As the capital of the world's second largest economy, Beijing does not lack impressive infrastructure like towering skyscrapers and a constantly expanding subway. But now there are yet more changes that are not as visible but still have far-reaching impacts. Chimneys that have stopped smoking, for instance.

March marked a milestone with two coal-fired power plants in Beijing being shut down. This move can slash the use of coal by 4.6 million tons per year. From the 1950s, four coal-fired plants were being used for electricity generation and centralized heating during winter in Beijing. Today, only one of them is still in operation and that too will be closed by 2017, the deadline in Beijing's five-year plan (2013-17) for achieving 100-percent clean power generation. They are being replaced by four natural gas-fired thermal power centers in the city's southeast, southwest, northeast and northwest.

The one in the northwest has been fully operational since October last year. Compared to the coal-fired plant with the same capacity, the new gas-fired center is "more efficient and occupies smaller area," according to its manager Zhao Jianbo. Most importantly, it can "reduce carbon dioxide, nitrogen oxide and sulfur dioxide emissions - the major air pollution contributors - by 2.45 million tons, 15.7 million tons and 7.42 million tons respectively" every year.

If you can't figure out from the numbers what is happening, try this. In the first four months of 2015, Beijing reported fewer "heavily polluted days," down by 42 percent from 2014. The density of PM2.5 (airborne particles measuring less than 2.5 microns in diameter and posing health risks) decreased by 19 percent. Reduced coal burning, according to Fang Li, Deputy Director of Beijing Municipal Environmental Protection Bureau, is one of the most important reasons for the improvement.

"There's a noticeable improvement [in air quality] compared with a year earlier," said Fang. "The past year witnessed our most aggressive measures to control air pollution."

Beijing's hazardous air made global headlines in recent years. The city's average PM2.5 density in 2014 was more than twice the safe standard laid down by the World Health Organization (WHO) - 35 micrograms per cubic meter. The smog problem not only endangered the health of the capital's more than 20 million residents, but also posed obstacles for Beijing to play an increasingly important international role.

While bidding for the 2022 Winter Olympics, Beijing has promised to greatly improve its air quality so that when the games are held, the air quality in the city would meet the WHO standard. After 2022, further measures will be taken to bring down the capital's annual average PM2.5 concentration to meet the national standard (35 micrograms per cubic meter) by around 2030, "so as to basically solve this problem [of air pollution]," according to the bid committee.

Under that pressure, in September 2013, the State Council, China's cabinet, issued the Action Plan for Air Pollution Prevention and Control. It set forth the goal of reducing the PM2.5 concentration in Beijing and its surrounding areas by 25 percent in 2017 to 60 micrograms per cubic meter. In the same month, Beijing also unveiled its five-year Clean Air Action Plan (2013-17). It includes a raft of measures to reduce coal consumption, vehicle emissions and industrial pollution. An estimated $12 million will be spent to achieve the goal. 

Experts observe that the plan sounds promising but is not enough on its own. Beijing is surrounded by mountains in the west and northeast, so its air quality largely depends on the wind's direction. The wind from the south and east, where the heavily industrialized provinces lie, brings in pollution. According to Fang, a third of Beijing's air pollution came from outside last year.

"The progress we achieved last year should also be attributed to our neighbors' efforts," said Fang. Hebei, Beijing's most polluted border province due to its industries that surround Beijing, has issued dozens of policies and measures to fight pollution. For example, it will reduced its steel production capacity by 60 million tons from 2013 to 2017. The reduction is equivalent to 1.5 times Germany's annual production of crude steel. The cut in cement production and coal consumption will also be higher than the annual figures in Japan and Canada respectively. Four other nearby areas - Tianjin, Shandong, Shanxi, and Inner Mongolia - are also taking action under a collaboration mechanism set up by the Central Government.

Even then it is still too early to make a positive forecast, according to observers. Despite the progress announced, in April, Beijing's air quality met the safety standards only in about 15 days. Each year, Beijing sees a population increase of 500,000 and new construction of 200,000 million square meters. Its energy consumption goes up by 7 percent. In addition, the 5.6 million registered vehicles in the capital contribute to 31 percent of Beijing's pollution.

"For any country in the world, air pollution control has to be a gradual process," said Zhang Dawei, Director of Beijing Municipal Environmental Monitoring Center.

Beijing's efforts to combat air pollution started as early as 1998. In the past decade, the average PM2.5 intensity fluctuated between 80 micrograms and 120 micrograms per cubic meter. "Compared to the GDP growth, the situation has not worsened," Zhang said.

Zhang's monitoring center has launched its website and app as well as a social media account to publish real-time air quality information. "The fight will require everyone's efforts," said Fang, "and those from non-governmental organizations are welcome."

The government will ensure that enterprises and factories actively provide their pollutant emission information. Tightening emission standards will also be a focus, according to Li Sufang, an official from the Beijing Municipal Commission of Development and Reform.

Now Beijing has begun drafting the next plan, Clean Air Action Plan 2018-22. But before more thought is given to that, it's important to make sure that the first five-year plan has achieved noticeable results.

Beijing's Clean Air Action Plan (2013-17)

Energy restriction

» Cut coal consumption from 25.4 percent to under 10 percent» Replace four coal-fired power plants with natural gas-fired thermal power centers» Increase efforts to develop clean and renewable energy

Motor vehicle emission reduction

» Implement new stringent emission standards » Limit the number of vehicles in use to 6 million (about 5.6 million at the end of 2014)» Phase out or upgrade 1.5 million old vehicles» Introduce 200,000 new-energy and clean-energy vehicles

Industrial emission reduction

» Shut down 1,200 heavily polluting enterprises» Implement more stringent and internationally advanced standards in heavily polluting industries

Dust control

» Build green spaces across the city and windbreak forests in surrounding areas» Monitor and control dust at construction sites