Lockdown's Impact: Pollution Levels Plummet

The COVID-19 pandemic saw around one-third of the world's population enter lockdown. With fewer cars on the road and a reduction in air travel and industrial activity, air pollution decreased in many parts of the world. Ultrafine particle concentration dropped by 48%-50% in some areas, and countries such as China, Russia, Germany, and Japan saw significant reductions in pollution levels in 2020 compared to 2019. However, the effects were not universal, with some countries and cities experiencing worsening pollution during lockdowns.

Ultrafine particle pollution decreased by 48%-50%

Ultrafine particles (UFPs) are aerosols with a diameter of 0.1 µm (100 nm) or less. They are the most common airborne particles and are 800 times smaller than a human hair. UFPs are released from auto exhaust, factory emissions, and wood burning. These particles can cause severe harm to human health, as they can enter the body through the lungs and disperse to other organs, causing inflammation and cellular toxicity. Their size allows them to penetrate the deepest lung passageways, sometimes carrying toxic metals or organic compounds that trigger inflammation and disease.

During the COVID-19 pandemic, global road travel and commercial flight activity decreased by 50% and 60%, respectively. This presented a unique opportunity for researchers to study the impact of reduced mobility on air pollution, specifically ultrafine particles. A study by the School of Public Health found that the concentration of ultrafine particles dropped by nearly 50% due to decreased aviation and road activity during the pandemic's initial months. This decrease in pollution was also observed in specific cities during lockdown. For example, in Daegu, the percentage of "unhealthy" days due to mid-level air pollution decreased during the lockdown period.

The study's findings highlight the link between transportation activity and air pollution, specifically regarding ultrafine particle concentration. The reduction in aviation and road traffic during the pandemic resulted in a significant decrease in UFP concentration, indicating that these particles are predominantly emitted from aircraft and road vehicles.

While the decrease in ultrafine particle pollution during lockdown is encouraging, it also underscores the challenge of consistently maintaining clean air. The brief "blue skies" during lockdowns provided a glimpse of improved air quality, but more permanent solutions are needed to address the stubborn problem of pollution. Policy changes and technological advancements, such as sustainable aviation fuel and improved combustion technology, can help reduce UFP emissions and exposure, ultimately mitigating their harmful health effects.

Pollution decreased in China, Russia, Germany, and Japan

The COVID-19 pandemic and subsequent lockdowns across the globe have impacted pollution levels in many countries. According to studies, human activities, a major source of pollutants, were partially or completely halted during the lockdown, leading to reduced pollution levels worldwide.

China, Russia, Germany, and Japan were among the countries that experienced a significant decrease in pollution levels during the lockdown in 2020 compared to 2019. In Wuhan, China, the origin point of the COVID-19 pandemic, the air quality index (AQI) improved during the lockdown, with a notable decrease in unhealthy days due to reduced PM2.5 and PM10 pollutants. Similarly, cities in Japan, such as Tokyo and Daegu, observed lower levels of air pollution during the lockdown, with a reduction in unhealthy days, particularly attributed to decreased PM2.5 levels.

Russia also witnessed a significant drop in pollution during the same period. While specific data for Russian cities is not readily available, the overall decrease in pollution in the country is noteworthy. Germany, another highly industrialized nation, saw reduced pollution levels during the lockdown. Although city-specific information is not specified, the overall improvement in air quality in Germany is worth noting.

It is important to acknowledge that the impact of lockdowns on pollution levels varied within countries. For instance, while India experienced an average increase in particulate pollution, its city, Delhi, saw a decrease of approximately 6% from 2019 to 2020. Additionally, the University of Chicago reports little change in global average particulate pollution in 2020, indicating that the impact of lockdowns on pollution levels is complex and influenced by various factors, such as economic activities and natural disasters like wildfires.

India's pollution levels increased, except in Delhi

During the first year of the COVID-19 pandemic, global road travel and commercial flight activity decreased by 50% and 60% respectively. This led to a decrease in pollution levels worldwide. However, India's pollution levels increased by 2.9% during the pandemic, except in Delhi, which experienced a decrease of roughly 6% from 2019 to 2020.

Delhi has consistently been ranked as the world's most polluted city, with other Indian cities close behind. The air quality index (AQI) in Delhi generally falls within the "Satisfactory" (51-100) and "Moderate" (101-200) ranges between March and September, but deteriorates to "Poor" (201-300), "Severe" (301-400), or even "Hazardous" (401-500+) levels between October and February. The poor air quality in Delhi is attributed to various factors, including the burning of effigies during Vijayadashami, the bursting of firecrackers during Diwali, emissions from thermal power plants, stubble burning, road dust, vehicle pollution, and cold weather.

The Indian government has implemented several measures to combat pollution in Delhi, including banning the entry of commercial petrol and diesel vehicles, adding 1000 extra CNG buses to the fleet, and instructing fuel stations to stop providing fuel to vehicles older than 15 years. Despite these efforts, pollution levels in Delhi remain a serious issue, with the air quality index reaching hazardous levels in recent years.

While India's pollution levels have shown a slight increase during the pandemic, with particular severity in Delhi, it is important to note that pollution is a widespread problem in the country. Out of the world's 30 cities with the worst air pollution, 21 are in India, and over 80% of India's cities have polluted air. The main causes of air pollution in India include vehicular emissions, dust, industrial emissions, and the burning of wood and dirty fuels for cooking and heating. The effects of air pollution in India are devastating, causing more than 2 million deaths per year and contributing to respiratory and cardiovascular diseases.

Pollution decreased due to transport and industry shutdowns

The COVID-19 pandemic saw a global reduction in road travel and commercial flight activity, with air traffic decreasing by 60%. This presented an opportunity for researchers to study the impact of reduced mobility on air pollution. Ultrafine particle concentration, which can cause inflammation in the lungs, brain, and other organs, decreased by 48-50% due to diminished aviation and road activity.

In South Asia, cities with typically high pollution levels, such as Delhi, Dhaka, Kathmandu, Colombo, Islamabad, and Kabul, recorded an improvement in air quality during the lockdown. The shutdown of transportation and industrial activities contributed to this improvement, with a notable decrease in harmful gaseous pollutants like CO, NO2, and SO2.

Nepal, for instance, witnessed a significant reduction in AQI values during the lockdown. The virtual halt in vehicle movement and the closure of industries, including power plants, positively impacted air quality. Similarly, Colombo, the capital of Sri Lanka, saw a significant decrease in AQI attributed to lower emissions from vehicular and thermal power plants.

China also experienced a decrease in pollution during the lockdown. There was a sharp decline in car mileage and oil sales, leading to reduced emissions from mobile sources. NASA detected a considerable decrease in NO2 concentration, attributed to the decrease in anthropogenic activities during the lockdown.

While the lockdown measures implemented during the COVID-19 pandemic resulted in decreased pollution levels in some regions, it is important to note that the overall impact on global pollution levels was mixed. Some countries, such as India, experienced an increase in pollution levels during this period.

Wind speed and temperature impacted air pollutant dispersion

During the COVID-19 pandemic, global road travel and commercial flight activity decreased by 50% and 60% respectively. Flight activity in particular was reduced to a near standstill, decreasing by 96%. This halt in travel provided an opportunity for researchers to study the impact of these mobility changes on air pollution. Studies have shown that air pollution levels decreased in many countries during the lockdown. For example, Indonesia saw a 20% decrease in pollution levels due to a reduction in haze caused by fires. Similarly, pollution in Russia, China, Germany, and Japan decreased in 2020 relative to 2019. However, some countries like India, Bangladesh, Nigeria, Pakistan, and the US experienced worsening air quality during this period.

Wind speed and direction play a crucial role in the dispersion of air pollutants. By understanding wind patterns, we can determine the origin and travel path of air pollution. Higher wind speeds generally result in greater dispersion of pollutants, leading to lower pollution concentrations in areas with stronger winds. During the 2021 wildfire season, smoke from fires in California and Oregon was carried by wind to states on the East Coast, impacting air quality thousands of miles away.

While wind helps disperse pollutants, it can also transport them over long distances, affecting air quality in new locations. The dispersion of pollution is influenced by horizontal and vertical factors. Horizontally, wind speed and direction determine how far and wide pollution spreads at a given level of the atmosphere. For example, a controlled burn emitting smoke particles will impact areas immediately downwind, with concentrations decreasing as the smoke drifts outward.

Vertically, thermodynamics come into play, with the concept of "warm air rises" being key. As the ground heats up during the day, air turbulence increases, dispersing pollutants. Conversely, cooler night-time conditions create more stable air, reducing the dispersion of pollutants. Temperature inversions, where warm air is trapped above a layer of cooler air, can prevent the vertical dispersion of pollutants, trapping them near the surface. This phenomenon is more common in cities surrounded by mountains or located in mountain basins or valleys, such as Los Angeles, Denver, and Mexico City.

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