Monday evening, March 16th 2015, the smog is still visible
The AQI for PM2.5 reached 171 yesterday in Taipa’s Central Park
Yesterday was a very smoggy day in Macau. Today was not better. Walking outside in Taipa, one could taste the air. Checking out the official SMG website its front indicator showed 40 to 60 on the air quality index, i.e. Good to Moderate. How can that be when one cannot see the sun or blue sky? The answer is further hidden on the SMG website (see definitions):
The calculation period for daily AQI is from 12:00 noon of yesterday to 12:00 noon of today. Each sub-index is calculated from at least 18 hours of sampling data for that period. Otherwise, it is considered to be fallacious. If the AQI is above 100, the pollutant which results in that index will also be indicated.”
Sunday afternoon, no blue sky, no sun.
What does that mean? It means that the AQI as shown on SMG reflects a 24 hour period for PM 2.5 and NOT the current or real time data. In fact, looking at the concentrations for Sunday one can see the spike starting at morning time:
Concentration levels for PM2.5 on Sunday
Monday was by far not better:
Concentration levels for PM2.5 on Monday evening
These concentration levels are being recorded on a real time basis with an hourly publication on the SMG website within the section ‘Concentrations’. The daily index however is being calculated on a 24 hour basis, backdated to the last noon-to-noon period. Details on the standard way of calculation can be found here. That means when one wakes up and sees the smiley faces and the weather forecast states “mist” or “fog”, one cannot trust these statements.
Monday Evening, Home Page of SMG showing the AQI
Screenshot, taken Monday evening, showing the weather cam and the indication ‘Mist’
In fact, let’s have a look at the real time data collected from the very same Taipa Central Park station:
Real time data overview of AQI for Central Park Station Taipa, by AQICN.ORG
This website shows the current AQI for the corresponding PM 2.5 concentration in that particular hour. Going from this chart 6 hours of yesterday and over 8 hours of today had been “unhealthy”. And what does that mean? According to Technical Assistance Document for the Reporting of Daily Air Quality – the Air Quality Index (AQI) by the US Environmental Protection Agency an ‘unhealthy’ PM 2.5 figure means:
Increased aggravation of heart or lung disease and premature mortality in people with cardiopulmonary disease, older adults, and people of lower SES; increased respiratory effects in general population
The air quality can change dramatically within a short period of time and due the backdated nature of SMG’s AQI, one can endanger oneself’s health by only following the smiley face picture without checking the accurate real time data provided otherwise.
- The SMG website shows AQI as a daily average figure that does not represent correctly the real time situation in Macau and Taipa
- Real time data is available at AQICN (there is also an app for downloading)
- When the air is unhealthy, please please please wear an appropriate respiratory protection mask