Non-exhaust PM emissions from electric vehicles

Abstract

Particulate matter (PM) exposure has been linked to adverse health effects by numerous studies. Therefore, governments have been heavily incentivising the market to switch to electric passenger cars in order to reduce air pollution. However, this literature review suggests that electric vehicles may not reduce levels of PM as much as expected, because of their relatively high weight. By analysing the existing literature on non-exhaust emissions of different vehicle categories, this review found that there is a positive relationship between weight and non-exhaust PM emission factors. In addition, electric vehicles (EVs) were found to be 24% heavier than equivalent internal combustion engine vehicles (ICEVs). As a result, total PM10 emissions from EVs were found to be equal to those of modern ICEVs. PM2.5 emissions were only 1-3% lower for EVs compared to modern ICEVs. Therefore, it could be concluded that the increased popularity of electric vehicles will likely not have a great effect on PM levels. Non-exhaust emissions already account for over 90% of PM10 and 85% of PM2.5 emissions from traffic. These proportions will continue to increase as exhaust standards improve and average vehicle weight increases. Future policy should consequently focus on setting standards for non-exhaust emissions and encouraging weight reduction of all vehicles to significantly reduce PM emissions from traffic.

Full text

DOI: 10.1016/j.atmosenv.2016.03.017
© 2021. This manuscript version is made available under the CC-BY-NC-ND 4.0
license http://creativecommons.org/licenses/by-nc-nd/4.0/
Non-exhaust PM emissions from electric vehicles
1
Victor R. J. H. Timmersa*, Peter A. J. Achtena
2
aINNAS BV, 15 Nikkelstraat, 4823 AE Breda, Netherlands
3
4
*corresponding author; email: vrjhtimmers@gmail.com
5
6
7
Abstract
8
Particulate matter (PM) exposure has been linked to adverse health effects by numerous studies.
9
Therefore, governments have been heavily incentivising the market to switch to electric passenger
10
cars in order to reduce air pollution. However, this literature review suggests that electric vehicles
11
may not reduce levels of PM as much as expected, because of their relatively high weight. By
12
analysing the existing literature on non-exhaust emissions of different vehicle categories, this review
13
found that there is a positive relationship between weight and non-exhaust PM emission factors. In
14
addition, electric vehicles (EVs) were found to be 24% heavier than equivalent internal combustion
15
engine vehicles (ICEVs). As a result, total PM10 emissions from EVs were found to be equal to those
16
of modern ICEVs. PM2.5 emissions were only 1-3% lower for EVs compared to modern ICEVs.
17
Therefore, it could be concluded that the increased popularity of electric vehicles will likely not have
18
a great effect on PM levels. Non-exhaust emissions already account for over 90% of PM10 and 85% of
19
PM2.5 emissions from traffic. These proportions will continue to increase as exhaust standards
20
improve and average vehicle weight increases. Future policy should consequently focus on setting
21
standards for non-exhaust emissions and encouraging weight reduction of all vehicles to significantly
22
reduce PM emissions from traffic.
23
24
Keywords: electric vehicle, particulate matter, non-exhaust, PM10
25
26
27

2
1. Introduction
28
Air quality is a large concern in Europe. According to the European Environmental Agency (EEA), PM
29
is one of Europe's most problematic pollutants in terms of harm to human health, being responsible
30
for several hundreds of thousands of premature deaths in the European Region every year [1].
31
Traffic is one of the main reasons why PM levels are too high, and is the primary source of PM in urban
32
areas [2-4]. Vehicles emit PM through their exhaust and through non-exhaust sources, such as tyre
33
wear, brake wear, road surface wear and resuspension of road dust [5].
34
PM is often divided into PM10 and PM2.5, which represent particles with a diameter of less than 10 µm
35
and 2.5 µm, respectively. The link between exposure to PM and adverse health effects has been well
36
documented [1, 6-10]. However, the precise effects on health due to exhaust and non-exhaust
37
emissions are less well understood.
38
Exhaust PM emissions are mainly made up of PM2.5 and contain a variety of hydrocarbons, which can
39
contribute to respiratory disease or lead to increased incidence of cancer [11]. Non-exhaust emissions
40
tend to contain mostly PM10, but a significant proportion of the emissions contains fine PM2.5 as well.
41
The chemical characteristics of non-exhaust PM emissions vary per source, but are mainly made up of
42
heavy metals such as zinc (Zn), copper (Cu), iron (Fe) and lead (Pb), among others [5]. There are several
43
toxicological studies that have found links between non-exhaust emissions and adverse health effects,
44
such as lung-inflammation and DNA damage [12-16], and a review of epidemiological studies
45
concluded that PM10 indeed has an effect on mortality [17].
46
Because of the chemical differences between non-exhaust and exhaust emissions, they result in
47
different secondary PM. Secondary PM is formed in the atmosphere through chemical reactions,
48
rather than being directly emitted by a source. The volatile organic compounds in exhaust gases
49
react with sunlight in the atmosphere to form secondary organic aerosols (SOAs) whereas non-
50
exhaust emissions are mainly inorganic and therefore form secondary inorganic aerosols (SIAs).
51
However, it is exceedingly difficult to model SOAs and SIAs emissions [18,19]. Not only do many
52
studies have difficulty determining the fractional contribution vehicles make to SOAs, but it is also
53
problematic to differentiate between primary and secondary PM [20-22]. Therefore, there is always
54
the risk of double-counting PM [23]. SOAs may have a significant influence on PM levels. However,
55
more research is needed to determine their relative importance. The largest part of the non-exhaust
56
emissions is resuspended PM, possibly including secondary PM emissions. For that reason we have
57
not differentiated between primary and secondary PM emissions.
58

3
One of the strategies being adopted in many European countries to improve air quality is incentivising
59
the electrification of passenger cars [24, 25]. The switch to EVs has been proposed as a solution to air
60
pollution, offering zero emissions and promising cleaner air for everyone [26-28]. However, when
61
modelling the impact of EVs on air quality, Soret et al. [29] found that fleet electrification would not
62
significantly reduce PM emissions due to the importance of non-exhaust emissions.
63
This literature review attempts to investigate this further by determining the weight difference
64
between EVs and ICEVs, quantifying the impact this has on non-exhaust emissions and finally
65
comparing the total PM emissions from EVs and ICEVs. It is important to note that this literature
66
review is only concerned with the PM emissions from EVs and ICEVs. A complete understanding of the
67
value of EVs versus ICEVs is beyond the scope of this study.
68
69
2. Weight and Emission
70
2.1 Hypothesised influence of weight
71
It can be hypothesised that each of the sources of non-exhaust PM emissions should be influenced
72
by vehicle weight.
73
We know that road abrasion and tyre wear are caused by the friction between the tyre thread and
74
road surface. Friction is a function of the friction coefficient between the tyres and the road, as well
75
as a function of the normal force of the road. This force is directly proportional to the weight of the
76
car. This means that increasing vehicle weight would increase the frictional force and therefore the
77
rate of wear on both the tyre and road surface.
78
Brake wear is caused by the friction between the brake pads and the wheels. The energy needed to
79
reduce the momentum of a vehicle is proportional to the vehicle’s speed and mass. Therefore, as the
80
mass of the vehicle increases, more frictional energy is needed to slow it down, leading to greater
81
brake wear.
82
Resuspension is caused by the wake of a vehicle, which in turn is determined by the size, weight and
83
aerodynamics of the vehicle. Furthermore, heavier vehicles are able to grind down larger particles
84
into smaller, more easily suspended PM. In addition, many heavier vehicles will also be larger,
85
resulting in a larger wake. These factors together should cause increased resuspension.
86
2.2 Evidence for influence of weight
87

4
In his paper, Simons [30] presented new and updated datasets for emissions of passenger cars. He
88
distinguishes between vehicle exhaust and non-exhaust emissions and is one of the first to define
89
non-exhaust emissions as a factor of vehicle weight, with the intention of being applied to studies on
90
hybrid and electric vehicles. Simons suggests that PM10 emission factors could be scaled directly to
91
vehicle weight and provides emission factors for tyre, brake and road wear per kg of vehicle weight.
92
For example, tyre, brake and road wear increase by around 50% when comparing a medium
93
(1600kg) and small (1200kg) car. Compared to a small car, large cars (2000kg) emitted more than
94
double the amount of PM10. See Figure 1.
95
Figure 1 Non-exhaust PM emissions by source and car size, from Simons [30] based on Ntziachristos and
96
Boulter [31]
97
98
There is very little other research that directly links non-exhaust PM emissions to vehicle weight.
99
Some authors have speculated about the possible influence of weight, but not directly measured it.
100
Barlow [32] mentions that vehicle weight is likely to be one of the factors affecting tyre wear. He
101
also says that in general, larger vehicles produce larger non-exhaust emissions. These assertions are
102
only explained qualitatively, however. Similarly, Garg et al. [33] mention that the inertia weight
103
being stopped is one of the factors contributing to brake wear rate, but does not perform any tests
104
with varying weights to confirm this.
105
Despite the lack of direct research, there is significant indirect evidence for the positive relationship
106
between weight and non-exhaust PM emissions. Many studies and emission inventories suggest that
107
heavier vehicle categories emit more PM.
108

5
The European Environmental Agency (EEA) publishes an Emission Inventory Guidebook [34] which
109
provides emission factors for different vehicle types. In this emission inventory, passenger cars are
110
defined as vehicles carrying up to nine passengers, whereas light duty vehicles (LDVs) are defined as
111
vehicles with a gross weight of up to 3500kg. LDV emission factors of total suspended particles (TSP),
112
PM10 and PM2.5 were 57% higher than those of passenger cars for both tyre and brake wear, but road
113
surface wear was the same for both.
114
The U.S. Environmental Protection Agency (EPA) [35] has their own emission inventory called
115
MOVES2014, which contains emission factors for tyre and brake wear. They distinguish between
116
passenger cars (< 2720kg) and passenger trucks (< 3855kg), and assert that the latter emit 67% more
117
PM10 and PM2.5 due to brake wear but only 2% more due to tyre wear.
118
The Pollutant Release and Transfer Register in The Netherlands (PRTR) provide their own emission
119
inventory with emission factor estimates for tyre wear [36] based on extensive research. They
120
consider the average empty weight of a passenger car to be 850-1050kg and the gross weight of a
121
van to be around 2000kg. They suggest that that the total tyre wear, PM10 and PM2.5 emissions were
122
40% higher for vans compared to regular passenger cars. The PRTR also has a report on calculating
123
emissions per tyre for different vehicle categories [37]. In this report, wear rate per tyre is 10%
124
higher for passenger cars than for motorcycles, 20% higher for delivery vans than for passenger cars
125
and 130% higher for lorries than for passenger cars.
126
Several individual studies measuring non-exhaust emissions differentiate between passenger cars
127
and LDVs. Despite varying definitions for the weight of vehicle categories, the general consensus is
128
that LDVs emit more PM than passenger cars. For example, Garben et al. [38] found tyre wear of
129
LDVs to be 75% higher than that of passenger cars. Similarly, Gebbe et al. [39] found tyre wear for
130
LDVs to be more than twice that of passenger cars. BUWAL [40] found that the PM10 emissions of
131
passenger cars’ brakes were twice as much as those from motorcycles. LDVs on the other hand,
132
emitted over two and a half times more PM10 than passenger cars. Research by Garg et al. [33]
133
distinguishes between brake emissions from small cars, large cars and large pickup trucks. They
134
found that the brakes of large cars emit 55% more TSP, PM10 and PM2.5 than small cars. Large pickup
135
trucks were found to emit more than double the amount of particulates compared to small cars.
136
Very little data is available on resuspension of road dust for different vehicle categories. Gillies et al.
137
[41] investigated emissions of vehicles on unpaved roads and found that emissions had a strong
138
linear relationship with not only vehicle speed but also vehicle weight. The EPA’s AP42 Method [42]
139
for estimation of resuspension includes a factor based on vehicle weight to the power 1.02,
140

6
suggesting resuspension increases almost linearly with weight. This is in line with the results from a
141
study by Amato et al. [43] which used the same vehicle categories as the EPA [35] and found that
142
PM10 resuspension rates were 10 times higher for passenger cars than for motorcycles, and 3-4 times
143
higher for LDVs than for passenger cars. See Table 1 for an overview of the results.
144
Table 1 Comparison of non-exhaust emissions for different vehicle categories
145
(s) = only includes suspended particles (u) = urban roads, (r) = rural roads
146
147
2.3 Weight comparison of electric and conventional passenger cars
148
Reference
Vehicle type
Non-exhaust
source
Total wear
(mg/vkm)
PM10
(mg/vkm)
PM2.5
(mg/vkm)
Simons [30]
Per vehicle kg
Tyres
0.0573
0.00408
0.00286
Brakes
0.00445
0.00396
0.00174
Road
0.00979
0.00490
0.00264
EEA [34]
Passenger car
Tyres + Brakes
18.2 (s)
13.8
7.4
Light duty truck
Tyres + Brakes
28.6 (s)
21.6
11.7
Dutch PRTR [36]
Passenger car
Tyres
100
5
1
Van
Tyres
140
7
1.4
Dutch PRTR [37]
Motorcycle
per tyre
30 (u)/19 (r)
-
-
Passenger car
per tyre
33 (u)/21 (r)
-
-
Delivery van
per tyre
40 (u)/26 (r)
-
-
US EPA [35]
Passenger car
Brakes
-
18.5
2.3
Passenger truck
Brakes
-
30.9
3.9
Passenger car
Tyres
-
6.1
0.9
Passenger truck
Tyres
-
6.2
0.9
Garben et al. [38]
Passenger car
Tyres
64
-
-
LDV
Tyres
112
-
-
Gebbe et al. [39]
Passenger car
Tyres
52.8
-
-
LDV
Tyres
110
-
-
BUWAL [40]
Motorcycle
Brakes
-
0.9
-
Passenger car
Brakes
-
1.8
-
LDV
Brakes
-
4.9
-
Garg et al. [33]
Small car
Brakes
11.2/3.4 (s)
2.9
1.8
Large car
Brakes
17.4/5.3 (s)
4.5
2.8
Amato et al. [43]
Motorcycle
Resuspension
-
0.8-3.3
-
Passenger car
Resuspension
-
9.4-36.9
-
LDV
Resuspension
-
33.5-131.5
-

7
In order to determine the additional non-exhaust emissions that EVs produce, a comparison must be
149
made between the weight of EVs and ICEVs. The best way to do this is by determining the difference
150
in weight between a highway-capable EV and its equivalent non-electric version. For example, the
151
Ford Focus Electric and gasoline-powered Ford Focus hatchback have almost exactly the same
152
specifications. The Electric, however is 219kg heavier. The same applies to the Honda Fit: the electric
153
version is 335kg heavier than the conventional version. The Kia Soul EV is 311kg heavier than the
154
regular Kia Soul, etc. See Table 2 for the complete list. On average, the electric versions are 280kg or
155
24% heavier than their ICE counterparts.
156
Table 2 Comparison of weight between EVs and their ICEV counterparts, based on manufacturer information
157
158
It is important to note that comparing electric vehicles and their conventional counterparts is not
159
entirely straightforward. For example, the weight of the body of electric vehicles is often reduced
160
significantly by using aluminium instead of steel to improve the range of the vehicle [44]. If this
161
would be done with conventional cars, the weight difference would be even greater than it already
162
is. Furthermore, EVs have many limitations that ICEVs do not have. For example, the Volkswagen e-
163
Golf has a top speed of 140 km/h, a range of 133 km and cannot carry any trailer load. The
164
Volkswagen Golf on the other hand, has a top speed depending on engine size between 179-203
165
km/h, a range of over 1000 km and can carry a trailer load up to 1100kg. This all makes direct
166
comparison problematic, especially since only limited data on vehicle specifics is publicly available.
167
EV
ICEV
Mass in
running
order EV (kg)
Mass in
running
order ICEV
(kg)
Weight
difference (kg)
Weight
difference
(%)
Ford Focus Electric
Ford Focus
1719
1500
+219
+14.6
Honda Fit EV
Honda Fit
1550
1215
+335
+27.6
Fiat 500e
Fiat 500
1427
1149
+278
+24.2
Smart Electric Drive
Coupe
Smart Coupe
1055
820
+235
+28.7
Kia Soul EV
Kia Soul
1617
1306
+311
+23.8
Volkswagen e-Up!
Volkswagen Up
1289
1004
+284
+28.3
Volkswagen e-Golf
Volkswagen Golf
1617
1390
+227
+16.3
Chevrolet Spark EV
Chevrolet Spark
1431
1104
+327
+28.6
Renault Fluence EV
Renault Fluence
1618
1300
+318
+24.4

8
Very few other studies compare the weight of vehicles by their power train technology. Bauer et al.
168
[45] used a simulation of a mid-size vehicle to compare the weight of ICEVs and EVs in 2012 and
169
projected in 2030. They found that in 2012, ICEVs were 1567 kg on average, whereas EVs were
170
1944kg (24% heavier). The projected values for 2030 were 1383kg and 1613kg for ICEVs and EVs,
171
respectively.
172
3.4 Expected effect on emissions of EVs
173
More research is needed to determine the exact relationship between weight and non-exhaust
174
emissions, but a reasonable estimate can be made using existing research. Based on the research by
175
Simons [30] an increase in weight of 280kg will result in a PM10 increase of 1.1 mg per vehicle-
176
kilometre (mg/vkm) for tyre wear, 1.1 mg/vkm for brake wear and 1.4 mg/vkm for road wear. For
177
PM2.5, these values are 0.8 mg/vkm, 0.5 mg/vkm and 0.7 mg/vkm for tyre, brake and road wear,
178
respectively. However, brake wear of EVs tends to be lower because of their regenerative brakes
179
[32]. There is very little literature which has investigated the actual reduction in emissions, so we
180
have assumed a conservative estimate of zero brake wear emissions for EVs. For resuspension, it is
181
reasonable to assume based on the research by Gillies et al. [41] that there is a linear relationship
182
between weight and resuspension, and therefore a 24% increase in resuspension is to be expected.
183
184
3. Exhaust and non-exhaust emission factors
185
In order to put this increase in emissions into perspective, the average PM10 and PM2.5 emissions of
186
passenger cars must be determined. As we know, passenger cars emit PM through exhaust and non-
187
exhaust pathways.
188
3.1 Exhaust emissions
189
Before the introduction of air quality standards, exhaust emissions used to be a major source of PM,
190
especially for diesel cars [46]. Since then, PM emission standards for vehicle exhausts have become
191
increasingly strict and now all new diesel passenger cars are fitted with a diesel particulate filter (DPF).
192
Bergmann et al. [47] found that DPFs are very effective at reducing PM emissions, lowering the
193
emitted mass of PM by 99.3%. This has resulted in greatly reduced particle emissions from diesels in
194
the last ten years [5, 48].
195

9
The current instalment of European emission standards, EURO 6, dictates that new diesel and petrol
196
cars must emit less than 5 mg/vkm to be allowed on the market [49]. It is expected that within the
197
next decade, the majority of vehicles will comply with these regulations.
198
Many studies have been done to determine the amount of PM emitted by vehicle exhausts [50-54].
199
Earlier studies tend to report higher emission factors than more recent ones, which is indicative of the
200
improving exhaust emission standards and higher measurement accuracy.
201
The most reliable indicators of emission factors are generally European and national emission
202
inventories. These emission inventories compile data from vast amounts of measurements and studies
203
to provide emission factors that can be used to estimate contributions to national air pollution.
204
Moreover, emission inventories are revised every couple of years as new research becomes available.
205
One of these emission inventories is the EMEP/EEA Emission Inventory Guidebook [55]. This
206
guidebook is used by EU countries to determine emissions from their vehicle fleets and report them
207
annually to the EEA. The latest Emission Inventory Guidebook provides emission factors for different
208
vehicles by fuel type, engine displacement and technology. The PM emission factors for gasoline and
209
diesel passenger cars are generally very low, well below the EURO 6 limits.
210
Another emission inventory is available from the U.S. EPA [56]. For passenger cars, their model
211
predicts that average exhaust emissions of both PM10 and PM2.5 are much lower than the EURO 6 limit.
212
Cai et al. [57] used the EPA’s Motor Vehicle Emission Simulator (MOVES) to estimate the exhaust PM
213
emissions of passenger cars by model year. They found that exhaust emissions tend to decrease with
214
newer models. Older gasoline cars emitted slightly more than the limits set by EURO 6, whereas newer
215
models had much lower emission factors, on average. All diesel models with DPFs emit less than the
216
EURO 6 limits, according to the computer model.
217
The Dutch PRTR [37] has exhaust emission factors in their emission inventory as well. For gasoline
218
passenger cars, these are just below EURO 6 standards, whereas diesel vehicles with DPFs produce
219
almost no emissions at all. This is in contrast with the UK national atmospheric emission inventory
220
(NAEI) [58], which specifies that petrol cars emit almost no PM and diesel cars emit more than gasoline
221
cars, depending on their engine technology. All of the reported emission factors for diesels are below
222
EURO 6 limits.
223
If we average the suggested emission factors from theses emission inventories, we obtain a PM10
224
emission factor of 3.1 mg/vkm for gasoline cars and 2.4 mg/vkm for diesel cars. In terms of PM2.5,
225
these values were 3.0 mg/vkm and 2.3 mg/vkm for gasoline and diesel cars, respectively.
226

10
227
Table 3 Exhaust emission factors for gasoline and diesel passenger cars
228
Reference
Gasoline PM10
emissions
(mg/km)
Gasoline PM2.5
emissions
(mg/km)
Diesel PM10
emissions
(mg/km)
Diesel PM2.5
emissions (mg/km)
US EPA [56]
2.7
2.5
2.7
2.5
Cai et al. [57]
4.7-6.4
4.3-5.9
3.1-4.7
3.0-4.5
EEA [55]
1.1-2.2
1.1-2.2
1.5-2.1
1.5-2.1
Dutch PRTR [37]
4.0-5.0
4.0-5.0
1.0
1.0
UK NAEI [58]
1.0
1.0
1.6-3.2
1.6-3.2
Average
3.1
3.0
2.4
2.3
229
3.2 Non-exhaust emissions
230
Numerous studies have investigated the non-exhaust emission factors of passenger cars. There are
231
several ways to do this. The most common methods are:
232
i) Estimation
233
Emission factors can be estimated based on national statistics of tyre use and brake use, average
234
weight lost per tyre and brake, and average distance before a tyre/brake needs to be replaced. Some
235
manufacturers also provide information on the rate of wear on tyres and brakes, which can be used
236
to estimate emission factors. Examples of studies that use this method are those by Barlow [32] and
237
Legret & Pagotto [59].
238
ii) Laboratory measurements
239
Laboratory measurements usually use a circular road simulator and weighted wheels, with or
240
without brakes to test tyre, brake and road wear. Alternatively, tests can be done on a track in a
241
wind tunnel to more closely simulate reality. Examples of studies which use a road simulator are
242
Cadle and Williams [60], Kupiainen et al. [61, 62], Garg et al. [33], Dahl et al. [63, 64], Gustafsson et
243
al. [65, 66], Sakai [67] and Bukowiecki et al. [68]. Sanders et al. [69] used a wind tunnel and track,
244
while Chow et al. [70] used a resuspension chamber to investigate the composition of road dust.
245
iii) Roadside and tunnel measurements
246

11
It is possible to calculate exhaust and non-exhaust emission factors by measuring PM levels near a
247
road or at the inlet and outlet of a tunnel, comparing this to the background levels of PM and
248
apportioning the difference to exhaust and non-exhaust sources by analysing the chemical
249
composition of PM. Examples of tunnel studies are those by Lawrence et al. [53] and Luhana et al.
250
[54]. Roadside measurement studies were done by Bukowiecki et al. [52], Johansson et al. [71],
251
Sjöberg and Ferm [72], Abu-Allaban [50], Thorpe et al. [73], Nicholson [74] and Omstedt et al. [75].
252
iv) Mobile on-board measurement
253
Mobile on-board measurement is done by attaching sampling devices directly onto a moving vehicle
254
or in a trailer behind a moving vehicle. This type of study was performed by Fitz and Bufalino [76],
255
Bukowiecki et al. [68] and Mathissen et al. [77] and to determine resuspension emission factors.
256
Many of these studies find very different results, depending on the method of measurement,
257
location and types of vehicles tested. Therefore, emission inventories from the EEA [34], U.S. EPA
258
[35] Dutch PRTR [37, 78] and UK NAEI [58] analyse these studies to come up with the most
259
representative emission factors for tyre wear, brake wear and road wear. Resuspension is currently
260
only included in the UK emission inventory.
261
If we take the average results of these emission inventories, we obtain PM10 emission factors of 6.1
262
mg/vkm, 9.3 mg/vkm, 7.5 mg/vkm and 40 mg/vkm for tyre wear, brake wear, road surface wear and
263
resuspension of road dust, respectively. PM2.5 emissions are 2.9 mg/vkm, 2.2 mg/vkm, 3.1 mg/vkm
264
and 12 mg/vkm for tyre wear, brake wear, road wear and resuspension, respectively. See table 4.
265
These results are in line with those found by the literature review of Grigoratos and Martini [79].
266
Table 4 Emission inventories on average tyre wear, brake wear, road wear and resuspension for passenger cars
267
Reference
Emission Source
PM10 (mg/vkm)
PM2.5 (mg/vkm)
EEA [34]
Tyres
6.4
4.5
Brakes
7.4
2.9
Road
7.5
4.1
US EPA [35]
Tyres
6.1
0.9
Brakes
18.5
2.3
Dutch PRTR [37]
Tyres
5
1
Brakes
4.3
0.6
Dutch PRTR [78]
Road
7
1.1
UK NAEI [58]
Tyres
7
5

12
268
4. Comparison EV and ICEV emissions
269
By using the data from Simons [30] on the effect of weight on emissions and the average exhaust
270
and non-exhaust emission from the various emission inventories, we can compare the total PM
271
emissions from EVs with those from gasoline and diesel cars. When we do this, we find that EVs
272
emit the same amount of PM10 as modern gasoline and diesel cars. See Table 5 for the comparisons.
273
Table 5 Comparison between expected PM10 emissions of EVs, gasoline and diesel ICEVs
274
275
When we compare PM2.5 emissions, we can see that EVs bring about a negligible reduction in
276
emissions. Compared to an average gasoline ICEV, the EV emits 3% less PM2.5. Compared to an average
277
diesel ICEV, the EV emits 1% less PM2.5. See table 6 for the comparisons.
278
Table 6 Comparison between expected PM2.5 emissions of EVs, gasoline and diesel ICEVs
279
280
From these calculations, it is clear that EVs are not significantly less polluting than modern ICEVs in
281
terms of PM. We can also see that non-exhaust emissions currently account for more than 90% of
282
Brakes
7
3
Road
8
4
Resuspension
40
12
Average
Tyres
6.1
2.9
Brakes
9.3
2.2
Road
7.5
3.1
Resuspension
40
12
Vehicle
Technology
Exhaust
Tyre wear
Brake wear
Road wear
Resuspension
Total
EV
0 mg/vkm
7.2 mg/vkm
0 mg/vkm
8.9 mg/vkm
49.6 mg/vkm
65.7 mg/vkm
Gasoline ICEV
3.1 mg/vkm
6.1 mg/vkm
9.3 mg/vkm
7.5 mg/vkm
40 mg/vkm
66.0 mg/vkm
Diesel ICEV
2.4 mg/vkm
6.1 mg/vkm
9.3 mg/vkm
7.5 mg/vkm
40 mg/vkm
65.3 mg/vkm
Vehicle
Technology
Exhaust
Tyre wear
Brake wear
Road wear
Resuspension
Total
EV
0 mg/vkm
3.7 mg/vkm
0 mg/vkm
3.8 mg/vkm
14.9 mg/vkm
22.4 mg/vkm
Gasoline ICEV
3.0 mg/vkm
2.9 mg/vkm
2.2 mg/vkm
3.1 mg/vkm
12.0 mg/km
23.2 mg/vkm
Diesel ICEV
2.4 mg/vkm
2.9 mg/vkm
2.2 mg/vkm
3.1 mg/vkm
12.0 mg/vkm
22.6mg/vkm

13
PM10 and 85% of PM2.5 emissions from traffic. These proportions are likely to keep increasing in the
283
future as increasingly strict emission limits result in higher exhaust standards [49].
284
Several studies have reached the same conclusion on the importance of non-exhaust emissions. Rexeis
285
and Hausberger [80] predicted that the percentage of non-exhaust PM of the total PM emissions will
286
increase from 50% in 2000 up to 80-90% by 2020. Jörß and Handke [81] modelled non-exhaust
287
emissions of PM2.5 in Germany and found that non-exhaust sources accounted for 25% of traffic PM2.5
288
emissions in 2000 and are expected to contribute 70% of traffic PM2.5 by 2020. This conclusion was
289
also reached by Denier van der Gon et al. [82], who predicted non-exhaust will likely be the dominant
290
source of total PM emissions from traffic by 2020.
291
Worryingly, over the last decade, we have seen a steady increase in vehicle weight in almost all
292
segments [48]. See Figure 2. This trend is expected to apply to EVs as well, as demand for longer
293
range EVs increases. In order to achieve a longer range, EVs need larger batteries and require more
294
structural weight to accommodate these batteries [83].
295
Figure 2 Mass in running order by vehicle segment 2001-2014, adapted from [48]
296
297
Therefore, non-exhaust emissions from EVs and ICEVs are likely to keep increasing in the future.
298
Strategies designed to reduce PM pollution by restricting vehicle exhaust emissions alone will no
299
longer be very effective [3]. There is a need for new policies and measures that specifically target
300
non-exhaust PM emissions [84].
301

14
5. Implications for policy
302
There are several options for future policy that have potential to reduce non-exhaust emissions. A
303
good start would be to create maximum limits for non-exhaust emissions that all new vehicles (ICEVs
304
and EVs) need to comply with. However, measurements of non-exhaust emissions so far have
305
produced divergent results, depending on the measurement method used. So in order to introduce
306
non-exhaust limits, a standardised measurement method would need to be introduced.
307
Further improvements can be made by encouraging innovation on reducing vehicle weight. This is
308
currently being done by the European Green vehicle Initiative [85] to improve the range of EVs, but
309
should also be applied to conventional passenger cars. EV technology such as lightweight body
310
design, improved tyre design and regenerative brakes could all be applied to ICEVs to further
311
decrease their non-exhaust emissions.
312
Finally, we recommend that governments create incentives for consumers and car manufacturers to
313
switch to more lightweight passenger cars, in order to reverse the trend of increasing vehicle weight
314
in all market segments.
315
6. Conclusions
316
Air quality in numerous places in Europe does not reach EU standards. As a result, many people
317
experience adverse health effects due to very high concentrations of PM. Traffic is one of the major
318
sources of ambient PM, especially in urban areas. The EV has been proposed as a solution to air
319
pollution. Therefore, many countries are incentivising alternative fuel vehicles such as EVs.
320
Vehicle weight was expected to play a role in emission factors, since each of the non-exhaust
321
emission sources is affected by weight. Several studies provided evidence that there is indeed a
322
positive correlation between weight and non-exhaust emissions. However, more research is needed
323
into the exact impact additional weight has on emission factors. EVs were found to be 24% heavier
324
than equivalent non-electric models. Based on the available data, we calculated that EVs produce
325
the same amount of PM10 as average conventional vehicles. EVs have slightly lower PM2.5 emissions,
326
emitting 1-3% less than ICEVs, on average. However, these differences are likely to disappear
327
completely as exhaust emission standards become even stricter.
328
Therefore, EVs are not likely to have a large impact on PM emissions from traffic. Non-exhaust
329
sources account for more than 90% of PM10 and 85% of PM2.5 emissions from passenger cars, and
330
this proportion is likely to increase in the future as vehicles become heavier. Policy so far has only
331
focused on reducing PM from exhaust emissions. Therefore, future European legislation should set
332

15
non-exhaust emission standards for all vehicles and introduce standardised measurement methods.
333
In addition, it is recommended that EV technology such as lightweight car bodies and regenerative
334
brakes be applied to ICEVs, and incentives provided for consumers and car manufacturers to switch
335
to less heavy vehicles.
336
337

16
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