Calculating a model Air Quality Index for countries
In principle, a single air quality indicator would combine ambient concentrations of various air pollutants, most notably various sulphur oxides (SOx), nitrogen oxides (NOx), non-methane volatile organic compounds (NMVOC), certain heavy metals (like lead), and particulate matter (PM) of various sizes (i.e., PM10 for particles of 2.5–10 micrometers and PM2.5 for 0–2.45 micrometers). For many areas, data on the levels of these compounds are not available, or at least not easily found. While a comprehensive global monitoring programme on air quality does not exist, for various large cities in the world at least some figures are known, although the data are not always comparable and often lack regular updating. The OECD reports regularly on urban air pollution for some 40–50 cities in member countries, and in Europe the EEA does similar reporting, but other than that the data are rather dispersed, not always up-to-date, not easily available outside the city, country or region, or do not exist.
In cases where direct measurements are not available for deriving or constructing an indicator, one can try to find approximate or indirect variables (proxies), which are not prefect but are still considered good enough for the intended purpose. In case of air quality, instead of air concentrations, emissions are often used, deals with the apparent sources of air pollution and for which data are usually better available. But even then, proxies are sometimes used, such as SO2 for SOx, NO2 for NOx, and PM10 for all small particulates. In addition, various emissions (e.g., from road transport) are not measured directly, but estimated on the basis of underlying activities in the economy (e.g., for transport the number of cars in a country, the type of engines they use, etc.).
For the purpose of this exercise—how to construct an indicator from data variables—we will derive a virtual air quality index (AQI) for a country and use Kenya as an example. However, you are invited to do this exercise for another country, or other area like a city, of your choice.
Kenya’s virtual AQI will be derived by combining emissions of SO2, NOx and NMVOC using a hypothetical formula created for this exercise. Data for other substances, like PM10 or PM2.5 emissions are not available. Many countries report CO2 and other GHG emissions to UNFCCC as required of participating developed countries under the UN Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol. Other emissions are often reported to UNFCCC, but still many data gaps persist making it very difficult to show comprehensive time-series. Various emission estimations for countries, regions and the world as a whole are provided by several agencies, including the Carbon Dioxide Information and Analysis Center in the United States (CDIAC), the International Energy Agency in Paris (IEA) and the Environment Assessment Agency in Netherlands, formerly part of RIVM (RIVM/MNP).
Here we will try to calculate a simple, virtual AQI for Kenya for the year 1995, using data from RIVM/MNP and CDIAC through the GEO Data Portal.
- Log on to GEO Data Portal web site. In the search box, type “SO2.” Choose the national “Emissions of SO2 – Total (RIVM/MNP)” option, and press continue. Select the data for the year 1995, and press continue. Fill out the following table.
- Repeat this query for the compounds of NOx and NMVOC
- Summarize Kenya Air Emission Indicators
- Using this data, complete the following formula to elaborate Kenya’s Air Quality Index (AQI):
- Repeat the AQI calculation for the neighbouring countries like Uganda, Tanzania, Sudan and Ethiopia, and create a bar graph and a map to visualize the differences. When ranking all countries of the world, in this hypothetical case Kenya would rank 107 out of 182.
- Using the US EPA’s AIRNow air quality index, what can you say about Kenya’s air quality?
The purpose of the AQI is to help understand what local air quality could mean for public health. To make it easier to understand, the AQI is divided into six categories:
Each category corresponds to a different level of health concern. The six levels of health concern and what they mean are:
Good: The AQI value for your community is between 0 and 50. Air quality is considered satisfactory, and air pollution poses little or no risk.
Moderate: The AQI for your community is between 51 and 100. Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people. For example, people who are unusually sensitive to ozone may experience respiratory symptoms.
Unhealthy for Sensitive Groups: When AQI values are between 101 and 150, members of sensitive groups may experience health effects, because they are likely to be affected at lower pollution levels than the general public. For example, people with lung disease are at greater risk from exposure to ozone, while people with either lung disease or heart disease are at greater risk from exposure to particulate pollution. The general public is not likely to be affected when the AQI is in this range.
Unhealthy: Nearly everyone will begin to experience health effects when AQI values are between 151 and 200. Members of sensitive groups may experience more serious health effects.
Very Unhealthy: AQI values between 201 and 300 trigger a health alert, meaning everyone may experience more serious health effects.
Hazardous: AQI values over 300 trigger health warnings of emergency conditions. The entire population is more likely to be affected.