http://www.aqhi.gov.hk/en/what-is-aqhi/faqs.html#e_01
The New AQHI System – Purpose Purpose and Use 1. What is the Air Quality Health Index (AQHI)?
The Air Quality Health Index (AQHI) is a health risk-based air pollution index. It provides an estimate of the short-term (hospital admission) risk of heart and respiratory diseases from air pollution. The AQHI is reported on a scale of 1 to 10 and 10+, and is grouped into five health risk categories: low, moderate, high, very high, an d serious.
2. How is the hourly AQHI calculated?
The AQHI of the current hour is calculated from the sum of the percentage added health risk (%AR) of daily hospital admissions attributable to the 3-hour moving average concentrations of four criteria air pollutants: ozone (O3), nitrogen dioxide (NO2), sulphur dioxide (SO2), and particulate matter (PM) (respirable (respirable suspended particulates (RSP or PM10) or fine suspended particulates (FSP or PM2.5), whichever poses a higher health risk). The %AR of each pollutant depends on its concentration and a risk factor which was derived from local health statistics and air pollution data. The %AR is then compared to a scale to obtain the appropriate banding of AQHI. The equations are as follow: %AR = %AR (NO2) + %AR (SO2) + %AR (O3) + %AR (PM) where %AR (PM) = %AR (RSP) or %AR (FSP), whichever is higher %AR(NO2) = [exp (β(NO2) × C(NO2)) – 1] 1] × 100% %AR(SO2) = [exp (β(SO2) × C(SO2)) – 1] 1] × 100% %AR(O3) = [exp (β(O3) × C(O3)) – 1] 1] × 100% %AR(RSP) = [exp (β(RSP) × C(RSP)) – 1] 1] × 100% %AR(FSP) %AR(FSP) = [exp (β(FSP) ×FSPFSP)) – 1] 1] × 100% where %AR(NO2), %AR (SO2), %AR (O3), %AR (PM), %AR (RSP) and %AR (FSP) are the added health risk of NO2,SO2, O3, PM, RSP and FSP respectively; C(NO2), C(SO2), C(O3), C(RSP) and C(FSP) are the 3 -hour rolling average concentration of the respective pollutants in microgram per cubic meter (µg/m3); and
β(NO2), β(SO2), β(O3), β(RSP) and β(FSP) are added health risk factors (technically known as regression coefficients) of the respective pollutants. β(NO2) = 0.0004462559 β(SO2) = 0.0001393235 β(O3) = 0.0005116328 β(RSP) = 0.0002821751 β(FSP) = 0.0002180567 For further details, please refer to the Study Report . 3. What is the basis for the AQHI health risk categories?
In establishing the cut-points for the different bands, the AQHI system takes into account the Air Quality Guidelines (AQG) for air pollutants, developed by the World Health Organization (WHO), as well as the local hospital admissions risk. The health risk levels associated with the short-term WHO AQG for the air pollutants are used for determining the AQHI cut-points for the ‘high’ and ‘very high’ risk categories, corresponding to an increase in the risk of hospital admissions of 11.29% and 12.91% respectively. The cut- points for the ‘high’ and ‘very high’ categories respectively demarcate the air pollution levels for which p eople who are sensitive to air pollution and the general public are advised to take precautionary actions for health protection. Other AQHI categories are derived based on these cut-points, as shown in the table below. Health Risk Category
Low
The label
Added Health AQHI Risk (%AR) 1 0 - 1.88 >1.88 2 3.76
3 4 Moderate
5 6
High
7
Remark
>3.76 5.64 >5.64 - %AR of 5.64: 0.5 x 7.52 threshold for people >7.52 - who are sensitive to 9.41 air pollution (%AR of >9.41 - 11.29 ) to take 11.29 precautionary actions %AR of 11.29: threshold for people >11.29 who are sensitive to 12.91 air pollution to take precautionary actions
8 Very High
9 10
Serious
10+
>12.91 15.07 %AR of 12.91: >15.07 - threshold for the 17.22 general public to take >17.22 - precautionary actions 19.37 %AR of 19.37 : 1.5 x threshold for the >19.37 general public (%AR of 12.91) to take precautionary actions
For further details, please refer to the Study Report . 4. What is the purpose of the AQHI?
The AQHI is a tool for communicating the short-term health risk posed by air pollution to the general public. It provides information on the possible risks to health from exposure to different levels of air pollution in the outdoor environment. This information allows people to make informed decisions on their outdoor physical activities. Individuals with heart or respiratory illnesses, who are on regular medication, may need to consult their doctors on adjusting the doses they take.
5. Why did we replace the Air Pollution Index (API) system (in use from 1995 to 2013) with the new AQHI system?
The previous Air Pollution Index (API) categorised air quality into different levels according to the values of the Air Quality Objectives (AQOs). The Environmental Protection Department (EPD) engaged a joint team of public health and air science experts from the Chinese University of Hong Kong and the Hong Kong University of Science and Technology to conduct a review of the API system. The study recommended replacing the API with a health risk-based AQHI system, which can provide better communication on health risk and thus improve the protection of public health. 6. What improvements does the AQHI have over the API system?
The AQHI system features the following improvements over the API s ystem: (a) The AQHI system is a health risk-based reporting system based on the relationship between local air pollution and hospital admissions, thus providing a locally relevant index that is more useful a health reference than the older system; (b) The AQHI takes into account the combined effects of the major air pollutants in Hong Kong;
(c) The use of 3-hour moving average pollutant concentrations in calculating the AQHI enables the changes in air quality to be closely followed, and hence will provide more timely health risk communication to the public.
7. How is the AQHI reported and forecasted?
The AQHI is reported hourly at each general (ambient) and roadside station. The AQHIs reported at general monitoring stations are referred to as ‘General AQHIs’, while those reported at roadside monitoring stations are referred as ‘Roadside AQHIs’. The EPD calculates and releases the AQHIs every hour; it also provides forecasts of roadside and general AQHIs for the next 12 to 24 hours in two time blocks, i.e. both a.m. and p.m. sessions. 8. Where can I get the latest AQHIs and forecasts?
There are a number of ways that you can get the latest hourly AQHI and forecast: (i) Visit the EPD website at http://www.aqhi.gov.hk by using a personal computer or a mobile device such as a smart phone; (ii) Download, from the above EPD website, an AQHI app for mobile devices or an AQHI alert wizard for desktop computers; these can readily access the AQH I and forecast; or (iii) Call an AQHI hotline through an interactive voice recording system at 2827 8541 for verbal updates, or obtain a copy of this information by the fax-on-demand service. All of the above methods can provide you with AQHI information 24 hours a day. There are also updates provided at regular intervals by the mass media, on different TV and radio channels.
9. What are the General AQHI and Roadside AQHI?
The General AQHI reflects the level of air pollution to which you are exposed most of the time. It comes from measurements at twelve general air quality monitoring stations in the EPD’s air monitoring network . The Roadside AQHI tells you the level of air pollution specifically at the roadside, with very heavy traffic and tall surrounding buildings. Measurements are taken from the three roadside air quality monitoring stations. 10. Which AQHI is more relevant to me – General or Roadside?
The health effects of air pollution result from exposure to a combination of air pollutants, in different concentrations, over a period of time. Exposure to moderately high pollution levels for a short time normally will not lead to significant problems. If you spend most of your time away from the roadside, the General AQHI is more relevant. The Roadside AQHI is more relevant to people who spend most of their daily activities on the roadside, near heavy traffic and surrounded by tall buildings.
11. Which General Station is most relevant to me?
Areas of similar land uses, traffic conditions and levels of urban development would tend to have similar air pollution levels. You may refer to the AQHI of those stations with similar development characteristics closest to the area you live in. If you live in a district that does not have an air quality monitoring station, you may refer to the AQHI measured by a neighbouring station, as shown in the table below:
District Hong Kong Island Central & Western Eastern Southern Wan Chai Kowloon Kowloon City Kwun Tong Sham Shui Po Yau Tsim Mong Wong Tai Sin New Territories Islands Kwai Tsing North Sai Kung Sha Tin Tai Po Tsuen Wan Tuen Mun Yuen Long
Correlated Monitoring Station Central/Western Eastern Central/Western or Eastern, whichever is nearer Central/Western Sham Shui Po Kwun Tong Sham Shui Po Sham Shui Po Kwun Tong Tung Chung Kwai Chung Tai Po Sha Tin Sha Tin Tai Po Tsuen Wan Tuen Mun Yuen Long
12. Can the new AQHI provide information/alerts on the long-term impact of air pollution?
The new AQHI aims to give short-term health advice. The long-term impact of air pollution on the general population is communicated by means of the annual Air Quality Index (AQI).
Health Advice 13. What health advice is provided by the new AQHI system?
Different health advices are given to people with different degrees of susceptibility to air pollution, including: (i) People who are sensitive to air pollution, i.e. (a) people with existing heart or respiratory illnesses, and (b) children and the elderly; (ii) Outdoor workers, and (iii) The general public. 14. What are the differences between ‘reduce’, ‘reduce to a minimum’ and ‘avoid’ in the health advice?
These terms are used to express the different extent of curtailment of strenuous outdoor activities. ‘Reduce’ refers to a lowering of the intensity or duration of these activities, while ‘avoid’ means to refrain from such activities completely. To ‘reduce to the minimum’ is to cut down to only those activities that are essential.
15. What preventive measures should I take when the AQHI is at an alert level?
You should reduce exposure to air pollution in the outdoor environment and avoid outdoor physical exercise. If you stay indoors, make sure the indoor environment is not polluted by sources such as cigarette smoking, cooking fumes, and open flames, or by air pollutants emitted from furniture, carpets, and other household items. If you are not fit, or have heart or respiratory diseases, consult the doctor on your medications and on the amount of physical exercise you should perform.
Annual Air Quality Index 16. What is annual Air Quality Index (AQI)?
The annual Air Quality Index (AQI) aims to communicate the health risks caused by long-term exposure to air pollutants. The index is derived from the ratio of the annual mean concentration of an air pollutant to that of the corresponding WHO annual AQG. An annual AQI of one means that the air pollutant concentration is equal to the WHO annual AQG level. An AQI greater than one would indicate that the health risk resulting from long-term exposure to an individual air pollutant is higher than that caused by exposure to the WHO reference value, whereas an value
below one means a lower risk. The annual AQIs are calculated for those air pollutants with annual WHO AQGs, i.e. NO2 and PM10 or PM2.5, based on 12-month moving average concentrations of these pollutants.
17. What information does the annual AQI convey?
For those air pollutants with annual WHO AQGs, i.e. NO2 and PM10 or PM2.5, the annual AQI tells us how good (or poor) the Hong Kong air quality has been in the past 12 months, as compared with the WHO AQGs. 18. How should I interpret the annual AQI?
An annual AQI of an air pollutant of greater than one means residents in that district are at a higher risk to the long-term health effects caused by that air pollutant. For example, a long-term 3 concentration of 35 µg/m for PM2.5 implies a 15% increase in the risk of death from heart and respiratory diseases, including respiratory cancer, compared to the risk if the concentration of 3 PM2.5 were 10 µg/m (at which level a small risk still exists). It should be noted that the risks to health differ for different air pollutants and in different age groups. As a whole, the greater the index, the more we as a community need to do to improve our air quality by reducing the release of air pollutants from various sources.
19. Which index – the hourly AQHI or the annual AQI – should I refer to?
For decisions relating to daily physical activities, you should refer to the hourly AQHI and consider the relevant health advice. The annual AQI is relevant only if you would like to assess the health risks caused by long-term exposure to air pollution.
Source: http://wtienyit.wordpress.com/2011/11/02/air-pollution-indexapi-in-china-vs-air-qualityindexaqi-in-america/
Air Pollution Index(API) in China vs Air Quality Index(AQI) in America Posted on November 2, 2011 by wtienyit The air pollution problem in China has bothered Chinese residents for decades. More and more people realize that air pollution affects their health seriously. A good air pollution monitoring system can help people reduce or avoid harm from pollutants. Chinese officials apply Air Pollution Index (API) as their monitoring system. In the U.S., E PA uses Air Quality Index (AQI). What’s the difference between API and AQI? What factors make great gaps when API value is relatively low(the lower the better for both API and AQI) but AQI value is high in the same area?( U.S. readings challenge China’s smog cl aims,Josh Levs, CNN, 2011) Calculation. Both API and AQI share the same formula. So it is not the factor that makes difference between API and AQI.
AQI=(AQI,h-AQI,l)*(Concentration-BP,l)/(BP,h-BP,l)+AQI,l BP,h and BP,l are concentration breakpoints, equal to AQI,h and AQI,l values.; Concentration is the monitoring reading of a pollutant. Breakpoints. There is slightly different between API and AQI when ch oosing breakpoints. For example, for category Unhealthy for Sensitive Groups, the AQI breakpoints of ozone ( 1-hour) are 0.125 and 0.164 ppm, which equal to AQI value 101 and 150 separately. But for API, the breakpoints are 0.102 and 0.164 ppm.Chart 1 shows the slight difference.
Chart 1 Chart 2 shows the tiny difference of PM10 (24-hour) between API and AQI.
Chart 2 Therefore, breakpoints choosing is not the factor that makes API and AQI value different dramatically. Monitoring Method. For some pollutants, China and U.S. apply different monitoring methods. For example, U.S. monitors running 8 hou r ozone reading from its hourly concentration. China only read daily average from hourly ozone concentration. Chart 3 indicates the great difference.
Chart 3 From this chart, AQI value(O3, 8-hour) rises dramatically. When ozone concentration is 0.1 ppm, API value (O3, 1-hour) stays under 100 which indicates moderate category, whereas AQI value (O3, 8-hour) goes above 150 which means unhealthy. Therefore, monitoring method makes great gap between API and AQI values. PM2.5. Particle matter 2.5(PM2.5), which means particulates less than 2.5 micrometers in diameter, leads to respiratory diseases. It is a very important pollutant monitored b y EPA in the U.S. Trace concentration of PM2.5 contributes to high AQI value. In China, PM2.5 concentration in some cities are relatively high. Unfortunately, China excludes the item out of the daily API report.
Daily API or AQI value is the maximum reading of all pollutants’ API or AQI values. For instance, if AQI(NO2)= 101, AQI(PM2.5)=120 and AQI(O3)=85, AQI daily is reported as 120 .
Therefore, API daily value in China is lower than AQI daily reported by U.S. embassy also because of the absence of PM2.5. Reference: http://www.airnow.gov/ http://www.cnn.com/2011/11/01/world/asia/china-air/index.html?hpt=wo_bn4
