This is the 1018th most frequent Russian word.
добровольно
Voluntarily.
In this sentence, "добровольно" is used to signify a voluntary, self-decided action by the subject without external pressure.
Я решил добровольно участвовать в благотворительной акции.
I decided to voluntarily participate in the charity event.
Here, "добровольно" indicates that the action (donating part of their salaries) was taken freely without compulsion.
Сотрудники компании пожертвовали часть зарплаты добровольно.
The company employees voluntarily donated part of their salaries.
In this example, "добровольно" emphasizes the voluntary nature of the individual's agreement to assist with the project.