LANZHOU, March 16 (Xinhua) -- Researchers have disclosed that the average mercury concentrations in the northwestern Chinese city of Lanzhou decreased in the last two decades.

The researchers from the Northwest Institute of Eco-Environment and Resources of the Chinese Academy of Sciences conducted atmospheric mercury measurements in Lanzhou, capital of Gansu Province, from October 2016 to October 2017.

"It was the first continuous real-time measurement of atmospheric mercury in this once-polluted city Lanzhou," said Kang Shichang, a leading researcher of the study.

The results showed that the atmospheric mercury concentrations in recent years in Lanzhou had a clear decrease when compared with the limited monitoring data from the early 21st century, indicating an improvement in the city's air quality in recent years, according to their recent study published in the journal Science of the Total Environment.

Lanzhou's air was polluted over the past few decades because of its narrow valley topography and industrial emissions. Thanks to various control measures on atmospheric pollution such as reducing the use of coal for both industry and residents, and shutting down and suspending polluting enterprises, the city's air quality has largely improved.

The researchers suggested that long-term atmospheric mercury observations in urban and background sites in China should be conducted to assess mercury pollution and the effectiveness of China's mercury control policies.