Meghan Hodges
Asia is home to the world's worst air pollution, with 83 of the 100 most polluted cities in the world located on the continent. South Asian cities are of particular concern, with 29 of the 30 most polluted cities in India, Pakistan, or Bangladesh. The average Indian's life expectancy is reduced by 5.3 years, and in New Delhi by 10 years, due to PM2.5 pollution. Seasonal variations contribute to fluctuating pollution levels throughout the year, with the winter months generally experiencing the highest concentrations across the region. In Southeast Asia, pollution worsens during the dry season, with a lack of moisture in the atmosphere and other meteorological conditions combining with pollutants from fossil fuels and other sources to degrade air quality.
| Characteristics | Values |
|---|---|
| Worst Polluted Countries in Asia | Bangladesh, India, Pakistan, Laos, China, Tajikistan, Nepal, North Korea, Mongolia, South Korea, Burma, Indonesia, Sri Lanka, Kazakhstan, and Thailand |
| Worst Polluted Cities in Asia | Begusarai, Guwahati, Assam, Delhi, Mullanpur, Punjab, Lahore, Dhaka, and Chiang Mai |
| Months with Worst Pollution | Dry months, winter months (November to February) |
| Reasons for Pollution | Brick kiln and other industrial emissions, agricultural waste burning, cremation practices, burning of solid fuel for cooking and heating, plastic rubbish incineration, vehicle fumes, coal burning, crop burning, dust storms, poor infrastructure, and urban planning practices |
| Health Risks | Respiratory diseases, cardiovascular problems, low birth weight, miscarriages, stillbirths, hindered development |
| Effects on Life Expectancy | Average Indian's life expectancy reduced by 5.3 years, and by 10 years in New Delhi |
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What You'll Learn
- November to February: the worst months for pollution in Asia
- Seasonal variations: agricultural burning, dry seasons, and winter inversions
- Industrial emissions: brick kilns, power plants, and refineries
- Vehicle emissions: combustion engines, motorcycles, and transport
- Natural factors: dust storms, wildfires, and wind
November to February: the worst months for pollution in Asia
Asia is home to some of the most polluted countries and cities in the world. South Asian countries, in particular, suffer from the worst pollution overall. Bangladesh, India, and Pakistan consistently rank among the most polluted countries in Asia and the world. In 2023, Bangladesh recorded the worst air quality of 134 countries monitored by IQAir, with Pakistan and India close behind. According to the IQAir report, 83 cities in India have air pollution levels more than 10 times the recommended limit set by the World Health Organization (WHO). Other highly polluted countries in Asia include Laos, China, Tajikistan, Nepal, North Korea, Mongolia, South Korea, Indonesia, Sri Lanka, and Thailand.
The winter months of November to February generally experience the highest concentrations of pollution across the region. Several factors contribute to the worsening air quality during these months. One significant factor is the increased use of solid fuels for cooking and heating during the colder months, which adds to the air pollution. For example, the burning of coal for residential heating is a major contributor to air pollution in Ulaanbaatar, Mongolia, where severe air quality issues persist year-round, especially during the winter.
The geography of South Asia also plays a role in the accumulation of air pollution during the winter months. Pollutants emitted from the Indo-Gangetic Plain, which includes Bangladesh, eastern Pakistan, northern and eastern India, and southern Nepal, become trapped by the Himalayas to the north. This geographic condition exacerbates the pollution levels in the region, particularly during the winter when atmospheric inversions occur, trapping pollutants closer to the ground.
In Southeast Asian cities, pollution tends to worsen during the dry seasons. Warmer temperatures, lack of rainfall, increased sunshine, and changes in wind speed and direction degrade air quality in tropical monsoon climates. Fine particles like PM2.5, PM10, and Black Carbon, associated with vehicle exhaust, coal plants, industrial processes, and open waste burning, build up in the surrounding air during the dry months. Jakarta, Indonesia, and Bangkok, Thailand, are among the Southeast Asian cities that experience severe air pollution, often ranking as some of the most polluted cities in the world.
The impact of air pollution on health is significant. According to the Environmental Research Group at Imperial College London, air pollution is linked to adverse effects on the health of newborn babies, including low birth weight, miscarriages, and stillbirths. Early exposure to air pollution can also hinder development. Additionally, the Air Quality Life Index (AQLI) found that the average Indian's life expectancy is reduced by 5.3 years due to PM2.5 pollution, with a more drastic reduction of 10 years in New Delhi.
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Seasonal variations: agricultural burning, dry seasons, and winter inversions
The worst months for pollution in Asia are influenced by seasonal variations, including agricultural burning, dry seasons, and winter inversions.
Agricultural Burning
The burning of agricultural waste is a significant contributor to air pollution in South Asian countries like India, Pakistan, and Bangladesh. The annual crop burning practice involves farmers burning plant residue after harvesting rice to prepare the fields for wheat plantation. This activity releases fine particulate matter (PM2.5), which is dangerous as it can penetrate deep into the human respiratory tract. While the burning typically occurs after the rice harvest, the specific months can vary across the region. For instance, in Northern Thailand, burning may start as early as January, while in other areas, it might begin in February or March. The burning season generally lasts for about 2-3 months and can extend until April or May in some places.
Dry Seasons
The dry seasons in Asia can exacerbate pollution levels, particularly in countries like Indonesia, which experiences a dry season from April to October. During this period, rainfall occurs in short bursts, and the lack of substantial rain can hinder the natural cleansing of the atmosphere. Indonesia's dry season coincides with its hot season, further contributing to the pollution challenge. Similarly, Cambodia's dry months from November to April are recommended for tourists due to lower humidity and temperatures. However, the lack of rainfall during these months can impact the dispersion of pollutants.
Winter Inversions
The winter months in Asia can also influence pollution levels due to temperature inversions. The Asian landmass, including regions like Siberia, Mongolia, and the Plateau of Tibet, experiences a persistent high-pressure winter anticyclone characterized by temperature inversions and cold, calm weather. This weather pattern propels cold, dry air eastward and southward, affecting eastern and southern Asia. The temperature inversions during winter can trap pollutants, leading to a buildup of air pollution in certain regions. The mountainous belt stretching from West Asia through the Himalayas to southern China and Southeast Asia further influences the movement of air masses and can impact the dispersion of pollutants.
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Industrial emissions: brick kilns, power plants, and refineries
South Asia is the second-largest brick-producing region in the world, with India, Pakistan, Bangladesh, and Nepal being the biggest producers in the region. Brick kilns are a major contributor to air pollution in the region, with an estimated 8,000 brick kilns in Bangladesh alone, some of which operate illegally. In South Asia, bricks are typically made in coal-fired kilns, which are a significant source of greenhouse gas emissions and air pollution, leading to a substantial public health burden. The smoke emitted during brick firing contains particulate matter (PM) and gaseous pollutants such as sulfur dioxide (SO2), carbon monoxide (CO), and nitrogen oxides (NOx).
Various studies have been conducted to assess the impact of brick kiln emissions on air quality and public health. Results indicate that brick kilns emit pollutants such as SOx, NOx, RSPM, NRSPM, and SPM, which far exceed the limits set by National Ambient Air Quality Standards (NAAQS). The high concentration of these pollutants in the air has severe health implications for the local population, particularly respiratory health.
Interventions have been implemented to reduce emissions and improve energy efficiency in brick kilns. For instance, a randomized controlled trial in Bangladesh introduced operational practices to 276 "zigzag" brick kilns, resulting in reduced energy use, decreased CO2 and PM2.5 emissions, and improved brick quality. However, regulating the brick kiln industry is challenging due to its informal nature and limited regulatory capacity in many low- and middle-income countries.
In addition to brick kilns, power plants and refineries also contribute significantly to industrial emissions in Asia. In Southeast Asian cities, the manufacturing and energy sectors are the biggest contributors to sulfur dioxide (SO2) and nitrogen dioxide (NO2) emissions. Power plants, along with vehicle emissions and industrial processes, are responsible for the high levels of PM2.5, PM10, and Black Carbon pollutants in the region.
While specific monthly data for industrial emissions from brick kilns, power plants, and refineries is limited, it is evident that these sources contribute significantly to the overall air pollution in Asia, particularly in South and Southeast Asian countries. The accumulation of pollutants is influenced by the region's geography, with the Himalayas trapping pollutants from the Indo-Gangetic Plain. Additionally, during the dry seasons, the lack of moisture in the atmosphere and increased sunlight exacerbate the formation of ground-level ozone (O3), further degrading air quality.
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Vehicle emissions: combustion engines, motorcycles, and transport
While the data does not specify the worst months for pollution in Asia, several sources point to the dry season as a time when air pollution is exacerbated. This is due to a lack of moisture in the atmosphere, increased sunshine, and changes in wind speed and direction, which combine with pollutants from fossil fuels and other sources to worsen air quality. Warmer temperatures during this time can also degrade air quality in tropical monsoon climates.
Vehicle emissions from combustion engines, motorcycles, and transport are significant contributors to air pollution in Asia. In Southeast Asia, cities like Jakarta, Bangkok, and Manila experience high levels of pollution from vehicles. Jakarta, for example, has seen a steady increase in the number of motorized vehicles, including motorcycles, contributing to poor air quality.
Motorcycles are a popular mode of transport in many Asian cities, including Tehran, where they are used for personal transportation and small parcel deliveries. Studies have shown that despite their small engine volume and low fuel consumption, motorcycles can produce emission rates of carbon monoxide (CO) that are significantly higher than European certification limits. In the case of Tehran, motorcycles were found to be the third most common means of transportation, and their emissions were compared to those of passenger cars.
In Metro Manila, two-stroke-powered tricycles, which are a popular mode of transport, produce considerable hydrocarbon and particulate emissions due to air fuel mixture short-circuiting and the use of two-stroke lubricating oil. Similarly, in Bangkok, combustion engines were attributed to 72% of the city's pollution in 2022.
In addition to motorcycles and combustion engines, other forms of transport also contribute to air pollution. Road travel, including passenger vehicles such as cars and buses, as well as trucks carrying freight, account for a significant portion of transport emissions. In particular, road transport is responsible for a substantial percentage of total CO2 emissions.
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Natural factors: dust storms, wildfires, and wind
Asia is known for having the worst air pollution in the world, with South Asian countries like Bangladesh, Pakistan, and India at the top of the list. While human activities such as industrial emissions, agricultural waste burning, cremation practices, and vehicle emissions are the primary contributors to air pollution in Asia, natural factors like dust storms, wildfires, and wind also play a significant role.
Dust Storms
Dust storms, also known as sandstorms, are common in arid and semi-arid regions, including parts of Asia. They occur when strong winds blow loose sand and dirt from dry surfaces, carrying fine particles over long distances. These storms can cause reduced visibility, disrupt transportation, and have serious health risks. Repeated dust storms contribute to desertification and reduce agricultural productivity by removing nutrient-rich particles from the soil. Asia, particularly North Africa, the Middle East, Central Asia, and China, is a major source of airborne dust due to poor management of drylands and farming practices that expose dust and sand to the wind.
Wildfires
Wildfires are another natural factor that contributes to air pollution in Asia. They release smoke and PM2.5 (fine particulate matter) into the atmosphere, which can drift for thousands of miles when carried by prevailing winds. Wildfires are often caused by a combination of land management practices, human actions, and climate change, which increases the frequency and intensity of heatwaves and droughts. The smoke from wildfires contains a mix of chemicals that not only affects air quality and health but also damages plants, ecosystems, and crops, leading to more carbon emissions and greenhouse gases.
Wind
Wind can have both positive and negative impacts on air pollution. On the one hand, wind can disperse pollutants over a large area, reducing their concentration in any one region. However, in certain geographical settings, such as valleys surrounded by mountain ranges, wind may be unable to effectively push pollutants out, trapping them in specific areas. Additionally, wind can carry pollutants from distant sources, as seen with wildfire smoke reaching western Europe from North American wildfires.
While natural factors like dust storms, wildfires, and wind contribute to air pollution in Asia, the interaction of these factors with human activities and the unique geography of the region further exacerbates the problem. The Indo-Gangetic Plain, which includes Bangladesh, eastern Pakistan, northern and eastern India, and southern Nepal, experiences a mix of pollutants from various sources that become trapped by the Himalayas. This complex interplay of natural and human-induced factors makes addressing air pollution in Asia a significant challenge.
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Frequently asked questions
While the months with the worst pollution can vary from city to city, the winter and dry months tend to be the worst for pollution in Asia. Warmer temperatures, lack of rainfall, increased sunshine, and changes in wind speed and direction can degrade air quality.
Bangladesh has been reported to have the worst air quality in Asia, with India and Pakistan close behind.
In 2023, Begusarai, a city in Bihar state, was the most polluted city in India, with an average annual PM2.5 concentration of 118.9. This was followed by Guwahati, Assam; Delhi; and Mullanpur, Punjab.
The main causes of pollution in South Asian cities are vehicles, power plants, and industrial emissions.
Air pollution has been linked to low birth weight, miscarriages, stillbirths, hindered development, respiratory diseases, and cardiovascular problems. According to the Air Quality Life Index, the average Indian's life expectancy is reduced by 5.3 years.
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