What substance is primarily responsible for the aging process of newspapers?

The aging process of newspapers is primarily influenced by the presence of acid, but specifically, it is the acidic compounds that lead to the degradation of cellulose, which is the main component of paper. Newsprint is often made from wood pulp, which contains both cellulose and lignin, but the aging and yellowing of the paper are largely due to acid hydrolysis. As the acidic components break down cellulose fibers, it results in the loss of structural integrity and leads to discoloration and brittleness, which are characteristic of aging newspapers.

Lignin can contribute to the quality of the paper, but it is the acidic conditions that predominantly cause the degradation over time. Therefore, while lignin is a significant component in understanding the material properties, it is the reaction involving acids that plays the critical role in the deterioration associated with aging newspapers.