With thick smoke covering the roads, the AQI has become an important parameter. The cold and fog of winter has brought an unexpected guest for millions of residents of Delhi-NCR: bad air. India Today has explained the science behind this word in common language.
A measurement called the Air Quality Index (AQI) tells us how bad the air has become in a particular location. Its readings often serve as a warning to people suffering from respiratory diseases. According to data from the Delhi Pollution Control Committee in the national capital, the air quality has recently fallen to dangerous levels and the AQI has reached 999 in Indirapuram.
Elsewhere in Delhi, the 24-hour average stood at 453 for the first time in the “severe+” category. While 35 of 36 monitoring stations were in the 400+ AQI category, the question was asked: “What exactly is the Air Quality Index? How do we interpret it? Where does the data come from to calculate it?” These questions are on the minds of many people across the country.
In simple words, the AQI is an index from 0 to 500 of harmful pollutants present in the air, such as carbon monoxide, sulfur oxide, ozone, nitrogen dioxide and particulate matter (PM2.5 and PM10). The higher this number, the worse the air will be.
How is the ICA calculated?
The calculation involves converting the concentration levels of pollutants in the air into index values using a formula. The formula provides an index value for each pollutant, allowing you to independently understand the impact of each pollutant on air quality.
The highest value of these becomes the AQI, that is, the pollutant with the highest value determines the final AQI. PM2.5 and PM10 particles are the main polluting particles in most areas of the national capital. Its size is 2.5 micrometers or more, about 30 times smaller than the width of a human hair.
How is it monitored?
Air quality monitoring activity is carried out by regional governing bodies. There are three main governing bodies responsible for data calculation and processing in India: Central Pollution Control Board (CPCB), Delhi Pollution Control Committee (DPCC) and researchers at IITM (Indian Institute of Meteorology Tropical). The air monitoring process is basically the same for all of these institutions. Data on pollutant concentration levels is collected at monitoring stations. There are currently two types of ground-based monitoring stations in India: manual monitoring stations and continuous ambient air quality monitoring stations (CAAQMS).
The main difference between them is the time period. While the response time of AQI calculated through manual monitoring stations is approximately 8 hours and is mainly used for chemical analysis. Continuous ambient air quality monitoring stations provide real-time AQI that is used nationwide for public information.
Where are these monitoring centers?
There are 1,296 air quality monitoring stations in the country, including 401 manual and 895 CAAQMS stations, which use ground-based electronic sensors to measure air pollutants through a process called beta attenuation technology. Many experts say there are not enough monitoring centers in India to accurately assess air quality.
“The number of CAAQMS in Delhi is optimal. However, more stations need to be set up across the country,” Mohan George, former additional director of the Delhi Pollution Control Board, told India Today. Data from the Center for Science and Environment (CSE) shows that the air quality monitoring network covers only 12 percent of the 4,041 cities and towns across the country.
What is the procedure to calculate contaminant concentrations?
Ground monitoring stations with electronic equipment use a technique called beta attenuation technology to measure air pollutants. Simply put, it works in such a way that, upon colliding with a particle, beta rays can be absorbed, reflected or transmitted directly.
When these rays pass through columns of polluted air, part of their energy is absorbed by the particles. The more pollution there is, the more energy will be absorbed. By measuring this energy loss, the system can determine how much pollution is in the air. Several international space agencies, such as NASA and ESA, have a fleet of Earth observation satellites, whose instruments observe air pollutants around the world, including our planet’s oceans, biosphere and atmosphere.
Although the Central Pollution Control Board (CPCB) does not currently use satellite data to monitor air quality, it has commissioned IIT Delhi to conduct a study to correlate aerosol optical depth (AOD) estimation based on PM 2.5 satellites. research project.
Do all apps show the same air quality data?
Most AQI apps and services display data obtained from CPCB. Government-owned web applications such as SAFAR app provide real-time AQI readings, forecasts and health advisories based on CPCB data. Third-party apps like AirVisual, WAQI, and Plume also use government data.
However, smart devices, such as indoor air purifiers and air quality monitors, are equipped with low-cost sensors that provide localized AQI readings based on the room environment, although these sensors are typically less accurate.
