AQI, PM2.5, smog tower: A simple guide to understanding Delhi’s air pollution

“The choking air quality is responsible for the murder of people’s health,” noted the Supreme Court today while hearing the case on stubble burning in the states of Punjab and Haryana and its impact on Delhi’s deteriorating air quality. The pollution levels in Delhi continue to remain bad, with the National Capital recording an air quality index of 394, placing it in the “very poor” category. Such is the situation that a throat-searing blanket of smog has enveloped New Delhi, forcing schools to shut and disrupting the Cricket World Cup. According to officials, the concentration of PM2.5, the fine particulate matter capable of triggering health problems, has exceeded the government-prescribed safe limit of 60 micrograms per cubic metre by seven to eight times in the capital. It was 30 to 40 times the healthy limit of 15 micrograms per cubic metre set by the World Health Organization (WHO). As air pollution in Delhi becomes the biggest headline-maker and the biggest talking point for people, here’s a simple guide which unlocks the meaning behind these complex terms. AQI AQI, Air Quality Index, is an index for reporting air quality on a daily basis. It is a measure of how air pollution affects one’s health within a short time period; the higher the AQI value, the greater the level of air pollution and the greater the health concern. The AQI is differentiated into six categories: good (0-50) – having minimal impact. The other categories are satisfactory, with an AQI of 51-100, which could cause minor breathing difficulties in sensitive people. Then there’s the moderately polluted category (101-200); air in this category can cause breathing difficulties in people with lung disease like asthma, and discomfort to people with heart disease, children and older adults. The poor category (201-300) causes breathing difficulties in people on prolonged exposure, and discomfort to people with heart disease. In the very poor (301–400) category, it caused respiratory illness in people on prolonged exposure. Effect may be more pronounced in people with lung and heart diseases. The severe (401-500) category can cause respiratory issues in healthy people, and serious health issues in people with lung/heart disease. Difficulties may be experienced even during light physical activity. Incidentally, last Thursday, Delhi’s Anand Vihar recorded an AQI of 999, the highest it has ever been in the Capital. [caption id=“attachment_13359712” align=“alignnone” width=“640”] Visitors wearing mask walk at the Kartavya Path amid dense smog near the India Gate in New Dellhi. Delhi-NCR region is witnessing smog amid a surge in farm fires and unfavourable weather conditions leading to a spike in the air pollution levels. PTI[/caption] Particulate Matter Particulate matter, also known as particle pollution or PM, is a term that describes extremely small solid particles and liquid droplets suspended in air. Particulate matter can be made up of a variety of components including nitrates, sulfates, organic chemicals, metals, soil or dust particles, and allergens (such as fragments of pollen or mould spores). Particle pollution mainly comes from motor vehicles, wood burning heaters and industry. Particulate matter comes in different sizes – one is known as PM10, where particulate matter is smaller than 10 micrometres in diameter. The other is PM2.5 – where the particulate matter is smaller than 2.5 micrometres in diameter. **Also read: Can masks save people from Delhi’s hazardous air pollution?** The concentration of PM2.5 is dangerous to human health; it can also lead to chronic diseases such as asthma, heart attack, bronchitis and other respiratory problems. Owing to their small size, these particulates can get into our lungs, where they can reach the alveoli and eventually enter the bloodstream. A recent study also revealed that the total number of premature deaths and years of disability from cardiovascular diseases attributable to particle air pollution rose from 2.6 million in 1990 to 3.5 million in 2019, a 31 per cent worldwide increase. Nitrogen Dioxide (NO2) This gas, a subtype of a class of air pollutants, primarily results from fuel combustion from sources such as motor vehicles and industrial activities. Nitrogen dioxide has significant impacts on human and environmental health, most notably when it comes to respiratory and cardiovascular health. A recent study by AIIMS, Delhi, showed that exposure to NO2, even for a short duration, between zero and seven days, leads to an increase in the number of emergency room visits by 53 per cent. According to medical experts, NO2 is known to increase inflammation in the lungs, reduce lung function and increase wheezing and coughing. [caption id=“attachment_13359762” align=“alignnone” width=“640”] Smoke billows after a farmer burned paddy stubble in a field, on the outskirts of Jalandhar. PTI[/caption] Farm fires Many experts note that farm fires or stubble burning is one of the biggest contributors to Delhi’s chronic air pollution crisis. For the unaware, stubble burning is the act of intentionally setting fire to the stubble that remains after grains like paddy, wheat, etc, have been harvested. This burning is carried out to remove the residue from the field and prepare the farm to sow the next crop. **Also read: Living in ‘gas chambers’: What is making Delhi’s air so toxic?** On Sunday (5 November), the neighbouring state of Punjab recorded 3,230 farm fires, the highest in a single day this season, taking the total number of stubble-burning cases to 17,403. According to Decision Support System (DSS), the share of stubble burning in the PM2.5 has remained mostly 20-25 per cent so far. In 2022, the share of stubble burning to the PM2.5 concentration was 34 per cent, and a whopping 48 per cent in 2021. Anumita Roychowdhury, executive director, research and advocacy, Centre for Science and Environment, told the Times of India, “Even if the number of fire counts have reportedly gone down over the years, the problem persists. While solutions have been well identified, their implementation at scale within a short time span hasn’t been possible. On ground preparedness is needed to ensure each and every farmer has affordable access to the machinery for mulching the straw in the fields.” [caption id=“attachment_13359662” align=“alignnone” width=“640”] A view of Humayun’s Tomb amidst the morning smog as air pollution levels declined slightly in New Delhi. Reuters[/caption] GRAP Graded Response Action Plan, popularly known as GRAP, is a set of emergency measures that kick in to prevent further deterioration of air quality once it reaches a certain threshold in the Delhi-NCR region. These preventive measures were first notified in January 2017 on the basis of a report submitted by the Central Pollution Control Board (CPCB) in November 2016. GRAP is incremental in nature, which means that when the air quality dips, certain measures kick in to prevent further deterioration. The first stage of GRAP is imposed when the air quality falls to the poor category. In this, the government imposes a heavy fine on garbage burning and sweeping without sprinkling water. The second stage of GRAP is imposed when the air quality enters the ‘very poor’ category. This necessitates a ban on diesel generators, use of coal or firewood in hotels, restaurants, and open eateries, increased parking fees, and increased bus and metro frequency. The government also issues an advisory for children, the elderly, and those with respiratory problems under this stage. The third stage of GRAP is imposed when air quality becomes ‘severe’ and under this, the government imposes a strict ban on construction and demolition activities, hot mix plants, brick kilns, and stone crushers. The fourth and final stage of the GRAP is enforced when the air quality is in the ‘severe plus’ category. This stage entails stopping entry of trucks in Delhi except for LNG/CNG trucks and those involved in essential services, imposing a ban on Delhi-registered diesel-operated Medium Goods Vehicles (MGVs) and Heavy Goods Vehicles (HGVs) and also empowers authorities to take a decision on discontinuing physical classes even for classes VI - IX, class XI and conduct classes in an online mode. [caption id=“attachment_13359632” align=“alignnone” width=“640”] Motorcyclists drive wearing pollution masks amid smog in New Delhi. Masks are back on the streets as residents of the capital city grapple with the annual surge in air pollution that has engulfed the region. AP[/caption] Odd-even policy In light of the hazardous air in Delhi, the Arvind Kejriwal-led Aam Aadmi Party government has announced the implementation of the odd-even car policy from 13 November to 20 November. The car-rationing scheme, which was first instituted in the United State in 1979, allows cars with only odd or only even number plates to ply on a particular day. This time around, cars whose number plates end with odd numbers – 1, 3, 5, 7 and 9 – will be allowed to ply on odd-numbered dates – 13, 15, 17 and 19 November. Similarly, vehicles whose number plates end with even numbers – 0, 2, 4, 6 and 8 – will be allowed to ply on even-numbered dates – 14, 16, 18 and 20 November. However, many experts are questioning if this scheme helps in tackling air pollution. In fact, even the Supreme Court has rapped the Delhi government, with Justices SK Kaul and Sudhanshu Dhulia saying, “Odd-even has been implemented in Delhi, but has it ever succeeded? It’s all optics.” [caption id=“attachment_13359612” align=“alignnone” width=“640”] The smog tower at Delhis Connaught Place is locked up amid severe pollution, in New Dellhi. PTI[/caption] Smog Tower One of the other methods to tackle air pollution is the use of a smog tower. Smog towers are structures designed as large-scale air purifiers to reduce air pollution particles from the atmosphere. These towers are fitted with multiple layers of filters, which trap fine dust particles suspended in the air. Air is typically drawn through fans installed at the top of the tower, passed through filters, and then released near the ground. The first ever smog tower was erected in 2015 in Rotterdam, in the Netherlands. In Delhi, it was inaugurated by Chief Minister Arvind Kejriwal in 2021 amid much fanfare, but it has now been reported that two of these structures now lie shut at a time when Delhi is choking. With inputs from agencies