This post originally appeared on The Metric, the blog of the Yale Center for Environmental Law and Policy.
By Angel Hsu and William Miao, Yale Center for Environmental Law & Policy
Beijing’s air quality once again is making international headlines for off-the-chart measurements of air pollution. Images of Beijing show China’s capital city completely shrouded in gloomy shades of grey. According to Jan. 12 readings of the city’s official real-time air quality monitoring platform, air pollution levels exceeded the upper limit of 500 on the Air Quality Index (click here to read an explanation of China’s newly adopted AQI) in many of Beijing’s districts, meaning that air pollution was beyond “hazardous” levels. The US Embassy in Beijing, which has been independently monitoring air pollution since the 2008 Olympics, independently measured and reported AQI values topping 755 .
The most significant contributing pollutant by far, as reported by both the Chinese and US measuring capacities, is fine particulate matter, or PM 2.5. Readings that topped 500 in November 2010 prompted a US Embassy official to tweet that the air was “crazy bad,” although this outtake was quickly recinded.
PM 2.5 – Small Particle, Big Threat
PM 2.5 represents fine particles suspended in the air with a diameter of less than 2.5 microns (about one thirtieth of the width of human hair). Particles of this size are capable of passing through the respiratory track and remaining in the human lungs, causing a range of short-term and chronic conditions such as asthma, lung cancer, and cardiovascular disease.
So how PM 2.5 being measured and reflected in air quality indices, communicated by both the U.S. Embassy and Chinese government? Last March the Chinese Ministry of Environmental Protection (MEP) released new national air quality standards and an index, the AQI, for communicating air quality that was more consistent with U.S. standards. The main difference between the Chinese and U.S. AQIs for PM 2.5 is the pollutant concentration thresholds used. While the U.S has adopted a PM 2.5 concentration threshold close to the World Health Organization (WHO)’s recommended levels of 10 μg/m3, China has opted for thresholds similar to the interim guidelines the WHO has set for developing countries.
In Table 1, above, we see US and China AQI breakpoints for PM10 and PM 2.5. Note that the descriptions in column 2 are based on the Chinese AQI standards, not US standards.
Because the official AQI measurements are capped at 500, the real extent of PM 2.5 concentrations citizens faced this past weekend in Beijing are understated. In fact, the PM 2.5 readings of all regions across the city in the evening of Jan. 12 were above 700 μg/m3, peaking at 993 μg/m3) When the US Embassy reported AQI values above 500 some asked whether their monitors were broken.
When the US Embassy air monitor started reporting values above 500, some thought these were measurement errors, as the upper-end of the AQI only reaches 500. How were AQI values beyond 500 determined? Vance Wagner, a long-time Beijing air quality analyst, wrote a post explaining the linear estimation of the AQI beyond 500, demonstrating that the US monitor uses the relationship for concentration levels at 400 μg/m3 to 500 μg/m3.
In the figure, above, we see the relationship between PM 2.5 concentrations and AQI. The red line is based on the China AQI, while the blue is interpolated values used by the US Embassy monitor AQI. Note that the official PM 2.5 concentration to IAQI conversion isn’t linear, an online calculator is available to perform the conversion.
Therefore, the equivalent-AQI of 755 reported by the US Embassy’s monitor, would have corresponded to a PM 2.5 concentration of 668 μg/m3. As a comparison, UN WHO recommends a safe level of PM 2.5 of 15 μg/m3, with an interim goal of 75 μg/m3.
These highly hazardous levels of PM 2.5 have prompted Chinese authorities to urge all residents to remain indoors and to order schools to cancel outdoor activities for children.
What’s Causing the Scale-tipping Smog?
Beijing’s air quality is the result of a complex interaction of many climactic, geographic, and anthropogenic factors. Here are some of the explanations set forth to explain why air quality is so hazardous:
· Winter weather conditions and “haze”: According the official Chinese news channel, China Daily, the main reason for such record-setting pollution islingering fog and haze. The article states, “Experts and residents in the worst-hit areas such as Shijiazhuang are becoming increasingly worried about the air pollution brought by frequent winter haze.” In the same article, Ma Xuekuan from the National Meteorological Center attributed the formation of fog and haze to the wet air, little wind, and stable atmosphere conditions common in winter. Hazy, humid and stagnant air are perfect for trapping pollutants such as fine particles, which lead to the smog. While there is logic to this explanation, as Beijing lacks precipitation during the winter months and a few days without wind prevents pollutants from being blown away, the weather and natural causes can’t be entirely to blame for off-the-charts pollution. Even long-term residentsare shocked by the recent smog levels.
· Heating from coal-fired power plants. Around 80 percent of China’s power comes from coal-fired power plants, although Beijing does have plans to eliminate the capitol’s coal plants by 2020.
· Increasing car ownership. Beijing now has 5 million vehicles, and the number is increasing. Authorities are now owning upto these staggering statistics and are beginning to think of more aggressive measures to curb emissiosn from vehicles.
· Industrial activities in neighboring provinces. Beijing is bordered by Shandong and Hebei provinces, which are some of the most industrially intensive provinces in China. In 2011, according to official Chinese Statistics, Shandong had the third-highest industrial output GDP, while Hebei came in sixth.
· Agricultural biomass burning. While it is unlikely that the severe pollution in Beijing this month is due to agricultural burning because January is not a harvest month, extreme air pollution last May in Wuhan was due to multiple fires of burning biomass, which puts a significant amount of dust, soot, and particulate matter in the atmosphere.
What can be done?
While China’s recent move to release PM 2.5 data for 74 major cities in China, with more plans to release data for all 113 key environmental protection cities by the end of this year, the beyond 500 AQI readings have called into question whether China should revise its AQI to account for pollution levels beyond the index. The meaningfulness of an index that reads “beyond Index” in determining the severity of air pollution is questionable. Our observations of theMEP’s official PM 2.5 data in previous months show that air pollution is not as severe on a daily basis for all of China. However, considerations for increasing the scale beyond 500 would be helpful for situations like we’re seeing now.
The good news is that the Chinese government is being more responsive and transparent than they have in the past. The government has been more open to official media reports covering the severity of air pollution and to citizens publicly airing grievances in media outlets. However, the more challenging task will be how the government can take this momentum and translate it quickly into enforcable policies addressing the root causes of the pollution, instead of shifting blame to uncontrollable, natural factors like wind or climate.