On October 17, the “fog” was unusually heavy, and I couldn’t figure out why. All I knew was that I was glad to be leaving Harbin for 9 days. I should have taken a photo of what the sky looks like on a normal and polluted day. But I stumbled upon this air quality reading from the SEPA website:

The red line is Harbin.

For those of you who can’t read it, it says that Harbin’s AQI is: TWO HUNDRED AND SEVENTY-THREE. 2-7-3.

Here are the Air Quality Index (AQI) ratings:

• 0-50 Good is usually green
• 51-100 Moderate is usually yellow
• 101-150 Unhealthy for sensitive groups is usually orange
• 151-200 Unhealthy is usually red
• 201-300 Very unhealthy is usually purple

I think they chose the color purple because that’s what color you turn into after breathing dirty air for a long time. I still wonder what caused such heavy pollution in Harbin that day, though I would guess it could be the coal plants firing up to start government regulated heating.