Natural Emissions and Their Impacts on Air Quality

EM – October 2021: Natural emissions have profound impacts on air quality and the Earth's atmosphere. This month's EM describes several important examples of natural emissions and their impacts.
by James T. Kelly and Golam Sarwar

Natural emissions have profound impacts on air quality and the Earth's atmosphere. Natural emissions, or emissions of trace gases and particles in the absence of anthropogenic activity, can occur through episodic events that dramatically affect the environment. For example, the 1991 eruption of Mt. Pinatubo in the Philippines injected a volcanic plume of gases and particles into the stratosphere that was estimated to cool the planet by about 0.5 °C during the following year. The 2010 eruption of the Eyjafjallajökull volcano in Iceland caused the largest disruption of air traffic in Europe since World War II. Massive dust storms that advance on cities and essentially eliminate visibility have received attention in popular culture through news media and tv and film, including the 2011 blockbuster movie, “Mission: Impossible Ghost Protocol.”

Natural emissions also occur from persistent sources that affect air quality through direct emission and subsequent influence on air pollution chemistry. The bursting of ocean whitecaps is a continuous source of aerosol that contributes to particulate matter levels in both marine and continental regions. Emissions of biogenic gases, including isoprene and monoterpenes, dominate the global budget of non-methane volatile organic compounds. Nitric oxide (NO) emissions from soils contribute approximately 15% of the global nitrogen oxides (NOx) budget, marine halogen emissions influence oxidation cycles and ozone concentrations in coastal urban regions, and essential fertilization occurs when iron and phosphorus-containing mineral dust is emitted from the Earth's deserts and deposits to oceans.

Air quality management relies on reliable characterizations of natural emissions and their influence on air pollution formation cycles. Apportioning the natural and anthropogenic contributions to pollution enables air quality managers to focus control programs on the key anthropogenic sources. In this context, atmospheric models that simulate the complex nonlinear and interactive relationships among anthropogenically and naturally derived species are essential to account for the strong chemical coupling among atmospheric pollutants.

In this issue, important examples of natural emissions and their impacts are described. First, Hosein Foroutan discusses haboob dust storms that are formed during cold pool outflows and often occur as a magnificent churning wall of dust. 

Second, Syuichi Itahashi, et al. discuss the influence of persistent volcanic degassing on air quality over the United States.
Third, Emily Saunders and William Stockwell discuss the chemistry of natural marine emissions of halogens on coastal urban air quality. 

Fourth, Rosa Fitzgerald, et al. discuss optical measurements of particulate matter in the El Paso–Juárez region that is surrounded by the Chihuahuan desert, where severe dust storms lead to high mineral dust concentrations. 

Lastly, Daiwen Kang, et al. describe recent improvements to the characterization of natural emissions in the CMAQ model. 

Continue reading the full October 2021 issue of EM.


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