The Environmental Protection Department has rejected Greenpeace's 'Air Pollution Index', which is unscientific and misleading.

The department said Greenpeace is applying indiscriminately the European Union's air quality standards to compute its API, without recognising that scientifically these standards are not designed for API reporting.

The EU has not set a standard nor a methodology for computing an API, and no other places in the world have used Greenpeace's method to calculate one.

No comparison

The department said the EU's air quality standards cannot be compared to Hong Kong's Air Quality Objectives directly because the former allow many exceedances in a year. For example, the EU allows the hourly average Sulphur Dioxide standard to be exceeded 24 times a year, whereas Hong Kong allows only three times.

The EU also allows the daily average Respirable Suspended Particulates standard to exceed 35 days in a year, whereas in Hong Kong it would be considered falling short of the objectives if it is exceeded by more than one day. Having more allowable exceedances, the EU standards thus have numerical values significantly lower than those of Hong Kong.

The department said the introduction of more measures to improve air quality is strongly supported, but the measurements have to be objective and scientific, adding it is wrong to report air pollution levels in an arbitrary and unscientific manner.

More stringent

The methodology and values of Hong Kong's API system are similar to those being used by some other places in the region such as Singapore and Taipei. There is no standard method for calculating API values internationally.

Hong Kong's API values range from one to 500. Sydney has a range of one to 100. London and Paris adopt a 10-grade system, and the computation methods of these two cities also vary.

For places adopting similar API methodology as Hong Kong, values of one to 50 are normally classified as "good" and 51 to 100 as "moderate". Hong Kong's API system is particularly stringent as it classifies API values of 26 to 50 as "medium", and 51 to 100 as "high".

The department has also introduced roadside monitoring stations and announced the roadside API, in advance of many other countries and cities.