Here are some details on how three other host cities dealt with similar concerns about summer smog:

ATHENS, Aug. 13-29, 2004:

-- Typically polluted and hot in July and August, Athens feared summer smog and Mediterranean heat and humidity would make the Games the hottest in modern history, with expected temperatures of 24-34 degrees Celsius (75-93 degrees Fahrenheit).

-- The Greek capital expanded its metro, built a new tramway, and used natural gas powered buses to combat air pollution. Thousands of trees were planted and factories closed for August.

-- An uncovered swimming pool, the first roof-less Olympic pool since Barcelona in 1992, caused pre-Games uproar among swimmers fearing summer heat. Officials said cold water would be added if water temperatures exceeded 27 Celcius (80 Fahrenheit).

-- Hoped-for late summer sea winds off the Mediterranean helped sweep away pollution, alleviating Athens' worst smog fears.

ATLANTA, July 19-Aug. 4, 1996

-- Summertime ozone pollution was one of officials' biggest fears as hot, humid Atlanta prepared for the Games.

-- At the time the city's ozone readings exceeded federal standards by about 12 days each year, due to emissions from cars, trucks and power plants during hot summer months.

-- About 30,000 trees were planted, car-pool lanes added to highways, traffic banned from downtown, and local businesses allowed telecommuting to clear the air and reduce congestion.

-- Bus and rail fare was included in Olympic ticket prices and about 5,200 natural gas buses -- the first alternative fuel fleet to be used at an Olympic Games -- were deployed.

-- The mass-transit push overcrowded subways, and strained the bus system, but along with fresh winds it also helped lower air pollution, officials concluded.

LOS ANGELES, July 28-Aug. 12, 1984

-- Set in a coastal basin that traps smog, the city of angels issued dozens of smog alerts and sank under its worst brown haze in a decade just weeks before the Games. Britain's equestrian team said they would take oxygen masks for their horses.

-- About 4,000 big businesses and industries, including refineries and chemical plants, were asked to voluntarily cut production by 10 to 20 per cent during the Games.

-- Men's and women's marathons were run in the early morning and late afternoon when smog levels are lower, and were routed through beach communities rarely affected by air pollution.

-- Spectators took Olympic buses and commuters worked different hours, used car pools or took vacations to lessen pollution from industry and the city's 5 million cars.

-- The Games' first week saw "abnormally healthy" air, local media said. Smog levels climbed later as traffic picked up.

-- In one pre-Games dud note, the death of Bomber, a bald eagle being trained to star in the opening ceremony, was blamed partially on smog-induced lung damage.

Sources: Reuters, local media (Writing by Gillian Murdoch; Beijing Editorial Reference Unit; Editing by Alex Richardson)