Wondering what the massive, yet brief, spikes in Guangzhou are...the ceiling of the Hazardous category of the AQI is capped at 500. That would mean that readings like the 1/12/13 of 827 are quite literally 'off-the-chart.'
Did a bit more poking around. Could be a temperature inversion causing a spike (http://www.wrh.noaa.gov/slc/climate/TemperatureInversions.ph...). Would be heavily dependent on the location of the sensor and surrounding topography, which all fits. If I find time, I might overlay weather data and see what it looks like.