Domains
| Year | 1986 | 1991 | 1996 | 1997 | 1998 | 1999 | 2000 | 2001 |
| Mg/ cubic metre | 20 | 19 | 18 | 17 | 13 | 18.45 | 16.09 | 16.33 |
| Year | 2002 | 2003 | 2004 | 2005 | 2006 | 2007 | 2008 | 2009 |
| Mg/ cubic metre | 17.35 | 17.33 | 24.33 | 21.50 | 22.07 | 21.80 | 20.06 | 13.83 |
| Year | 2010 | 2011 | 2012 | 2013 | 2014 | 2015 | 2016 | 2017 |
| Mg/ cubic metre | 11.92 | 13.23 | 11.19 | 12.64 | 11.32 | 9.30 | 8.57 | 7.60 |
| Year | 2018 | |||||||
| Mg/ cubic metre | 6.58 |
Operational Definitions
The Air Pollution Index (API) converts air pollution data from several types of pollutants into a value ranging from 0 to 500. These pollutants are Nitrogen Dioxide (NO2), Ozone (O3), Respirable Suspended Particulate (RSP), Carbon Dioxide (CO2). The highest number among all the four pollutants is reported as the API hourly. Figures shown in the table are ratio of Annual Average Concentration of the pollutants to the Air Quality Objectives set by the Environmental Protection Department and annually average concentration rates of SO2.
