- Air pollution does not know boarders
- What is black carbon?
- BC has natural and anthropogenic sources
- Trans-border transport of BC
- Why do we care about BC in the Arctic (and elsewhere)?
- BC may affect weather, air quality and climate
- BC is health adverse
- Black carbon is not just bad
- How are Alaskans exposed
Air pollution does not know boarders
Some time ago, I wrote a post on ship emissions in the Arctic and their impact on air quality. Among the various gases and particles In released is also black carbon. In today’s post, I want to introduce you to black carbon in the Arctic and its potential impacts on climate, air quality and health.
What is black carbon?
Black carbon (BC) is a component of fine particulate matter with diameters of less than 2.5 micrometer often called PM2.5. It is about 70 times smaller than the diameter of a human hair. The term black carbon refers to the strongly absorption light in the visible spectral range. It serves as a synonym for elemental and graphitic soot. In conjunction with thermal and wet chemical determinations often the term elemental carbon is used. The term graphitic carbon refers to graphite-like micro-crystalline structures being present that can be detected by Raman spectroscopy.
BC has natural and anthropogenic sources
Black carbon is emitted by burning of biomass, biofuel or fossil fuels. In Alaska, BC from natural sources stems from wildfires in Alaska and Siberia. Major anthropogenic sources of BC emitted in Alaska are wood burning for heating and power generation in winter, burning of diesel by heavy equipment, diesel locomotives, diesel vehicles, and power plants, burning of coal for energy generation. Add on-shore and offshore emissions of BC from oil drilling and oil production to the mix.
Trans-border transport of BC
Air does not know any borders. Thus, under certain weather situations, pollutants emitted by ships in the international shipping lane between Asia and North America reach Southwest or Southeast Alaska. Other weather situations bring BC emitted in northern Europe and Siberia to Alaska. For long-range transport, the BC must be lifted into the upper troposphere by the updrafts of pyro-clouds (clouds caused by wildfires)or high reaching clouds. Here wind speed is very high and permits BC to travel far away from its sources despite the BC is subject to gravitational forces.
Why do we care about BC in the Arctic (and elsewhere)?
BC may affect weather, air quality and climate
Since BC strongly absorbs in the visible spectrum, it affects the energy budget of the atmosphere. Once it deposited on the ground it also may alter the surface energy budget as it darkens light surfaces. Consequently, it has a potential impact on climate on long time scales when its concentration changes. Note that changes can be increases meaning more BC is present or decreases meaning less BC is present due to emission control measures.
BC is health adverse
Unfortunately, the hairs in our noses fail to scavenge out PM2.5. Thus, any particles of this size or smaller can reach deep into our lungs. Black carbon, which is one of the components of particulate matter, itself is not toxic or health-adverse. However, during the emission process carcinogen gases or components can adhere on the carbon-particle. Thus so contaminated BC may lead to premature deaths. Medical studies also showed that long-term exposure to BC can inflame the respiratory system of children.
Black carbon is not just bad
The satellite image composite below shows smoke from summer wildfires. The smoke transports black carbon among other pollutants. When black carbon sediments out of the atmosphere and gets incorporated into soils. Here it acts as a fertilizer because it enables plants to absorb important nutrients. When I was a kid, farmers in Europe often burned their fields after the harvest for cheap fertilization.
How are Alaskans exposed
As said before, in Alaska, the exposure to BC varies by regions. The largest impacts from local sources are commercial shipping and cruise ships in the port cities, and ship emissions in the international shipping lane for coastal communities. On the North Slope, emissions related to exploration and oil production are major local sources. In the Interior, wildfires and the “let burn policy” are the major local sources in summer, while diesel engines from various industrial sectors, energy production and residential heating are the major sources in winter. Since these sources are very localized and the impact of BC decreases strongly with the distance from the sources, Alaska’s air is still pristine in remote areas away from these major sources.
What are the major sources of BC where you live? Just curious.
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Mölders, N. and Edwin, S. (2018) Review of Black Carbon in the Arctic—Origin, Measurement Methods, and Observations, Open Journal of Air Pollution, 7, 181-213.
Photos: G. Kramm
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