Smog, a term originally coined to describe a mix of smoke and fog, represents a dense layer of atmospheric contamination that obscures visibility and can severely compromise respiratory health. This pollution is a direct result of human activity and the release of pollutants from combustion sources. Understanding the global distribution of this pollution requires examining how its prevalence has shifted with industrial and regulatory changes across different nations.
What is Industrial Smog?
Industrial smog, also called London Smog or sulfurous smog, is a specific type of air pollution linked to the burning of high-sulfur fossil fuels, primarily coal, for heating and industrial power generation. The primary components are sulfur dioxide (SO2), soot, and other particulate matter, which combine with atmospheric water vapor under cool, humid conditions to create a thick, grey haze.
When sulfur-containing fuels are combusted, SO2 gas is released. This gas reacts with oxygen and moisture to form droplets of sulfuric acid (H2SO4). This mixture of acidic aerosols and solid particles gives industrial smog its characteristic toxicity.
Industrial smog is distinct from photochemical smog (Los Angeles Smog), which results from sunlight-driven reactions between nitrogen oxides and volatile organic compounds, typically emitted by vehicle exhaust, to produce ground-level ozone. Industrial smog is a winter-time, coal-burning pollution problem, while photochemical smog is an oxidizing, warm-weather problem.
The Historical Shift in Smog Control
Industrial smog was historically a defining feature of large, industrialized cities in Western Europe and North America, resulting from the Industrial Revolution’s heavy reliance on coal power. The most infamous example occurred in London in December 1952, known as the Great Smog. An anticyclone trapped cold, stagnant air over the city for five days, concentrating pollutants from domestic coal fires and power stations until visibility dropped to mere meters.
This catastrophic event caused up to 12,000 excess deaths and served as a catalyst for legislative action. In response, the United Kingdom passed the Clean Air Act of 1956, which introduced “smoke control areas” and offered incentives for householders to switch from coal to cleaner fuels like gas or electricity.
Subsequent legislation and technological shifts, such as moving power generation facilities outside of urban centers and adopting modern emission controls, led to a sharp decline in sulfur dioxide emissions. By the latter decades of the 20th century, this pollution was largely mitigated in developed nations due to stringent environmental policies and a transition away from high-sulfur fuels.
Current Global Distribution and Contributing Factors
Industrial smog is currently far more common in rapidly industrializing nations than in established developed economies. As North America and Europe reduced sulfur dioxide emissions from the 1970s onward, emissions in East and South Asia grew strongly, dominating the global total by the early 21st century. This shift correlates with the rapid industrial expansion and urbanization occurring in emerging economies.
A primary contributing factor is the heavy and often unregulated reliance on coal and other high-sulfur fuels to power factories and meet growing energy demands. Many of these nations utilize older, less efficient industrial technology, which lacks the sophisticated emission control systems common in developed countries. Rapid growth often outpaces the establishment and effective enforcement of stringent environmental standards.
Cities in countries like India and China have experienced significant air quality issues, including high concentrations of particulate matter and sulfur dioxide, the hallmarks of industrial smog. The economic pressure to prioritize industrial output and energy security often means that environmental concerns are relegated, leading to weaker regulatory frameworks. This combination of cheap, dirty fuel, outdated technology, and weak enforcement concentrates industrial smog in the urban and industrial centers of the developing world.