Delhi's Air Pollution: Why It's Worse Than Mumbai

Despite having a vast coastline and generally better air quality, Mumbai has experienced worse air pollution than Delhi on several occasions in 2023. In January and February, Mumbai's air quality index (AQI) was higher than Delhi's for 12 days, reaching a four-year high for October in particulate matter (PM)-10 and temperature. The primary cause of Mumbai's poor air quality is believed to be dust arising from construction sites, road and metro development projects, and cooking with unclean oils. On the other hand, Delhi, which has been dubbed worse than hell by the Supreme Court of India, faces significant air pollution due to vehicle emissions, road dust, biomass burning, stubble burning, and industrial activities. With Delhi's air quality showing slight improvements, Mumbai's deteriorating air quality has raised concerns among citizens and authorities alike.

Mumbai's air quality is impacted by construction sites and unclean kitchens

Mumbai, India's financial capital, has been struggling with poor air quality, with the Air Quality Index (AQI) exceeding 200 in several parts of the city. The primary cause of Mumbai's poor air quality is believed to be the dust arising from construction sites. The booming real estate development and the rush to enhance transportation systems post-pandemic have exacerbated the city's air quality. Mumbai's local municipality has taken steps to mitigate the damage, issuing guidelines to construction sites, such as the use of barricades and the proper disposal of construction materials.

Unclean kitchens in restaurants, dhabas, bakeries, and roadside eateries also contribute to Mumbai's poor air quality. These kitchens often use unclean oils and fuels to fire their ovens, producing harmful concentrations of nitrogen di-oxide, carbon mono-oxide, and formaldehyde. In addition, the open burning of solid waste and the use of Ready Mix Concrete (RMC) plants and casting yard plants further deteriorate the air quality in Mumbai.

The IT sector in Mumbai, a crucial contributor to the country's economy, loses $1.3 billion annually due to reduced productivity caused by pollution. The national capital region's IT industry alone stands to lose over $2.5 billion annually unless the city's air quality improves. Mumbai's air pollution has also impacted sports, with England cricketer Joe Root commenting on the difficulty of playing in such conditions during a match in the city.

While Mumbai's air quality has been a concern, it is important to note that Delhi, India's capital, also faces severe air pollution, with the city being engulfed by a thick layer of smog every winter. The cold, heavy air traps vehicle emissions, smoke, and dust, posing serious respiratory issues for its residents. However, in recent times, Mumbai has recorded air quality worse than that of Delhi on certain days, highlighting the severity of the issue in both cities.

Delhi's air quality is affected by vehicle emissions and road dust

Delhi, India's capital city, has the worst air pollution of any city in the world. From October to February, the air quality index (AQI) in Delhi often exceeds 700, presenting significant health risks. Vehicular emissions and road dust are two critical factors that affect Delhi's air quality.

Delhi's air quality is significantly impacted by vehicle emissions. Cars, buses, and trucks emit carbon monoxide (CO), nitrogen oxides (NOx), and particulate matter (PM). According to estimates, vehicles contribute to 20% of PM2.5 and 36% of NOx emissions in the city. During certain periods, Delhi's air quality fluctuates between ""very poor"" and ""severe"" due to unfavourable meteorological conditions, with vehicular emissions accounting for 38-40% of the pollution.

Road dust is another major contributor to Delhi's poor air quality. According to the US Environmental Protection Agency, road dust is earthen material or dirt that becomes airborne due to the friction of tires on unpaved or dust-covered roads. With over 33,000 kilometres of roads and approximately 9.7 million registered vehicles, the interaction between Delhi's poorly maintained roads and vehicle tires creates a significant amount of dust. Studies have found that road dust accounts for more than 50% of PM10 particles and about 38% of PM2.5 particles in Delhi's air.

The combination of road dust and vehicular emissions creates a dangerous mixture. Harmful aerosols from vehicles cling to the surface of dust particles, and emissions that would typically be dispersed by wind instead settle on these particles. Additionally, Delhi's geographical proximity to Rajasthan results in a constant influx of dust carried by winds, further exacerbating the problem.

To address the issue of vehicular emissions, the Delhi government has implemented measures such as stricter vehicle emission checks and the odd-even scheme, which restricts cars from operating on certain days based on their registration numbers. To mitigate road dust, the government has announced initiatives like vacuum cleaning of roads and sprinkling water using cranes, although the effectiveness of these measures has been questioned.

Mumbai's air pollution is worsened by cyclone season

Mumbai's air pollution is generally worse during the cyclone season due to several factors, including geographical location, meteorological phenomena, and human activities.

Mumbai, a coastal city, typically enjoys a natural cleansing advantage due to stronger surface winds and wind reversal cycles of strong sea breezes that dissipate air pollutants. However, during the cyclone season, wind patterns can change, bringing calmer winds and delaying the cleaner sea wind reversals. These changes reduce the dispersal of pollutants and trap dust emissions at higher altitudes. The cyclone season also brings withdrawing monsoon rains, which, coupled with construction work, can further deteriorate air quality.

Human activities significantly contribute to the worsening air pollution during the cyclone season in Mumbai. The number of registered vehicles in the city has been increasing, with approximately 3.5 million recorded in 2019. Vehicle emissions, including transport and road dust, account for a substantial portion of the airborne particulate matter, with power plants and industrial activities also playing a role. Additionally, the illegal burning of waste products and poor planning for transportation and industrial units in residential areas exacerbate the situation.

The impact of these factors was evident in the winter months of November to January in 2022-23, when Mumbai experienced a noticeable deterioration in air quality. Out of 92 winter days, 66 were recorded as having poor or very poor air quality, a significant deviation from previous years.

To address the issue of worsening air pollution in Mumbai during the cyclone season, it is essential to focus on reducing anthropogenic emissions. This can be achieved through measures such as encouraging carpooling or public transportation, transitioning to greener fuels, and implementing better waste management practices. Ensuring smooth traffic flow and taking steps to minimise dust emissions from construction sites, such as using green curtains and sprinkling water on truck tyres and debris, can also help mitigate the problem.

While Mumbai's coastal location can provide some natural relief from air pollution, the cyclone season's impact on wind patterns and the combination of human activities can lead to a significant deterioration in air quality during this period.

Delhi's air quality is impacted by biomass burning and stubble burning

Delhi's air quality is impacted by a range of factors, including biomass burning and stubble burning, which are significant contributors to the city's poor air quality, particularly during the winter months.

Biomass burning, including crop and wood burning in the countryside surrounding Delhi, has been identified as a major source of the city's air pollution. A study by IIT Delhi found that biomass burning emissions, rather than fireworks during Diwali, were the primary driver of poor air quality in the days following the festival. The study noted that biomass burning-related emissions rose steeply post-Diwali, with levels almost doubling compared to pre-festival concentrations. The investigators, Prof Vikram Singh and Chirag Manchanda, attributed this to increased heating requirements and stubble burning, which is common during the crop harvesting season that often coincides with Diwali.

Stubble burning, or crop residue burning, is considered the primary contributor to Delhi's air pollution due to its impact on atmospheric conditions and emission levels. Transboundary pollutant transport, influenced by meteorological conditions, brings pollutants from as far away as Pakistan, further exacerbating the issue. The interaction between these external pollutants and local emissions creates a complex dynamic that severely affects Delhi's air quality.

The impact of biomass and stubble burning on Delhi's air is part of a larger regional issue. A study by Liu et al. examined the seasonal impact of biomass burning on air pollution in three Indian cities: Delhi, Bengaluru, and Pune. This study highlights that Delhi's air pollution is not an isolated issue but rather a symptom of a broader challenge facing India's sustainable development.

Addressing Delhi's air quality crisis requires a multifaceted approach. While relocating air quality monitors can provide valuable data, it is crucial to tackle the root cause of the problem: anthropogenic emissions. This includes implementing measures to reduce emissions from transport, industries, and construction sites, as well as promoting sustainable agricultural practices that minimize the need for stubble burning.

In summary, Delhi's air quality is significantly impacted by biomass burning and stubble burning, which contribute to the city's already high levels of air pollution. By understanding the complex interactions between various emission sources and atmospheric conditions, policymakers can work towards effective solutions to alleviate the extreme air pollution events in India's capital.

Mumbai's air quality is affected by industrial activities and power plants

Mumbai's air quality is impacted by a range of factors, including industrial activities and power plants, which play a significant role in the city's pollution levels.

Mumbai, India's financial capital, is one of the world's most polluted cities. Its coastal location, which should naturally provide cleaner air, is often overcome by the high levels of pollution. Industrial activities contribute significantly to this issue. The presence of industrial units in residential areas, for instance, has been identified as a key factor in the city's poor air quality. Unauthorized garages near slums, for example, release industrial chemicals into the atmosphere, adding to the pollution.

Major industrial polluters in Mumbai include Bharat Petroleum Corporation, Hindustan Petroleum Corporation, Rashtriya Chemicals and Fertilizers, and Tata Power. These companies have come under scrutiny, with the BMC pledging to monitor them closely and take necessary action.

Power plants also contribute to Mumbai's air pollution. According to the Airpocalypse-IV report, power plants account for 20% of the PM (particulate matter) levels in the city's air. The report analyzed data from 2013 to 2018 and found that Mumbai's pollution levels exceeded safety standards for PM10 particulate matter on more than 52 days during that period.

The impact of industrial activities and power plants on Mumbai's air quality is further exacerbated by other factors. Vehicular emissions, construction activities, biomass burning for cooking, and crop burning around Diwali all contribute to the city's poor air quality. The delayed monsoon withdrawal, real estate development, and the rush to enhance transportation systems post-pandemic have also played a role in deteriorating air quality.

Mumbai's local municipality has recognized the urgency of the situation and implemented initiatives to mitigate the damage. These include measures such as sprinklers, vehicle tire-washing stations, and proper disposal of construction materials, with a particular focus on construction sites. Despite these efforts, Mumbai's air pollution remains a significant challenge, impacting the health and economy of the city and the country.

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