November 2016 Newsletter: Natural Air Pollution - Non-Anthropogenic Causes of Air Pollution

fire air pollution north carolina — Image of Clear Creek fire in NC (from www.wlos.com)

The recent forest fires in the western portion of the state have reminded us of how much air pollution is of natural origin. When we hear the words, “air pollution,” our thoughts immediately go towards things like automobile emissions and industrialization. While these man-made sources of air pollution are significant contributors to pollution in our atmosphere, did you know that there are several natural processes and sources across the globe that also contribute to air pollution? This month, we briefly highlight some of these sources and how they contribute naturally to polluting the earth’s atmosphere.

“Air pollution occurs in many forms but can generally be thought of as gaseous and particulate contaminants that are present in the earth’s atmosphere.” (from www.nps.gov). A general list of gaseous and particulate contaminants that can be generated naturally includes:

sulfur dioxide (SO₂)
nitrogen oxides (NO_x)
ozone (O₃)
volatile organic compounds (VOC)
particulates

Natural sources of sulfur dioxide include forest fires, volcanoes, and biological decay. It can be difficult to quantify the volumes of naturally-produced sulfur dioxide. “In 1983 the United Nations Environment Program estimated a figure of between 80 million and 288 million tons of sulphur oxides per year (compared to around 69 million tons from human sources world-wide).” (from www.enviropedia.org).

African dust pollution — View of African dust streaming off of the Sahara (from www.eos.org)

Nitrogen oxides are also released by volcanoes and biological decay, as well as the oceans and lightning strikes. “Estimates range between 20 million and 90 million tons per year nitrogen oxides released from natural sources (compared to around 24 million tons from human sources worldwide).”

Ozone is classified as a secondary pollutant, meaning that it is formed by chemical reactions altering two primary pollutants. In the case of ozone, it can be formed when nitrogen oxides and VOCs are mixed in the atmosphere and warmed by sunlight. It is important to note that the ozone present high in the atmosphere (the stratosphere) is beneficial and helps protect the earth from ultraviolet light. The ozone that is considered a pollutant is formed closer to the ground in the troposphere.

VOCs are naturally produced by plants and trees. They can be oxidized in the atmosphere to form aerosols that are considered pollutants. “Isoprene is a common VOC emitted by vegetation, and some believe it to be a more significant trigger for asthma and other allergic reactions than man-made irritants.”

Natural sources of particulate matter are typically less significant than man-made sources. Natural sources include such things as volcanic eruptions and dust storms in arid regions of the world. However, there is evidence to suggest that locations such as the Sahara Desert generate dust in such quantities that it can be transported north west across the Atlantic where it can be deposited in shallow tropical seas and affect coral growth.

Air pollution, both natural and man-made, is a serious issue that can have long-term effects on both the world’s ecosystems as well as our own facilities and structures. It is important to continue to monitor and quantify not only human-induced pollution, but the ways in which natural air pollution may be changing over time. Below is a link to the Environmental Protection Agency’s web page describing the Clean Air Act, which contains useful links and information regarding air pollution and regulation.

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