In an unprecedented move, Beijing has issued its first “red alert” as a result of very elevated smog within the city. The alert is the most severe of the four level system rating air quality within Beijing, China. As a result, schools and some industrial plants have been closed until the red alert is lifted. A cold front forecasted to arrive Thursday will likely lessen the dense smog and trigger a downgrade in pollution levels.
In the past 24 hours, Beijing’s real-time air quality index (AQI) reached 400 micrograms per cubic meter, a level that results in serious risk of adverse respiratory effects in the general population. Despite the significant risk associated with these levels of pollution, Beijing has seen over double the AQI without issuing a red alert. The World Health Organization (WHO) deems anything over 25 micrograms per cubic meter as unsafe. Beijing has had a long history of pollution, much of which is associated with widespread coal fired power plants.
The dangerous smog can be seen from NASA’s Suomi NPP satellite, which took photos of China on November 30th using a Visible Infrared Imaging Radiometer. As annotated in the image below, there is a dense fog or haze over eastern China with hints of gray and yellow indicative of air pollutants. The pollution haze over Beijing covers hundreds of kilometers of China’s coastline. November 30th, 2015 measured a peak of 666 micrograms per cubic meter, the day the image was taken.
The Science of Beijing’s Pollution Problem
Scientists have determined that the vast majority of Beijing’s aerosol pollution results from sulfate particulates produced when coal is burned. Coal burning provides over two-thirds of China’s energy output and therefore relies heavily on coal for continued economic development.
The same way that carbon is oxidized when burning coal to produce CO2, sulfur is oxidized when burning coal to produce SO2. Sulfur dioxide can then form sulfur trioxide, weak sulfuric acid with the combination of water, and sulfate aerosols with the combination of particulates within the atmosphere.
The combination of sulfate aerosols, coal ash, industrial pollution, and combustion engines (cars) produces a thick layer of smog that envelops Beijing. However, why is Beijing a common culprit of high pollution levels when there are comparable polluting cities around the world? It is a combination of the volume of pollutants and the climate of Beijing, especially during the winter months.
During Beijing’s winter, cool air is trapped by above lying warm air that acts as a blanket prohibiting circulation and trapping pollution. This temperature inversion is an important reason why Beijing is hit with widespread and long lasting high pollution levels. In addition, the winter months experience the lowest average wind speed and highest demand for coal fired electricity to provide heat. The combination of widespread coal combustion and unfavorable climate conditions often lead to extreme pollution levels in Beijing during winter months. Often times, during periods of dense pollution and fog, the only remedy is to wait for easterly winds and hope they’re strong enough to push the pollution westward.
This article was written by Trevor Nace from Forbes and was legally licensed through the NewsCred publisher network.
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