The phrase "an additional contribution" is correct and usable in written English.
It can be used when referring to an extra input or donation, whether in a financial, intellectual, or physical context.
Example: "The committee decided to make an additional contribution to the charity to support their ongoing projects."
Alternatives: "an extra input" or "a supplementary donation."
Maybe you can think of the $8 as an additional contribution to an organization you support.
Some of the high-Tc superconductors provide an additional contribution to the specific heat, which is proportional to the temperature.
I will not accept a new wave of what they call fiscal retrenchment, belt-tightening, without asking people at the top to make an additional contribution.
As a result of that it "made an additional contribution of £2.3m to the ITN defined benefit pension scheme in excess of the funding agreement with the trustees".
Genting, a subsidiary of Southeast Asia's largest gambling company, made an additional contribution of approximately $400,000 to the group allied with Mr. Cuomo during 2011.
Over the summer, his foundation announced an additional contribution of $15 million to a handful of cultural institutions to help them enhance visitors' experiences through mobile technology.
With an additional contribution from the Gerry Charitable Trust, a key supporter of the Roslyn Landmark Society, the restoration funds were in place.
Corning's vice chairman and chief financial officer, Jim Flaws, said Corning planned to use the proceeds to reduce debt and strengthen its balance sheet, including making an additional contribution to its pension plan.
"I will not accept a new wave of fiscal retrenchment, of belt-tightening, without asking people at the top to make their contribution, to make an additional contribution," Clegg told Marr.
Changes to the draft budget mean an additional contribution of £120m will be made to the Department of Health over the next four years and following an internal reclassification of money, a further £69m is also to become available.
In particular, an additional contribution by fluid flow to the heat transport is likely.
