is overwhelming preference for "impact on". But in those questions/answers, "impact on" is followed by a noun/noun phrase. None of them specifically talks about the use of "in" when what follows "impact in" is a verb+ing. That is what I am asking about. Here are a few that I have gone through:
Best Answer
I think this question has been sufficiently answered on ELU. As you've noted, there have been several similar questions over yonder and here on ELL too. That said I understand where your bewilderment comes from.
When you say someone/something has an impact on a thing, that thing is the object that the impact works on. In your example "the impact on the reduction of carbon emission", the noun phrase "the reduction of carbon emission", the object of the preposition on, is also the object of the impact at issue.
A footnote to this: the noun impact came from the verbal form, meaning "collide, strike against" (see its etymology), much as a strong force on an entity. It later evolved to include a figurative usage.
When you say something has an impact in a thing, that thing is a scope or context. This has been explained by several answers, and I won't go into much detail. Your suggestion is reasonable, but I wouldn't consider it absolute. The preposition in goes more with what comes after instead of before it. Think of "have an impact in reducing carbon emission" in this context:
Here in NP/gerund is the context/scope something happens. "such a scheme could also have an impact in reducing the climate footprint of the global plastics" means the impact is within the context of reducing the climate footprint of the global plastics. In other words, "such a scheme" (whatever it may be) could contribute to this goal: reducing the climate footprint of the global plastics.