Suspended and deposited microplastics in the coastal atmosphere of southwest England

Full text

Chemosphere 343 (2023) 140258
Available online 24 September 2023
0045-6535/© 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Suspended and deposited microplastics in the coastal atmosphere of
southwest England
Giannis Kyriakoudes , Andrew Turner
*
School of Geography, Earth and Environmental Sciences, University of Plymouth University Plymouth, PL4 8AA, UK
HIGHLIGHTS GRAPHICAL ABSTRACT
•Microplastics (MPs) captured during 12
periods over 42 d from the atmosphere
of SW England.
•MP concentrations in suspension ranged
from 0.016 to 0.238 items m
−3.
•Depositional MP uxes ranged from
0.47 to 3.30 m
−2
h
−1
and inversely
related to rainfall.
•Synthetic polymers present but rayon
bres were dominant particle type.
•MP shape and polymer type exhibit
fractionation between suspension and
deposition.
•Calculated, local settling velocities of
MPs ranged from about 7 to 180 m h
−1.
ARTICLE INFO
Handling Editor: Michael Bank
Keywords:
Microbres
Paints
Airborne
Settling
Scavenging
Rayon
ABSTRACT
Atmospheric microplastics (MPs) have been sampled from coastal southwest England during twelve periods over
a 42-day timeframe in late autumn. MPs were dominated by bres, with foams, fragments and pellets also
observed. The majority of bres were identied as the semisynthetic polymer, rayon, while other shapes were
dominated by various petroleum-based thermoplastics (including polyvinyl acetate, polyvinyl alcohol, poly-
amide and polyester) and paints. MP concentrations suspended in air ranged from 0.016 to 0.238 items per m
3
but displayed no clear dependence on wind speed or direction. Total depositional uxes ranged from 0.47 to
3.30 m
−2
h
−1
and showed no clear dependence on wind conditions or electrical conductivity of precipitation (as
a measure of maritime inuence). However, the concentration of deposited MPs in rainwater was inversely
related to rainfall volume, suggesting that incipient precipitation acts to efciently washout microplastics. A
comparison of deposited and suspended MPs by size, shape and polymer type suggests that larger bres con-
structed of rayon, polyamide and acrylic are preferentially removed from the atmosphere relative to smaller,
non-brous MPs and particles constructed of polyester. A quantitative comparison of deposited and suspended
MPs provided estimates of location- and environment-specic net settling velocities of between about 7 and 180
m h
−1
and corresponding residence times for an air column of 5000 m of between about 30 and 700 h. The
* Corresponding author.
E-mail address: aturner@plymouth.ac.uk (A. Turner).
Contents lists available at ScienceDirect
Chemosphere
journal homepage: www.elsevier.com/locate/chemosphere
https://doi.org/10.1016/j.chemosphere.2023.140258
Received 12 April 2023; Received in revised form 21 September 2023; Accepted 22 September 2023

Chemosphere 343 (2023) 140258
2
ndings of the study contribute to an improved understanding of the occurrence, transport and deposition of MPs
in the atmosphere more generally.
1. Introduction
With regard to the concentration and distribution of microplastics
(MPs; primary and secondary plastics in the size range 1
μ
m–5 mm), the
atmosphere has received considerably less attention than aquatic sys-
tems, and in particular the oceans (Zhang et al., 2020; Allen et al., 2021;
Gonz´
alez-Pleiter et al., 2021; Long et al., 2022). Aside from the potential
health risks arising from airborne MPs via inhalation (Gasperi et al.,
2018; Mehmood et al., 2021), evidence suggests that, given the right
meteorological conditions and air mass movements, plastics emitted to
the atmosphere, and in particular small MP bres, are subject to
long-range transportation. Moreover, the global atmospheric transport
of MPs is more efcient than the oceanic or terrestrial pathways because
of the much shorter timescales involved (Evangeliou et al., 2022).
Consequently, particles have been detected in regions distant from any
primary or secondary sources and major waterways that include sub-
tropical deserts (Abbasi et al., 2021) and remote national parks and
mountains (Allen et al., 2019; Feng et al., 2020).
MPs in the atmosphere are, ultimately, subject to removal at the
Earth’s surface by dry, gravitational deposition, or wet deposition
through in-cloud scavenging and below-cloud interception (Aes-
chlimann et al., 2022). Although the signicance of and mechanisms
involved in wet deposition of MPs are not well understood, precipitation
is considered as a key, positive driver for their removal in the lower
troposphere that is likely related to the frequency, intensity and duration
of rainfall or snowfall (Bergmann et al., 2019; Zhang et al., 2020; Abbasi,
2021; Purwiyanto et al., 2022). To this end, climatic factors are also
important. For example, in semi-arid regions, wet deposition may be
constrained to rainfall events in certain months of the year (Abbasi and
Turner, 2021) while in temperate, maritime climates, wet deposition
during persistent periods of rain may outweigh annual dry deposition
(Roblin et al., 2020).
In order to improve our understanding of the transport of micro-
plastics by air masses and their deposition, Zhang et al. (2020) suggest
that multiple sampling methods are required over an extended period of
time at a given location. Specically, and in order to gauge the impor-
tance of removal relative to MP availability, it would be useful to
consider both the concentrations of MPs in the atmosphere and the
depositional uxes from the atmosphere. This approach was recently
adopted by Yuan et al. (2023) in a study of MPs in the atmosphere of
Guangzhou, China, where a washout ratio was proposed to measure the
removal efciency by precipitation (but not dry deposition).
The present study sets out to address and compare the quantities and,
through infrared spectroscopy, chemical characteristics, of MPs sus-
pended in air and captured actively, but not necessarily deposited
locally, and MPs subject to local deposition and captured passively. We
hypothesise that the concentrations and signatures of MPs resident in
the atmosphere might be different to those that are deposited through
gravitational settlement and captured by rainfall capture. The study is
conducted over an urban area of coastal southwest England for a period
of about six weeks that encapsulates different meteorological conditions
and rainfall events and intensities. We also hypothesise, therefore, that
the concentrations and deposition of MPs are related to environmental
conditions.
2. Methods
2.1. Sampling
Plymouth is a maritime city (population ~ 260,000) on the English
Channel coast of southwest England. It has a temperate oceanic climate
and experiences a mean annual precipitation of about 1000 mm. The
prevailing wind is from the west to southwest and the annual average
wind speed at 10 m above ground level is about 5 m s
−1
(11.2 miles per
hour; mph).
Sampling was undertaken from the roof of a teaching building (co-
ordinates: 50.3751; −4.1385) at a height of 30 m above ground level on
the University of Plymouth main (city centre) campus over a 42-day
timeframe in late autumn (November and December of 2021). Specif-
ically, material suspended in air and material deposited from the at-
mosphere were sampled during twelve, 70-to-100-h periods (Table 1),
beginning at 12 noon. During each period, air was sampled though a
Whatman GF/A, 25 mm-diameter, 1.6
μ
m-pore size glass lter housed in
an adaptor with a circular aperture of 1 cm diameter. The adaptor was
connected to one end of a 1 cm-diameter, 3 m-long PVC exi-tube and
was clamped to a metal railing at a forward angle of 45◦in order to
shield the lter from falling rain. Air was drawn through the lter at a
rate of 9.0–10.5 L min
−1
(monitored with a 393–1130 rotameter; SKC
Ltd) by a vacuum pump connected to the other end of the tube inside the
building, resulting in, on average, about 42 and 60 m
3
of air ltered for a
70- and 100-h sampling period, respectively. At the end of the sampling
period, the lter was carefully retrieved with stainless steel tweezers and
stored in aluminium foil in a metal cabinet.
Deposition during each period was sampled via 10-cm diameter glass
funnels into two, 1 L amber glass bottles that were secured to a
galvanised steel frame on the balcony of the roof. On completion of
sampling, the combined contents of the bottles were vacuum-ltered
through a 47-mm diameter, 0.45
μ
m-pore size Whatman cellulose ni-
trate membrane lter housed in a glass-ceramic Buchner system. The
lter was stored as above while the ltrate volume was determined in a
series of 10 mL, 50 mL and 250 mL glass measuring cylinders before the
contents were transferred to a narrow, 100 mL glass beaker. Provided
sufcient volume was obtained, the electrical conductivity, κ (
μ
S cm
−1
),
as an indicator or marine inuence, was measured with a WTW Tetra-
Con electrode.
2.2. Identication and counting of suspected microplastics
Without further processing, all lters were examined under a Nikon
SMZ800 stereomicroscope tted with a 1x Achro objective (and
attaining a magnication up to 63 X) that was connected to an Olympus
SC30 camera operated by Olympus Stream software. Suspected MPs
were identied with the aid of a metal probe and using criteria outlined
in MERI (2014). That is, the response to the metal probe; lack of organic
structures evident, except for biofouling; homogeneity of width (for
plastic bres); homogeneity in colour (except for possible partial
bleaching of plastic bres). For paint particles, identication was based
on colour, brittleness and layering (Turner, 2021). Particles were clas-
sied according to colour, size (diameter or length; <100
μ
m and with a
detection limit of 30–50
μ
m; 100–500
μ
m; >500
μ
m) and shape. With
regard to the latter: bres were dened as exible, individual or inter-
twined particles with a ratio of length to diameter exceeding ten; frag-
ments were irregular particles that included transparent and translucent
lms and layered structures, or more regular shapes that appear to have
become detached from a larger structure; pellets were distinctly rounded
or spherical entities; and foams were irregular but porous, sponge-like
particulates.
2.3. Polymer identication by FTIR
With the aid of stainless-steel tweezers or the wetted tip of a sable
hair paint brush (size 000) and under an OLYMPUS SZ40
G. Kyriakoudes and A. Turner

Chemosphere 343 (2023) 140258
3
stereomicroscope, all suspected MPs that were large enough or not
damaged or lost (n =160) were transferred from lters to a 2 mm-
diameter Specac diamond compression cell. Individual particles were
then analysed by Fourier transform-infrared (FTIR) spectroscopy in
transmission mode with a Bruker Vertex 70 spectrometer coupled with a
Hyperion 1000 microscope. Absorption spectra were recorded using
OPUS software by averaging 32 scans in the region of 4000 to 600 cm
−1
and at a resolution of 4 cm
−1
. Sample spectra were compared with
various spectral databases of polymers and common materials, with a hit
rate of >65% dened as our acceptance criterion for positive
identication.
2.4. Cleanliness and controls
All glassware involved in sampling, measuring or analysis was
washed three times with Millipore Milli-Q water (MQW) before being
used or reused, and container openings and slide surfaces were covered
with aluminium foil when not in use. Local laboratory surfaces were pre-
cleaned with MQW or ethanol and nitrile gloves were worn by the
operator during microscopic analysis. Analysis of blank glass bre and
membrane lters under the stereomicroscope as above revealed no
visible contamination from suspected MPs. As sampling controls, two
35-mL aliquots of MQW were poured into individual 1-L glass bottles via
a glass funnel and the contents were subject to transference and ltra-
tion as above. Inspection under the microscope revealed the presence of
four bres in total and two on each lter, and subsequent analysis by
FTIR identied rayon (n =3) and cotton (n =1). The total number of
suspected MPs on sample lters that were observed under the micro-
scope was subsequently corrected for this level of contamination (i.e.,
two brous particles) by subtraction.
3. Results
3.1. Environmental conditions
The meteorological conditions over the periods sampled in south-
west England are summarised in Table 1. Thus, hourly wind speeds
ranged from 2 to 29 mph, with directions most commonly from the north
and northwest, and hourly temperatures ranged from 0 to 15 ◦C, with
cooler temperatures generally associated with northerly winds. Rainfall
over each sampling period ranged from <1 to about 14 mm, or 12–288
mL, and totalled about 60 mm, or 938 mL, with κ ranging from 55.7 to
329
μ
S cm
−1
. There were 18 days that were rain-free and the highest
volumes of rainwater were generally associated with winds with a
westerly component.
3.2. Number, concentration and deposition of suspected microplastics
Fig. 1 exemplies a selection of suspected MPs identied under the
stereomicroscope that had been suspended in air (SMPs) and deposited
from the atmosphere (DMPs) over southwest England. Overall, 45 par-
ticles of various colours, but mainly black or transparent, were identied
in the twelve suspended samples, and, factoring in contamination from
the controls, 117 particles of various colours, but mainly black, trans-
parent or blue, were identied in the twelve deposited samples. Note
also that deposited samples appeared to be cleaner (with regard to
additional particulate matter on the lter) than suspended samples.
Table 2 shows the concentrations of suspected SMPs in the atmo-
sphere and the depositional uxes of DMPs. SMPs were calculated from
particle number on each lter sampling suspended material, the dura-
tion of each sampling period (Table 1) and the time-averaged air ow,
and resulting concentrations range from 0.016 m
-3
during a period of
southerly and easterly winds (period 12) to 0.238 m
-3
during a spell of
north/northwesterly winds (period 3). DMPs were calculated from the
particle number on each lter isolating deposited material (after
correction for contamination), sampling period duration (Table 1) and
the capture area of the two funnels (157 cm
2
). Here, uxes ranged from
0.47 m
−2
h
−1
during winds with a southerly or easterly component
(period 12, and with a total rainfall of 1.53 mm and κ =66.9
μ
S cm
−1
) to
3.30 m
−2
h
−1
for a spell of north/northeasterly winds (period 6, and
with a total rainfall of 0.96 mm and κ =82.3
μ
S cm
−1
). Although,
overall, there was no signicant relationship between the concentration
of suspected SMPs and the depositional ux of suspected DMPs, there
appears to be a group of seven points that are closely and signicantly
associated (Fig. 2). However, these data were not distinctive in terms of
wind speed or direction, temperature, rainfall or κ.
Relative to the volume of rainfall captured, concentrations of sus-
pected DMPs ranged from 36 to 1400 L
−1
. While there was no clear
dependence of suspected DMP concentration or deposition on wind
speed or direction or on κ, there was a signicant and non-linear (power
law), inverse relationship between concentration in rainwater and
rainfall volume (Fig. 3a). A weaker inverse relationship of the same form
was also evident between the concentration of particles classied as -
bres and rainwater volume (Fig. 3b).
3.3. Shape and size distribution of suspected microplastics
Table 3 shows the distribution of suspected SMPs and DMPs by shape
and size sampled from the atmosphere of southwest England. Fibres
were the dominant shape of particle in both cases. However, there was a
greater proportion of bres and a lower proportion of fragments subject
to deposition than captured in suspension, and pellets were absent in
deposited samples whereas foams were absent in suspended samples.
With respect to size, there was a clear difference between particles
suspended in and deposited from the atmosphere, with a lower pro-
portion of ne particles (<100
μ
m) and a greater proportion of coarser
particles (>500
μ
m and up to 5 mm for bres) in the latter.
Table 1
Dates and durations of the atmospheric sampling periods of southwest England, along with a summary of the (hourly) meteorological conditions (temperature range,
wind speed range and principal wind direction). Rainfall was calculated from the volume of rainwater captured in the two collection bottles and specic conductance,
κ, was determined by direct measurements of rainwater provided that sufcient sample was available.
Period Start date Duration, h Temperature range,
o
C Wind speed range, mph Wind direction Rainfall, mm κ, mS cm
-1
1 05/11/2021 70 2–14 2–11 N/NW 0.76
2 08/11/2021 100 11–14 6–22 S/SW 7.71 55.7
3 12/11/2021 70 8–15 3–17 N/NW 0.76
4 15/11/2021 100 9–13 2–11 W/NW 1.40 158
5 19/11/2021 70 4–12 2–17 N/NE 0.76
6 22/11/2021 100 2–11 2–19 N/NE 0.96 82.3
7 26/11/2021 70 0–10 2–29 N/NW 3.69 329
8 29/11/2021 100 0–12 2–22 N/NW 12.36 115
9 03/12/2021 70 4–11 4–19 W/NW 14.14 42.2
10 06/12/2021 100 3–11 5–29 S/SW 11.97 260
11 10/12/2021 70 3–12 3–21 S/SW 3.69 92.6
12 13/12/2021 100 8–12 3–18 S/SE/E 1.53 66.9
G. Kyriakoudes and A. Turner

Chemosphere 343 (2023) 140258
4
3.4. Origin and polymeric makeup of suspected microplastics
Table 4 summarises the results arising from the FTIR analysis of
suspected SMPs and DMPs sampled from the atmosphere, with examples
of sample and matching reference spectra shown in Fig. 4. Here, DMP
data have been corrected for the presence of two cellulosic bres as
contaminants in each sample; specically, one cotton bre and one
rayon bre, or two rayon bres where cotton was not present, were
subtracted from each tally. Overall, about 70% of particles analysed
returned a positive identication, and of these about 46% were syn-
thetic, and largely petroleum-based polymers. The most abundant
thermoplastics were polyamides (including nylon), acrylic, polyester
(including polyethylene terephthalate) and polyvinyl alcohol, and about
30% of synthetic polymers were identied as paints. About 50% of
positively identied particles were semi-synthetic bres, with the re-
generated cellulosic, rayon (viscose), present in all but one case, and
<5% of particles were natural (including cotton).
There was a lower proportion of synthetic polymers and a higher
proportion of semi-synthetic particles among DMPs than SMPs.
Regarding the synthetic polymers, there appeared to be some
Fig. 1. Various suspected SMPs and DMPs sampled from the atmosphere of southwest England observed under the stereomicroscope. (a) A black bre, (b) a
translucent, blue lm, (c) a multi-coloured fragment, (d) a white fragment, (e) various bres and fragments, and (f) a blue bre. Note the contamination of suspended
samples (a) and (e) by dark particulate matter.
Table 2
Number of suspected MPs and their concentrations suspended in air (SMPs), and
the number, concentrations (relative to rainfall volume) and uxes of suspected
MPs deposited from the atmosphere (DMPs) during the twelve sampling periods
of southwest England.
Period No. SMPs SMP m
−3
No. DMPs DMP L
−1
DMP m
−2
h
−1
1 3 0.068 9 750 2.02
2 4 0.067 15 124 2.36
3 9 0.238 8 667 1.79
4 2 0.037 7 318 1.10
5 2 0.053 8 667 1.79
6 1 0.018 21 1400 3.30
7 5 0.119 7 121 1.57
8 3 0.055 10 52 1.57
9 5 0.119 8 36 1.79
10 6 0.095 18 96 2.83
11 4 0.095 3 52 0.67
12 1 0.016 3 125 0.47
mean 3.8 0.082 10 367 1.77
median 3.5 0.068 8 124 1.79
total 45 117
Fig. 2. Depositional ux of suspected DMPs versus concentration of suspected
SMPs. Data highlighted by the red ellipse exhibit a signicant relationship
whose best-t line and statistical parameters are annotated.
G. Kyriakoudes and A. Turner

Chemosphere 343 (2023) 140258
5
fractionation between the two media, with a greater proportion of
acrylic being deposited and a greater proportion of polyester in
suspension.
4. Discussion
Not all particles considered in the present study were petroleum-
based MPs, although the semi-synthetic cellulosic that is shaped by
extrusion, rayon, is often reported in the MP literature (Woodall et al.,
2014; Comnea-Stancu et al., 2017; Higgins and Turner, 2023). Never-
theless, all but at most four particles identied were anthropogenic in
origin, and all anthropogenic particles that were not thermoplastics or
paints (rayon, methyl cellulose and cotton) were brous. Thus, for the
purposes of the discussion, we hereafter refer to MPs as petroleum-based
particles and other anthropogenic microbres, and with regard to any
quantitative comparisons or calculations, we assume that all particles
not analysed or unidentied by FTIR are MPs based on their visual
characteristics.
The concentrations of MPs are heterogeneous in both suspended and
deposited samples collected in Plymouth, southwest England, during
twelve periods in late autumn. This observation reects the multitude of
local and more distal primary and secondary sources (including the
ocean; Brahney et al., 2021) and variety of meteorological conditions
and air masses encountered. In suspension, there is some evidence that
wind direction and speed are partly responsible for this variation, while
an inverse relationship between deposited MPs and volume of rainfall
suggests that a high proportion of particles is washed out with incipient
rain and that the abundance or availability of particles progressively
declines as rainfall continues. Concentrations of particulate matter in the
lower troposphere are known to be responsive to and/or negatively
correlated with the length or intensity of precipitation (Ribeiro et al.,
2003; Luan et al., 2019; Zhou et al., 2021), although confounding factors
include time of day, wind speed and direction, air humidity and rainfall
height (Dris et al., 2016; Kluska et al., 2020). Despite these observations,
rainfall intensity or duration in the present study was not inversely
related to the concentration of SMPs subsequently encountered in the
atmosphere. This suggests that the stock of airborne MPs is relatively
rapidly replenished by the passage of air masses of different origin and
age.
The concentrations of SMPs and uxes of DMPs sampled from the
atmosphere over southwest England are compared with values reported
in the literature in Table 5. Here, inter-study differences in the type of
particle considered have been noted; specically, whether cellulosic
semi-synthetic bres (e.g., rayon) and natural bres (e.g., cotton) have
been included (based on sample digestion), or whether all particle
shapes or just bres have been counted. With these differences in mind,
concentrations of SMPs in Plymouth air (0.082 ±0.060 m
-3
) are similar
to concentrations reported for the coastal atmosphere of Pacic China
and the French Pyrenees, greater than concentrations given for the open
Pacic Ocean, and lower than concentrations measured in large cities
(Paris, Shanghai, Guangzhou). The mean depositional ux of DMPs for
southwest England (1.77 ±0.81 m
−2
h
−1
) is on the same order of
magnitude as most mean uxes reported in the literature but is
considerably lower than the value reported for the city of London.
Amongst the studies in Table 5, Yuan et al. (2023) have reported
both concentrations of SMPs and depositional uxes of DMPs. The au-
thors propose that the two measures can be combined to calculate a
dimensionless washout ratio, W, in order to evaluate removal efciency,
(a)
y= 5990x-0.912
r² = 0.630
p= 0.037
10
100
1000
10000
10 100 1000
DMP L-1
rainfall, mL
(b)
y= 4080x-0.880
r² = 0.488
p= 0.056
10
100
1000
10000
10 100 1000
DMF L-1
rainfall, mL
Fig. 3. Concentrations of (a) suspected DMPs and (b) suspected DMP bres, DMF, per L of rainwater versus volume of rainfall captured. Also shown are the best
power line ts through the dataset along with related statistical parameters.
Table 3
Percentage distribution of suspected SMPs and DMPs by shape and size sampled
from the atmosphere of southwest England.
SMPs (n =45) DMPs (n =117)
bres 64.4 80.3
fragments 24.2 12.8
pellets 11.1 0
foams 0 6.8
<100
μ
m 15.6 1.7
100–500
μ
m 42.2 24.8
>500
μ
m 42.2 73.5
synthetic 35.6 31.6
semi-synthetic 26.7 37.6
natural 0 4.3
unidentied 37.8 26.5
Table 4
Polymeric or material composition of suspected SMPs and DMPs that were
positively identied based on FTIR analysis. Synthetic polymers are petroleum-
based thermoplastics and paints (with the latter identied from resins and/or
additives and pigments). Note that nylon is included under polyamide and
polyethylene terephthalate is included under polyester.
Polymer/material SMPs (n =28) DMPs (n =86)
synthetic 16 37
acrylic 1 6
epoxy resin 0 1
expanded polyurethane 0 1
polyamide 3 9
a
polyester 5
b
1
polyetherimide 1 1
polypropylene 0 1
polyvinyl acetate 0 2
polyvinyl alcohol 1 4
polyvinyl chloride 0 1
other 5 10
paints 4 12
semi-synthetic 12 44
rayon 11 44
other 1 0
natural 0 5
cotton 0 1
Other 0 4
a
One sample returned a match for nylon and silk combined.
b
One sample returned a match for polyester and cotton combined.
G. Kyriakoudes and A. Turner

Chemosphere 343 (2023) 140258
6
assuming that the majority of DMPs are subject to wet deposition:
W =DMP L
−1
*10
3
/SMP m
−3
(1)
In the present study, both variables on the right-hand side of Eq. (1) are
given in Table 2 and yield periodic values of W ranging from 3.0 ×10
5
(period 9) to 7.7 ×10
7
(period 6) and a median value of 1.8 ×10
6
. By
comparison, Yuan et al. (2023) report a range for Guangzhou City from
2.2 ×10
3
to 1.5 ×10
6
. Thus, despite the present study not targeting
specic rainfall episodes (that is, not discriminating dry and wet depo-
sition), environmental conditions over southwest England appear to be
more favourable at removing MPs from the atmosphere.
A similar approach can be adopted to evaluate the removal efciency
of MPs by size, shape (specically, brous versus non-brous) and
polymer type. Here, the data in Tables 3 and 4 have been used for the
whole timeframe of sampling (1020 h) and summed volumes collected
(593 m
3
of air and 938 mL of rainwater) because many polymers or
shapes were not detected during specic periods. Polymer-specic
values of W shown in Fig. 5 reveal a range from about 1.3 ×10
5
for
polyester to about 3.8 ×10
6
for acrylic, while values for microplastic
bres (~5 ×10
6
) are considerably greater than values for non-brous
MPs (~7 ×10
5
) and values for larger (>500
μ
m) MPs (~2.8 ×10
6
)
are an order of magnitude greater than values for smaller (<100
μ
m)
MPs (~2.3 ×10
5
). That is, acrylic is considerably more prone to at-
mospheric removal than polyester, and removal favours larger particles
that are brous in nature.
The reasons for these differences amongst polymer types are unclear
but could be related to variations in their precise size or shape, or to
more general aerodynamic properties (hence vertical distribution in the
atmosphere) or hygroscopicity. Nevertheless, our observations suggest
that polymers like acrylic have a tendency to be readily removed from
the atmosphere whereas polymers like polyester have a greater pro-
pensity to remain airborne and, therefore, be transported longer dis-
tances. Partly consistent with this assertion, we note that Wei et al.
(2022) reported a reduction in the proportion of total microplastics as
polyethylene terephthalate (included as a polyester in Fig. 5) in the Qing
River, Beijing, following a rainfall event.
Periodic data can also be employed to estimate, empirically, the net
depositional velocities of MPs, v
d
(m h
−1
), in the atmosphere of south-
west England:
v
d
=DMP m
−2
h
−1
/SMP m
−3
(2)
The value of v
d
reects the time integration of both dry and wet
deposition of all MP shapes, sizes and polymer types and ranges from
7.1 m h
−1
for period 11 to 183 m h
−1
for period 6, with an overall pe-
riodic median of 37.5 m h
−1
. Although wet deposition was incorporated
into these estimations, v
d
was not correlated with rainfall, presumably
because of the confounding effects of rainfall intensity and duration and
other environmental variables. Nevertheless, and despite being specic
to the location and conditions encountered, we note that Wright et al.
(2020) provide a theoretical estimate of v
d
for representative bres (400
μ
m by 20
μ
m and a density of 1.184 g cm
−3
) falling through a dry at-
mosphere of 216 m h
−1
that is similar to our highest value. For MPs
raised to an elevation of 5000 m (or about halfway up in the tropo-
sphere), the range in v
d
is equivalent to a range of residence times from
about 27 h to 700 h.
An additional, important nding of the present study that is consis-
tent with other recent investigations (e.g., Liu et al., 2019b; Roblin et al.,
2020) is the signicance of semi-synthetic polymers (bres) in the
Fig. 4. Reference spectra (blue) and sample FTIR spectra (red) for (a) a polyvinyl acetate fragment, (b) a vehicle paint ake, (c) a rayon bre and (d) a polyester
bre. Note the broad peak centred on 3300 cm
−1
(O–H stretching) in (c) that distinguishes it from cotton (a narrower and less distinctive peak).
G. Kyriakoudes and A. Turner

Chemosphere 343 (2023) 140258
7
atmosphere, or a classication of anthropogenic particles that is often
deliberately excluded through chemical destruction (Allen et al., 2019;
Klein and Fischer, 2019; Liu et al., 2019a; Abbasi and Turner, 2021;
Purwiyanto et al., 2022). Finnegan et al. (2022) recently reviewed
existing literature on anthropogenic particles (mainly microbres) re-
ported in the atmosphere. Where polymer identication had been un-
dertaken, the collective data revealed that 57% of particles were
semi-synthetic (cellulosic) and 23% were petroleum-based. By com-
parison, data for suspended and deposited MPs in the present study yield
respective values of 49% and 46%. Currently, synthetic polymers like
polyester dominate the global production of textile bres (>60%;
Textile Exchange, 2022) and a higher proportion of semi-synthetic bres
in the atmosphere (and in particular, rayon), therefore, may be attrib-
uted to their lower durability and greater release from in-life and
end-of-life products (Finnegan et al., 2022).
While both plastic and semi-synthetic types of bre are predicted to
pose similar health risks through inhalation (Athey and Erdle, 2021), the
lower environmental persistence of cellulosic material means that
semi-synthetic bres may release chemical additives, like colourants,
ultraviolet light stabilisers and antimicrobial agents, as well as any
contaminants acquired from the environment, more readily (Ladewig
et al., 2015). In the present study, a maximum microplastic concentra-
tion in air of 0.238 m
-3
is equivalent to the daily inhalation by an adult
standing still of about ve particles, at least within the size range
detected microscopically.
5. Conclusions
SMPs and DMPs sampled from the atmosphere of southwest England
during twelve periods over a 42-day timeframe exhibit temporal varia-
tions in abundance but bres of the semi-synthetic cellulosic, rayon,
were persistently the most common type of particle. Incipient rainfall
appears to washout SMPs from air, with the volume of precipitation
displaying an inverse relationship with DMP concentration. However,
the combined periodic data reveal that SMPs are removed by deposition
differentially and according to size, shape and polymer type, suggesting
that these characteristics may be critical to the transportation and
residence times of MPs in the atmosphere. The combined data also allow
site- and environment-specic MP settling velocities to be calculated,
with estimates ranging from about 7 to 180 m h
−1
and a similar order of
magnitude to published, theoretical values. Although the precise results
of the study are specic to the location and environmental conditions
encountered, the broad ndings are likely to be more generally appli-
cable in improving our understanding of atmospheric MP occurrence,
transport and removal.
CRediT authorship contribution statement
Giannis Kyriakoudes: Conceptualization, Methodology, Investiga-
tion, Formal analysis, Writing – original draft. Andrew Turner:
Conceptualization, Investigation, Formal analysis, Writing – original
draft, Writing – review & editing.
Declaration of competing interest
The authors declare that they have no known competing nancial
interests or personal relationships that could have appeared to inuence
the work reported in this paper.
Data availability
Data will be made available on request.
Table 5
Mean (±one standard deviation) or range of concentrations of MPs (including or
excluding cellulosics) suspended in and deposited from the atmosphere that
have been reported in the literature.
SMPs Particle type SMP m
−3
Reference
Paris, France Fibres, including
cellulosic
0.3 to 1.5 Dris et al. (2017)
Open Pacic Ocean Excluding
cellulosic bres
~0.01 Liu et al. (2019a)
Shanghai, China Including rayon
bres
up to 4.2 Liu et al. (2019b)
Coastal Pacic Ocean
of China
Including cellulosic
bres
0.042 ±
0.025
Wang et al. (2020)
Open East Indian
Ocean
Including cellulosic
bres
0.004 ±
0.006
Wang et al. (2020)
French Pyrenees Including cellulosic
bres
0.09 to
0.66
Allen et al. (2021)
Guangzhou, China Including cellulosic
bres
0.17 ±
0.01
Yuan et al. (2023)
Plymouth, UK Including cellulosic
bres
0.082 ±
0.060
This study
DMPs DMP m
−2
h
−1
Paris, France Including cellulosic
bres
4.58 ±
4.00
Dris et al., 2016
Dongguan, China Including cellulosic
bres
7.29 to
13.0
Cai et al. (2017)
French Pyrenees Including cellulosic
bres
15.2 Allen et al. (2019)
Northern Germany Excluding
cellulosic bres
11.5 Klein and Fischer
(2019)
Protected US areas Including cellulosic
bres
5.50 ±
0.25
Brahney et al.
(2020)
Irish Atlantic Coast Fibres, including
cellulosic
4.17 Roblin et al. (2020)
London Including cellulosic
bres
32.1 ±
6.96
Wright et al. (2020)
Mount Derak, Iran Excluding
cellulosic bres
0.51 ±
0.20
Abbasi and Turner
(2021)
Shiraz, Iran Excluding
cellulosic bres
2.65 ±
1.44
Abbasi and Turner
(2021)
Gulf of Gdansk, Poland Including cellulosic
bres
0.41 ±
0.33
Szewc et al. (2021)
South Central Ontario,
Canada
Including cellulosic
bres
2.38 Welsh et al. (2022)
Coastal Indonesia Excluding
cellulosic bres
0.63 ±
0.54
Purwiyanto et al.
(2022)
Guangzhou, China Including cellulosic
bres
2.75 ±
0.31
Yuan et al. (2023)
Plymouth, UK Including cellulosic
bres
1.77 ±
0.81
This study
Fig. 5. Relative efciency for atmospheric removal of MPs, W, by polymer type
(and in grey, by shape, and in green, by size) over southwest England.
G. Kyriakoudes and A. Turner

Chemosphere 343 (2023) 140258
8
Acknowledgements
We are grateful to Mr Billy Simmonds and Mr Richard Hartley
(University of Plymouth) for technical support. The comments of two
anonymous reviewers greatly improved the manuscript.
References
Abbasi, S., 2021. Microplastics washout from the atmosphere during a monsoon rain
event. J. Hazard. Mater. Adv. 4, 100035.
Abbasi, S., Turner, A., 2021. Dry and wet deposition of microplastics in a semi-arid
region (Shiraz, Iran). Sci. Total Environ. 786, 147358.
Abbasi, S., Turner, A., Hoseini, M., Amiri, H., 2021. Microplastics in the Lut and Kavir
deserts, Iran. Environ. Sci. Technol. 55, 5993–6000.
Aeschlimann, M., Li, G., Kanji, Z.A., Mitrano, D.M., 2022. Microplastics and nanoplastics
in the atmosphere: the potential impacts on cloud formation processes. Nat. Geosci.
15, 967–975.
Allen, S., Allen, D., Phoenix, V.R., Le Roux, G., Jimenez, P.D., Simonneau, A., Binet, S.,
Galop, D., 2019. Atmospheric transport and deposition of microplastics in a remote
mountain catchment. Nat. Geosci. 12, 339–344.
Allen, S., Allen, D., Baladima, F., Phoenix, V.R., Thomas, J.L., Le Roux, G., Sonke, J.E.,
2021. Evidence of free tropospheric and long-range transport of microplastic at Pic
du Midi Observatory. Nat. Commun. 12, 7242.
Athey, S.N., Erdle, L.M., 2021. Are we underestimating anthropogenic microber
pollution? A critical review of occurrence, methods, and reporting. Environ. Toxicol.
Chem. 41, 822–837.
Bergmann, M., Mützel, S., Primple, S., Tekman, M.B., Trachsel, J., Gerdts, G., 2019.
White and wonderful? Microplastics prevail in snow from the Alps to the Arctic. Sci.
Adv. 5, eaax1157.
Brahney, J., Hallerud, M., Heim, E., Hahnenberger, M., Sukumaran, S., 2020. Plastic rain
in protected areas of the United States. Science 368, 1257–1260.
Brahney, J., Mahowald, N., Prank, M., Prather, K.A., 2021. Constraining the atmospheric
limb of the plastic cycle. Earth, Atmos. Planet. Sci. 118, e2020719118.
Cai, L., Wang, J., Peng, J., Tan, Z., Zhan, Z., Tan, X., Chen, Q., 2017. Characteristic of
microplastics in the atmospheric fallout from Dongguan City, China: preliminary
research and rst evidence. Environ. Sci. Pollut. Control Ser. https://doi.org/
10.1007/s11356-017-0116-x.
Comnea-Stancu, I.R., Wieland, K., Ramer, G., Schwaighofer, A., Lendl, B., 2017. On the
identication of rayon/viscose as a major fraction of microplastics in the marine
environment: discrimination between natural and manmade cellulosic bers using
Fourier transform infrared spectroscopy. Appl. Spectrosc. 71, 939–950.
Dris, R., Gasperi, J., Saad, M., Mirande, C., Tassin, B., 2016. Synthetic bers in
atmospheric fallout: a source of microplastics in the environment? Mar. Pollut. Bull.
104, 290–293.
Dris, R., Gasperi, J., Mirande, C., Mandin, C., Guerrouache, M., Langlois, V., Tassin, B.,
2017. A rst overview of textile bers, including microplastics, in indoor and
outdoor environments. Environ. Pollut. 221, 453–458.
Evangeliou, N., Tichý, O., Eckhardt, S., Zwaaftink, C.G., Brahney, J., 2022. Sources and
fate of atmospheric microplastics revealed from inverse and dispersion modelling:
from global emissions to deposition. J. Hazard Mater. 432, 128585.
Feng, S.S., Lu, H.W., Tian, P.P., Xue, Y.X., Lu, J.Z., Tang, M., Feng, W., 2020. Analysis of
microplastics in a remote region of the Tibetan Plateau: implications for natural
environmental response to human activities. Sci. Total Environ. 739, 140087.
Finnegan, A.M.D., Susserott, R., Gabbott, S.E., Gouramanis, C., 2022. Man-made natural
and regenerated cellulosic bres greatly outnumber microplastic bres in the
atmosphere. Environ. Pollut. 310, 119808.
Gasperi, J., Wright, S.L., Dris, R., Collard, F., Mandin, C., Guerrouache, M., Langlois, V.,
Kelly, F.J., Tassin, B., 2018. Microplastics in air: are we breathing it in? Curr. Opin.
Environ. Sci. Health 1, 1–5.
Gonz´
alez-Pleiter, M., Edo, C., Aguilera, A., Viúdez-Moreiras, D., Pulido-Reyes, G.,
Gonz´
alez-Toril, E., Osuna, S., de Diego-Castilla, G., Legan´
es, F., Fern´
andez-Pi˜
nas, F.,
Rosal, R., 2021. Occurrence and transport of microplastics sampled within and above
the planetary boundary layer. Sci. Total Environ. 761, 143213.
Higgins, C., Turner, A., 2023. Microplastics in surface coastal waters around Plymouth,
UK, and the contribution of boating and shipping activities. Sci. Total Environ. 893,
164695.
Klein, M., Fischer, E.K., 2019. Microplastic abundance in atmospheric deposition within
the Metropolitan area of Hamburg, Germany. Sci. Total Environ. 685, 96–103.
Kluska, K., Piotrowicz, K., Kasprzyk, I., 2020. The impact of rainfall on the diurnal
patterns of atmospheric pollen concentrations. Agric. For. Meteorol. 291, 108042.
Ladewig, S.M., Bao, S., Chow, A.T., 2015. Natural bers: a missing link to chemical
pollution dispersion in aquatic environments. Environ. Sci. Technol. 49,
12609–12610.
Liu, K., Wu, T., Wang, X., Song, Z., Zong, C., Wei, N., Li, D., 2019a. Consistent transport
of terrestrial microplastics to the ocean through atmosphere. Environ. Sci. Technol.
53, 10612–10619.
Liu, K., Wang, X., Fang, T., Xu, P., Zhu, L., Li, D., 2019b. Source and potential risk
assessment of suspended atmospheric microplastics in Shanghai. Sci. Total Environ.
675, 462–471.
Long, X., Fu, T.M., Yang, X., Tang, Y., Zheng, Y., Zhu, L., Shen, H., Ye, J., Wang, C.,
Wang, T., Li, B., 2022. Efcient atmospheric transport of microplastics over Asia and
adjacent oceans. Environ. Sci. Technol. 56, 6243–6252.
Luan, T., Zhang, T., Guo, L., 2019. Below-cloud aerosol scavenging by different-intensity
rains in Beijing City. J. Meteorol. Res. 33, 126–137.
Mehmood, T., Hassan, M.A., Faheem, M., Shakoor, A., 2021. Why is inhalation the most
discriminative route of microplastics exposure? Environ. Sci. Pollut. Control Ser. 29,
49479–49482.
MERI, 2014. Guide to Microplastic Identication. Marine & Environmental Research
Institute, Blue Hill, ME, USA.
Purwiyanto, A.I.S., Prartono, T., Riani, E., Naulita, Y., Cordova, M.R., Koropitan, A.F.,
2022. The deposition of atmospheric microplastics in Jakarta-Indonesia: the coastal
urban area. Mar. Pollut. Bull. 174, 113195.
Ribeiro, H., Cunha, M., Abreu, I., 2003. Airborne pollen concentration in the region of
Braga, Portugal, and its relationship with meteorological parameters. Aerobiologia
19, 21–27.
Roblin, B., Ryan, M., Vreugdenhil, A., Aherne, J., 2020. Ambient atmospheric deposition
of anthropogenic microbers and microplastics on the western periphery of Europe
(Ireland). Environ. Sci. Technol. 54, 11100–11108.
Szewc, K., Graca, B., Dolega, A., 2021. Atmospheric deposition of microplastics in the
coastal zone: characteristics and relationship with meteorological factors. Sci. Total
Environ. 761, 143272.
Textile Exchange, 2022. Preferred Fiber & Materials Market Report. https://textileexch
ange.org/knowledge-center/reports/preferred-fiber-and-materials/.
Turner, A., 2021. Paint particles in the marine environment: an overlooked component of
microplastics. Water Res. X 12, 100110.
Wang, X., Li, C., Liu, K., Zhu, L., Song, Z., Li, D., 2020. Atmospheric microplastic over the
south China sea and east Indian Ocean: abundance, distribution and source.
J. Hazard Mater. 389, 121846.
Wei, Y., Dou, P., Xu, D., Zhang, Y., Gao, B., 2022. Microplastic reorganization in urban
river before and after rainfall. Environ. Pollut. 314, 120326.
Welsh, B., Aherne, J., Paterson, A.M., Yao, X., McConnell, C., 2022. Atmospheric
deposition of anthropogenic particles and microplastics in south-central Ontario,
Canada. Sci. Total Environ. 835, 155426.
Woodall, L.C., Sanchez-Vidal, A., Canals, M., Paterson, G.L., Coppock, R., Sleight, V.,
Calafat, A., Rogers, A.D., Narayanaswamy, B.E., Thompson, R.C., 2014. The deep sea
is a major sink for microplastic debris. R. Soc. Open Sci. 1, 140317.
Wright, S.L., Ulke, J., Font, A., Chan, K.L.A., Kelly, F.J., 2020. Atmospheric microplastic
deposition in an urban environment and an evaluation of transport. Enviro. Int. 136,
105411.
Yuan, Z., Pei, C., Li, H., Lin, L., Liu, S., Hou, R., Liao, R., Xu, X., 2023. Atmospheric
microplastics at a southern China metropolis: occurrence, deposition ux, exposure
risk and washout effect of rainfall. Sci. Total Environ. 869, 161839.
Zhang, Y., Kang, S., Allen, S., Allen, D., Gao, T., Sillanp¨
a¨
a, M., 2020. Atmospheric
microplastics: a review on current status and perspectives. Earth Sci. Rev. 203,
103118.
Zhou, B., Liu, D., Yan, Y., 2021. A simple new method for calculating precipitation
scavenging effect on particulate matter: based on ve-year data in eastern China.
Atmosphere 12, 759.
G. Kyriakoudes and A. Turner