In 1987, ozone levels had dropped by 50 percent.

1987年，臭氧水平下降了50%。

Trucks loaded with mobile instruments can be sent to different areas, measuring carbon monoxide and ozone levels.

装载着移动设备的卡车可以前往不同的区域, 测量一氧化碳及臭氧水平。

Next, Gaudel said her team plans to take a closer look at ozone levels in the tropics.

高德尔说，她的团队接下来计划更仔细地观察热带地区的臭氧水平。

The team said it found some of the sharpest increases in areas where ozone levels were once the lowest.

该研究小组称，他们发现臭氧水平增长最显著的地区曾经臭氧水平最低。

On its website, the WHO says decreasing ozone levels is making the problem worse.

世界卫生组织在其网站上表示，臭氧水平下降使问题变得更糟。

Scientists have observed a drop in ozone levels over the Antarctic.

【observe】科学家已经观察到南极洲上方的臭氧浓度下降了。

The study found that overall, ozone levels in most parts of Earth's atmosphere increased in the Northern Hemisphere during the past 20 years.

这项研究发现，总的来说，在过去的20年里，北半球地球大气层大部分地区的臭氧含量有所增加。

He says new requirements that decrease pollution have lowered ozone levels in American cities, but he notes that pollution in remote areas continues to increase.

他说，减污新规定降低了美国城市的臭氧污染水平，但他指出，偏远地区的污染仍在上升。

Gaudel said the data collected by international aircraft was very valuable in creating a clear picture of ozone levels over the Northern Hemisphere over long periods.

高德尔说，国际飞机收集的数据对于长期清晰地描绘北半球的臭氧水平非常有价值。