PSI reading of
0—50 means the air quality is in the good range;
51—100 moderate;
101—200 unhealthy;
201—300 very unhealthy;
and above 300 hazardous.
For the past 12 hour 3-hour PSI values, please click the link http://www.nea.gov.sg/
Source: http://www.channelnewsasia.com/stories/singaporelocalnews/view/1088767/1/.html
