The Role of Black Carbon in Climate Change

Post-industrial surges in atmospheric black carbon have contributed massively to the warming of the Earth’s climate, but exactly how these tiny particles contribute to climate change is unclear. However, an advanced new model designed to assess its impact could solve this mystery.

Credit: Nagoya University in Japan

Black carbon (BC) is formed during the incomplete combustion of carbon-based fuels. Minute particles of this pollutant absorb sunlight, and for this reason they are considered to contribute to global warming. Current models which assess the warming effect that black carbon has on the atmosphere help scientists to understand their contribution to climate change, but they do not take into account the mixing state of carbon particles, nor their size – both of which strongly influence their ability to absorb the sun’s rays.

The new model – developed by researchers in Japan and the US – evaluates the capacity of black carbon to absorb sunlight while also considering particle size and their complex mixing states in air. This has allowed the model to achieve a greater degree of sensitivity than previous representations, and will help in future evaluations into the efficiency of removing black carbon from the atmosphere to curb climate change.

Researchers from Nagoya University in Japan and Cornell University in the US joined forces to develop a model capable of predicting the direct radiative effect of black carbon, with high precision.

Many black carbon particles are emitted as pure black carbon particles, so have no coating. However, black carbon particles are progressively coated by other aerosol species, such as sulfate and organic aerosols, via processes in the atmosphere that boost black carbon absorption efficiency by up to a factor of two.

Most aerosol models are using one or two black carbon mixing states, which are not sufficient to accurately describe the mixing state diversity of black carbon in air. Our model considers that black carbon particles have multiple mixing states in air. As a result, we can model the ability of black carbon particles to heat air more accurately than in previous estimates.

Hitoshi Matsui, PhD Researcher, Nagoya University

The researchers ran through multiple simulations in their model, using small size and large size carbon particles to simulate various coating states of their black carbon particles – 'no coating', 'thick', or 'thinly coated'. The team employed a multiple-mixing-state global aerosol microphysics model to show how the current sensitivity of the black carbon direct radiative effect (DRE) is amplified between five and seven times when the variety in the mixing state is suitably resolved, due to current uncertainties in emission size distributions

The direct radiative effect of black carbon forecast by the researchers’ model was incredibly sensitive to particle size distribution only when complex mixing states of black carbon were suitably described. Such a high sensitivity was achieved because the model considered factors such as the lifetime of black carbon in the atmosphere, its ability to absorb sunlight and the effect that materials covering the black carbon particles have on the pollutant's capacity to absorb sunlight persuasively.

The results show that an accurate description of the particle size and mixing states of black carbon is essential to understanding how such particles contribute to climate change and global warming.  The data proposes that the interactions between black carbon and subsequent atmospheric effects (e.g. rain patterns) are probably more complex than previously thought.

Reducing uncertainties in emission size distributions and how they change in the future, while also resolving modeled BC mixing state diversity, is now essential when evaluating BC radiative effects and the effectiveness of BC mitigation on future temperature changes.

Research team, Nagoya University (Japan) and Cornell University (US).

This newly developed model advances our capacity to approximate the efficacy of removing black carbon from the atmosphere to overturn future fluctuations in temperature, which should help impending research strategies aimed at mitigating climate change.

Source: http://en.nagoya-u.ac.jp/

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