A farmer wearing a military jacket fires shells from a double-barrelled 37-mm anti-aircraft gun into the sky over Beijing, aiming at clouds drifting toward the Bird's Nest stadium. The shells contain silver iodide -- a chemical that makes clouds weep. If successful, the rain will wash the smog from the air.

More than a dozen such guns are operating in farming communities around the city. Cloud-seeding may not be a permanent solution to Beijing's notorious smog problem, but it shows that China is trying nearly anything possible to clean the air for the 2008 Summer Games.

Canadian Olympian Jessica Zelinka has already stood in the hazy air near the Bird's Nest and walked through the city; she dreads what will happen to her performance if the Chinese authorities fail to dissipate the smog.

"You'd go on the bus with the window open and you'd be dirty after the ride," Zelinka, 26, told CTV.ca by telephone from Calgary.

Her main concern is whether she's even slightly asthmatic. One of the top endurance-runners in the world, Ethiopia's Haile Gebrselassie, has pulled out of the marathon event for that very reason.

"At the sport centre here in Calgary, that's their concern, too," she said. "So they've actually tested athletes to see if they had that -- a minor case of asthma that would become inflamed if they ever go there."

Doctors told her she will likely be fine. But her fianc�, Nathaniel Miller, a member of Canada's Olympic water polo team, will have to take precautions, along with several other Calgary-based athletes.

"They're prepared and they have their puffers," she said.

Zelinka will be performing in the open air. She's a heptathlete, an extreme athlete even among Olympians. Her event combines a variety of track and field events and she will be running for several different distances, including 800 metres.

She'll have to battle both her competitors and the nasty chemicals that might be in the city's air, including sulfur dioxide, carbon monoxide, and volatile organic compounds.

Worse than a war zone

Factory chimneys and car exhaust pipes belch primary air pollutants into the sky, while secondary air pollutants are formed in the sky when those chemicals mix with the atmosphere and create ozone.

Smog is mostly created from secondary air pollutants. Some types, like photochemical smog, can create a thick, hazy mixture of ground-level ozone.

CTV correspondent Steve Chao has lived in Beijing for four years. He said there has been a "noticeable improvement" in the city's smog problem, but the pollution levels are still unacceptable, relative to World Health Organization standards. In the past, Chao could drive five hours out of town before seeing the smog clear. Now, it's a two-hour drive.

"In the past, you would constantly feel like you had the flu. You constantly feel like your sinuses are blocked," he told CTV.ca by phone. "You go outside all day, you come back to blow your nose and it's covered in soot. A lot of people liken it to the Industrial Revolution that London underwent, when there was lots of coal use."

He said he plans his vacations out of the city every few months to let his lungs recover and "expel whatever is in there." Even his stints reporting on Canada's military operations in southern Afghanistan, one of the most dangerous places in the world, are a relief to his lungs.

"I was telling (CTV cameraman) Tom Michalak, when we were in Kandahar, how ironic it is. We're in a war zone, but in a lot of ways it's healthier to be there," he said, laughing.

The World Health Organization says 105,000 particles per litre of air is a health risk. Recent studies conducted by the Daily Telegraph near the Bird's Nest have shown levels in excess of 750,000 particles per litre, a thick soup of chemicals and pollutants.

But the levels fluctuate on a daily basis, and can quickly improve if there's a high wind to blow the pollution away. Canada measures its air pollution using an Air Quality Index, which scores the concentration of pollutants in the air. In Ontario, a score of anything less than 31 is considered good. Last Wednesday, Beijing showed an incredible improvement from the past weeks, but it was still a moderate 44.

Officials downplay pollution

The twisting metal bars of the Bird's Nest are often shrouded in a thick mist, as if the stadium were situated on a mountain. Du Shaozhong, deputy chief of the Beijing Environmental Protection Bureau, told reporters that's not a sign of pollution -- just humidity.

"If we were sitting in a bath house there would be a lot of steam," he said at a press conference. "Maybe you couldn't see the person sitting across from you, but there is no pollution there."

Guo Wenli, director of the Beijing Meteorological Center, said the city's humid weather conditions will not last throughout the Games. He forecasted an average temperature of 24.9 degrees Celsius, based on three decades of data.

"The temperature and humidity will gradually drop and we will have better air quality and more comfortable weather in August," he said in an interview with the People's Daily newspaper.

That could considerably clean up the air and help Canada's athletes. But what about after the Games, when the world's focus is no longer on Beijing?

Lo Sze Ping, campaign director of Greenpeace China, acknowledged that Beijing has been working to clean the city's air since 1998.

"They have upgraded over 16,000 large coal-burning boilers into using gas instead, they have moved and upgraded some of the most heavily polluting factories and they have expanded the city's public transport system," he wrote in an email to CTV.ca.

But he said that the city's air pollution problem is the result of more than four decades of heavy industry and heavy traffic congestion.

"It is easy to pollute but much harder to clean up the damage," he wrote. "Air quality in Beijing is such an example. Despite the series of long- and short-term plans by Beijing, air pollution remains one of the toughest challenges for the city."