China Air Quality

There is a lot of confusion regarding the various terms and data related to China air quality used on 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 the terms and explain the reasons for the widely differing data numbers so you have a better understanding of China air quality.

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)
  • fine particulate matter (aka PM2.5)
  • ground-level ozone (O3)
  • carbon monoxide (CO)
  • sulfur dioxide (SO2)
  • nitrogen dioxide (NO2)

Our bodies are able to block or exhale most PM10 particulate matter before it enters our bloodstream. So PM10 is not considered the most dangerous pollutant, although it can get stuck in your throat and nostrils causing irritation and infection.

Particulate matter smaller than 2.5 micrometers, aka PM2.5, on the other hand, 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 real-time PM2.5 readings in some cities in 2012 including in Shanghai in June of that year.

Dangers of Ozone

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

Ozone air pollution can be caused when volatile organic compounds (VOCs) are exposed to 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 translates each air pollutant concentration into scores from 0 to 500 and levels from 1-6 reflecting their impact on our health. The China air quality index follows this same format.

Each level has a corresponding Description; 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 within 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:

PM2.5 China Air Quality Index

IAQI Score

Description

PM2.5 ug/m3
24hr average

0-50
51-100
101-150
151-200
201-300
301-500

Exellent
Good
Lightly Polluted
Moderately Polluted
Heavily Polluted
Severely Polluted

0-35
35-75
75-115
115-150
150-250
250-500

PM2.5 US Air Quality Index

IAQI Score

Description

PM2.5 ug/m3
24hr average

0-50
51-100
101-150
151-200
201-300
301-500

Good
Moderate
Unhealthy for Sensitive Groups
Unhealthy
Very Unhealthy
Hazardous

0-12
12.1-35.4
35.5-55.5
55.6-150.4
150.5-250.4
250.5-500

Primary Pollutant, IAQI

Each pollutants' individual AQI is called its IAQI. The highest IAQI among these six pollutants at a given time is called the 'Primary' or 'Dominant' Pollutant and is chosen as 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. That is why the PM2.5 concentration is often used as a proxy for China air quality, as it is in many parts of the world.

In summer months, however, ozone pollution can sometimes be more serious to our health than the concurrent PM2.5 concentration 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 Ecology and Environment and its various environmental testing branches in each city, such as The Shanghai Environmental Monitoring Center (SEMC) under the Shanghai Municipal Bureau of Ecology and Environment (SEPB), monitor and publish the six key pollutant values. The SEPB also has an English website.

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 AQI page and English version, and the 24-hour average AQI below. This, however, might not be the case for all cities in China or for all mobile apps in China.

Shanghai's Air quality alarm system still uses 24-hour average concentrations, not real-time measurements, to trigger emergency measures when certain pollution levels are exceeded.

Average AQI vs. Individual Station AQI Readings

Another issue when looking at the AQI of a city in China is that it is actually an average of the test results from several monitoring stations around the 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 Shanghai Environmental Monitoring Center (SEMC) does list the individual AQI readings from its various air quality monitoring stations around Shanghai on their Chinese website, as does Beijing on its website.

Some mobile apps allow you to display the pollutant readings from individual stations around the city, but others 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 several reasons that comparing the US embassy AQI reading to the official China AQI reading for Beijing, 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 or an average of results from several monitoring stations?

Best Mobile App for China Air Quality

Some of the most popular and best mobile apps for checking China air quality include the Air-Matters app from Fresh-Ideas and the AirVisual app owned by IQAir.

With these apps you can see the concentrations of all pollutants such as ground-level ozone in addition to the real-time PM2.5 concentration. 

These apps let you set the displayed AQI reading by the US standard or the China ambient air quality standard.

You can select the AQI for many cities around China and many individual testing stations located in different districts of the cities, including the US embassy or consulates. 

The Air Matters app can be connected to the Laser Egg air pollution monitor from Kaiterra. This device is quite cheap, RMB 500-600 depending on the model. It will allow you know your indoor air quality in real-time so you can adjust your air purifiers accordingly.

China Air Quality
Indoor Air Quality Test

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