api vs aqi vs aqhi

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http://www.aqhi.gov.hk/en/what-is-aqhi/faqs.html#e_01

The New AQHI SystemPurpose 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 anestimate 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, and 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 suspended particulates (RSP or PM10) or fine suspendedparticulates (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 ((NO2) C(NO2)) 1] 100%

%AR(SO2) = [exp ((SO2) C(SO2)) 1] 100%

%AR(O3) = [exp ((O3) C(O3)) 1] 100%%AR(RSP) = [exp ((RSP) C(RSP)) 1] 100%

%AR(FSP) = [exp ((FSP) FSPFSP)) 1] 100%

where

%AR(NO2), %AR (SO2), %AR (O3), %AR (PM), %AR (RSP) and %AR (FSP) are the addedhealth 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 (g/m3); and


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(NO2), (SO2), (O3), (RSP) and (FSP) are added health risk factors (technically known as

regression coefficients) of the respective pollutants.

(NO2) = 0.0004462559

(SO2) = 0.0001393235

(O3) = 0.0005116328(RSP) = 0.0002821751

(FSP) = 0.0002180567

For further details, please refer to theStudy 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 forthe high and very high risk categories, corresponding to an increase in the risk of hospitaladmissions 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 people who are sensitive to

air pollution and the general public are advised to take precautionary actions for healthprotection. Other AQHI categories are derived based on these cut-points, as shown in the tablebelow.

Health

Risk

CategoryThe label AQHI

Added

Health

Risk

(%AR)

Remark

Low

1 0 - 1.88

2>1.88 -

3.76

3>3.76 -

5.64

Moderate

4>5.64 -

7.52%AR of 5.64: 0.5 x

threshold for people

who are sensitive to

air pollution (%AR of

11.29 ) to takeprecautionary actions

5>7.52 -

9.41

6 >9.41 -11.29

High 7>11.29 -

12.91

%AR of 11.29:threshold for people

who are sensitive to

air pollution to takeprecautionary actions
http://www.aqhi.gov.hk/pdf/related_websites/APIreview_report.pdfhttp://www.aqhi.gov.hk/pdf/related_websites/APIreview_report.pdfhttp://www.aqhi.gov.hk/pdf/related_websites/APIreview_report.pdfhttp://www.aqhi.gov.hk/pdf/related_websites/APIreview_report.pdf


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Very High

8>12.91 -

15.07 %AR of 12.91:threshold for the

general public to take

precautionary actions

9>15.07 -

17.22

10>17.22 -

19.37

Serious 10+ >19.37

%AR of 19.37 : 1.5 xthreshold for the

general public (%AR

of 12.91) to take

precautionary actions

For further details, please refer to theStudy 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 thegeneral 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 respiratoryillnesses, 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 tothe 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 ofthe 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 system:

(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 moreuseful a health reference than the older system;

(b) The AQHI takes into account the combined effects of the major air pollutants in Hong Kong;
http://www.aqhi.gov.hk/pdf/related_websites/APIreview_report.pdfhttp://www.aqhi.gov.hk/pdf/related_websites/APIreview_report.pdfhttp://www.aqhi.gov.hk/pdf/related_websites/APIreview_report.pdfhttp://www.epd.gov.hk/epd/english/environmentinhk/air/studyrpts/files/APIreview_report.pdfhttp://www.epd.gov.hk/epd/english/environmentinhk/air/studyrpts/files/APIreview_report.pdfhttp://www.epd.gov.hk/epd/english/environmentinhk/air/studyrpts/files/APIreview_report.pdfhttp://www.aqhi.gov.hk/pdf/related_websites/APIreview_report.pdf


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(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 andreleases 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 websiteat http://www.aqhi.gov.hk by using a personal computer or a mobiledevice such as a smart phone;

(ii) Download, from the above EPD website, an AQHIappfor mobile devices or an AQHIalert

wizardfor desktop computers; these can readily access the AQHI 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 arealso 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 EPDsair

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 meGeneral 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 awayfrom 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.
http://www.aqhi.gov.hk/enhttp://www.aqhi.gov.hk/enhttp://www.aqhi.gov.hk/en/download/aqhi-mobile-apps.htmlhttp://www.aqhi.gov.hk/en/download/aqhi-mobile-apps.htmlhttp://www.aqhi.gov.hk/en/download/aqhi-mobile-apps.htmlhttp://www.aqhi.gov.hk/en/download/aqhi-alert-wizard.htmlhttp://www.aqhi.gov.hk/en/download/aqhi-alert-wizard.htmlhttp://www.aqhi.gov.hk/en/download/aqhi-alert-wizard.htmlhttp://www.aqhi.gov.hk/en/download/aqhi-alert-wizard.htmlhttp://www.aqhi.gov.hk/en/monitoring-network/air-quality-monitoring-network.htmlhttp://www.aqhi.gov.hk/en/monitoring-network/air-quality-monitoring-network.htmlhttp://www.aqhi.gov.hk/en/monitoring-network/air-quality-monitoring-network.htmlhttp://www.aqhi.gov.hk/en/monitoring-network/air-quality-monitoring-network.htmlhttp://www.aqhi.gov.hk/en/monitoring-network/air-quality-monitoring-network.htmlhttp://www.aqhi.gov.hk/en/monitoring-network/air-quality-monitoring-network.htmlhttp://www.aqhi.gov.hk/en/download/aqhi-alert-wizard.htmlhttp://www.aqhi.gov.hk/en/download/aqhi-alert-wizard.htmlhttp://www.aqhi.gov.hk/en/download/aqhi-mobile-apps.htmlhttp://www.aqhi.gov.hk/en


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11. Which General Station is most relevant to me?

Areas of similar land uses, traffic conditions and levels of urban development would tend to havesimilar 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 neighbouringstation, as shown in the table below:

District Correlated Monitoring Station

Hong Kong Island

Central & Western Central/Western

Eastern Eastern

Southern Central/Western or Eastern,whichever is nearer

Wan Chai Central/Western

Kowloon

Kowloon City Sham Shui Po

Kwun Tong Kwun Tong

Sham Shui Po Sham Shui Po

Yau Tsim Mong Sham Shui Po

Wong Tai Sin Kwun Tong

New Territories

Islands Tung Chung

Kwai Tsing Kwai Chung

North Tai Po

Sai Kung Sha Tin

Sha Tin Sha Tin

Tai Po Tai Po

Tsuen Wan Tsuen Wan

Tuen Mun Tuen Mun

Yuen Long 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 theannual Air Quality Index (AQI).
http://www.aqhi.gov.hk/en/annual-aqi/latest-annual-aqi.htmlhttp://www.aqhi.gov.hk/en/annual-aqi/latest-annual-aqi.htmlhttp://www.aqhi.gov.hk/en/annual-aqi/latest-annual-aqi.htmlhttp://www.aqhi.gov.hk/en/annual-aqi/latest-annual-aqi.html


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Health Advice

13. What health advice is provided by the new AQHI system?

Differenthealth advicesare given to people with different degrees of susceptibility to airpollution, including:

(i) People who are sensitive to air pollution, i.e. (a) people with existing heart or respiratoryillnesses, 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 cutdown 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 outdoorphysical exercise. If you stay indoors, make sure the indoor environment is not polluted bysources 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 concentrationof 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 airpollutant is higher than that caused by exposure to the WHO reference value, whereas an value
http://www.aqhi.gov.hk/en/health-advice/sub-health-advice.htmlhttp://www.aqhi.gov.hk/en/health-advice/sub-health-advice.htmlhttp://www.aqhi.gov.hk/en/health-advice/sub-health-advice.htmlhttp://www.aqhi.gov.hk/en/health-advice/sub-health-advice.html


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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. NO2and PM10or 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

concentration of 35 g/m

3

for PM2.5implies a 15% increase in the risk of death from heart andrespiratory diseases, including respiratory cancer, compared to the risk if the concentration ofPM2.5were 10 g/m

3(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 indexthe hourly AQHI or the annual AQIshould I refer to?

For decisions relating to daily physical activities, you should refer to the hourly AQHI andconsider the relevant health advice. Theannual AQIis relevant only if you would like to assess

the health risks caused by long-term exposure to air pollution.
http://www.aqhi.gov.hk/en/annual-aqi/latest-annual-aqi.htmlhttp://www.aqhi.gov.hk/en/annual-aqi/latest-annual-aqi.htmlhttp://www.aqhi.gov.hk/en/annual-aqi/latest-annual-aqi.htmlhttp://www.aqhi.gov.hk/en/annual-aqi/latest-annual-aqi.html


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Source: http://wtienyit.wordpress.com/2011/11/02/air-pollution-indexapi-in-china-vs-air-quality-

indexaqi-in-america/

Air Pollution Index(API) in China vs Air

Quality Index(AQI) in America

Posted onNovember 2, 2011bywtienyit

The air pollution problem in China has bothered Chinese residents for decades. More and morepeople 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., EPA uses Air Quality Index

(AQI). Whats the difference between API and AQI? What factors make great gaps when APIvalue 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 Chinas smog claims,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 choosing breakpoints. Forexample, 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.
http://wtienyit.wordpress.com/2011/11/02/air-pollution-indexapi-in-china-vs-air-quality-indexaqi-in-america/http://wtienyit.wordpress.com/2011/11/02/air-pollution-indexapi-in-china-vs-air-quality-indexaqi-in-america/http://wtienyit.wordpress.com/2011/11/02/air-pollution-indexapi-in-china-vs-air-quality-indexaqi-in-america/http://wtienyit.wordpress.com/author/wtienyit/http://wtienyit.wordpress.com/author/wtienyit/http://wtienyit.wordpress.com/author/wtienyit/http://wtienyit.files.wordpress.com/2011/11/chart-1.jpghttp://wtienyit.wordpress.com/author/wtienyit/http://wtienyit.wordpress.com/2011/11/02/air-pollution-indexapi-in-china-vs-air-quality-indexaqi-in-america/


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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 hour ozone reading from its hourly concentration. Chinaonly 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 AQIvalue (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 by 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 ofthe 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.
http://wtienyit.files.wordpress.com/2011/11/chart3.jpghttp://wtienyit.files.wordpress.com/2011/11/chart22.jpghttp://wtienyit.files.wordpress.com/2011/11/chart3.jpghttp://wtienyit.files.wordpress.com/2011/11/chart22.jpg


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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
http://www.airnow.gov/http://www.airnow.gov/http://www.cnn.com/2011/11/01/world/asia/china-air/index.html?hpt=wo_bn4http://www.cnn.com/2011/11/01/world/asia/china-air/index.html?hpt=wo_bn4http://www.cnn.com/2011/11/01/world/asia/china-air/index.html?hpt=wo_bn4http://www.airnow.gov/

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