In China it is illegal to mention smog AQI level > 500, app developers have been told to incorporate the limit in applications so a higher level can never be reported: http://mashable.com/2017/01/12/china-caps-air-matters/
And in Chengdu which has been suffering, someone was locked up for 5 days for commenting: https://www.hongkongfp.com/2017/02/07/chengdu-man-detained-posting-air-pollution-warning-social-media/
The government’s argument is that the public outrage over the pollution level is destabilising to society.
It’s a vast country of course and Shanghai and Southern areas are not so badly affected as the North, a lot of work is being done to improve the situation and one shouldn’t overgeneralise. Nevertheless affected areas cover many hundreds of square kilometers and hundreds of millions of people.
Western reports also have a tendency to bias and sensationalism,even Greenpeace: http://energydesk.greenpeace.org/2016/07/20/daily-dispatch-war-on-coal-fracking-spies-uk-and-australia-roll-back-green-policy/ reports in the middle of the last year that “103 of the 359 cities monitored by Greenpeace East Asia have been enduring dirtier air than they did this time last year — that’s nearly 30%.” By the same statistic that 70% of cities – including Beijing – recorded improvements.
It was widely reported that these improvements were not sustained for the second half of 2016 with significant smoggy periods arising over winter in Beijing, Tianjin and other areas.
Although this report (January 23, 2017) which is more informative than most:
still shows a slight improvement year on year (though unfortunately data only complete to 27 Dec 2016, omitting a few additional smoggy days at the end of the year).