Authorities in the Chinese capital Beijing have started releasing more detailed data on air quality.
It comes in response to public criticism of levels of pollution and official openness about measuring it.
Beijing previously released levels of air-borne PM10 – particles more that 10 microns across.
But officials on Saturday released data for PM2.5, smaller particles which can penetrate deep into the lungs and are seen as better indicators of pollution.
An online campaign calling for reform of the monitoring system in Beijing was launched last year, and received widespread support.
More here: BBC News – Beijing releases air pollution data.