Final answer:
The National Trends Network (NTN) shows lower rainfall pH levels in the Northeastern US due to high urbanization and industry, with improvements depending on emissions control and regulations.
Step-by-step explanation:
Long-Term Trends in Rainfall pH
The National Trends Network has been instrumental in monitoring the long-term trends of rainfall chemistry across the United States. The data from the NTN indicate that rainfall pH levels are generally lower in the Northeastern United States, which can be attributed to the high concentration of urban areas, industrial plants, and power generation facilities.
Furthermore, these regions are exposed to pollution from the Midwest due to prevailing wind directions, and the soil composition is less effective in neutralizing acidic precipitation. Over time, measures taken to reduce emissions from vehicles and power plants have focused on diminishing the levels of nitrogen and sulfur oxides in the atmosphere, which are principal contributors to acid rain.
However, the overall improvement or change in rainfall pH levels can vary depending on a myriad of factors including regulatory practices, technological advancements, and shifts in energy sources.