经过多年的改善 美国空气质量依旧下降

（单词翻译）

US Air Quality Dropping After Years of Improvement

New data shows that air quality across the United States is dropping after many years of improvement.

Over the last two years, the U.S. had more polluted air days than just a few years earlier, official data showed. The information was collected by the Environmental Protection Agency, or EPA, and examined by the Associated Press.

Climate experts say it is too early to know whether the recorded drops are the beginning of a long-term situation. But health officials say it is troubling to see the changes following years of progress.

In 2017 and 2018, there were 15 percent more unhealthy air days than in the previous four years, the data shows. The 2013-2016 period saw the fewest number of unhealthy air days the U.S. had ever had since at least 1980.

Air quality is affected¹ by a complex mix of conditions, both natural and man-made. Federal rules that limit emissions³ material from factories, cars and trucks have greatly helped improve air quality over the past 20 years. But scientists say that in any given year, air quality can also be affected by natural changes. Some believe that may be causing the latest drops.

Bob Perciasepe is a former EPA official who is now president of the not-for-profit Center for Climate and Energy Solutions. He says the current data does not necessarily mean the changes will be permanent. “What you’re seeing is a flattening⁴ off of progress as opposed to a major change in the wrong direction,” he told the Associated Press.

In 2018, more than 500 American cities reported days when the official air quality index passed 100, the data showed. This level means the air is unhealthy for people with heart and lung disease, as well as for older people and young children.

The EPA information showed that on average in 2017 and 2018, there were nearly 140 times when a city’s air pollution reached the worst two levels - “very unhealthy” and “hazardous⁵.” That was up from the average of 55 from 2013 to 2016.

The EPA told the Associated Press in a statement the increase in unhealthy air days in 2017 was largely related to wildfires in the western U.S. It said it was still studying 2018 levels before officially announcing more data.

Air pollution experts agree that wildfires likely played a part in the air quality changes in recent years. They said other causes included higher fuel usage⁶ and warmer climate. Higher temperatures increase the chances for fires and air pollution.

U.S. President Donald Trump⁷ has taken steps to remove several environmental policies put in place by the administration of Barack Obama.

In mid-June, U.S. officials ordered an end to rules contained in Obama’s Clean Power Plan, which was introduced in 2015. The policy was meant to limit emissions from coal-burning power plants. Coal plants give off air pollutants⁸ and heat-trapping gases that have been linked to climate change.

The Clean Power Plan is being replaced with new rules that give states more control in deciding what emissions limits to put on power plant operators. The measure was signed by EPA chief Andrew Wheeler, who said it was designed to help bring back America’s coal industry.

The U.S. coal industry saw near-record numbers of plant closings in 2018, with increased competition from lower cost natural gas and different forms of renewable energy.

After the new rules were announced, New York state immediately said it would go to court in an effort to block them. Environmental experts said court cases in other states are also likely to be brought.

I’m Bryan Lynn.

Words in This Story

emission² – n. the act of producing or sending out something (such as energy or gas) from a source

hazardous – adj. dangerous

renewable – adj. any naturally occurring source of energy, such solar or wind