Eerie images from Beijing hit the news last January. Dust and other pollution particles had reached such high levels that the sun struggled to shine through the megacity's smog-laden atmosphere. A giant toxic cloud had descended on China's eastern coast sparking a dramatic rise in the number of people suffering from respiratory and cardiovascular diseases.

Such happenings are the cause of growing concern for young scientist Yu Lei. The Beijing resident has been studying the phenomenon on behalf of a think tank of the Chinese environment ministry. For instance, he is trying to find answers on how to best help the fast-growing megacities in emerging nations. He is also focusing on lessons to be drawn from mistakes made by industrialized Western metropolises.

'Birds dropped dead in flight'

One of the megacities known for its hazardous levels of air pollution is Mexico City. With a population of over 20 million, the Mexican capital recorded in 1990 only eight days with "good" air quality. However, year-long efforts have led to a dramatic change. Last year the number of days with "good" air amounted to 237. The city's former Environment Minister, Martha Delgado Peralta, played a key role in this positive development. "Twenty years ago, air quality was so bad that birds simply dropped dead in flight,” she said. The record pollution levels prompted municipal authorities to rethink their environmental policies and introduce long-term reforms.

As a first measure, factories with high industrial emissions, such as refineries, were forced out of the city. Fuel quality was improved and residents were ordered to leave their cars at home one day per week. Furthermore, planers overhauled the city's subway and bus connections and introduced a bicycle sharing system. Delgado says there has been much improvement in the past years but stresses that there are still over 100 days where air quality isn't yet good enough. "It's a daily struggle," she points out.

'A policy shift is necessary'

However, the struggle seems to be paying off. Mexico City's recent success has made Yu Lei optimistic about developments in his home country. Nonetheless, he believes it's still a long way before people in Beijing or Shanghai can once again breathe fresh air. Yu Lei is of the opinion that the Chinese government should switch from coal to gas and other alternative energy sources and set absolute caps on emissions. "In the long run the country's economic infrastructure must change," he says, referring to a policy shift towards less industrial production and a more service-oriented economy.

According to the CIA World Factbook, which provides statistical data of all nations in the world, China's services sector generated 44.6 percent of the country's gross domestic product (GDP) last year. By comparison, Germany's and France's services sectors accounted for 70 and 80 percent of their respective GDP's.

'European Green Capital'

There have also been changes in Europe. Since the early 1970s, the European Union has been working to improve air quality by controlling emissions of harmful substances into the atmosphere, improving fuel quality, and integrating environmental protection requirements into the transport and energy sectors. The levels of sulphur dioxide, for instance, have dropped by almost 55 percent in the past two decades.

A textbook example of this development can be found in the capital of the Basque Country, Vitoria-Gasteiz. The city located in northern Spain was awarded the title of "European Green Capital 2012."

Just like in Mexico City, the local government relocated polluting industrial factories, improved the city's public transport network and increased the number of pedestrian ways and bicycle lanes. Besides, according to Mayor Javier Maroto Aranzábal, 65 percent of households in Vitoria-Gasteiz have already switched to heating systems powered by gas.

The mayor says that the hardest part has been to make the people of this town rethink their behavior. "The improvements we now have are the result of joint efforts made by the municipality, the manufacturing sector and the townspeople," he stressed, adding that there was no other alternative.