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Microplastics in the atmosphere: useful or harmful?

A research team led by atmospheric chemist Laura Revell from the University of Canterbury in Christchurch, New Zealand, has for the first time investigated a possible greenhouse effect caused by microplastic particles in the atmosphere. The researchers have now presented their results in a study in the trade journal Nature before.

Until a few years ago, research assumed that microplastics were the main ones from the abrasion of tires and the decomposition of plastic waste is mainly transported into the oceans via rivers. In the meantime, however, there are more and more studies that show that microplastic particles are not only in the air, but are distributed over a wide area across the atmosphere – even as far as the Arctic.

Estimating the effects of these particles on the climate is not easy, however, because the concentrations and sizes of the particles vary greatly. The concentrations measured so far are between 0.01 microplastic particles (MP) per cubic meter in the Western Pacific and 5650 MP / cubic meter in Beijing. For comparison: the total concentrations of aerosols over Europe and East Asia are usually in the order of 109 until 1010 Particles per cubic meter. On the other hand, microplastic particles are comparatively large – typically between 15 and 250 micrometers. That is one to two orders of magnitude larger than other types of atmospheric aerosols.

To investigate the effects on the climate, the research team fed a mean, uniform concentration of 100 particles per cubic meter into a climate model. The result: the effect of the particles was almost zero. The effect microplastics have on the climate depends on many factors – including the wavelength of the incident solar radiation: They absorb long-wave light and thus heat the air, while they tend to scatter and reflect short-wave light and thus cool the earth. With a homogeneous distribution, the heating and cooling effects largely cancel each other out. If one assumes, however, that the particles are predominantly in the lower atmosphere up to a height of two kilometers, the calculation looks quite different. Then the “radiation pressure” of the particles is in the same order of magnitude as with the other aerosols.

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The only good news – at least at first glance – is that the particles lead to a cooling because the effects of reflection and scattering predominate. However, the net effect is not great because the concentration of plastic particles in the air is much lower than that of natural aerosols. That could change in the future, however, because according to the study, around five billion tons of plastic waste has accumulated in landfills or in the environment to date. And the study’s authors assume that this amount will double in the next 30 years. Since plastic is broken down by aging and exposure to light, and microplastics are created, more and more microplastics enter the earth’s atmosphere.

However, there are already first clues that microplastics also influence cloud formation. More and more plastic particles in the air could therefore expand into an uncontrolled variant of geoengineering, the effect of which we cannot yet foresee.

(wst)

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