Opinion | It's as clear as day - China needs its own Clean Air Act

Last week, a pleased Shanghai doctor who performed a successful cataract operation gingerly led his patient to the window for him to see the city's skyline for the first time, but instead of a delightful cry, the patient batted his eyelids several times and began to shout at the doctor for botching the job.

That is one of the dozens of jokes flying around the country's social media as Shanghai and more than 100 other major mainland cities were enveloped in the choking and hazardous smog last week.

Visibility in some eastern cities was reduced to less than 50 metres and to less than five metres in the worst hit places, where PM2.5 concentrations hit 500 micrograms per cubic metre. The World Health Organisation's recommended level for the pollutant is 25mcg per cubic metre.

To be sure, air quality in China typically plummets in winter months as the heating systems in cities north of the Yangtze River depend on coal. But the scale and severity of the smog last week was the worst in recent memory as it covered not only the northern cities like Beijing but also a large number of cities south of the Yangtze which do not burn coal for heating, including Shanghai, Nanjing , and other parts of the Yangtze River delta.

According to the national observatory, 104 cities in more than 20 provinces last Friday reported PM2.5 readings at more than 300, classified as severe, the highest in the six-level rating system.

The authorities blamed the lack of wind, coal burning in the north, exhaust emissions from the massive number of cars, and industrial pollution from the large concentration of steel and cement factories in the Yangtze River delta. But officials failed to explain that, given that none of the above factors is new, why was the smog last week the most severe in recent years.