China is known for having some of the most polluted air in the world.
But officials in one Chinese city found a way to at least make that air appear cleaner, for awhile.
Like many Chinese cities, Xi'an, the provincial capital of Shaanxi, in the northern part of the country, has air-monitoring equipment.
Officials recently realized that if they stuffed cotton into the equipment, the air could be filtered and read as cleaner, reports The New York Times (subscription required).
The head of the air-monitoring station in the city's Chang'an district and several members of his staff were caught employing the cotton cheat, according to the paper.
The incident has reportedly created doubt about the air-quality readings regularly taken in other Chinese cities.
This includes monitoring for PM2.5, a fine particulate matter that is particularly harmful to humans.
The New York Times noted that analysts believe the vast majority of Chinese cities fail to meet air-quality standards.
In June 2015, China's Ministry of Environmental Protection said it had uncovered seven cases of falsified air-quality data.
The Xi'an case dates back to February of this year, when the affected station moved.
During that time, the station chief reportedly copied the station's key and a computer password.
Coal, by Flicker user oatsy40 (Used Under CC License)
Xi'an reportedly has particularly poor air quality because of the prevalence of industrial coal burning in its area.
MORE: Beijing Smog So Severe It Requires Headlights At Noon (Dec 2015)
Last December, the smog in Beijing got so bad that drivers needed to use their headlights at noon.
At the time, levels of PM2.5 reached 17 times the World Health Organization's recommended limit.
Cooling tower at power plant, by Flickr user Paul J Everett (Used under CC License)
China has also made significant investments in renewable energy, although growth has largely come as part of an overall increase in electricity demand, meaning renewable energy isn't replacing fossil fuels.
Bloomberg recently predicted that China will continue to build coal power plants, although perhaps at a slower rate than before.