The Dirtiest Air: A Historical Pollution Perspective

Air pollution is a significant global issue, causing approximately 7 to 8 million deaths annually and contributing to various diseases and environmental degradation. It is the fourth-largest risk factor for early death and affects people worldwide, with those in low- and middle-income countries suffering the most. While air pollution has been recognised as a threat to human health since Hippocrates around 400 BC, the Industrial Revolution accelerated emissions, culminating in the Great Smog of London in 1952. However, the biggest air pollution crisis in recent times is attributed to the rapid economic growth and industrialisation in Asia, particularly in countries like India and China, which now have the worst air quality worldwide.

The Industrial Revolution

One of the most notable consequences was the sharp increase in air pollution. The heavy industrial machinery that was central to this era required vast amounts of energy, which was primarily derived from fossil fuels like coal. This led to a rapid growth in coal combustion in developing cities, significantly increasing emissions of SO2, NO2, NH3, and smoke. The widespread use of coal and, later, oil-powered machinery, resulted in a surge of carbon emissions, with far-reaching environmental implications.

The shift to industrialised cities also led to urban overcrowding, poor sanitation, and a decline in air quality, causing serious public health issues. The rapid pace of industrial growth outstripped the capacity to manage waste and emissions, resulting in long-term environmental damage and adverse effects on public well-being. This period, which prioritised productivity and economic growth, set a precedent for unchecked resource exploitation and high emissions that continue to impact the planet today.

The Second Industrial Revolution, from the late 19th to the early 20th centuries, further intensified these issues. This phase, often called the Technological Revolution, introduced electricity, steel production, and the internal combustion engine, driving mass production and the expansion of heavy industries. Countries like the UK, Germany, and France rapidly industrialised, leading to exponential increases in energy consumption and resource extraction. Each phase of industrialisation compounded the environmental strain, with significant rises in air pollution, deforestation, and greenhouse gas emissions.

Fossil Fuels

Burning fossil fuels has been a major source of air pollution since humans started using them for energy. Fossil fuels include coal, oil, and natural gas, and they produce hazardous air pollutants when burned, such as sulfur dioxide, nitrogen oxides, particulate matter, carbon monoxide, and mercury. These pollutants have severe environmental and health impacts, causing acid rain, eutrophication, damage to crops and forests, and harm to wildlife and human health.

The combustion of fossil fuels releases large amounts of carbon dioxide, a greenhouse gas that traps heat in the Earth's atmosphere, leading to global warming and climate change. The average global temperature has already increased by 1°C, and warming above 1.5°C risks further sea level rise, extreme weather events, biodiversity loss, species extinction, food scarcity, and worsening health and poverty for millions worldwide.

Air pollution from fossil fuels has been linked to various health issues, including asthma, cancer, heart disease, and premature death. It is considered an "invisible killer," as the fine particulate matter (PM2.5) from fossil fuel combustion is tiny, lingering in the air, easily inhaled, and capable of penetrating deep into the lungs, where it can enter the bloodstream and damage multiple organs. Globally, air pollution from burning fossil fuels is responsible for about one in five deaths, or approximately 8.7 million people annually, with even higher proportions in certain countries like India and China.

In recent years, there has been a push for a transition to renewable energy sources and stricter air quality measures. As a result, some countries have successfully reduced emissions and improved air quality. For example, the global phase-out of fossil fuels is projected to have significant health benefits, with one study suggesting that it could prevent 5.1 million deaths annually. Additionally, tightening air quality measures in China led to a decrease in exposure to particulate matter from fossil fuels, resulting in a decline in associated deaths from 21.5% in 2012 to 18% in 2018.

Despite these efforts, fossil fuel companies continue to be major polluters, and their products contribute significantly to climate change and air pollution. It is crucial to address this issue and accelerate the transition to clean, renewable energy sources to mitigate the health and environmental impacts of burning fossil fuels.

Wildfires

Wildfire smoke is a mixture of gaseous pollutants, hazardous air pollutants, water vapour, and particle pollution. These particles, known as particulate matter or PM, are a combination of solid and liquid droplets suspended in the air. The main pollutant emitted by wildfires is fine particulate matter (PM2.5), which makes up approximately 90% of the total particle mass. These particles are less than 2.5 microns in diameter and can cause serious respiratory issues when inhaled. Coarse particles (PM10-2.5), larger than 2.5 microns but smaller than or equal to 10 microns, are also present in smaller amounts in wildfire smoke.

The health effects of exposure to wildfire smoke are well documented. Particle pollution from wildfires can aggravate asthma, trigger lung disease, cause heart attacks, and lead to premature death. The economic impacts are also significant, with exposure to wildfire smoke reducing employment and labour force participation. For example, in the United States, wildfire smoke was estimated to have reduced earnings by an average of $125 billion per year between 2007 and 2019. Additionally, the impact on labour market earnings is estimated to be $123 billion for each 1 μg/m3 annual increase in PM2.5 due to smoke.

The relationship between wildfires, climate change, and air pollution is complex and interconnected. Human activities, such as burning fossil fuels, transportation, and industrial processes, release greenhouse gases and black carbon emissions, contributing to climate change. Climate change, in turn, increases the likelihood of wildfires by creating more erratic weather patterns and exacerbating drought conditions. Wildfires then release additional pollutants, including black carbon, carbon monoxide, nitrogen oxides, and particulate matter, further intensifying climate change and air pollution. This creates a vicious cycle that governments and policymakers must address through interdisciplinary research and comprehensive strategies.

Recent examples of the devastating impact of wildfires on air pollution include the Australian wildfires of 2019-2020, which produced carbon emissions estimated to be 1.6 times greater than the country's total emissions for that year. Additionally, the Chilean wildfires in January and February 2023 resulted in increased levels of all air pollutants, with short-term exposure to ozone rising drastically. The WMO bulletin also highlighted the impact of wildfires on crop yields, with particulate matter reducing yields by up to 15% in highly polluted areas.

Agriculture

The production of artificial fertilizers has skyrocketed from about 20 million tons in 1950 to nearly 190 million tons today, with about a third of them being nitrogen-based. This excess fertilizer often washes off fields and pollutes watersheds, creating "dead zones" where oxygen is virtually eliminated, and fish and other marine life can no longer exist. In addition, the use of pesticides and herbicides in agriculture can contaminate water, air, and food, posing risks to both human health and the environment. For example, populations of insects such as bees and butterflies have declined due to these toxins.

Livestock operations, particularly cattle, pigs, and chickens, also release methane, nitrous oxide, and ammonia into the air, impacting the environment and human health. Manure management alone accounts for 12% of all agricultural greenhouse gas emissions in the United States and 14.5% globally. Additionally, the feed for these animals is typically grown using pesticides and fertilizers, further contributing to air pollution. The shift from forests and other vegetation to livestock rearing also releases stored carbon and destroys diverse ecosystems.

The impact of air pollution on agriculture is also significant, with poor air quality causing lower crop yields and damaged crops. Ground-level ozone pollution, for example, is estimated to cause between 5% and 12% yield losses globally in staple crops such as wheat, rice, and maize, resulting in significant economic losses. According to the United Nations Environment Programme (UNEP), ground-level ozone pollution created by fuel burning and chemical use will reduce staple crop yields by 26% by 2030. Therefore, tackling agriculturally caused air pollution is imperative for the food system.

Waste

Agricultural waste is a significant contributor to air pollution. Ammonia (NH3), emitted mainly by agricultural waste, can react with other gases to form small particulates that are harmful to human health. Studies suggest that ammonia could contribute to hundreds of thousands of premature deaths annually. The use of synthetic fertilizers and manure in agriculture also contributes to NH3 emissions, and these emissions have continued to rise with increased livestock production and synthetic fertilizer use.

To address waste-related air pollution, it is essential to improve waste management practices. This includes promoting recycling, composting, and safe waste treatment methods. Individuals can play a role by reducing waste generation, reusing and recycling materials, and properly separating waste. Companies can also contribute by reducing packaging, designing easily recyclable products, and supporting improved waste management regulations.

Additionally, national and city-wide waste management systems are important. These systems can include managed landfills, landfill gas capture for electricity production, and waste separation. Technologies such as general circulation models (GCMs) and chemical transport models (CTMs) can be used to simulate pollutant levels in the atmosphere and inform decision-making.

Furthermore, the combustion of fossil fuels and solid fuels contributes significantly to indoor and outdoor air pollution. Developing nations, in particular, rely heavily on coal power plants and solid fuels like wood, crop wastes, charcoal, and coal for cooking, heating, and lighting. Transitioning to renewable energy sources and improving waste management practices in cities are crucial steps in reducing air pollution and mitigating its impacts on human health and the environment.

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