DOI: 10.5061/dryad.qrfj6q5bx
title: Atmospheric transport is a major pathway of microplastics to remote regions

description: 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).
description: 1. Tire wear particle (TWP) emission calculations based on a CO2
 ratio method. Top-down estimates of total annual TWP emissions reported
 for Norway, Sweden and Germany, based on measurements of lifetime weight
 loss of returned tires, were used here as a proxy to extrapolate
 globally. Assuming a constant ratio of TWP emissions to
 CO<sub>2</sub> emissions from the road transport sector (0.49
 mg TWP/g CO<sub>2</sub>) from the CMIP6 (Coupled Model
 Intercomparison Project phase 6) inventory (0.5°×0.5° resolution), we
 created global TWP emissions for the year 2014. 2. TWP and BWP (brake wear
 particle) emission calculations with the GAINS model. We also used the
 emissions model GAINS (Greenhouse gas – Air pollution Interactions and
 Synergies; http://gains.iiasa.ac.at) to create global emissions for both TWPs and BWPs. The model gets emissions of air pollutants and Kyoto gases for nearly two hundred regions globally considering key economic activities, environmental regulation policies, and regionally specific emission factors and provides size speciated PM (particulate matter), as well as carbonaceous particles (BC, OC) for different emission sectors (transport, energy, industry, domestic and waste combustion, etc.). 3. Flexpart model outputs. The Lagrangian particle dispersion model FLEXPART (FLEXible PARTicle Dispersion Model) version 10.4 (https://www.flexpart.eu) was set to run in forward mode for year 2014 with a spin-up period of 3 months (September 2013) in 0.5°×0.5° resolution globally with a daily temporal resolution using 3-hourly 1°×1° operational analyses from the European Centre for Medium Range Weather Forecast (ECMWF).
description: <strong>SupInfoMetaData</strong><br> Metadata
 explaining emissions and model simulations.
 <strong>TWP_CO2_ratio_EMI</strong><br> One (1)
 file with global TWP emissions calculated with the CO2 ratio
 method.
 <strong>TWP_BWP_GAINS_EMI</strong><br> One (1)
 file with global emissions of both TWPs and BWPs.
 <strong>1.flexout_CO2_ratio_TWP_0.5um,
 2.flexout_CO2_ratio_TWP_1.0um, 3.flexout_CO2_ratio_TWP_2.1um,
 4.flexout_CO2_ratio_TWP_3.2um, 5.flexout_CO2_ratio_TWP_6.0um,
 6.flexout_CO2_ratio_TWP_9.5um</strong><br> Six (6) files with
 results from FLEXPART model simulations for TWP with emissions calculated
 using the CO2 ratio method and different particle diameter.
 <strong>1.flexout_GAINS_TWP_0.5um, 2.flexout_GAINS_TWP_1.0um,  3.flexout_GAINS_TWP_2.1um, 4.flexout_GAINS_TWP_3.2um, 5.flexout_GAINS_TWP_6.0um, 6.flexout_GAINS_TWP_9.5um.nc</strong> Six (6) files with results from FLEXPART model simulations for TWPs using emissions calculated with the GAINS model and different particle diameter. <strong>1.flexout_GAINS_BWP_0.5um, 2.flexout_GAINS_BWP_1.0um, 3.flexout_GAINS_BWP_2.1um, 4.flexout_GAINS_BWP_3.2um, 5.flexout_GAINS_BWP_6.0um, 6.flexout_GAINS_BWP_9.5um.nc</strong> Six (6) files with results from FLEXPART model simulations for BWPs using emissions calculated with the GAINS model and different particle diameter. <strong>ECMWF_lsm_si_720x180_2014_daily</strong> Sea-ice area fraction (siconc) and snow depth (sd) masks from ECMWF. <strong>ECMWF_precip_720x180_2014_daily</strong> Snowfall (sf) and total precipitation (tp) from ECMWF. <strong>lsm_mask, ocean_mask</strong> Land-sea mask Mask for oceanic regions