India's Air Pollution: Measurement Methods And Strategies

Air pollution is a pressing issue in India, with the air quality index of New Delhi dropping into the severe category in November 2024. The government has taken measures such as closing schools and implementing the Odd-Even Rule to tackle the problem. India's central pollution control board has found that most Indian cities continue to violate air quality targets, with respirable particulate matter pollution remaining a key challenge. To measure air pollution, India monitors meteorological parameters such as wind speed and direction, relative humidity, and temperature, along with the concentration of fine suspended particles of less than 2.5 microns in diameter, known as PM2.5.

The monitoring of meteorological parameters such as wind speed and direction, relative humidity and temperature

The monitoring of these meteorological parameters is integrated with the monitoring of air quality, which is measured through the concentration of fine suspended particles of less than 2.5 microns in diameter. This is known as PM2.5 and is regularly measured from fixed-site, population-oriented monitors located within metropolitan areas. The measurements from all the monitors in a metropolitan area can be averaged to develop a single estimate of the air quality.

Despite this monitoring, most Indian cities continue to violate India's and the world's air quality PM10 targets. Respirable particulate matter pollution remains a key challenge for India, as evidenced by the air quality index of New Delhi, the capital of India, which dropped into the severe category in November 2024. The government has implemented measures such as the Odd-Even Rule to tackle this issue, which involves allowing cars with number plates ending in odd digits to be driven on certain days of the week, while cars with even digits are driven on the remaining days.

The monitoring of gaseous pollutants and particulate matter

One key challenge identified by the board is the high levels of respirable particulate matter pollution in Indian cities. This type of pollution, known as PM10, refers to particles with a diameter of 10 microns or less, which can penetrate deep into the respiratory system and pose significant health risks. Despite some improvements in certain cities, most Indian urban areas continue to violate national and international air quality standards for PM10.

To address this issue, various measures have been implemented, such as the Odd-Even Rule in New Delhi, which restricts car usage based on number plates ending in odd or even digits on alternate days. This rule was introduced in November 2017 to reduce vehicle emissions and improve air quality. Additionally, the government has ordered schools to close and construction to cease during periods of severe air pollution, as seen in November 2024 when New Delhi was ranked as the world's most polluted city.

To measure air pollution accurately, fixed-site monitors are placed within metropolitan areas to measure the concentration of fine suspended particles, known as PM2.5. These particles have a diameter of less than 2.5 microns and are considered a common measure of air pollution. By averaging the high-quality measurements from these monitors, a single estimate of PM concentration for the entire metropolitan area can be developed. However, it is important to note that the number of monitors can vary across different geographical areas, with some regions having little or no monitoring capabilities.

The air quality index of New Delhi

Air pollution in India is measured by monitoring meteorological parameters such as wind speed and direction, relative humidity and temperature, alongside the monitoring of air quality. The monitoring of pollutants is carried out for 24 hours, with 4-hourly sampling for gaseous pollutants and 8-hourly sampling for particulate matter.

The Air Quality Index (AQI) of New Delhi, India's capital, dropped into the severe category in November 2024, according to SAFAR, India's main environmental agency. On 18 November, Swiss group IQAir ranked New Delhi as the world's most polluted city, with air quality at a 'hazardous' 1,081. The government ordered schools to close and construction to cease. The reading dropped to 489 the next day, although it was still the most polluted in the world.

The AQI levels in New Delhi have been fluctuating. On 13 March 2025, the current real-time AQI level was 166 (unhealthy). The best AQI level in the last 24 hours was 108 (poor) at 6:14 pm on 12 March 2025. The worst AQI level in the last 24 hours was 212 (severe) at 8:14 am on 12 March 2025. The current New Delhi AQI is 166 (unhealthy) with real-time air pollution PM2.5 (77µg/m³), PM10 (164µg/m³), and a temperature of 27°C.

The raw measurements are then converted by Plume Labs into values comprising the AQI, using standards and guidelines developed by the Environmental Protection Agency (EPA) and the World Health Organization (WHO), among other scientific studies by Plume Labs.

The Odd-Even Rule in Delhi

Air pollution in India is a serious issue, with most Indian cities continuing to violate India's and the world's air quality PM10 targets. To measure air pollution, India monitors meteorological parameters such as wind speed and direction, relative humidity and temperature. The concentration of fine suspended particles of less than 2.5 microns in diameter is also measured as a common indicator of air pollution.

One of the key challenges for India is respirable particulate matter pollution. To tackle this issue, the government in Delhi launched an Odd-Even Rule in November 2017. This rule is based on the Odd-Even rationing method, where cars with number plates ending in odd digits can only be driven on certain days of the week, while cars with even-numbered plates can be driven on the remaining days. The aim of this rule is to reduce the number of cars on the road and, consequently, the amount of pollution they produce.

The Odd-Even Rule is an example of road space rationing, which has been used in other cities around the world to tackle air pollution and reduce traffic congestion. This method of traffic restriction has been shown to be effective in improving air quality, particularly in urban areas. By limiting the number of cars on the road, the Odd-Even Rule helps to reduce the emission of pollutants from vehicles, which are a major contributor to air pollution in cities.

While the Odd-Even Rule in Delhi was a temporary measure, it highlighted the importance of finding long-term solutions to the city's air pollution problem. The success of this rule in improving air quality, even if only temporarily, demonstrates the potential for more permanent road space rationing or other traffic restriction measures to be implemented in the future.

The World Air Quality Index project

The mean annual concentration of fine suspended particles of less than 2.5 microns in diameter is a common measure of air pollution. The mean is a population-weighted average for the urban population in a country. High-quality measurements of PM concentration from all the monitors in the metropolitan area can be averaged to develop a single estimate. Although PM is measured at many thousands of locations throughout the world, the amount of monitors in different geographical areas vary, with some areas having little or no monitoring.

The air quality index of New Delhi (the capital of India) dropped into the severe category in November 2024 according to SAFAR, India’s main environmental agency. On 18 November, Swiss group IQAir ranked New Delhi as the world's most polluted city with air quality at a 'hazardous' 1,081. The government ordered schools to close and construction to cease to tackle the issue. The reading of the city dropped to 489 the next day (19 November), although it was still the most polluted in the world. The government in Delhi launched an Odd-Even Rule in November 2017, which meant that cars running with number plates ending in odd digits could only be driven on certain days of the week, while the even digit cars could be driven on the remaining days of the week.

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