The U.S. Consulate in Shanghai began posting hourly air quality readings for the city this week, with data showing "very unhealthy" conditions at times on Tuesday afternoon.
The consulate's classification reflects U.S. pollution standards but operates on a different scale than the Shanghai Environmental Protection Bureau, which called conditions "slightly polluted".
Denied access to official data, Chinese citizens take their own pollution readings
A similar monitor on the roof of the U.S. Embassy in Beijing has long been seen as the most reliable source of information on air quality in the Chinese capital.
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Read more about the Shanghai monitor at the US Consulate's website and find the latest readings on their dedicated Twitter feed.
Reuters contributed to this report