(CNN) -- Beijingers are once again choking as smog levels hit "heavy or even worse" levels in the capital and a number of other cities across the country.

Persistent problems with city air have prompted officials and entrepreneurs to consider ways to protect their citizenry from the pollution.

Beijing was under an "orange" smog alert Monday, which marks the first time the second-highest warning level of a new system introduced last year has been raised. The National Meteorological Center (NMC) Tuesday continued the alert for another 24 hours.

Capital measures come amid fog of pollution

Heavy smog routinely blankets the capital, all but blotting out the sun and forcing residents inside. Australian Open champion Li Na revealed she's had to train indoors in Beijing due to the high levels of pollution, while smog across most of northern and eastern China has prompted officials to send teams of investigators to the worst-hit parts of the country.

Smog blankets Beijing traffic -- a regular experience in the Chinese capital in recent times. An empty playground at the International School of Beijing as students are kept indoors due to heavy smog. Basketball courts in the city lie deserted as pollution levels reach dangerous levels. The ISB's new "smog dome" functions as a sports center for students. The school's dome has a pressurized, soft Teflon roof. Students Hanna and Emily Merritt: "We have the dome but it would be great if we can go outside and play." Air is filtered to keep harmful particulates out of the dome. Soccer practice is held on artificial turf under the dome. Students spend their break times under the school's clean-air dome. A sign points students and visitors in the direction of the dome as smog levels rise. Grey skies and regularly high levels of particulates have forced ISB students indoors. Bad day, good day: CNN's views of Beijing on smoggy and clear days. Life under the dome: How kids play at a Beijing schoolKids at play under the smog domeLife under the dome: How kids play at a Beijing schoolLife under the dome: How kids play at a Beijing schoolLife under the dome: How kids play at a Beijing schoolLife under the dome: How kids play at a Beijing schoolLife under the dome: How kids play at a Beijing schoolLife under the dome: How kids play at a Beijing schoolLife under the dome: How kids play at a Beijing schoolLife under the dome: How kids play at a Beijing schoolLife under the dome: How kids play at a Beijing schoolLife under the dome: How kids play at a Beijing schoolHIDE CAPTION<<< 1 2 3 4 5 6 7 8 9 10 11 12 >>>

In pictures: Kids inside smog dome

Your video will begin momentarily.China's toxic smog problem

China's smog soars

Smog in China kills millions prematurely Officials at the Ministry of Environmental Protection cited "unfavorable meteorological conditions and firework and firecracker spree(s)" as the cause of the heavily polluted air. China's Lunar New Year celebrations, which took place earlier this month, are often accompanied by firework displays, and neighborhoods resound with the sound of firecrackers。

The air pollution index recorded levels of over 400, referring to the number of PM2.5 -- harmful particulates measuring 2.5 microns or larger -- per cubic meter of air. The World Health Organization recommends guideline values of 25 PM2.5 in a 24-hour period.

The smog is expected to ease towards the end of the week.

Many are at least trying to tackle the matter themselves. From ubiquitous air filters in people's homes to the near-mandatory facemasks that Beijingers wear outdoors on heavily-polluted days, personal health is a priority. Given the restrictions in place on residents -- particularly the young and the elderly -- when the warnings go up, some more extreme measures have been taken.

Life under the dome

The International School of Beijing has taken to shielding their young charges from the city's air as the next logical step. At a cost of $5 million, the school has constructed two domes that enclose the entirety of its outdoor areas, allowing students to play and exercise year-round, regardless of how smoggy life is outside the enclosure. While it is a costly solution, other schools, alongside sports facilities and even wealthy individuals are placing orders. Until the skies clear, life in the bubble seems surprisingly good.

The world's factory

China's aggressive economic growth model means that heavy industrial activity also contributes heavily to the degradation of the air quality. As part of their anti-pollution measures, some factories surrounding the capital -- Hebei is a huge steel-producing region -- have been forced to close temporarily following the raising of the orange alert.

Earlier in the year, the ministry upgraded emission standards for various heavy industries and waste disposal processes, upgrading protocols that were in some cases legacies of original standards, set in the 1980s before the onset of much of China's present industrial capacity. Problems, however, persist.

The Shanghai Academy of Social Sciences and the Beijing-based Social Science Academic Press released a report in early February which ranked the two cities towards the top of a list of the worst-polluted cities. Beijing ranked second, just behind Moscow.

Blue-sky thinking?

In the face of growing social unease at worsening environmental conditions, authorities are committed to rectifying the problem, and Beijing will allocate 760 billion yuan (about 124.64 billion dollars) to improve the city's air quality by 2017, Mayor Wang Anshun said last month at a municipal NPC meeting.

The figure includes incentives for clean factories, and the municipal government has also improved the case for electric vehicles (EVs) by granting subsidies and license plate lottery waivers to those buying Chinese-made cars, while switching government fleets to electric.

The country is one of the world's largest producers of green energy technology, although much of it is exported at present.

More ambitious fixes have been proposed, including more "meteorological support services" -- such as cloud seeding -- as well as a giant "vacuum cleaner" designed by a Dutch artist, and skyscraper-mounted sprinklers. These solutions, their inventors promise, will either trap or wash the smog away.

Naked run

A novel approach to highlighting the problem came on Sunday as more than 300 runners, according to official news sources, took to Beijing Olympic Park wearing no more than their underwear -- and in at least one instance a gas mask -- to join a "naked run" protesting the city's poor air quality.

The best defense is a good smog

A silver lining to the smog-cloud might be the military advantage it offers. Chinese military theorist Rear Admiral Zhang Zhaozhong told the Beijing Youth Daily that smog could be a defense against "laser weapons", given that heavy smog can impede or block the technology.

"Smog with PM2.5 readings of 500-600 is virtually impenetrable to lasers. In clear weather, laser weapons have a range of 10 kilometers, but smog can reduce this to less than 1 kilometer," he said, although later was forced to defend his remarks against accusations of naivety and advocating a reckless defense theory。

It's another bad-air day in Beijing. You can barely see. You can barely breathe. But you can feel -- and even taste -- the grit floating in the air.

The World Health Organization has set healthy level of Air Quality Index at 25 micrograms, while Beijing considers a 300 reading as "Bad" and 500 as "Hazardous." Last weekend, however, it breached 700!

"I'm getting itchy," complained my daughter Michelle, 22, visiting us from New York. "I could feel it at the back of my throat."

Longtime expatriate residents in the Chinese capital jokingly call it the "Beijing tickle," a nagging cough that takes a long time to shrug off.

Beijing adopts emergency measures for hazardous pollution

Air pollution is a major problem in China because of the country's rapid pace of industrialization, reliance on coal power, explosive growth in car ownership and the sometimes disregard for environmental laws.

It is now paying the price of rapid development.

In 2007, China overtook the United States as the world's biggest emitter of greenhouse gases, according to China's Ministry of Commerce. It is also the No. 1 source of carbon emission worldwide, state-run China Daily reported recently.

Beijing experiences terrible air quality Added to this, the World Bank says 20 of the 30 most polluted cities in the world are in China.

Health is the big casualty.

Greenpeace on Beijing's hazardous smog Almost 400,000 premature deaths are recorded in China each year, with the majority related to pollution, according to the World Bank's "Cost of Pollution in China," a report based on official Chinese figures.

Beijing's pollution merely 'hazardous' A growing number of individuals and institutions are looking to find last-gasp solutions.

I could feel it at the back of my throat

Michelle FlorCruz, daughterThe government has already shut down high-polluting factories, built new subway lines, and allocated state subsidies to reduce the cost of public transport.

Beijing bans vehicles from the road one day a week to reduce heavy traffic and vehicle emissions.

It also imports natural gas from other provinces to rely less on coal for heating and cooking.

As part of a long-term solution, Chinese researchers are producing prototypes of solar and electric cars to replace gas-fueled vehicles.

So far, these measures have not produced consistently blue skies and clean air.

Green activists complain that even though government regulations have improved, laws are often ignored.

One of Beijing's big problems has been the city's geography, as it is surrounded by mountains shaped like a horseshoe.

When pollution blows in from the heavily industrial neighboring towns and cities, it builds up and, in windless days, gets trapped over the capital.

Off-the-charts pollution in China

In fact, this is not the first time bad air has bedeviled Beijing. I remember one day last year when the U.S. embassy's air monitoring system reported the pollution level as "crazy bad."

What can we Beijing residents do about it?

Wear face masks? Unless you use heavy-duty ones, I am told, they do not really make much difference.

Turn on air-purifiers full blast? We've never used one at home, although my friends swear they help.

"The truth is there isn't a lot people can do about ambient air pollution," said Deborah Soligsohn, an environment and energy specialist at the World Resources Institute, a U.S. based think tank.

"Ambient air pollution is not nearly as large a health risk as more immediate forms of air pollution. Tobacco is a much larger killer, and indoor air pollution from poorly ventilated wood and coal fires has traditionally been a much larger killer in the developing world. Smoky restaurants and bars can have levels as high as these recent air pollution numbers."

I know a few expat friends who have decided to relocate out of Beijing and were mainly turned off by its bad air.

"What did you think of Beijing?" I asked David Van Dyke, who lived and worked in Beijing for nearly seven years before relocating to Canada last year.

"Mostly liked it, save for the Internet (censorship) and pollution," he said.

Meantime, some residents have resorted to humor and sarcasm online to vent their frustration.

"I love my city, but I refuse to be a human vacuum cleaner," netizens re-tweeted on Weibo, China's microblogging social media. "We want clean air, and we want to breathe freely."

Others posted pictures wearing face masks of various shapes and designs.

A page of Sohu.com featured a section covered with haze, with a note saying the headlines have been obscured by a massive smog. "Click on it, and it will clear up." Once it cleared it, the title read: "We live in a "toxic gas.'"

"Don't worry," Henry Ngo posted on my Facebook page. "Smokers are inhaling worst air than this. And they did not die immediately!"

Is this now the new "normal"?

Soligsohn, who lived in Beijing for 14 years, does not think so.

"This is a confluence of bad events," she assured me. "Pollution is definitely a problem. It hasn't gone away, but there is no reason to believe an extreme reading is anything other than an extreme."

There seems to be no quick solution.

"This is complex and takes time, but the work has begun," Soligsohn added.

"It took cities like London and Los Angeles almost half a century to get from really dirty air to pretty clean air, and LA has never actually fully met EPA standards, which have become tougher with new information."

Five days after what some have dubbed Beijing's "air-mageddon," the sunshine has reappeared, and the air has actually turned relatively clear.

My daughter points out that London and Los Angeles have confronted pollution as well. As long as the Chinese recognize it is a problem, they will eventually be able to strike a balance between a clean environment and a thriving economy."

Wind has dispersed some of the smog, although my chest remains heavy and my throat is still itchy.

中国的雾霾