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Death by Air Pollution

September 16, 2019

For most of our existence, humanity has had a negligible environmental impact, since our population was so small. In analogy to a thermal reservoir in thermodynamics, we could take as much as we wanted from our environment without depleting its resources. All this changed at the end of the Middle Ages, when the world's population began to sharply rise, as the table shows.

Table - World population estimates from 10000 BC to the present day. The 10000 BC-1925 data from Colin McEvedy and Richard Jones, Atlas of World Population History, Facts on File, (New York, 1978), ISBN 0-7139-1031-3, sourced from Wikipedia.

Year Millions   Year Millions
10000 BC 4   1850 1,200
5000 BC 5   1900 1,625
2000 BC 27   1925 2,000
1000 BC 50   1950 2,486
200 BC 150   1975 4,089
1 170   2000 6,088
1000 265   2010 6,858
1400 350   2015 7,247

This trend caught the attention of English cleric, Thomas Malthus (1766-1834), in 1798 when he published An Essay on the Principle of Population at the time when the world population had reached a billion. Malthus saw that an increased food supply led to population growth, with the increased population requiring even more food. Eventually, the food supply would collapse, causing a Malthusian catastrophe.

Thomas Malthus (1766-1834)

Thomas Malthus (1766-1834) in an 1834 portrait by John Linnell (1792–1882).

(Wikimedia Commons image, modified for artistic effect. Image source is Wellcome Images of the Wellcome Trust, Iconographic Collection 727250i, Photo number: L0069037.)

Although pockets of famine still exist in the world, a Malthusian catastrophe has not yet happened. The avoidance of such a collapse is principally a consequence of improved agricultural techniques, including today's advanced techniques of genetic modification, that have kept pace with the increasing world population. However, we shouldn't be too complacent, since there are factors, such as global warming, working against progress in agriculture. While lack of food has not limited population increase, the rate of population increase has been somewhat dampened by diminished lifespan caused by pollution.

Mercury pollution has been a problem since the time of the Roman Empire, when it was used in the concentration of gold and silver by the chemical process of amalgamation.[1] The advent of silver and gold mining in the New World caused a release of more than 260,000 tons of mercury into the environment by 1930.[1] The use of mercury in gold purification was described by Georgius Agricola in 1556 in his De re metallica. Agricola also described the use of another industrial pollutant, lead, in the separation of silver from copper or iron.

Mercury and lead are insidious, since they are toxic at very low concentrations and are usually invisible. After the Industrial Revolution, however, air pollution became widespread, and air pollution in the form of smog is hard to miss (see photograph). Smog contains sulfur oxides, nitrogen oxides, ozone, smoke and other particulates that derive from such sources as coal combustion, vehicle exhaust, industrial emissions, and open-air burning of agricultural waste.

Figure caption

Smog in Beijing, China, as photographed on February 22, 2014.

(Wikimedia Commons image by Kentaro Iemoto. Click for larger image on the Flickr website.)

The archetypal smog is the dark, yellow-green pea soup fog associated with pre-Victorian and Victorian London. coal burning from the 17th century onward proved lethal to elderly Londoners and those with respiratory problems, and this smog is even mentioned in the Sherlock Holmes stories of Arthur Conan Doyle. A particularly lethal smog affected London in 1952, and this led to legislation for reduction of sulfur dioxide emissions and coal smoke.

In 1955 the somewhat lackluster Air Pollution Control Act was enacted in the United States, but it was replaced by the more effective Clean Air Act in 1963, and the additional Motor Vehicle Air Pollution Control Act in 1965. The US is fortunate in having an Environmental Protection Agency to protect its citizens.

A lot has been done to limit air pollution, but much more work remains. A recent study by an international team of researchers from the Center for Air, Climate, and Energy Solutions has concluded that air pollution in the United States from 1999 to 2015 is associated with 30,000 deaths and reduced life expectancy.[2-4] The team, led by Majid Ezzati of Imperial College London (London, United Kingdom), included members from Health Canada (Ottawa, Ontario, Canada), Brigham Young University (Provo, Utah), the University of Washington (Seattle, Washington), and the Harvard T. H. Chan School of Public Health (Boston, Massachusetts). This research is published in an open access article in a recent issue of PLOS Medicine, and the study was funded by the Environmental Protection Agency and the Wellcome Trust.[2]

Air pollution in the form of particulate matter of particle size 2.5 micrometers or less, called PM2.5, is a health hazard.[2] Such particulates, emitted from power plants, automobiles, and factories, can be inhaled deep into the lungs, and they are associated with cardiovascular disease.[3] PM2.5 pollution has been regulated since 1999, and the study assessed the benefit of such regulation and the present impact of these particulates on health for the population of the contiguous United States (Alaska and Hawaii excluded).[2]

The present PM2.5 standard is 12 micrograms per cubic meter of air (μg/m3). Fresno County, California, scored the highest value in 1999 at 22.1 μg/m3. Tulare County, California, had a reading of 13.2 μg/m3 in 2015, while Apache County, Arizona, scored the lowest amount, 2.8 μg/m3, in that same year.[3] Considerable modeling was needed in the analysis of the data, since there are other factors that affect the outcome, such as cumulative smoking, mean temperature, and relative humidity.[2]

PM2.5 concentrations in the contiguous United States 1999-2015

Left, reductions in PM2.5 concentrations from 1999 to 2015. Right, PM2.5 concentrations in 2015. (Portion of fig. 1 from the paper, released on a Creative Commons Attribution License.[2] Click for larger image.)

In the United States, there were 41.9 million deaths from 1999 to 2015, and 18.4 million of these deaths were from from cardiorespiratory disease.[3] The data analysis showed that PM2.5 pollution in excess of 2.8 μg/m3, the lowest observed concentration, was responsible for an estimated 15,612 deaths in females and 14,757 deaths in males.[2-4] These deaths result in a lowered life expectancy of of about seven weeks for both men and women.[2-4] The life expectancy loss was largest around Los Angeles and in the southern states of Arkansas, Oklahoma. and Alabama. Life expectancy loss was larger in poorer counties.[2-4] Scientists are always cautious, so the paper states that in observational studies such as this the associations are not guaranteed to be causal.[2]

Life expectancy loss from fine particulate matter emissions

Life expectancy loss in 2015 from fine particulate matter exceeding the observed minimum of 2.8 μg/m3. These values should also correlate with cardiovascular disease in general, so this map highlights one specific area in which I would not want to live. (Portion of fig. 3 from the paper, released on a Creative Commons Attribution License.[2] Click for larger image.)

Says lead author of the paper, Majid Ezzati,
We've known for some time that these particles can be deadly. This study suggests even at seemingly low concentrations - mostly below current limits - they still cause tens of thousands of deaths. Lowering the PM2.5 standard below the current level is likely to improve the health of the US nation, and reduce health inequality... US PM2.5 concentrations are generally lower than those in many Europe cities - which suggests there may also be substantial number of deaths in Europe associated with air pollution."[3]

Premature deaths due to air pollution in 2010 were about 50% more common in cities than in rural areas. This percentage could increase to 90% by 2050, fueled by growth of urban populations and their pollution sources at current rates.[5] As the maps above indicate, some areas of California are especially plagued by PM2.5 particulates. In order to understand trends of this particulate pollution, a team of scientists from Lawrence Berkeley National Laboratory and the University of California, Berkeley, have developed an inexpensive sensor for black carbon aerosols, the Aerosol Black Carbon Detector (ABCD), and deployed a hundred of them in a 15 square kilometer area of West Oakland, California, a community that's surrounded by freeways and is also affected by industrial emissions and emissions associated with a local port.[5-6]

The ABCD pulls air through a white filter that captures black carbon particles, and the amount of light transmitted through the darkening filter is measured to indicate the degree of particulate pollution. The materials for each ABCD costs less than $500, while commercial instruments are much more costly.[6] The devices use 2G cellular signals to transmit their data hourly, and the database now contains more than twenty million lines of data.[6] The network of a hundred sensors, called the 100×100 BC Network, is the largest black carbon monitoring network deployed in a single city.[6]

Figure caption

Left image, the Lawrence Berkeley National Laboratory/University of California, Berkeley black carbon aerosol detector. Right image, 8:00 AM weekday readings across West Oakland, California, when the concentrations are the highest. (Left image, from Lawrence Berkeley Laboratory. Right image, a screen capture from a YouTube video. Click for larger image.)

Data taken from May 19, 2017 to August 27, 2017, showed that black carbon concentrations varied sharply over short timespans (∼1 hour) and short distances (∼100 m).[5] There were both diurnal and weekly cycles that reflected traffic emissions and industrial production.[5-6] black carbon concentrations peaked at the start of business, around eight in the morning (see figure), and the lowest black carbon concentrations were recorded on Sundays.[6] The granularity of this network is much finer than that of other monitoring networks, such as those in London and Hong Kong that have one monitor per 10 square kilometers.[5]


  1. L. D. Lacerda, "Global mercury emissions from gold and silver mining," Water Air Soil Pollution, vol. 97, no. 3-4 (July, 1997), pp. 209-221, https://doi.org/10.1007/BF02407459.
  2. James E. Bennett, Helen Tamura-Wicks, Robbie M. Parks, Richard T. Burnett, C. Arden Pope III, Matthew J. Bechle, Julian D. Marshall, Goodarz Danaei, and Majid Ezzati, "Particulate matter air pollution and national and county life expectancy loss in the USA: A spatiotemporal analysis," PLOS, July 23, 2019, https://doi.org/10.1371/journal.pmed.1002856. This is an open access article with a PDF file available here.
  3. Kate Wighton, "Air pollution in US associated with 30,000 deaths and reduced life expectancy," Imperial College Press Release, July 23, 2019.
  4. Air pollution in US is associated with mortality and lower life expectancy, PLOS Press Release, July 23, 2019.
  5. Julien J. Caubel, Troy E. Cados, Chelsea V. Preble, and Thomas W. Kirchstetter, "A Distributed Network of 100 Black Carbon Sensors for 100 Days of Air Quality Monitoring in West Oakland, California," Environ. Sci. Technol., vol. 53, no. 13 (July 2, 2019), pp. 7564-7573, https://doi.org/10.1021/acs.est.9b00282.
  6. Laurel Kellner, "Making the Invisible Visible: New Sensor Network Reveals Telltale Patterns in Neighborhood Air Quality, Lawrence Berkeley Laboratory Press Release, July 22, 2019.
  7. New Sensor Network to Monitor Local Air Quality, Berkeley Lab YouTube Video, July 24, 2019.

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