The phrase "become aware of" can be replaced with several synonyms depending on the context of the sentence. For example, "realize" can be used when someone has had a sudden understanding or revelation about something. "Notice" can be used when one has observed something for the first time, while "perceive" can be used when one becomes aware of something through their senses. "Recognize" can be used when someone has identified something they were previously unaware of, and "apprehend" can be used when one has gained a full understanding of something complex or difficult to comprehend. Overall, there are many synonyms available that can be used to replace "become aware of" to add variety and clarity to your writing.