Final answer:
The release of lead into the atmosphere has declined due to regulations that have phased out leaded gasoline, reducing emissions from vehicles and industry. This has resulted in a significant drop in atmospheric lead levels since the 1980s. Acid rain, caused by SO2 and NOx emissions, has also been reduced through regulatory efforts in North America and Europe. Therefore, the correct option is 1.
Step-by-step explanation:
The amount of lead released into the atmosphere has significantly declined since the introduction of lead-free gasoline. In the past, lead emissions were primarily from fuels in on-road motor vehicles and industrial sources. Due to regulatory efforts, especially in the U.S. to remove lead from on-road motor vehicle gasoline, lead emissions have dramatically declined. For example, between 1980 and 1999, emissions of lead from the transportation sector dropped by about 95%, and levels of lead in the air decreased by 94%.
Acid rain, another environmental concern, is caused mainly by emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) resulting from the combustion of fossil fuels. These substances can lower the pH of lakes and water bodies and harm the natural and man-made environments, including damaging forests, soil, lakes, buildings, and statues made of marble and limestone. Regulations have been implemented to limit the amount of SO2 and NOx released into the atmosphere, which has reduced the severity of acid rain in North America and Europe.
Today, the highest levels of lead in the air are often found near lead smelters. The primary sources of lead to the atmosphere now are from ore and metals processing and piston-engine aircraft operating on leaded aviation gasoline.