Image copyright Reuters Image caption All downhill from here? China wants to arrest the decline in air quality in urban centres

Officials in China say they are confident green technology will help overcome the country's notoriously polluted air.

Apocalyptic scenes of dense smog have recently forced major cities including Shanghai and Harbin to virtually shut down.

The capital Beijing is among urban areas where pollution routinely exceeds safety limits set by the World Health Organization (WHO).

In a rare interview, a senior environmental official told the BBC he was "optimistic" that the problems would be overcome.

Media playback is unsupported on your device Media caption How China is trying to battle the smog

The Chinese government has launched an effort worth 1.7 trillion yuan (£180bn) to clean up power stations and traffic fumes.

The head of air quality at Beijing's Environmental Protection Bureau, Wang Bin, pointed to the success other major world cities have had in tackling smog.

"You can see in those big cities like in London in Britain, Los Angeles in America and Tokyo in Japan, they all had huge air problems in the past - for example, London was nicknamed Smog City - which was caused by fast industrialisation.

Image copyright KATE STEPHENS/BBC Image caption Pollution monitoring equipment is an outward sign that China is taking air quality seriously

"But their situation has improved a lot and their air is really better now. Beijing's pollution is not that severe.

"We have already moved fast to cope with this issue. So we are very confident about reaching a good level of air quality and changing our capital into a green Beijing in future."

Specific measures include closing down any power stations within the city that burn coal - or switching them to burning cleaner gas instead.

A new lottery system with very few winners is restricting the rise in the number of new cars and drivers. Beijing already has five million cars on its roads, and greener cars will get priority.

Beyond that, a major push for renewable energy including hydroelectric, wind and solar is designed, in part, to help replace power generation by coal, the cheapest but most polluting fuel.

But many people will remain to be convinced that these actions are drastic enough - or that any official optimism is justified.

One mother, Jia Yi, told me of her fears for the health of her twin seven-year-old daughters.

She insists that Ji Xiang and Ru Yi wear face masks on days when the pollution levels are high.

"There are so many people and cars in Beijing and that will influence my children's health - I do believe Beijing is not a place to live.

"So if it won't affect my children's education, we'd rather go to the southern part of China which has better air and environment."

Image copyright KATE STEPHENS/BBC Image caption Twins Ji Xiang and Ru Yi wear face masks on days when pollution levels are high

Prof Pan Xiao-chuan of Peking University's School of Public Health has led studies into air pollution.

"My personal feeling is that in the last two years the smog frequency in Beijing has been rising - we have figures to prove that - and also the density of the smog is increasing.

"This means the figures of PM 2.5 and PM 10 are really high when there's a big smog in Beijing."

PM 2.5 and PM 10 are two types of pollution involving particles too small to see with the naked eye - less than 2.5 or 10 microns in diameter.

Often these consist of fragments of unburned fuel and are small enough to reach the lungs or, in the smallest cases, to cross into the bloodstream as well.

The World Health Organization (WHO) sets a maximum safe limit of exposure over a 24-hour period: 25 of the PM 2.5 particles in every cubic metre of air.

Most Chinese cities routinely experience levels well in excess of 200 and, on one occasion in Beijing, of 800.

Given the risks of respiratory and cardiovascular problems, Prof Pan says the regular publication of pollution data has "a very important public health value".

Until recently, the Chinese authorities did not release data on PM2.5, even though readings on this pollution type were published by the US Embassy in Beijing.

This led to an outcry on social media during a particularly bad smog event in 2011 and forced a change in policy.

Prof Pan said: "This will warn the public when they can go outdoors and when it's better to stay indoors, and how the old and children should protect themselves."

The threat of air pollution has become so serious that one school for expatriate children has taken the drastic step of sealing off part of its playground.

Image copyright KATE STEPHENS/BBC Image caption A social media outcry led to changes on the publication of pollution data

A giant inflatable dome at the International School of Beijing now provides an insulated space where the air is filtered and positive pressure ensures any pollution is kept at bay.

Gerrick Monroe, the school's operations director, said the dome was bought after one pollution spell kept children indoors for a 20-day period.

"One of the first questions prospective parents will ask is 'what is the air quality like?'

"This is one of the selling points - we take indoor air quality very seriously here."

For the longer term, the hope is that the government's measures will start to take effect.

But one leading environmental scientist, Prof Zhang Shiqui of Peking University, says it is "a really big challenge for China" trying to balance economic growth and poverty reduction with public health.

Image copyright Getty Images Image caption Some commentators are less than optimistic about the prospects for a greener environment in the near term

"I think it's highly dependent on whether China can successfully introduce a restructuring strategy and, second, can China can switch to cleaner sources of energy, and can consumers change their behaviours?

"In previous years, if the government wanted to slow down the economy to get a greener environment, the public would not have agreed.

"But after the PM2.5 event in 2011, the public has a high awareness of air pollution and they are eager to improve the environment here.

"But although China has huge GDP growth, per capita it's still very low, so China should maintain proper economic growth to solve the poverty issue."

The reality is that it will take years or even decades to reduce China's pollution problem - but a combination of public awareness and cleaner technology may help accelerate the process.