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How much do you know about AQI?

Posted on October 30, 2019
by Misha Ma

Opening mobile phones to check the AQI index before going out every day has become a compulsory course for people in morden city. When the AQI is lower than 50, we hang out with friends to enjoy the sunshine and the warm wind. When the AQI breaks through 300, we armed ourselves with a mask, try not to close the door, and be an otaku at home with the purifier. A small number has touched our mood all day long.

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Since AQI is so important, what real information that is related to air it can provide us? Today, we will explain AQI for you in detail, including what is AQI, how to calculate AQI, how to compare Chinese and American standards, and how to use AQI to guide our lives.

The Air Quality Index is referred to AQI, which represnets an index for air quality. It is a dimensionless index that quantitatively describes the state of air quality. Just as our familiar BMI can be used to imply body types, AQI is able to tell us the severity of air pollution, which helps us take appropriate actions in our life. However, just like BMI does not represent specific weights or body fat data, AQI cannot directly tell us the specific concentration of pollutants in the air.

The specific values of AQI are obtained by calculating the concentration of pollutants. For China, there are five main air pollutants involved in the AQI evaluation:

  • Fine Particles (ie PM2.5)

  • Respirable Particulate Matter (ie PM10)

  • Sulfur Dioxide

  • Ozone

  • Carbon Monoxide

What the majority of people do not recognize is that AQI is fixed in the range from 0 to 500. Taking PM2.5 as an example, when the daily average concentration reaches 500 μg/m3, the calculated AQI is 500. After that, regardless of the increase in the concentration of PM2.5, the AQI index will remain unchanged at 500. Therefore, if you have seen AQI is 600 or 700 on some applications or websites, please remember that the data is only estimated by them. Definitely, when the AQI is extremely high, you can still check the specific PM2.5 concentration value to learn about the severity of air pollution.

By the way, Pureliving's monitors strictly follow the AQI standard algorithm, so when the weather is extraordinaryly bad, you find that the AQI showed by the monitor stops at 500, do not think that is broken! Meanwhile, as long as the monitor is adjusted to PM2.5 concentration level, the specific situation of air pollution can be known.

Many people believe that AQI is the demonstration of PM2.5, but in fact for China, the six pollutants involved in air quality assessment are directly related to AQI. By calculating the concentrations of the six pollutants, we get an individual air quality index (IAQI), and the maximum of the six sub-indices is the final AQI. Of course, in most cases, PM2.5 is the main reason of air pollution, so AQI usually reflects the concentration of PM2.5. We can not only calculate AQI by PM2.5 concentration, but also get PM2.5 concentration by calculating AQI.

So, how are the concentrations of various pollutants specifically calculated? We will use the list of Chinese AQI standards below to explain to you.

Taking PM2.5 as an example, assume that we detect that its concentration in air for 24 hours is 450 μg/m3, then we can see this concentration is between 350 and 500, and its corresponding IAQI's range is 400 to 500. Meanwhile, the IAQI can be calculated by the following proportional conversion formula!

And if the IAQI calculated by PM2.5 is exactly the highest, then the AQI is 467 at this time. On the other hand, if we know the value of AQI and the current primary pollutants, we can also reverse our calculation to get the specific concentration of the pollutants.

People who are concerned about AQI may know that the AQI we see on Chinese websites often has a certain gap with the data released by the US Embassy. Please do not conclude that the Chinese or American testing methods are inaccurate.

In fact, China and the United States have different calculation methods for AQI, so the calculated values are totally different. Above all, we mentioned above that there are six pollutants involved in China's air quality assessment, and the monitoring stations in the US Embassy in Beijing usually only monitor PM2.5. Moreover, even for PM2.5, the corresponding limits for different AQI levels are distinguished.

So here comes the question -- What is the difference between the two standards in China and the United States?

Two AQI calculation methods actually have their own reasons. AQI itself is an artificial index, its purpose is to help people intuitively understand the severity of air pollution. Due to differences in geography, weather, man-made, and economic factors, China and the United States differ in air quality. Therefore, two countries have different definitions on the AQI algorithm, which is also considered from their respective national conditions.

As long as it can show AQI that can provide guidance for our daily life, it is useful data. At this point, no matter which kind of AQI, it can provide a certain degree of warning effect of air pollution, reminding us of taking protective measures. Certainly, in an ideal world, the air we breath in will contain no pollution. And AQI will be no longer meaningful at that time.

The most effective way for you is to set up a professional air quality testing device at home, and measure PM2.5 and other data you are interested in every day.

We have specially created a table below to help you visually understand the meaning behind AQI --

Monitors come in all shapes, sizes, price ranges, and at vastly different levels of efficiency. Not all sensors are created equal, and it is important to understand your goals so you can choose the right monitor for you.

The most important parameters which are most important in monitoring your indoor air quality are PM, carbon dioxide, TVOCs (Total Volatile Organic Compounds), relative humidity and formaldehyde, so ensure your monitor covers these five points adequately.

Make sure you choose a monitor which has been previously performance tested either by you or by a reputable multi-brand dealer. Another source is healthy building standard RESET™, which certifies monitoring hardware and is a good place for identifying the difference between good and poor sensors. RESET™ monitors into three groups: A for calibration-grade, B for commercial-grade suitable for office locations, and C for consumer-grade.

Only Grades A and B are suitable for RESET certification and are recommended for professional monitoring. In one study of 30 Grade C monitors, there was a 100% accuracy failure.

When choosing a monitor, also consider the ability of the device to transmit data, which can be done via a number of methods including Wi-Fi, Bluetooth, and LAN. Deployment location, choice of communications protocols, and power supplies should also be carefully planned to ensure representative data is gathered by the monitor for analysis.

If in doubt, speak with Pureliving, wewill be able to recommend appropriate monitoring solutions based on their experience and expertise.

Is that all clear now?

Congratulations to you for reading till the end! If you find this article useful, share it with your friends who love the air! Scan the QR code below to follow Pureliving and get all kinds of air knowledge at any time. See you next time!

About PureLiving

PureLiving is a leading indoor environmental consulting company with a simple mission: to help our clients create healthy homes and workplaces. Our expert team of building engineers, HVAC specialists, and environmental consultants advises clients on air and water quality, mold, asbestos and lead exposure issues and helps to improve their indoor environmental quality through testing to identify sources of pollution and then eliminating them. Our total range of solutions includes pollutant testing, design and installation of cutting-edge filtration systems, monitoring, and odor and chemical reduction. With operations in six cities across China, Hong Kong, and India, PureLiving is the industry’s provider of choice for assessment, engineering, implementation, and monitoring of indoor environmental quality. Find out more at www.purelivingchina.com.

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