Introduction
Particulate matter (PM) and nitrogen dioxide (NO2) are key species for
urban air quality in Europe. Whereas the exceedance of PM limiting values has
attracted considerable public attention during the last decade, NO2 is a
topical problem, which became prominent through the introduction of new European
limiting values in January 2010.
The reduction of nitrogen oxide (NOx= nitrogen monoxide
(NO) + NO2) emissions has historically been one of the key
objectives for improving air quality in Europe. NOx emissions have
started to decrease considerably since the mid 1980s
in many European areas. However, emissions from mobile sources are still
important contributors to air pollution, in particular NOx. Together
with NOx, non-methane volatile organic compounds (NMVOCs) undergo
photochemical reactions that produce secondary pollutants such as ozone
(O3), peroxyacetyl nitrate (PAN) and others (Chameides et al., 1997;
Atkinson, 2000).
According to the European Commission's White Paper (2011), 30 % of road
freight transported over more than 300 km distance should shift to other
transport modes such as waterborne or rail transport by 2030, and more than
50 % by 2050 (European Commission, 2011). Accordingly, such a shift will
result in an increase of emissions from inland water transportation in the
next years.
In Germany today, the contribution of inland navigation to the total freight
traffic is about 12 % (BDA, 2015a). In the Rhine corridor the
contribution is 16–18 % (BDA, 2015b). With respect to the
goods categories “coal, crude oil and petroleum gas”; “ores, industrial
rocks and minerals, and other mining products” and “coking plant and petroleum
products”, inland water navigation is the most important transportation mode.
In comparison to road transport, inland navigation has a contribution of
72 % for these goods categories and 52 % for container transport.
Inland water navigation is a competitive alternative to road and rail
transport because the energy consumption per km and ton of transported
goods is only approximately 17 % of road and 50 % of rail transport
(ECT, 2015). As a consequence of the lower energy consumption, inland water
transportation emits significantly less CO2 and, therefore, has a direct
impact on climate change.
In the European Union the emission of NOx, VOC, PM and CO from road and
rail transport decreased from 1990 to 2000, whereas emissions from inland
navigation remained more or less constant and emissions from sea transport
increased slightly (Trends, 2003). However, in the Netherlands a slight
reduction in inland shipping emissions was observed in the same time period
when modern engines were introduced into the fleet (CTRC, 2003).
It has also been conclusively demonstrated that the fuel has an important
impact on the emissions. Using liquid natural gas (LNG) as fuel for inland
water vessels leads to substantial emission reductions, i.e. 75 % for
NOx, 97 % for PM and 10 % for CO2 (Van der Werf, 2013).
The emissions from inland water transportation are regulated by several
national and international guidelines. In 2005 the German national guideline
“Binnenschiffabgasverordnung, BinSchAbgasV” was implemented for national
waterways, which defines engine-dependent emission indices, i.e. emitted mass of
pollutant per kg burnt fuel, for NOx and PM of EINOx:
30–42 and EIPM: 1.2–2.4 g kg-1 respectively
(BinSchAbgasV, 2005). In 2011 an international guideline for the Rhine river,
“RhineSchUO”, was implemented with engine-dependent EINOx:
28–36 g kg-1 and an EIPM: 0.9–3.1 g kg-1
(RheinSchUO, 2011). In addition, for river–sea ships the MARPOL guideline
(International Convention for the Prevention of Pollution from Ships) (IMO,
2012) has to be applied. For example, for marine diesel engine with a
medium speed of 720 min-1, NOx-emission indices of 58 g kg-1
since 2000 (Tier I), 56 g kg-1 since 2011 (Tier II) and
11 g kg-1 since 2016 (Tier III) have been introduced.
The correct determination of emission indices (EI) is prerequisite for
establishing and developing emission inventories (VBD, 2001; Klimont et al.,
2002; Browning and Bailey, 2006; Rohacs and Simongati, 2007; TNO, 2008; CBS,
2009; UBA, 2013). Up to now, several studies have been published in which NO,
NO2, SO2 and PM emissions from sea ships (Sinha et al., 2003; Chen
et al., 2005; Eyring et al., 2005; Petzold et al., 2008; Moldanova et al.,
2009; Murphy et al., 2009; Schrooten et al., 2009; Williams et al., 2009;
Eyring et al., 2010; Beecken et al., 2014; Jonsson et al., 2011; Lack et al.,
2011; Alfödy et al., 2013) and, in particular, from sea ferries (Cooper
et al., 1996, 1999; Copper, 2001, 2003; Copper and Ekström, 2005;
Tzannatos, 2010; Pirjola et al., 2014) were investigated. Motor test-bed
studies can also be used for the determination of EIs from single ship
engines (Petzold et al., 2008). However, up to now only a few studies have reported on
inland water transportation emissions (Trozzi and Vaccaro, 1998; Kesgin and
Vardar, 2001; Schweighofer and Blaauw, 2009; Van der Gon and Hulskotte, 2010)
In the present study, inland water transport emissions were investigated
under real world conditions along the riverside of the river Rhine in
Germany,
during a field campaign from 20 to 22 February 2013.
Description of the experimental procedures
Measurement site
The measurement campaign was carried out at the river Rhine in Germany, close
to the “Wunderland Kalkar” at Rhine kilometre 843. Figure 1 shows a map of
the measurement site. During the campaign emissions from both upstream and
downstream cruising inland ships were studied. The sampling point was located
50 m downwind from the river bank.
Location of the measurement site at Rhine kilometre 843. (This map
is made available under the Open Database License:
http://opendatacommons.org/licenses/odbl/1.0/. Any rights in individual
contents of the database are licensed under the Database Contents License:
http://opendatacommons.org/licenses/dbcl/1.0/; see more at:
http://opendatacommons.org/licenses/odbl/#sthash.hMw4LgYT.dpuf).
Temporal variation of the NO, NO2, O3 and CO2
concentration at the measurement site on 20 February 2013 from 11:30 to
14:00 LT from different ship types (G = goods ship, T = petroleum
tanker, PT = push–tow) and at different operation parameters
(L = loaded, U = unloaded, A = upstream and D = downstream).
Plot of Ox vs. NOx.
It is reasonable to assume that the engines of the ships passing the sampling
site were under warm operation conditions.
Analytical equipment
The analytical equipment used was installed in a mobile van with an external
power supply. NO and NO2 were measured online with a commercial
NOx chemiluminescence analyser (Environnemental, AC 31M with molybdenum
converter). The time resolution was 10 s and the detection limit, which was
calculated from the variation of the zero signal, was 2 ppbv for NO and
3 ppbv for NO2. The NO channel of instrument was directly calibrated by
diluted standard NO calibration mixtures (Messer, stated accuracy 5 %).
The NO2 channel was calibrated by using a NO titration unit
(Environnemental, GPT). NO2 was produced by the reaction of NO with
O3 in a flow reactor leading to the quantitative conversion of the
calibrated NO (ΔNO =ΔNO2).
Temporal variation of CO2, PM10 and PM1 at the
measurement site on 20 February 2013 from 11:50 to 12:10 LT for different
ship types (G = goods ship, T = petroleum tanker) and different
operation parameters (L = loaded, U = unloaded, A = upstream and
D = downstream).
Temporal variation of the NO, NO2, CO2 and PM1
concentration and the integrated emission peaks at ΔNO, ΔNO2, ΔCO2 and ΔPM1 peak area at the
measurement site on 20 February 2013 from 11:50 to 12:10 LT for goods-ship
(G) under-loaded (L) and upstream (A) conditions.
EINOx (as NO2) in g kg-1 burnt fuel of
single-motor ships [goods] and the weighted average value of
EINOx for different operation parameters, L = loaded,
U = unloaded, A = upstream and D = downstream. Red bars show
outliers (4σ limit) and were not taken into account in the
calculation of the weighted average value.
Lower limit EIPM1 in g kg-1 burnt fuel of single-motor ships [goods] and the weighted average EIPM1 for
different operation parameters, L = loaded, U = unloaded,
A = upstream and D = downstream.
Weighted average emission index for NOx (EINOx)
in g kg-1 burnt fuel for different motor ship types (G = goods,
T = tanker and PT = push–tow) at different operation parameters
(L = loaded, U = unloaded, A = upstream and D = downstream),
in comparison with German guidelines (BinSchAbgasV, 2005 (yellow) and
RheinSchUO, 2011 (green)).
Ozone (O3) was measured online with a commercial O3 monitor
(Environnemental, O3 41M with UV absorption). The time resolution was 10 s
and the detection limit, which was calculated from the variation of zero
measurements, was 1 ppbv. O3 was calibrated by using an O3
calibration unit (Environnemental; K-O3, accuracy 10 %). O3 was
produced by the photolysis of synthetic air in a flow reactor, leading to the
quantitative formation of O3.
Carbon dioxide (CO2) was measured online with a commercial CO2
monitor (LICOR 7100 with IR absorption). The time resolution was 1 s and the
detection limit, which was calculated from the variation of zero
measurements, was 0.5 ppmv. CO2 was directly calibrated by diluted
standard CO2 calibration mixtures (Messer, stated accuracy 2 %).
PM was measured by an optical particle counter (OPC) (Grimm Aerosol Technik
GmbH & Co. KG, Dust Monitor EDM 107). The OPC counts particles in a size
range from 0.25 to 32 µm in 31 size channels. The time resolution
was 6 s and the detection limit was 0.1 µg m-3. However, the
instrument only provided the concentrations of the fractions PM1,
PM2.5 and PM10.
Meteorological parameters, such as temperature, pressure, relative humidity
and wind speed were also measured. In addition to the measurement of
compounds in the ambient air, the number and types of ships passing the
measurement site were counted.
Samples were taken at a height of about 3 m above the stream gauge of the
river Rhine.
Results and discussion
Inland water transportation emissions
NO, NO2, O3, CO2, PM1 and PM10 concentrations, wind
speed and wind direction at the measurement site as well as movements of the
ships were measured. During the campaign more than 170 emission peaks from
motor ships were observed. From these peaks almost 140 could be attributed to
single ship types (G = goods ship, T = petroleum tanker,
PT = push–tow) and were analysed accordingly. Figure 2 shows as an
example the temporal variation of NO, NO2, O3 and CO2 mixing
ratios at the measurement site on 20 February 2013 from 11:30 to 14:00 LT.
The perfect correlation between NO and NO2 with CO2 confirms that
these compounds were emitted from the same source, i.e. the engine exhaust.
The anticorrelation between NO2
and O3 provides information about NOx chemistry in the ship exhaust
plumes, i.e. the formation of NO2 by the titration reaction of NO with
O3.
NO2 / NOx emission ratio
The NO2 / NOx ratio in the exhaust plume is an important parameter in obtaining information about the ship engine types and
estimating the impact of ship emissions on ozone formation.
It is well known that diesel engines without aftertreatment systems show
NO2 / NOx ratios of 0.10–0.12 for road traffic (Kurtenbach et
al., 2001; Kousoulidou et al., 2008; Carslaw and Rhys-Tyler, 2013) and
0.14 ± 0.04 for navigation (Cooper, 2001; Grice et al., 2009). In
contrast, the NO2 / NOx ratio from road traffic diesel engines
with aftertreatment systems, such as oxidation catalyst or PM filter systems,
are in the range of 0.25–0.30. The NO2 / NOx emission ratio
from navigation diesel engines with selective catalytic NOx reduction
systems (SCR) is 0.009 ± 0.003 (Cooper, 2001).
To obtain the correct NO2 / NOx emission ratio from the
measurements it is important to distinguish between primarily emitted
NO2 and NO2, which is formed by the reaction of NO with ozone in
the exhaust plume. The correct NO2 / NOx ratio is obtained by
plotting Ox, which is the sum of NO2 and O3 vs. the measured
NOx concentration as shown in Fig. 3 (Clapp and Jenkin, 2001). The
NO2 / NOx emission ratio and the local O3 background
mixing ratio are obtained from the slope and intercept of the regression line
respectively. From the data shown in Fig. 3 a NO2 / NOx
emission ratio of 0.08 ± 0.02 and a local ozone background volume
mixing ratio of 23 ± 2 ppbv were obtained. The obtained
NO2 / NOx ratio indicates that the ships passing the
measurement site were equipped with conventional diesel engines without
exhaust gas aftertreatment.
PM1 and PM10 emissions
Figure 4 shows the temporal variation of CO2, PM10 and PM1
concentrations at the measurement site on 20 February 2013 from 11:50 to
12:10 LT. Some PM1 peaks are well correlated with those of CO2
mixing ratios and therefore with ship plumes. In contrast, some PM10
peaks showed no correlation with ship emissions. This indicates that the main
PM emissions from ships with diesel engines are in the PM1 range. This
result is in good agreement with other studies e.g. from the United States
EPA (1996), Petzold et al. (2008), Beecken et al. (2014), Pirjola et
al. (2014) and Westerlund et al. (2015). Therefore, in the present study
particle ship emissions are defined as PM1. According to Westerlund et
al. (2015) the maximum in the particle number size distribution was observed
at about 10 nm and the maximum particle mass distribution at 250 nm.
Therefore, the optical particle counter (OPC) used detects only a lower limit
of the emitted particle mass.
Emission indices
From the measurement data, emission indices (EIs) for NOx (NO calculated
as NO2) and PM1 (unit: mass per kg burnt fuel) were calculated. In
Fig. 5 the integrated emission peak (peak area) for NO, NO2, CO2
and PM1 as ΔNO, ΔNO2, ΔCO2 and ΔPM1 are shown as an example for a single-motor ship. If one assumes
that the increase of NO, NO2, PM1 and CO2 in the plume is
proportional to the emission strength of the ship engine, an emission ratio
to CO2, e.g. ΔNOx / ΔCO2, can be easily
calculated (Petzold et al., 2008). In addition, the ΔNO, ΔNO2, ΔCO2 and ΔPM1 were also calculated using
the difference between background and plume mixing ratios (Schlager et al.,
2008) and considering the precision errors of the background data, which are
typically ±2, ±4, ±2 ppbv, ±1 ppmv and
±2 µg m-3 for NO, NO2, O3, CO2 and
PM1 respectively.
Weighted average lower limit emission index for PM1
(EIPM1) in g kg-1 burnt fuel for different motor ship
types (G = goods, T = tanker and PT = push–tow) at different
operation parameters (L = loaded, U = unloaded, A = upstream and
D = downstream), in comparison with German guidelines (BinSchAbgasV, 2005
(yellow) and RheinSchUO, 2011 (green)).
Both approaches were used to calculate the emission indices and were in good
agreement, in general better than ± 6 %. Caused by the slightly
different time responses of the instruments, the integrated peaks
results were finally specified. Elementary analysis of a typical ship diesel fuel
yielded: 86 wt % carbon and 14 wt % hydrogen (Cooper, 2001). From
the wt % carbon and under the assumption that all fuel is burnt to the
final end product, CO2, an emission index EI (CO2) of 3150 g
CO2 per kg burnt fuel was calculated and further used to calculate the
corresponding emission index (EI) for the ship engines. The emission index
(EI) is calculated by the following equation (1) (Petzold et al., 2008):
EI(X)=EI(CO2)×M(X)M(CO2)×Δ(X)Δ(CO2),
where M denotes the molecular weight and Δ the peak area, mixing
ratios, column densities, etc. of the species. The subsequent calculations
used M (CO2) with 44 g mol-1, M (NOx) with
46 g mol-1 and NOx as NO2. Table S1 of the Supplement
summarizes the calculated EIs of the different ship types and operation
conditions. Errors were calculated using error propagation for the different
measured compounds.
As an example, Fig. 6 shows the emission index for NOx (as NO2)
(EINOx) of single-motor ships [goods] and the weighted average
EINOx for different operation parameters, i.e. L = loaded,
U = unloaded, A = upstream and D = downstream.
Emission indices NOx and PM1 in g kg-1 burnt fuel
calculated from the measured values in comparison with different literature
data from inland water transportation.
Reference
Location
Sampling
EINOx
EIPM1
Ship types
period
(g kg-1)
(g kg-1)
(a) field measurements (inland, engine without exhaust gas aftertreatment system)
This study
Germany, Rhine (inland)
2013
54 ± 4
≥2.0±0.3
different
Kesgin and Vardar (2001)
Turkey, Bosporus (inland)
1998
57
1.2
domestic passenger ships (a)
Trozzi and Vaccaro (1998)
Italy, Tyrrhenian Sea (inland)
1998
51
1.2
domestic passenger ships (a)
Van der Gon and Hulskotte (2010)
Netherlands (inland)
2010
45
1.9
different
Schweighofer and Blaauw (2009)
inland
2009
39
0.73
research vessel (b)
(b) field measurements (inland, engine with exhaust gas aftertreatment system)
BMVBS (2012)
inland
2011
n.d.
0.08–0.48
research vessel
Futura Carrier (2010)
inland
2009
n.d.
0.29 ± 0.01
research vessel
Schweighofer and Blaauw (2009)
inland
2009
11–39
0.02
research vessel (c)
(c) inventories
Rohacs and Simongati (2007)
Average EU (inland)
2007
47
3.2
inventory
Van der Gon and Hulskotte (2010), CBS (2009)
Netherlands (inland)
2008–2009
46
1.9
inventory
Klimont et al. (2002)
RAINS, EU (inland)
2002
51
4.0
inventory
UBA (2013)
TREMOD, Germany (Inland)
2013
49 ± 6
1.5 ± 0.2
inventory
Remarks: n.d. is no data, (a) domestic passenger ships with diesel
engine (medium speed), (b) without exhaust gas aftertreatment system, (c)
with exhaust gas aftertreatment system.
As an example, Fig. 7 shows the obtained lower limit PM1 emission index
(EIPM1) for single-motor ships [goods] and the weighted
average EIPM1 for different operation parameters, i.e.
L = loaded, U = unloaded, A = upstream and D = downstream.
Red bars show outliers (4σ limit) and were not taken into account in
the calculation of the weighted average value. Values are lower limits because
of the detection range of the OPC system.
Although Figs. 6 and 7 show a large variation in the EIs for NOx and
PM1, the average data exhibit that the EINOx are almost
independent of engine operation parameters within the given error limits. The
same was found for tankers and push–tows; see weighted average emission
index in Figs. 8 and 9.
Figure 8 exhibits that the NOx emission indices of all motor ship types
investigated are above the engine rotation speed-dependent limit values of
the German guidelines, which are 29–37 g kg-1 for the RheinSchUO and
36–46 g kg-1 for the BinSchAbgasV guidelines.
Figure 9 exhibits that the obtained lower limit PM1 emissions values for
almost all motor ship types are just within the limit values of the German
guide lines, which are 0.9–3.1 g kg-1 for the RheinSchUO and
1.2–2.4 g kg-1 for the BinSchAbgasV guidelines, depending on the
engine rotation speed.
For comparison with literature data, uncertainty(2σ)-weighted
averaged EINOx and EIPM1 were calculated for
all motor ship types and operation condition investigated. An
EINOx of 52 ± 3 g kg-1 and a lower limit
EIPM1 of ≥ 1.9 ± 0.3 g kg-1 were obtained.
Minimum and maximum EIs for NOx and PM1 were found to be in the
range of 20–161 and ≥ 0.2–8.1 g kg-1
respectively. Table 1 shows the emission indices for NOx and PM1 in
g kg-1 fuel calculated from the measured values in comparison with
different literature data. Errors were calculated using error propagation for
the different measured compounds.
Between 1998 and 2013 only a few studies reported EINOx and
EIPM1 from inland water navigation (Trozzi and Vaccaro, 1998;
Kesgin and Vardar, 2001; Schweighofer and Blaauw, 2009; Van der Gon and
Hulskotte, 2010) in the range 39–57 and 0.7–1.9 g kg-1
respectively; see Table 1. The uncertainty(2σ)-weighted averaged
EINOx and EIPM1 were 48 ± 4 and 1.3 ± 0.2 g kg-1 respectively, which are in good
agreement with the present study.
Emission indices for NOx and PM1 from inland water navigation were
used in emission inventories by Klimont et al. (2002), Rohacs and
Simongati (2007), Van der Gon and Hulskotte (2010), CBS (2009) and
UBA (2013). The authors reported EINOx and
EIPM1 in the range 46–51 and 1.5–4.0 g kg-1
respectively (see Table 1). From these data uncertainty(2σ)-weighted
average values for EINOx of 48 ± 2 and
EIPM1 2.7 ± 1.2 g kg-1 were derived, which are in
a good agreement with the present study.
In order to comply with the limit values of the current RheinSchUO guideline
for inland water navigation for NOx with 29–37 g kg-1, a further
significant reduction of NOx emission is necessary. This can be achieved
by using exhaust gas aftertreatment
systems, whose functional capability have been demonstrated in recent studies
(Cooper, 2001; Schweighofer and Blaauw, 2009; BMVBS, 2012; Future Carrier,
2012; Hallquist et al., 2013; Pirjola et al., 2014). For example, the
European project “Cleanest Ship” (Schweighofer and Blaauw, 2009) shows that
NOx and PM emissions of a ship diesel engine equipped with an SCR
(selective catalytic reduction) system and particle filter can be reduced to
4 and 0.02 g kg-1 respectively.