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LCQ19: Data on concentrations of fine suspended particulates

Hong Kong (HKSAR) – Following is a question by the Hon Kam Nai-wai and a written reply by the Secretary for the Environment, Mr Edward Yau, in the Legislative Council meeting today (May 9):


The Environmental Protection Department (EPD) monitors the concentrations of air pollutants through its air quality monitoring network (including 11 general and three roadside air quality monitoring stations (AQMSs)), and on March 8, 2012, EPD started to collect and report on a real time basis the data on the hourly concentrations of fine suspended particulates (also known as “PM2.5”).In this connection, will the Government inform this Council:

(a) of the reasons why EPD only publishes the data on pollutant concentrations in the past 24 hours and does not keep the past relevant data on its web site for perusal of the public;

(b) of the details in table form of the unprocessed data directly recorded by all the 14 AQMSs in Hong Kong in each time slot since March 8, 2012;

(c) given that of the 14 AQMSs of EPD, only three are roadside ones, and the other 11 general AQMSs are installed at building rooftops over 19 metres above the ground on average, whether the Government will install more roadside AQMSs (including in areas with high pedestrian flow such as Tsim Sha Tsui and Yau Ma Tei, etc.); if it will, of the details; if not, the reasons for that;

(d) given that some members of the public have indicated that EPD carried out instrument upgrade work at the AQMS in Causeway Bay this year and, as a result, reports of data on concentrations of fine suspended particulates were suspended for several days, of the details of the incident; how the Government ensures that these instruments can function properly and the data are accurate; and

(e) given that some members of the public have reflected that it is difficult for them to find real time data on concentrations of fine suspended particulates on EPD’s web site, and they have found that the web page entitled “Past 24 Hours Pollutant Concentration” on the web site does not contain real time data on fine suspended particulates, how the Government ensures that the public can easily access the relevant information; whether it will consider releasing the information through weather reports of the media; if it will, of the details; if not, the reasons for that?



(a) In order to ensure the accuracy and reliability of the data of the air quality monitoring stations (AQMSs), the Environmental Protection Department (EPD) will verify and confirm the raw data collected at various AQMSs in accordance with a stringent quality assurance process before the publication of the official data. When verifying the raw data at various AQMSs each month, the EPD will examine factors such as the operation records of the instruments at the AQMSs during the relevant period, whether the instruments have been interfered by any external factors, for example, construction works in the vicinity, and whether there are any abnormal variations in specific monitoring data. The verification process takes time to complete due to the huge amount of monitoring data involved.

To cater for the public’s interest in the latest air quality information, the EPD has in parallel a special arrangement to publish on an hourly basis the real time concentrations of air pollutants recorded at various AQMSs for the past 24 hours on its website. Such real time data are raw data taken directly from the monitors at various AQMSs. As they have not been verified or confirmed, they are for preliminary reference only and would not be kept on EPD’s website. After verification of the data every month, we will upload the confirmed data onto the EPD website ( for public’s consumption.

At present, the verified data at various AQMSs from January 1990 to January 2012 are available on our website. Since March 8, 2012 when we began publishing the data on PM2.5, such data have been included in our data verification process and the validated PM2.5 data would be uploaded onto our website.

(b) The unverified concentrations of PM2.5 recorded hourly at AQMSs from March 8 to April 30, 2012 are at the Annex.As the data have yet to be verified, there may be some deviations from the final verified data.

(c) All of the three existing roadside AQMSs in Hong Kong are located in built-up urban areas with heavy vehicular and pedestrian traffic to monitor roadside air quality. The three roadside AQMSs are in Causeway Bay, Central and Mong Kok. They cover the most common types of land uses with a relatively high density in urban areas, including commercial, commercial-cum-residential and financial districts. Therefore, the data from these roadside AQMSs are representative of the roadside air quality in typical places with heavy vehicular and pedestrian traffic in the urban areas in Hong Kong. As such, we currently have no plan to increase the number of roadside AQMSs.

(d) The publication of data on PM2.5 concentrations recorded at the roadside AQMS at Yee Wo Street, Causeway Bay, was suspended from March 12 to 28, 2012 due to replacement of instrument. The replacement mainly involved replacing existing PM2.5 monitor with a new model of greater precision. In tandem we replaced other related facilities, which included conversion of the outdoor equipment cases, replacement of vibration-proof installation, conversion of sampling pipes, etc. Since the old and new monitors could not operate in parallel during replacement works due to the site constraint, we had to remove the old instrument before installing the new one. Data reporting resumed after the new instrument had been assessed and confirmed to be operating normally and reliably. The EPD had announced on its website that the reporting of data on PM2.5 concentrations at the said AQMS was suspended temporarily during the period.

To ensure the proper operation of instruments and the accuracy of data, the EPD has adopted internationally recognised operating procedures and strictly implemented a quality control and quality assurance system to ensure that the air quality data are highly accurate, reliable and representative. The monitoring network has been accredited with ISO17025:2005 and ISO9001:2008.We will continue to strictly implement the relevant quality control procedures in operating the PM2.5 monitors so as to ensure the accuracy and reliability of the data.

(e) On the EPD website there is a dedicated webpage providing data on air pollution ( provides, among other things, past 24-hours concentrations of fine suspended particulates and other major air pollutants recorded at AQMSs ( facilitate public access to past 24-hours concentrations of fine suspended particulates and other major air pollutants and verified past data, we have added links to the air pollution index webpage to provide the public with an additional channel to the above webpage. The real time data on the EPD website, which are updated hourly, provide the public with the most up-to-date information on air quality.

Source: HKSAR Government

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