The Vietnamese government websites frequently report air quality data with a delay of three or more hours. If the data aren’t timely enough, the stations don’t display on the map. The AirVisual map only displays real-time or near real-time data.
Below is a screenshot taken from the Hanoi Environment Monitoring Portal at 9:10 am on Oct. 10 Hanoi time. It shows that they haven’t updated the data for Hoan Kiem station since 6 a.m. At 6 a.m., the PM2.5 concentration value was 85.4 micrograms per cubic meter (μg/m3).
Here is a screenshot of the AirVisual app’s Hoan Kiem page at the same time. We clearly state that the time of the data is 6 a.m. and the PM2.5 concentration: 85.4 μg/m3.