Breather from Toxic Air: How the rain in Delhi improved its AQI

There was some relief in sight for the people in Delhi who were struggling to breathe due to the heightened air pollution. On the intervening night of Thursday and Friday, there was light rainfall in the National Capital and a number of surrounding regions like Noida, Gurugram. The timing of the showers in Delhi is notable since the city government is preparing to use cloud seeding to create artificial rain on 20 and 21 November in an effort to tackle the severe air pollution. Let’s take a closer look. A desperately needed break from toxic air Light to moderate rain showers were visible in the images taken from the Kartavya Path, ITO, and the Delhi-Noida border. According to The Hindu, prior to Diwali, the India Meteorological Department (IMD) had forecast a slight improvement in air quality due to favourable meteorological conditions, including light rain.

#WATCH | Delhi witnesses sudden change in weather, receives light rain

(Visuals from Kartavya Path) pic.twitter.com/IB9XyXIo21

— ANI (@ANI) November 9, 2023

According to the Central Pollution Control Board (CPCB), while the average AQI in Delhi’s Ashok Vihar was recorded at 462, severe category, it improved to the “moderate” category on Friday morning. Similarly, the CPCB statistics indicated that the air quality significantly improved (to a satisfactory level) in the morning, even if the average AQI in RK Puram stayed in the severe category at 461. In Noida Sector-62, the minimum AQI was satisfactory with the reading of 56, and the average was 425.

VIDEO | Air Quality Index improves after rain lashes Delhi-NCR. Visuals from Central Delhi. pic.twitter.com/skQElYfKU0

— Press Trust of India (@PTI_News) November 10, 2023

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A rapid improvement was also seen in Gurugram’s AQI, where the average AQI remained “very poor” at 399, while the AQI registered “good” at 50 around 6 am. The AQI is divided into six categories: “Good” (0-50),  “Satisfactory” (50-100), “Moderately polluted” (100-200), “Poor” (200-300), “Very Poor” (300-400), and “Severe” (400-500). As the day goes on, the AQI should show the improvement in the quality of the air. How rain cleanses air The dry weather this October was a big factor in making it the most polluted since 2020. There was only one rainy day in the National Capital last month compared to seven and six in the years prior. Rain is known to have the ability to clear smoke, reduce air pollution and improving AQI. This is because raindrops travel through the atmosphere and bring hundreds of PM2.5 particles to their surface before hitting the ground. This process of attraction between water droplets and aerosol is known as coagulation, explained India Today. Raindrops can thereby eliminate airborne pollutants such as particulate matter, a major pollutant in the winter, and toxic gases.

#WATCH | Delhi: Rain lashes several parts of the national capital; visuals from Chirag Delhi pic.twitter.com/FZyQyMTKXz

— ANI (@ANI) November 10, 2023

Notably, rain is more likely to wash away particles with greater sizes and concentrations, therefore the impact on the pollution is quite minimal. According to air quality app, NAFAS Indonesia, after precipitation, air quality usually improves because particle pollutants are effectively removed from the atmosphere. The degree of rainfall, the size of the particles, the concentration of pollutants, and the ambient temperature all influence particle clearance. Rain-induced particle removal is most effective when the starting concentration of particles is higher. When comparing PM10 to PM2.5, the effect is even more evident. Rainwater will more readily suspend PM10 particles, which have a diameter of less than 10 μm, than PM2.5 particles, which have a diameter of less than 2.5 μm. Delhi’s plan for artificial rain In an effort to tackle air pollution in Delhi, the Arvind Kejriwal government aims to use cloud seeding technology to create artificial rain, said Delhi Environment Minister Gopal Rai on Wednesday following a meeting with the IIT-Kanpur team. According to PTI, which cited officials, the administration has opted to bear the entire cost for artificial rain to address adverse air pollution in the city and has instructed the chief secretary to put the government’s case before the Supreme Court on Friday. The Delhi government can set up the first phase of artificial rain in the city by 20 November if the Centre approves of the move. The nation’s capital currently operates under Stage IV of the Graded Response Action Plan (GRAP) following a sharp decline in air quality to the “severe plus” level. Other factors that can improve AQI One of the other crucial factors affecting air quality is wind. According to Indian Express, a greater wind speed can aid in the rapid dispersal of particulate matter. This was also seen last week, when the AQI improved with a small rise in wind speed. An average wind speed of less than 10 kilometre per hour is not suitable for the dispersion of pollutants, according to the Delhi Air Quality Early Warning System. Still, a little rise is better than nothing. A fresh western disturbance sweeping northwest India has caused the wind direction to shift from northwest to southeast which would assist minimise the amount of smoke from stubble burning, according to The Hindu which quoted IMD authorities as saying. An IMD official stated that when the western disturbance passes, the wind speed would increase from its current level of five to six kilometres per hour to approximately 15 kilometres per hour on 11 November. This will aid in the dispersal of pollutants prior to Diwali (12 November). Another factor that may improve the AQI is temperature. According to Indian Express, temperature inversion is a phenomena caused by a drop in temperature, particularly during clear night skies. A clear sky during the winter indicates that the ground loses heat more quickly and the air around it cools down because of the higher atmospheric pressure. Warmer air above it traps the chilly air underneath it like a cover. In addition to the cold air, dust and vehicle emissions become trapped. The region available for the dispersal of pollutants is known as the mixing height, and it is determined by this inversion. Better is indicated by a higher mixing height. With inputs from agencies