Chinese authorities have found a number of companies faking monitoring data, during recent air pollution inspections.
The Ministry of Environmental Protection reported four cases where automatic monitoring facilities malfunctioned or companies interfered with data collection, according to its website.
In Tangshan, north China's Hebei Province, inspectors found that a steel company was pumping fresh air and nitrogen into pipes to dilute sample smoke collected by automatic monitoring facilities, creating fake results.
The density of a pollutant reported by the monitoring equipment in another company in Tangshan was almost half the actual level, indicating malfunction of the facility.
China's central government is fighting pollution and environmental degradation as decades of growth have left the country saddled with smog and contaminated soil.
The inspection teams have been conducting on-site checks in the Beijing-Tianjin-Hebei region and nearby areas, where smog has raised widespread concern.
The inspection teams will hand over issues uncovered to local authorities for further investigation.