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Background Paper Interpreting New Data PRD Regional Air Quality Monitoring Network Report Guangdong and Hong Kong’s ability to manage and understand regional air quality in Hong Kong and the greater Pearl River Delta (PRD) took an important step forward with the release of the first full year data from the 16 stations in the reporting network. Three of the stations are within Hong Kong and the rest in Guangdong. The regional ground monitoring station network provides site-specific monthly and annual averages, as well as minimum and maximum daily and hourly reading for each month for Respirable Suspended Particulates (RSP), Nitrogen Dioxide (NO2), Sulphur Dioxide (SO2), and Ozone (O3). The following figures from the report show the annual average readings for the four pollutants for the entire network. RSP are high throughout the region but especially so in the middle part. O3 is higher in the east than the west, while SO2 is worst in the northwest. NO2 hotspots are centred on Guangzhou / Foshan and western Hong Kong, although they are generally high throughout much of the region.

Source: EPD, 2006 Monitoring Report for the Regional Air Quality Monitoring Network


In addition to the spatial variation, the data showed pronounced seasonality. In 2006, the average readings for the four pollutants for the entire network was about 90% higher in October (the highest month for the year) than it was in June, the lowest. More broadly, the levels seen in February and March were not seen again until September and thereafter were exceeded for the reminder of the year. Seasonal variations for individual pollutants were even more pronounced with variations up to about a factor of three from the high to the low monthly average. Hourly O3 levels are reported with respect to the hourly maximums within a month. The inclusion and reporting of O3 concentrations in the regional air quality network is a significant improvement as O3 is not part of Mainland China’s Air Pollution Index and not routinely reported or measured in the Mainland. Ozone data from the report clearly shows that the PRD is suffering from severe secondary photochemical air pollution. In August 2006, the maximum hourly level of 240 micrograms per cubic meter was exceeded at 14 of the 15 stations reporting O3 data for that month. All three Hong Kong stations exceeded this hourly limit. The highest O3 reading for the year was nearly twice as high as the recommended maximum and was located near the centre of the PRD at Wanqingsha (Guangzhou) in August of last year. While O3 is generally worst in summer, the hourly limit of 240 micrograms are breeched throughout the year, with the maximum hourly reading from at least three stations exceeding the hourly limit each month. For the other pollutants, the Hong Kong and Shenzhen readings were among the lowest, though higher than the Zhuhai and Zhongshan stations. Those monitoring sites in Foshan had the highest readings with annual average RSP levels about double those in Hong Kong and Shenzhen. This spatial variation matches well with satellite-derived surface particulate distribution maps (see example below), which shows the most severe PM problem around the Foshan area. The annual average numbers are particularly telling since even the Hong Kong readings of about 60 micrograms per cubic meter already exceed the Hong Kong Air Quality Objective of 55 and are about three times as high was the level 20 recommended by the World Health Organization (WHO) to protect health. On an annual basis, nowhere within the area covered by the monitoring network is the air people breathe not a risk to their health. 2006 Annual average distribution of surface extinction coefficient from satellite.


The current network and reporting system is a major advance. It is useful to have a full year’s data and to start to accumulate such data year after year. Moreover, the network is capable of monitoring hourly readings as well and it will be most useful to have this data released in the future. In addition, the 16 station network may be expanded for greater accuracy to monitor variations in various locations. While a single year data is not sufficient to infer the long-term air pollution trend, we can better understand the year-to-year trend by referring the newly released 2006 data to existing satellite-derived PM distributions. As shown in the figures to the right, air quality has been worsening with 2003 being the turning point. Average pollutant levels for RSP for example in 2000, 2001 and 2002 are much lower than those in the following four years. Things were worst in 2004 and improved slightly for 2005 and 2006. The disadvantage of satellite data is that it is a series of snapshots limited to once or twice daily readings and unable to penetrate cloud cover. The ground level data provides much more complete information especially if hourly figures are released. If the Guangdong and Hong Kong authorities agree to release hourly data and expand the number of monitoring stations in the network, this will enhance understanding of where the pollution is centred and how it varies over time. This will be helpful in zeroing-in on emission hotspots and providing guidance for the location of future power plants, industrial facilities and the like.


Background Paper