China’s new Air Quality Index: How does it measure up?

Earlier this month, China’s Ministry of Environmental Protection (MEP) released the official (trial) revisions to the Ambient Air Quality Index (AQI, which is a notable shift from its previous form as the Air Pollution Index, or API).  I wrote last February about how the MEP was already revising the API to be more in line with the U.S.’s AQI, but with the notable exclusion of ambient air quality standards for fine particulate matter, or PM 2.5.  The omission was seen as a disappointing move by some of China’s leading environmentalists, who saw the failure to include PM 2.5 in the AQI revisions as a political sidestep.

Fast forward six months and PM 2.5 quickly dominated headlines both within China and abroad, particularly when Chinese netizens took to social media to point out discrepancies between China’s API communications and an independent air quality monitor atop the US Embassy in Beijing.  The government responded promptly through the release of trial PM 2.5 data in Beijing before the Lunar New Year holidays in January.  The MEP then followed with announcements that PM 2.5 would be additionally measured in all four municipalities, 27 provincial capitals, and key economic regions such as Beijing-Tianjin-Hebei, the Pearl River Delta, and the Yangtze River Delta.  Already, provincial governments have gotten an early start on releasing PM 2.5 data, with Guangdong and Zhejiang leading the charge.

But what about the ambient air quality standards themselves? How do they compare with those of the U.S?  I’ve already noted in a previous post the changes to the methodology that have been made in the Chinese AQI to more closely resemble the US AQI, so I won’t reiterate those here, other than to say that they now appear to be fairly consistent.

As for the standards on PM 2.5, there is a discrepancy between the U.S. and China AQIs, and the reason is that China has adopted the stage 1 interim recommendations set by the WHO.  The U.S., of course, uses a 15 micrograms/m3 guideline. You can see these differences in both Table 1 and Figure 1.

Table 1. US and China AQI breakpoints for PM10 and PM 2.5. Note: the Descriptions in column 2 are based on the Chinese AQI standards, not the US's.

Figure 1. A comparison between PM10 and PM2.5 AQI breakpoints between the US and China.

I am not particularly bothered by these discrepancies for PM 2.5, as the Chinese government was clear about their intention to adopt the lower level interim guidelines set by the WHO. To place the difficulty of achieving these PM 2.5 levels into perspective, scientists have predicted another 20 to 30 years.  However, I am optimistic that China might be able to cut pollution levels sooner than this, as they have technology and plans to reduce fossil fuel consumption that may help them “leapfrog.”

I also wonder about the potential effect the international attention on PM 2.5 may have had on the other ambient air quality standards for other pollutants, such as sulfur dioxide (SO2), ozone (O3), and nitrogen dioxide (NO2).  As you can see from Table 2, the differences in the pollutant breakpoints (i.e. what concentrations are considered “good” and “lightly polluted”) are pretty significant.  However, adjustments were made from the drafts considered last February.

Table 2. Pollutant breakpoints for US and China AQIs. 1) According to the USEPA, 8-hour O3 values do not define higher AQI values ($ 301). AQI values of 301 or higher are calculated with 1- hour O3 concentrations. 2) NO2 has no short-term NAAQS and can generate an AQI only above a value of 200. Note: the Descriptions in column 2 are based on the Chinese AQI standards, not the US's.


** Updates made May 15, 2012 thanks to comments and good catches by Erica Zell, Battelle Memorial Institute. 




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  • Fanyu Gao

    Accoring to the US standard of AQI, the indicator of SO2, O3 and CO is measured with unit of ppm. I am just wondering how you transform them from ppm to ug/m3, due to my study result is quite different from yours. Did you take the tempreature into account? THX

  • Fanyu Gao

    please replay to me… I based my thesis on this topic.