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The images coming out of Harbin China are hard to fathom – air so thick that people cannot see more than a foot or two. This isn’t fog but a deadly smog.  Thick smog enveloped the city for a third day on Tuesday, with schools and a regional airport shut and poor visibility forcing ground transport to a halt in places. Images from Harbin, a northeastern city of more than 10 million people, showed roads shrouded in smog, with visibility in some areas reduced to less than 50 metres.


So how bad is it? It is obviously awful, but how awful?!?!? To answer that question you have to understand the Air Quality Index (AQI), the air measurement tool used around the world to measure air quality.

Understanding the AQI

The purpose of the AQI is to help you understand what local air quality means to your health. To make it easier to understand, the AQI is divided into six categories. Each category corresponds to a different level of health concern. The six levels of health concern and what they mean are:

  • “Good” AQI is 0 – 50. Air quality is considered satisfactory, and air pollution poses little or no risk.
  • “Moderate” AQI is 51 – 100. Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people. For example, people who are unusually sensitive to ozone may experience respiratory symptoms.
  • “Unhealthy for Sensitive Groups” AQI is 101 – 150. Although general public is not likely to be affected at this AQI range, people with lung disease, older adults and children are at a greater risk from exposure to ozone, whereas persons with heart and lung disease, older adults and children are at greater risk from the presence of particles in the air. .
  • “Unhealthy” AQI is 151 – 200. Everyone may begin to experience some adverse health effects, and members of the sensitive groups may experience more serious effects. .
  • “Very Unhealthy” AQI is 201 – 300. This would trigger a health alert signifying that everyone may experience more serious health effects.
  • “Hazardous” AQI greater than 300. This would trigger a health warnings of emergency conditions. The entire population is more likely to be affected.

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Air pollution levels in Harbin were easing on Tuesday afternoon but remained as much as 15 times the levels deemed safe by WHO.  Figures from monitoring stations showed that concentrations of PM2.5 (the AQI), the tiny airborne particles considered most harmful to health, averaged 266, with one station showing 415. That figure was down from Tuesday morning’s level of 822 and Monday’s level of 1,000. By way of reference, my town, San Francisco had an AQI today of 50.

Residents of the far northeastern city described a smog that began choking people as much as a week ago but worsened considerably on Sunday night. In January thick smog blanketed Beijing – with similar PM2.5 levels to Harbin this week – garnering headlines, as well as a nickname “airpocalypse”, in news reports around the globe.

Do smog emergencies need to be added to your risk assessment and continuity planning?