+ "text": "Two examples: AQI and UV index\nLet’s talk about how the AQI and the UV index indicate danger, starting with the UV index.\n\nUV index\nCalculating the UV index involves a series of steps but ultimately it boils down to this:\n\\[ {\\rm UV \\, index} = ({\\rm Intensity \\, of \\, UV \\, light \\, from \\, the \\, sun}) \\cdot ({\\rm constant}) \\]\nThe people that created the UV index could have chosen that constant to be whatever they wanted. And they decided to use a constant so that the UV index ranges from 0 to 11 where 11 corresponds to the typical highest intensity UV light that occurs on the surface of the earth during the course of a year.\n\n\nAir Quality Index (AQI)\nThe AQI is different from the UV index in that there are multiple scientific measurements that go into the AQI.\nHere are the scientific measurements that are used to calculate the AQI\n\nTwo measurements of how much dust or exhaust there is in the air called PM2.5 and PM10\nGround level Ozone\nCarbon monoxide\nNitrogen dioxide\nSulfur dioxide\n\nIn most cities the PM2.5 and PM10 are the most significant cause for concern, but if you live close to a factory it may be one of the other items there that are the biggest concern for air quality. Another reason for air quality to be poor is smoke from a fire.\nPart of why the AQI was created is that there is a lot of information here about the quality of the air that needs to be summarized. Without the AQI you would have to remember the danger range for five different quantities. Or maybe there would be an indicator like the picture at the very top of this page for all five, and you might still be overwhelmed by that information.\nThe AQI solves this problem like this by deciding on a danger range for each of the scientific measurements, and calculating an AQI for each item on the list – specifically you have AQIPM2.5 , AQIPM10, AQIO3, AQICO, AQISO2, and AQINO2.\nTo calculate the overall AQI you take the max of all of these numbers:\n\\[ {\\rm AQI} = {\\rm max}({\\rm AQI}_{\\rm PM2.5}, \\, {\\rm AQI}_{\\rm PM10}, \\, {\\rm AQI}_{\\rm O_3}, \\, {\\rm AQI}_{\\rm CO}, \\, {\\rm AQI}_{\\rm SO_2}, \\, {\\rm AQI}_{\\rm NO_2}) \\]\nwhere the max() function used above only returns the largest quantity. There is actually a spreadsheet function called MAX that works like this which you can find in both Sheets and Excel.\nIf you think deeply about the equation above, you may realize that there are situations where you might have high levels of dust/exhaust AND high levels of Ozone but if for example AQIPM2.5 is larger than AQIO3 then the overall AQI comes only from AQIP2.5 ONLY. Having high levels of dust AND Ozone has the same overall AQI as having high levels of dust and no Ozone at all."
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