This morning Saigon suffered yet another bad air morning with the AQI (air quality indicator) at 162 (50 AQI and below is healthy). With cooler weather, the air pollution in Saigon tends to get worse in the morning due to temperature inversions.
What is Temperature Inversion?
Temperature inversion is when the surface air temperature is cooler then the air above it (air is warmer as the altitude increases). For a city like Saigon, situated in essence a high marsh and swampy area, cool foggy mornings become a norm from October until about April. Hence, you will see that between 2 – 5 am in the morning, the air pollution in Saigon tends to get worse. This tends to be about the same time that the fog appears and in some areas, people will burn their trash (illegally).
The type of temperature inversion Saigon experiences is known as “Surface inversion”. This is when the surface tends to cool rapidly overnight. Ironically, for Saigon, this tends to happen more in the dry season which tends to be cooler then the rainy season.
Luckily for Saigon, a temperature inversion related air pollution means the pollution will go away towards mid day. One most days, I notice that the AQI starts to lower around noon time and becomes good and moderate by 2 pm. The below pictures illustrate this from my photos today.
PM2.5 Saigon Gallery for December 12, 2018
10:44 am 162 AQI (Saigon – District 4) 
3:21 pm 60 AQI (Saigon – District 4) 
10:44 am 162 AQI (Saigon – District 4) 
3:21 pm 60 AQI (Saigon – District 4)
Is 2018 less polluted than 2017?
Last October, 2017, Saigon suffered several bad air days, some even lasting a couple of days. I personally started noticing this trend since October, 2012. The cause of this pollution is related to the slash and burn fires in Sumatra (Indonesia). This year, Indonesia decided to prevent similar forest and land fires. So far, it seems to have worked.
That is good news for Saigon. I am curious to see if the air will get much worse in Saigon but I suspect, we have seen the worse of it.