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BEIJING - I was still on vacation in the U.S. this past Saturday when my friend in Beijing texted me and told me to breathe as much as clean air as possible. She wrote to say she had never seen air so bad and she was scared.

The ultrafine airborne particles in the air in central Beijing on Saturday reached 993 micrograms per cubic meters according to the official measurements. That is far higher than in the middle of forest fires in the United States.

On Sunday at midnight, my plane landed at Beijing Capital Airport half an hour late because of the bad weather. The moment I walked out of the airport, I started to choke slightly and my eyes started to feel sore. The taxi driver thought I was crying. He started to chat with me to try and cheer me up. All the while he was driving just 20 miles per hour through a thick fog of pollution on the airport express highway.

"The weather has been very bad for driving these days. It has been very foggy," said the taxi driver. Most cars were covered in a fine dust from days in the bad air.

"Sure, it's always the 'fog'," I thought. I don't remember how many times I have argued with the local Beijing residents that it is not fog, it is smog.

On Monday, the ABC News Beijing Bureau went out to do interviews on the air pollution in Beijing. We visited the Torana Clean Air Center at Central Park in Beijing. The store is the official distributor in China for Blueair air purifiers of Sweden. In five minutes at the store, we saw 30 air purifiers loaded for delivery. The owner of the store told us that they were doing the business of an entire month every day.

This year for Christmas, I gave all my close friends in Beijing a protective mask, the kind with a small filter in it. Little did I know they would need them so soon into the new year. Even with the common smoggy air in Beijing, very few people wear masks on the street.

For the first time ever, Beijing implemented an emergency-response plan. It included ordering government vehicles off the roads, shutting down construction sites and industrial companies. Residents were advised to stay indoors while primary schools should reduce outdoor activities, according to Xinhua, the state-run news agency.

Since I was at Torana, I took out my own pink mask. It is the same type that is easily found in convenience stores and commonly used by the Chinese who do wear masks. I asked the owner of Torana, Chris Buckley, what he thought of my mask. Mr. Buckley told me my mask was not good enough to protect me from the polluted air. He said there were large amounts of air leaking around the edges, and I needed a tight mask with High-Efficiency Particulate Air or HEPA filters.

While my colleagues were busy testing the air pollution index with Mr. Buckley in the park, I hurried back to the Buckley's store and tried to buy a better mask with HEPA filters. The saleswoman at Torana told me their masks and filters have been sold out ever since the bad air started. After a long conversation, she agreed to sell me one of the only two masks they had in back. It cost me the equivalent of $40. The saleswoman told me the filter usually lasts about two weeks, but with this kind of pollution, I probably need to change it every two days.

According to the figures released by Taobao and Tmall, China's two biggest shopping websites, 500,000 masks were sold in two days. That number was three times more than the previous week.

The air quality index, or "AQI," is how both the U.S. Embassy and Chinese government computes air quality. As set by the Environmental Protection Agency (China uses its own environmental agency) the AQI measures five different pollution components. PM2.5, or particles smaller than 2.5 microns, are considered the most harmful to your health because they get deeper into the lungs and can be absorbed directly into the bloodstream. Short-term effects of air pollution commonly include coughing, shortness of breath, eye irritation, headaches, nausea and dizziness.

It has been three days since I got back to Beijing, I haven't seen the shape of the sun yet, and my chest has been feeling a consistent pain. Because Beijing sits in a basin, once the bad air gets in only a strong wind can push it out. Winds are expected in the coming days, and they can't get here soon enough.