Monday, November 09, 2009

Beijing's 'hazardous air' begins to dissipate

On Thursday morning at 01:00 hrs, the US Embassy's air monitoring station in Beijing posted a message via Twitter indicating that the air was 'Hazardous'. There was nothing immediately unusual about this particular tweet. The air in Beijing can get very bad at times. But as the flow of data continued to be issued it became clear that this wasn't just a isolated event. Throughout Friday the air quality remained 'Hazardous' and Saturday too brought no change. Only by mid-afternoon on Sunday could a noticeable difference in the air quality be observed.

The US Embassy's air monitoring station has been tweeting its data since early this year. Although they only have one monitoring station, the information gathered is considered to reflect a more accurate picture of true air quality. Following guidelines set by the Environmental Protection Agency [EPA] and the World Health Organisation [WHO] the US has set up air monitoring across the United States and gives out daily information via its website.

The US measure air quality using a PM 2.5 scale which is considered a more accurate reflection of the relative dangers the air can pose to health. Smaller particles are less easily coughed from the lungs and pose a greater risk to the individual. Some countries including China use a PM10 reading, larger particles which pose a hazard but are much more easily expelled from the body. The varying systems and the labelling associated with them produced widely different results. On Friday, the US Embassy's air monitoring station measured the average AQI [Air Quality Index] at 500 and Hazardous. However, China's Ministry of Environmental Protection, which does not Twitter its findings and only publishes the previous day's average readings, stated the Beijing API [Air Pollution Index] on Friday was 186 and labelled Grade 3B or Lightly Polluted. Saturday's reading was higher with an API reading of 276 and a Grade of 4B, or Heavily Polluted. Of course the @BeijingAir description is more emotive, but it is the same scale used in the US, though air quality there rarely exceeds Unhealthy.
Air quality hitting Hazardous would be considered an emergency in the US and public announcements would likely be made. People would be advised to avoid all physical activity outdoors. People with heart or lung disease as well as older adult and children would also be advised to remain inside. However, there was no public announcement. Few people are able to follow @BeijingAir's Twitter feed especially given that Twitter is one of the many foreign websites blocked in China. So many people continued to go about their daily business.

Seemingly oblivious to the polluted smog shrouding the city people could still be seen jogging in the Chaoyang district of east Beijing. An American exited Jenny Lou's [a store that specifically targets expats] near Ritan Park carrying a rucksack loaded with shopping and holding his small child. Neither were wearing face-masks. Near the Silk Marked there a few cyclists wearing suitable masks and some Chinese people could be spotted wearing the commonly seen surgical masks, though many may well have been using them to protect themselves from the A/H1N1 swine flu virus.

Many people did stay at home and some posted comments on Twitter. Many said it was the worst pollution they had seen. Even though Beijing's pollution has hit the top AQI level of 500 before it has not continued for more than a few hours. In fact many made note of the fact that the PM 2.5 reading continued to rise while the AQI remained stuck at 500. It seemed to indicate that the AQI may have continued well above that level, but equipment was not able to record higher readings. But what would you call the air quality above Hazardous?

Pollution in Beijing is partly created by its nearby industry and power stations, but also by its millions of cars. Partly surrounded by mountains, pollution can easily build up especially if the winds are light. The conditions over the last few days were exacerbated by what's called temperature inversion. Normally, air cools with altitude, but occasionally, a layer of cool air will be trapped beneath a layer of warm air. Since the cool air is more dense than the air above it, the two layers don't mix and pollutants build up in the cool air near Earth's surface. Temperature inversions develop most often during the winter, when long, cool nights chill the ground. The cold land cools the air nearest the ground, leaving the air at higher altitudes warmer. The two layers of air do not easily mix, and the temperature inversion can last for days if winds are calm.

But late afternoon of Sunday the pollution levels could be visibly seen to drop. The Twitter feed from @BeijingAir, which had halted at around 04:00 hrs, was not needed to see the change. At some points the bad visibility had led to some taxi drivers refusing to drive their passengers any further. But by Monday morning one could almost see the horizon. After 4 days of extreme pollution and mild temperatures, Beijingers are in for more meteorological surprises. Temperatures are dropping once again and air pressure is rising. According to Google weather, the BBC international weather reports and the Weather Channel, Beijing is likely to be hit by heavy snow tomorrow [Tuesday 10th November]. Night-time temperatures may fall as low as -6°C bringing winter to Beijing once again. As for China's own weather service, they are predicting only light snow and low temperatures of -2°C.

tvnewswatch, Beijing, China

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