Final answer:
Increased emissions of sulfur and nitrogen oxides from coal burning and vehicle exhaust have led to more acidic precipitation today than in 1900, resulting in acid rain with harmful environmental impacts.
Step-by-step explanation:
Two main reasons why precipitation is more acidic today compared to 1900 are due to increased emissions of sulfur oxides and nitrogen oxides. These substances primarily come from the burning of coal and motor vehicle exhaust. When these gases combine with water in our atmosphere, they form acids, leading to a lower pH in precipitation, which is known as acid rain. Acid rain has detrimental effects on soil, plants, aquatic ecosystems, and manmade structures. Due to human industrial activities, there has been a significant rise in these emissions, hence the increased acidity in precipitation.