Dust, smog and heavy wind made Li Yuan's weekend trip to Beijing's southern suburb in search of an affordable apartment a nasty experience.

Sandstorms from the north have swept across Beijing recently. Even wearing a mask, Li's nose was filled with dust and black gunk after a day's trekking around new-build housing blocks in Daxing District.

A native of southeast China's Fujian Province, he seldom uses masks except when he has caught a cold. Fujian boasts the country's highest forest coverage rate of 63 percent.

He came to Beijing in 2006 to attend college. But it was only in late January that he decided to buy a mask online after the lingering smog above the capital meant he could not stop coughing.

Li Yuan is just one of the thousands of mask users here.

Policemen in Beijing have worn masks when working outside since March 9 in response to a Public Security Ministry document issued on Jan. 30 calling for better care for police personnel faced with polluted environments.

Beijing has witnessed persistent smog since early January. Air quality indices were off the charts for seven days, exceeding the "maximum" level of 500, making this the worst period since the government began being more open about air-quality data.

China introduced measures of PM2.5, or fine particulate matter 2.5 microns or less in diameter, last year in its monitoring of air quality. For years, China's environmental authorities have monitored only PM10, which gauges particulate matter under 10 micrometers.

January's "airpocalypse," as it has come to be known, has pushed sales of PM2.5-blocking masks skyrocketing in the past few months.

There are 5,789 choices for PM2.5 masks on Taobao.com, China's largest online shopping platform.

Masks that are certified "N95," an official rating that the mask filters out 95 percent of particulate matter in the air, are the most desirable.

Li Yuan bought his N95 masks at the same time as five colleges from Amazon.cn, another online shopping platform. One of his colleagues even bought a gas mask.

The unpleasant air has also brought suffering to legislators and advisors who are in Beijing for the annual sessions of the 12th National People's Congress (NPC) and the National Committee of the Chinese People's Political Consultative Conference (CPPCC).

Lu Yonglan, an NPC deputy from east China's mountainous Jiangxi Province, prepared masks before she came to Beijing on March 2 as her friend told her about the pollution in the capital.

Lu, a textile worker in Jiujiang City, said she normally dons a mask only while at work in the factory. But now in Beijing, she feels she has to wear it when walking outside.

Air pollution control has been a hot topic among the legislators and advisors. More than 500 proposals submitted to the CPPCC National Committee were about environmental protection, including air pollution controls, ecological conservation and emission reduction.

The tackling of PM2.5 should be included in the government performance evaluation, said Zhou Weijian, deputy director of the Earth Environment Institute with the Chinese Academy of Sciences.

Zhou also called for the enforcement of an air pollution prevention and control law to curb the problem at its source.

Chinese Premier Wen Jiabao said in his government work report on March 5 that the government should resolve to solve the problems of serious air, water and soil pollution that affect people's vital interests, improve environmental quality, and safeguard people's health.

Li Yuan, a young man who is determined to build his career in Beijing, hopes the day when masks are no longer needed comes as soon as possible.