Thursday, Oct 06, 2022

Decoding Air Quality Index

AQI is just a guidance. It’s important that each one of us focuses on real impact and not just thresholds on ambient concentrations.

Air, Air pollution, Air quality, Air pollution in india, india air pollution, delhi pollution, delhi air pollution, health risks , air pollution health risks, Air Quality Index , china air, China air pollution, India news Over last few months there has been a lot of awareness around Air Quality Index and people have started to use the fluctuation in AQI to declare success or failure of various initiatives taken by communities and government. (AP photo)

Air pollution has become one of the biggest environmental health risks ever. Millions of people die each year due to ailments where the cause of death has been linked to constant exposure to polluted air. Of the 6-7 million premature deaths each year due to air pollution, more than 50% of those occur in China and India alone. As per a recent study air pollution is the fifth largest cause of deaths in India.

While air pollution has been impacting each one of us, it’s only lately that the subject has got the right attention from the policy makers and public at large. Educating the masses on the causes and impact of air pollution is the first step towards cohesive approach to executing solutions wherein everyone contributes to contain this problem. Air pollution is not an issue that can be addressed in isolation by an agency or government. Each citizen needs to contribute towards the larger good and pure air.

On occasions half-baked information or actions based on mere hear-say become showstoppers in taking forward larger agenda and policy decisions in the absence of adequate support from right stakeholders. I would like to demystify some of the misconceptions people have around the Air Quality Index (AQI).


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Over last few months there has been a lot of awareness around Air Quality Index and people have started to use the fluctuation in AQI to declare success or failure of various initiatives taken by communities and government. AQI is a good index to monitor air quality and tells how clean or unhealthy the air is and associated health effects, but one needs to understand the basic assumptions behind it to derive inferences. When looking at air pollution levels in a city it should be viewed from not only a city-wide level, but more importantly in localised zones given the impact some of the local actions could have on AQI.

While each country has its own parameters to calculate AQI and India has its own, most countries at a minimum monitor PM10, PM2.5, SO2, NO2, CO, and O3 on a continuous basis [online monitoring] to arrive at the AQI. Again, while looking at each of the parameters it’s not about a point in time but typically 24-hourly or 8 hourly average standard which are followed.

Secondly, when one talks of AQI measurement, distinction needs to be made if the reported reading refers to the average of readings across monitoring stations in a city or it refers to a specific monitoring station data. In countries like US there are thousands of online monitoring systems which monitor and record the concentration of major pollutants and provide a more holistic view in a locality of a city. In a city like Delhi there are only 9-10 such online stations that can measure the above stated parameters on a real time basis. This data set, while good to get a localised view, cannot provide a city wide view of the pollution. Therefore, when we draw inferences we need to factor in what data are we talking about, which location was it taken for and what time frame are we benchmarking.

Similarly, there are a lot of devices that have flooded the market which claim to showcase the AQI. Many of these devices actually show the pollutant concentrations and not the AQI. As per AQI standard one needs a minimum category of pollutants to be measured for AQI to be calculated which some of these devices are not capable of.


From an air pollution standpoint there are lot of environmental and atmospheric factors that go on to decide increase or decrease in pollutants of a particular type. Atmospheric temperature, humidity levels, wind flow etc. are only some of the very critical factors which need to be considered while talking about pollution levels. When comparing the air quality over any two days one has to necessarily factor in the atmospheric and environmental conditions prevalent during those days. To add to this local conditions in a zone or activities which could have contributed to increase or decrease of AQI should definitely be factored.

Another critical aspect is to understand that while AQI is a good parameter to keep track of air quality, more important to understand is what that really means for an individual, the quality of air one is breathing and the impact it has on one’s health. While lot of us are tuned in to monitor the reported AQI on a periodic basis what is missing is the understanding of the same. Some countries have come up with their own AQI standards and methods to arrive at the same. So it is not fair to benchmark the AQI value of country A vs country B, because the formula used to arrive at the same could be different, the weightage given to each parameter could be different. For example, if one compares the Indian AQI standard versus the US AQI, an AQI of 175 would fall under category “moderate” in India as against “unhealthy” or “Red” zone in US.

Continuing on the health impact, AQI has weightages attached to each pollutant, certain sensitive groups should keep a close eye on individual pollutant levels in their locality as well. As an example higher concentration of CO increases the risk exposure to people with heart disease as against higher concentration of SO2 which increases the risk exposure for people with asthma. Exposure to air pollution could have serious short term and long term impact on human health. From reduced lung function, aggravated asthma, mild depression to cardiovascular diseases and reduced fertility are only some of the serious health impact exposure to air pollution could have.


AQI is just a guidance. It’s important that each one of us focuses on real impact and not just thresholds on ambient concentrations. It is about what each one of us can and contribute in reducing various air pollutants that impacts each one of use indoor or outdoor. It is critical we spare a moment to think about the legacy we would leave behind – a gas chamber or a pure and healthy environment.

First published on: 22-04-2016 at 12:16:46 pm
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