Why do China and the US report conflicting air pollution numbers?

The air pollution app we use just did a major update. We can now track cities outside of China, and also choose Chinese or American Air Quality Index standards:USAvChinaAQIreporting
It’s not just that each country characterizes pollution levels differently (China’s “Moderately Polluted” = America’s “Unhealthy”), they’re calculating their AQI differently. The Air Quality Index number is what the average person uses to gauge the pollution level. These screenshots show China and the U.S. arriving at different AQIs, even though they’re dealing with the same pollution data:

American_Beijing_AQI China_AQI_Beijing

The Global Times, China’s English language international mouthpiece, explains it this way:

Qiu Qihong, an engineer of the Beijing Environmental Monitoring Center, said US and China use the same function to determine AQI figures from six different pollutants. However, he explained that the UStates uses a stricter system to determine what numbers to plug into the AQI formula. The formula requires a range of values of PM2.5 to calculate the number, and the US and China are using different ways to determine this range.

Qiu explained, “The US uses a stricter system because their society is further along in the industrialization process.”

This is why when PM2.5 density is transferred to AQI figures, the two countries have different readings, Qiu said.

For example, according to the standards published by both countries, if the PM2.5 density reaches 15.4 micrograms per cubic meter, according to US standards, the matching AQI figure is 50. But under Chinese standards, the density needs to reach 35 micrograms per cubic meter.

We usually turn on our DIY air purifiers when the AQI hits 200 (though the one in the kids’ bedroom is always on whenever the windows are closed). We can usually smell and/or see an AQI of 75 by China’s calculations.

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