China Air Quality: Terms and Data Explanation

There is a lot of confusion among expats regarding the wide variety of China air quality terms and data published through various websites and mobile Apps in China.

The reason for this is simple, it's complicated! Here we do not attempt to make the complicated sound simple, but we do attempt to define terms and explain the reasons for the widely differing numbers.

Air Quality Index Pollutants

International air quality indexes measure a few key pollutants which affect our health.

The US and China indexes both monitor six pollutants:

  • coarse particulate matter (aka PM10) 可吸入颗粒物
  • fine particulate matter (aka PM2.5) 细颗粒物、
  • ground-level ozone 臭氧(O3)
  • carbon monoxide 一氧化碳(CO)
  • sulfur dioxide二氧化硫(SO2)
  • nitrogen dioxide二氧化氮(NO2)

Our bodies are able to block or exhale most PM10 particulate matter before it enters our bloodstream, so it is not the most dangerous pollutant.

Particulate matter smaller than 2.5 micrometers, aka PM2.5, however, is much more dangerous to our health, as it can penetrate deep into our lungs and enter our bloodstream.

The World Health Organisation (WHO) has long pushed for all countries to monitor and report PM2.5 numbers. China began to publish theirs in 2012.

Dangers of Ozone

Apart from PM2.5, ozone at ground level is considered the most serious air pollutant in China, the US and Europe.

Ozone air pollution can be caused when volatile organic compounds are exposed to scorching sunshine and undergo photochemical reactions.

As the Shanghai Daily stated in its August 9, 2013 edition: "Ozone can affect lung or heart function and irritate the respiratory system. Long-term exposure to ozone may even increase the risk of death from respiratory illness."

Ozone pollution is sometimes a more serious issue than PM2.5 pollution during the summer months in Shanghai. Wearing a pollution face mask with a carbon filter can help to reduce inhalation of ozone.

Healthy Air Quality Standards

With ever growing evidence of their serious health effects, the WHO classified outdoor air pollution and particulate matter as Group 1 human carcinogens (cancer causing). This is the highest level possible and the same classification it gives to tobacco smoke and asbestos.

Different countries set their own standards for what is considered healthy air. Here is a list of the standards set by the WHO, The US, and China for maximum PM2.5 exposure measured in micrograms per cubic meter of air (μg/m3):

  1. The World Health Organization (WHO)
    Air quality standard released in 2005
    Maximum 24-hour average PM 2.5 exposure: 25 ug/m3
    Maximum annual average exposure: 10 ug/m3.  - 
  2. The US Environmental Protection Agency (EPA)
    Air quality standard released in 2012
    Maximum 24-hour average PM 2.5 exposure: 35 ug/m3
    Maximum annual average exposure: 12 ug/m3
  3. China National Standard
    National Ambient Air Quality Standard (GB3095-2012)
    Maximum 24-hour average PM 2.5  exposure: 75 ug/m3
    Maximum annual average exposure: 35 ug/m3

The WHO guideline for maximum safe doses of other pollutants can be found here.

China Air Quality Index (AQI)

It is difficult to understand the measurements of the the six pollutants and how these values affect our health. In order to make it easier to comprehend, therefore, in 1968 the US Air Pollution Control Administration developed the first Air Quality Index, aka AQI.

The US Air Quality Index (空气质量指数) translates each air pollutant concentration into scores (空气质量指数) from 0 to 500 and levels (空气质量级别) from 1-6 reflecting their impact on our health. The Chinese AQI follows this same format.

Each level has a corresponding Description (空气质量指数类别); the US AQI deteriorating from Good to Hazardous and the China air quality index deteriorating from Excellent to Severely Polluted.

Each level has a color representation which is the same for both the US and China AQIs.

Each level is further enhanced with a more detailed description of health effects and recommendations for preventative measures to be taken.

The US tightened its AQI standard in late 2012 when it was determined that lower levels of exposure to the pollutants caused more serious health damage than previously thought.

The China AQI standard is less strict than the US standard for PM2.5 concentrations below 150 ug/m3, but gives the same AQI value (200 and above) when the PM 2.5 concentration exceeds 150 ug/m3. 

The detailed break-down of China vs. US AQI for PM2.5 concentrations is shown here:

China: PM2.5 AQI

IAQI Score


PM2.5 ug/m3
24hr average


Lightly Polluted
Moderately Polluted
Heavily Polluted
Severely Polluted



IAQI Score


PM2.5 ug/m3
24hr average


Unhealthy for Sensitive Groups
Very Unhealthy


Primary Pollutant, IAQI

Each pollutants' individual AQI is called its IAQI (空气质量分指数). The highest IAQI among these six pollutants at a given time is called the Primary or Dominant Pollutant (首要污染物) and is chosen for the overall AQI value.

So AQI is not derived from a combination of the various measurements of the various pollutants, but rather only from the IAQI of the most hazardous pollutant at any given time.

In China, PM2.5 is the primary pollutant most of the time, and therefore its IAQI is usually the overall AQI. In summer months, however, Ozone pollution is sometimes more serious and, therefore, its IAQI occasionally becomes the overall AQI.

The US embassy and consulates in China monitor and publish only PM2.5 concentrations on their website, whereas China's Ministry of Environmental Protection and its various environmental testing branches in each city, such as the Shanghai Environmental Monitoring Center (SEMC), monitor and publish the measurements of all six key pollutants.

The US Environmental Protection Agency (EPA) has calculators on their website to help you convert concentrations into AQI values, or vice-versa convert AQI values into concentrations. These calculators use the US AQI standard.

24-hour Average vs. Real-time AQI

Traditionally, the standard way to calculate AQI, both in America and China and by the WHO, uses 24-hour average concentrations of PM2.5, when that is the Primary Pollutant.

When deciding if it is safe to venture outdoors, or open your windows to ventilate your home, however, it is more useful to know the real-time concentrations of pollutants and the real-time AQI as tested on an hourly basis.

The US embassy and consulates' air quality readings are real-time IAQI values of PM2.5. Below their AQI number they include the disclaimer that this AQI would be valid 'if at this level for 24 Hours'.

Previously, the AQI issued by Chinese authorities and which you see on many Chinese mobile apps was always the standard 24-hour average AQI. 

Fortunately the SEMC now places the real-time AQI in prominent position on its website and mobile app, and the 24-hour average AQI below. This, however, might not be the case for all cities in China or all mobile apps in China.

Air quality alarms and emergency measures in Shanghai are still triggered based on the 24-hour average concentrations, not real-time measurements.

Average AQI vs. Individual Station AQI Readings

Another issue with the main AQI issued by Chinese authorities is that it is actually an average of the test results from their many monitoring stations around each city.

As air quality is very location-sensitive, it is more meaningful to know the reading from a single test site, and preferably the one closest to you. 

The SEMC does list the individual AQI readings from its various air quality monitoring stations around Shanghai on their website, as does Beijing on its website. Some mobile apps allow you to display the results from these individual stations.

Some mobile apps, however, only display the highest AQI value chosen from all monitoring stations within a city, which can be misleading if you don't live near that site.

Summary: Discrepancies Between AQI Readings

So there are many reasons comparing the US embassy/consulates AQI to the official China AQI, or comparing one mobile app's AQI to another is like comparing apples to oranges. This is not due to false data reporting, but rather due to different standards and reporting methods. Questions to ask include:

  • Is this AQI value based on the US or China standard?
  • Is this AQI value derived from the PM2.5 concentration or another pollutant's concentration?
  • Is this AQI value derived from a real-time measurement or a 24-hour average?
  • Is this AQI value derived from a single test site (if so which one), or an average of results from several monitoring stations?

Best Mobile App for China Air Quality

The best mobile app for China air quality is simply called Air Quality China or its Chinese name 全国空气质量.

This app lets you set the AQI reading displayed by the US standard or the China standard. It also lets you set the AQI for real-time or 24-hour average measurements. 

You can select the AQI from many cities around China and many individual testing stations, including the US embassy or consulates.  

You can also choose the average or maximum AQI of all or a portion of the monitoring stations around the city.

With these many settings you can know exactly what AQI you are getting.

This app's one weakness is that it only shows PM2.5 data, and not the other pollutants.

Unfortunately, this app stops updating on occasion for a few days or few weeks, but so far comes back on line. 

The next most popular app in China for expats to monitor China air quality is the Air Quality app produced by Fresh-Ideas. This app has rebranded as Air-Matters to include more cities around the world.

The advantage of this app is that besides PM2.5 data it also shows the readings for other pollutants including ground level Ozone. 

Unfortunately you can not switch between Chinese AQI and US AQI standards, or between average 24-hour and real-time values. So the AQI numbers from the US Embassy/consulates and the Chinese authorities do not always have the same meaning, at least for values below 200.

Fortunately you can look at the PM2.5 concentration values in small print under the AQI for better comparisons.

You can also connect this app to the Laser Egg or iKair devices. These devices are quite cheap, under RMB 400 for the Laser Egg, and allow you to test the indoor air quality of your home in China and adjust your air purifiers accordingly. With this app you can then compare indoor air quality to outdoor air quality in China.

China Air Quality
Indoor Air Quality Test

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