Nearly 11 months ago I took my first air quality reading in Long An about 30 km south of Ho Chi Minh City, Vietnam. I was surprised that I got an AQI reading of 41 (about 10 micrograms which is the safe level for clean air based on WHO standards). 
Currently at the same location I got the following reading:
This is 58 micrograms or roughly 152 AQI which is unhealthy. This is nearly six times the WHO safe air levels. It is quite noticeable in the air as well. The same smog you are seeing all over Saigon is here now.
This is a drastic change for 11 months. It is safe to say that the high majority of people in this area are not wearing proper PM2.5 masks or using air purifiers.
The rise of air pollution is a result of new factories opening and possibly another coal plant being lit though.
Updated
Took some outside readings. It is now 72 micrograms outside or 160 AQI which is unhealthy.
You can see the haze in the distance.
