The purpose of this thesis was to use multiscale testing and simulation methods to better understand the role various atomistic processes play in the degradation of mechanical properties in harsh environments. Specifically, two environments were considered:​ the effect of atomic hydrogen in harsh offshore oil and gas environments and the effect of atomic oxygen impacts in space. This thesis is written in a manuscript format with 8 unique chapters all falling under the umbrella of atomistic processes and macroscale properties. The thesis begins with a detailed literature review of all necessary background research including a summary of molecular dynamics and a detailed explanation of the current gaps in knowledge. This is followed by 4 chapters that test various method and multiscale simulation tools. Finally, findings from these chapters are applied to two specific environments where multiscale challenges exist:​ hydrogen in offshore oil and gas, and atomic impacts in space. Each chapter is written as a standalone paper including separate cover pages, literature reviews and conclusions. The findings from these case studies are then summarized in a conclusion.