BEIJING: Days before the opening ceremony, the Beijing Olympics seemed beset with problems, none potentially more worrisome than air quality. Pollution levels remained high, despite government edicts that had removed two million vehicles from the city's streets and had closed down factories. But as of Sunday, halfway through the Olympics, the Games were operating smoothly and pollution levels have remained low, with previous days seeing either bright sunshine or clouds with sporadic showers. Friday and Saturday brought two of the clearest summer days in recent memory here, including minuscule pollution levels for a city that often ranks among the worst in the world when it comes to air quality. Julie Ertel and Matt Reed, two American triathletes, first arrived in Beijing the day before the opening ceremony and stayed for two nights, sometimes wearing masks outdoors, before returning to their training camp in South Korea. When they came back to Beijing over the weekend, they were stunned by how much the air quality had improved since the opening ceremony. "It's like night and day from when we flew in the first time," Reed said. "It's amazing. It's clear." For Beijing residents, the clean air is an Olympic bonus, if only a temporary one. The traffic and industrial restrictions are scheduled to be lifted in late September, after the conclusion of the Paralympics. Those restrictions began July 1, with the removal of 300,000 high-polluting vehicles, and were expanded on July 20, with the introduction of an alternate-day driving plan under which all motorists are limited to driving on either odd or even days, depending on the last number of their license plate. Many factories across the region were also required to either reduce operations or temporarily shut down, and construction in the city is now largely at a standstill. Despite such severe measures, air quality remained poor during the run-up to the Games, with four days in late July violating China's national pollution standards. Chinese officials blamed poor weather conditions, especially a lack of dispersing winds and rainfall to clear the smoggy haze. Those rains have come sporadically since the opening ceremony, including a deluge last Sunday night and subsequent showers. "Now we have much better air quality because of the efforts to reduce emissions and because we have had favorable meteorological conditions," said Zhu Tong, a professor at Peking University who is an air quality adviser to the Olympic organizers. For Olympic visitors unaccustomed to Beijing's air, the reaction has been mixed. Jason Dial of Cincinnati said he has been impressed with the hospitality of Beijing's people and also of how smoothly the Games were proceeding. But he said the air quality affected him from the moment his plane landed on Aug. 8. "I started coughing," Dial said. "Literally, we landed and you almost couldn't see the terminal where we were parking. But when it rains, it gets clearer." Kathy and Scott Cleveland of Eagle, Idaho, said the air quality had not been a problem. They had been concerned enough to bring masks, though they have not yet needed to use them. "I'm pleasantly surprised," Kathy Cleveland said. "Usually, with humidity and bad air, I have migraines. But I haven't had any." The potential still exists for pollution levels to increase. Wang Zifang, an expert on weather forecasting, noted that wind patterns could shift Monday and bring pollutants from industrial regions to the southeast of Beijing, according to Xinhua, the country's official news agency. For now, though, Beijing's air does not appear to be creating an impediment for athletes competing in the Games. Sunday saw the women's marathon held under cloudy skies and fairly cool temperatures for August. John Branch contributed reporting.