Atmospheric transport is a major pathway of microplastics to remote regions

In the recent years, a large attention has been given to pollution from
plastic products as a major environmental problem. Plastics degrade into
smaller particles in the environment via photodegradation, physical
abrasion, hydrolysis and biodegradation. Microplastics (1 um to 5 mm size
particles) have been reported to affect coral reefs,
marine and terrestrial animals, as well as humans. It
has been reported that about 30% of microplastics in freshwater and
oceanic ecosystems are tire wear particles (TWPs), while brake wear
particle (BWP) emissions constitute 55% of all non-exhaust traffic-related
particle emissions and 21% of all traffic-related PM emissions. There is a
general conviction that the relative contribution of TWP and BWP emissions
to total transport-related emissions will grow in the near future, due to
the continuous reduction of exhaust traffic-related emissions. Although
transport of TWPs and BWPs via runoff and wash-out processes to the marine
and/or freshwater ecosystem has been studied extensively, very little is
known about how these particles are dispersed in the atmosphere and where
they are deposited. This is important due to the
aforementioned impact in animals and humans. They also
have an environmental impact as they are derived by materials made from
fossil fuels such as ethylene and propylene. Thus, larger needs of
plastics result in larger emissions of greenhouse gases. Since TWPs and
BWPs can become airborne and have been detected already
in remote areas, they may absorbe light decreasing surface albedo
and accelerating ice melting. Here, we present for the first time the
results of the atmospheric dispersion and deposition of traffic-related
microplastics (TWPs and BWPs). We assess the suggested emissions using two
methods, one indirect based on CO2 country ratios with road microplastics
and extrapolation, and another employing an emissions model, which has
been extensively used to determine global emissions of various substances
by IIASA-International Institute for Applied Systems Analysis (GAINS
model). We calculate that 34.4–290 kt y-1 (mean: 100 kt
y-1), out of 102–787 kt y-1 (mean: 284 kt y-1) of PM10 TWPs
emitted, were deposited in the World Ocean, while the respective annual
terrestrial and riverine discharges are about 64 kt y-1. This shows that
direct deposition of airborne road microplastics is likely the most
important source for the ocean and marine biota. The calculated transport
of PM10 road microplastics shows a relatively high efficiency over remote
regions such as the Arctic Ocean (14%). High latitudes and the Arctic are
highlighted as an important receptor of mid-latitude microplastic
emissions, which may imply a future climatic risk taking into account that
TWPs and BWPs constitute a small portion of the total plastic emissions.
As of now, snow concentrations of road microplastics are 100 times lower
than those of black carbon or polymers of larger usage (e.g., PVC or PPC).
Around 15% of the PM2.5 road microplastic emissions were deposited in the
Atlantic Ocean, whereas coarse particles were less efficiently deposited
there (10-11%). The efficiency of PM2.5 deposition (TWPs: 19% - BWPs: 18%)
over the Pacific Ocean was even more strongly enhanced relative to PM10
deposition (TWPs: 12% - BWPs: 11%), due to their smaller size. Transport
efficiencies of coarse particles were up to twice of those for the fine
particles in areas surrounded by microplastic emissions sources (e.g.,
Alps, Mediterranean, Baltic and South China Seas).