The measurement is based on the observed relationship between the level of nitrogen dioxide (2NO) and the level of terrestrial ozone (O 3) and particles of substances that lead to the mortality rate (2.5PM) in many Canadian cities. Significantly, each of these three pollutants can pose a health hazard even at low levels of exposure, particularly among those with prior health problems.
In developing the Health Air Quality Index, the original analysis by the Health Ministry of Canada for health effects included the five major air pollutants: particulate matter, ozone, NO2, SO2 and CO. The other two contaminants provide little information about the expectation of health effects, and have been removed from the formulation of the health air quality index.
The health air quality index does not measure the effects of unpleasant odors, pollen, dust, heat or humidity.
These 3 answers have minutely covered everything about AQI. Nothing is left for me.
I therefore recommend the above answers K Karthik, Adriana and the author whose name appears in some other language. Regards to all these three RG Colleagues
There are AQIs for ozone, NO2, and carbon monoxide. But here in China, the AQI I’m most concerned about is fine particulate (). According to the WHO, particulate matter “.”
How They Measure It
To measure PM2.5, governments use fancy “beta attenuation monitors” (BAM). These machines suck in a cubic meter of air, push it through a filter, and measure how much particulate is on the filter. The number these machines put out is micrograms per meter cubed.
I describe more about how BAMs work here:
How They Calculate AQI
Let’s take the air on July 18th here in Beijing.
I talked about the air this day in (it has very little effect, contrary to popular belief).
At 3pm that day, the PM2.5 was 93 micrograms. The US government converts that to an AQI of 170. I’ve graphed out how those two numbers compare here. Micrograms are on the X axis; AQI is on the Y axis.
You probably noticed something strange about the formula. At low levels, adding 10 micrograms counts for 42 AQI points. Then around 100 micrograms, adding another 10 micrograms only counts for 5 AQI points! Then at really high levels, 1 microgram = 1 AQI point.
Why are some micrograms worth more than others? My guess is governments want to emphasize the difference between safe levels and levels just above that limit. But once levels are already dangerous, what’s another 10 micrograms?
What’s the Most Direct Way to Think About PM2.5?
For nerds like me who want the most direct measure of pollution, skip the AQI and look at the micrograms. As a rough guide, I use 25 micrograms. That’s the . Here’s how the air in Beijing compares to that guideline:
But keep in mind, studies have found health effects even below 25 micrograms. So the lower the better. A stricter guideline is the .
The AQI is an index for reporting daily air quality. The AQI is measured on a scale of 0 to 500. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 represents good air quality with little potential to affect public health, while an AQI value over 300 represents hazardous air quality.
An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is the level CENTRAL POLLUTION CONTROL BOARD has set to protect public health. AQI values below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is considered to be unhealthy - at first for certain sensitive groups of people, then for everyone as AQI values get higher.
The AQI considers major pollutants - PM (Coarse: PM-10, Fine: PM-2.5), NO2, SO2, CO, O3, NH3, and Pb - for which short-term (up to 24-hourly averaging period) National Ambient Air Quality Standards are prescribed.
(PM or Particulate Matter, is a mix of solids and liquid droplets freely floating in the air. Some particles are released directly from a specific source, while others form in complicated chemical reactions in the atmosphere. Particles come in a wide range of sizes. Particles less than or equal to 10 micrometers in diameter are so small that they can get into the lungs, potentially causing serious health problems.)
Based on the measured ambient concentrations, corresponding standards and likely health impact, a sub-index is calculated for each of these pollutants. The worst sub-index reflects overall AQI. Associated likely health impacts for different AQI categories and pollutants have been also been suggested, with primary inputs from the medical expert members of the group. The AQI values and corresponding ambient concentrations (health breakpoints) as well as associated likely health impacts for the identified eight pollutants are as follows:
Good (0–50) Minimal Impact
Satisfactory (51–100) May cause minor breathing discomfort to sensitive people.
Moderately polluted (101–200) May cause breathing discomfort to people with lung disease such as asthma, and discomfort to people with heart disease, children and older adults.
Poor (201–300) May cause breathing discomfort to people on prolonged exposure, and discomfort to people with heart disease
Very Poor (301–400) May cause respiratory illness to the people on prolonged exposure. Effect may be more pronounced in people with lung and heart diseases.
Severe (401-500) May cause respiratory impact even on normal healthy people, and serious health impacts on people with lung/heart disease. The health impacts may be experienced even during light physical activity.
http://pib.nic.in/newsite/PrintRelease.aspx?relid=110654
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