Air pollution incidents

Air pollution incidents

People started noticing air pollution as a serious problem after the Industrial Revolution, although people had been using fire and causing some pollution for a long time. Air pollution happens when the amounts of harmful substances released into the air exceeds the Earth's natural cleansing ability. These harmful substances include chemicals, dust, and biological elements that can harm both humans and the natural environment.

A famous example of air pollution is the London Smog. This event led many countries, including the UK, to establish air quality standards to reduce air pollution. Until the 1970s, there was mostly positive research on improving air pollution. However, in the early 1990s, a study by Harvard University suggested that even at levels below air quality standards, higher concentrations of fine particles increased the risk of death. This led to a trend of strengthening air quality standards.

In this text, I aim to introduce significant air pollution events like the London Smog and the LA Smog.

<Great Smog of London in December 1952: generated by AI>

 

■  London Smog

On December 4th, 1952, a stagnant humid anticyclonic weather pattern crossed the English Channel and flowed into London along the Thames River. This weather pattern prompted Londoners to return home early to seek warmth, as the primary heating fuel used in households at the time was bituminous coal. The following day, a dense fog formed due to the typical winter fog combined with the combustion of coal for heating purposes. This condition persisted until December 8th, with visibility becoming so poor that automobile and shipping accidents occurred during daylight hours.

After the dissipation of this four-day fog, London citizens faced dire consequences. During this period, there was a mortality rate 2.5 times higher than usual, with 2,851 individuals losing their lives, and an additional 1,224 deaths occurred in the subsequent week. The majority of excess fatalities were among children and the elderly suffering from respiratory or cardiovascular diseases.

The total suspended particulate (TSP) concentration measured during this period reached as high as 4.46 mg/m³. The primary cause of this event is believed to be the combustion of bituminous coal used for domestic heating, which emitted carbon monoxide, carbon dioxide, sulfur dioxide, tar, and various primary pollutants. These substances, combined with meteorological conditions such as fog and temperature inversions, led to a large-scale air pollution event.

In response to this incident, there was a shift from coal to petroleum-based fuels for domestic heating, and measures were taken to reduce coal usage during foggy days to prevent disasters. Additionally, in July 1953, the Beaver Committee was established to systematically study the impact of air pollution on health, leading to the formulation of the Clean Air Act in 1956.

 

■   LA Smog

 

In 1943, Los Angeles began experiencing sporadic, sometimes brownish, eye-stinging, and tear-inducing fog phenomena. Initially, the cause was speculated to be sulfur dioxide emitted from burning coal and petroleum, prompting recommendations for changes in fuel usage. However, the true cause of this brown smog was elucidated by A.J. Haagen Smit in 1951. He found that nitrogen oxides and hydrocarbons emitted from automobiles react under intense sunlight to form toxic smog.

Following this investigation, smog control measures focused on reducing hydrocarbon emissions, and emissions from oil refineries were strictly regulated. These efforts led to a significant reduction in hydrocarbon emissions from an average of 2,100 tons per day in 1940 to around 250 tons in 1957. However, despite these efforts, the smog situation in Los Angeles worsened, with high concentrations of smog occurring more frequently each year. Since 80% of daily hydrocarbon emissions came from automobiles, regulation of automobile exhaust emissions became essential, but it took considerable time and effort to implement.

Ultimately, in 1966, California began enforcing a policy requiring newly manufactured vehicles to be equipped with emission control devices. This marked a significant milestone in regulating automobile exhaust emissions.

 

■    London smog vs LA smog

London smog		LA smog
Sulfur dioxide gas, fog	Causal substances	Nitrogen oxides, hydrocarbons
Deep gray	color	Light brown
Heating fuel (coal)	Source of occurrence.	Automobiles (petroleum)
Night	Timing of occurrence.	Day
Respiratory system of humans, dry corrosion	Affected targets.	human eyes, plants,

 

 

■     References

• Curtis D. Klaassen. Casarett and Doull’s Toxicology. McGraw Hill / Medical; 9th edition (2018)
• Davis DL et al. A look back at the London Smog of 1952 and the half century since. Environmental Health Perspectives 2002;110:A734