Atmospheric deposition of long-range transport of anthropogenic reactive
nitrogen (Nr, mainly comprised of NHx, NOy and
water-soluble organic nitrogen, WSON) from continents may have profound
impact on marine biogeochemistry. In addition,
surface ocean dissolved organic nitrogen (DON) may also contribute to aerosol
WSON in the overlying atmosphere. Despite the importance of off-continent
dispersion and Nr interactions at the atmosphere–ocean boundary,
our knowledge of the sources of various nitrogen species in the atmosphere
over the open ocean remains limited due to insufficient observations. We
conducted two cruises in the spring of 2014 and 2015 from the coast of China
through the East China seas (ECSs, i.e. the Yellow Sea and East China Sea) to
the open ocean (i.e. the Northwest Pacific Ocean, NWPO). Concentrations of water-soluble total
nitrogen (WSTN), NO3- and NH4+, as well as the δ15N
of WSTN and NO3- in marine aerosol, were measured during both
cruises. In the spring of 2015, we also analysed the concentrations and
δ15N of NO3- and the DON of surface seawater (SSW; at a
depth of 5 m) along the cruise track. Aerosol NO3-, NH4+ and
WSON decreased logarithmically (1–2 orders of magnitude) with distance from
the shore, reflecting strong anthropogenic emission sources of NO3-,
NH4+ and WSON in China. Average aerosol NO3- and NH4+
concentrations were significantly higher in 2014 (even in the remote NWOP)
than in 2015 due to the stronger wind field in 2014, underscoring the role of
the Asian winter monsoon in the seaward transport of anthropogenic
NO3- and NH4+. However, the background aerosol WSON over the
NWPO in 2015 (13.3 ± 8.5 nmol m-3) was similar to that in 2014
(12.2 ± 6.3 nmol m-3), suggesting an additional
non-anthropogenic WSON source in the open ocean. Obviously, marine DON
emissions should be considered in model and field assessments of net
atmospheric WSON deposition in the open ocean. This study contributes
information on parallel isotopic marine DON composition and aerosol
Nr datasets, but more research is required to explore complex
Nr sources and deposition processes in order to advance our
understanding of anthropogenic influences on the marine nitrogen cycle and
nitrogen exchange at land–ocean and atmosphere–ocean interfaces.
Introduction
Atmospheric transport and deposition of anthropogenic reactive nitrogen (Nr)
to global oceans have increased considerably since the industrial revolution
(Duce et al., 2008). Due to accumulated atmospheric Nr deposition, the
stoichiometric relationship between nitrogen and phosphorus in the upper
North Pacific Ocean (where nitrogen is the limiting nutrient in surface
ocean) has been significantly altered (Kim et al., 2011). Such alterations
may in turn impact pristine oceanic ecosystems and biogeochemical cycles.
The Nr species deposited in the ocean include inorganic reduced nitrogen
species (NH3 and
NH4+),
oxidized nitrogen species (HNO3 and
NO3-) and organic nitrogen compounds
(Erisman et al., 2002). The depositional fluxes (both dry and wet) of
atmospheric Nr to global oceans have been studied previously through models
(Duce et al., 2008; Doney, 2010). Recent model (Kanakidou et al.,
2012) and observational (Altieri et al., 2014, 2016) studies have also
reported that the ocean may be a source of atmospheric water-soluble
organic nitrogen (WSON) and NH3.
Nevertheless, field observations in the open ocean remain scarce; thus, more
observations and new approaches, such as stable nitrogen isotopic
composition studies, are urgently needed to trace the sources of Nr and
investigate Nr exchange at the atmosphere–ocean interface.
Using organic nitrogen compounds, Cape et al. (2011) revealed several
possible sources of WSON in the atmosphere, including livestock and animal
husbandry, fertilizers, vehicle exhausts, biomass burning, secondary pollutants, and marine biological
sources. Cape et al. (2011) also explicitly noted that complex atmospheric
chemical processes may obscure source identification for individual organic
nitrogen compounds in atmospheric WSON. Stochastic analysis coupled with
molecular characterization using Fourier-transform ion cyclotron resonance
mass spectrometry revealed that biological organic nitrogen in surface
seawater can be a source of atmospheric WSON over the open ocean (Wozniak et
al., 2014; Altieri et al., 2016). Similar conclusions have been drawn from
the positive correlation between marine aerosol WSON concentration and wind
speed during a cruise in the Northwest Pacific Ocean (Luo et al., 2016).
The stable nitrogen isotopic composition (δ15N, δ15N(‰)sample= ((15N /14N)sample/ (15N /14N)standard-1)× 1000)
may be used to discriminate the sources of atmospheric NOx and NHx.
This approach (i.e. the use of δ15N-NOx) has successfully
distinguished fossil-fuel-burning NOx from soil biogenic-activity
NOx (Felix and Elliott, 2014), as well as coal combustion emissions
(Felix et al., 2012) from vehicle exhausts (Walters et al., 2015). Similarly,
atmospheric NHx can be measured and traced using δ15N-NHx
(Freyer, 1978; Heaton, 1987; Jickells, 2003; Altieri et al., 2014). However,
direct measurements of atmospheric δ15N-WSON are currently highly
impractical due to difficulties in completely separating organic and
inorganic nitrogen. Via isotope mass conservation, a few previous studies
have reported δ15N-WSON values in precipitation collected from
urban, rural and remote regions ranging from -7.3 to
+7.3 ‰ (Cornell et al., 1995), which is consistent with values
from precipitation sampled in a metropolis surrounded by agricultural areas
in southern South Korea(-7.9 to
+3.8 ‰ , with annual means of +0.3 ‰ and
+0.2 ‰ in 2007 and 2008, respectively; Lee et al., 2012), but
lower than the δ15N-WSON values (-0.5 to +14.7 ‰,
with a median of +5 ‰ and non-significant seasonal variation)
reported in precipitation over the United states East Coast area (Russell et
al., 1998). Compared with those for precipitation, aerosol δ15N-WSON values reported in various rural regions in the United Kingdom
cover a wider range (mainly caused by low values; the range covers -14.6 to
+12.5 ‰, with medians of -2 and -5 ‰ for the fine and
coarse mode, respectively; Kelly et al., 2005) (Fig. S1 in the Supplement).
Using δ15N, it is more difficult to identify the sources of
atmospheric WSON than it is to identify NOx and NHx sources.
However, the relatively uniform δ15N values (+2.2 to
+5.4 ‰) of dissolved organic nitrogen (DON) in surface seawater
worldwide (Knapp et al., 2005, 2011) enable the use of the isotope endmember
mixing approach for primary WSON aerosol; unfortunately, no cruises to date
have undertaken parallel marine aerosol sampling and SSW δ15N
identification.
In terms of the hemispheric wind field, the East Asian monsoon transition
from winter (October to April) to summer (May to September) influences the
entire East Asian region. During the East Asian winter monsoon period, strong
cold air masses mobilize rapidly through north-eastern China to the NWPO; in
contrast, summer monsoon air masses arise primarily from the tropical Pacific
Ocean (Wang et al., 2003). Air masses originating from China in winter have
been reported to contain higher concentrations of NO3- and
NH4+ than air masses arising from remote Pacific Ocean regions in
summer (Kunwar and Kawamura, 2014). Monitoring over the NWPO at Hedo Island
and Ogasawara-shotō island also shows that the dry deposition of aerosol
NO3- and NH4+ varies inter-annually by a factor of 2–5 due
to variable monsoon intensity (http://www.eanet.asia/, last access: 13
April 2018). Moreover, dust storms occur frequently during monsoonal
transition periods, and during
long-range transport in the upper and mid-troposphere through northern China
to the remote Pacific Ocean (Yang et al., 2013); these dust plumes contain
abundant crustal elements in addition to NOx and NHx (Duce et al.,
1980; Kang et al., 2009). In order to evaluate the seaward gradient of
atmospheric Nr concentrations and explore the sources and fates
of atmospheric NO3-, NH4+ and WSON from China (which features
the largest emissions of such species worldwide), we conducted cruises from
China to the NWPO during spring, when the East Asian monsoon transition
period occurs; cruises were complete during two different years to allow
comparison.
In this study, we measured water-soluble total nitrogen (WSTN), NO3-
and NH4+ concentrations, as well as
δ15N-WSTN and δ15N-NO3- in marine aerosols
collected over the ECSs and the NWPO during the spring of 2014 and 2015. The
concentrations and δ15N of DON and
NO3- in SSW (surface seawater,
collected at a depth of 5 m) were analysed in parallel along the cruise
track in 2015. The purposes of this study were (1) to investigate the
spatial distributions of concentrations of various Nr species in marine
aerosol from the ECSs to the NWPO, (2) to explore possible sources of
atmospheric WSON in marine environments and (3) to advance our understanding
of atmospheric Nr transport at the land–ocean boundary and potential
Nr exchanges between the atmosphere and the ocean.
Material and methodsSampling and background weather during cruises
Total suspended particulate (TSP) samples were collected using a high-volume
sampler (TE-5170D; Tisch Environmental, Inc.) with
Whatman®41 cellulose filters during two research
cruises (Fig. 1) aboard the R/V Dongfanghong II. The first cruise (Fig. 1a) spanned from
17 March to 22 April 2014 (44 samples were collected in total; detailed
sampling information can be found in Luo et al., 2016), and the second
cruise (Fig. 1b) lasted from 30 March to 3 May 2015 (38 samples were
collected in total; detailed sampling information, including the date, time
period and location for each sample are listed in Table S1 in the Supplement). To avoid
self-contamination from the research vessel, the TSP sampler was installed
on the top of the tower at the ship head, and aerosols were sampled only
during travel. More information about self-contamination from the ship
exhaust can be found in Luo et al. (2016). Both cruises were undertaken
during the East Asian monsoon transition period. The 2-month average (March
and April) wind streamlines at 1000 hPa over the NWPO show that the wind
speed ranged from 2 to 6 m s-1 in 2014 (Fig. 1a) and from 1 to 3 m s-1 in 2015 (Fig. 1b). In general, the wind was stronger in 2014 than
in 2015 over the open ocean during the sampling periods.
Regional wind streamlines (in m s-1) at 1000 hPa during the
Asian winter monsoon period (a, March and April in 2014 and
b, March and April in 2015) based on an NCEP dataset. Cruise tracks
are also shown (orange, pink and black indicate sea fog, dust and background
aerosol, respectively). The aerosol number and collection range are shown in
orange, pink and black for sea-fog modified, dust and background aerosol,
respectively. The blue open circles in (b) indicate the locations of
surface seawater sample (at a depth of 5 m) during the 2015 cruise. Hereafter, the Bgd. is the abbreviation of background aerosol in all the figures and tables.
Meteorological data, including wind speed, direction, relative humidity (RH)
and ambient temperature, are shown in Fig. S2 for the 2015 cruise (data
for the 2014 cruise are reported in Luo et al., 2016). In the ECSs, both
cruises encountered sea fog, which inevitably influenced aerosol sampling
and aerosol chemistry. Because of the analogous weather conditions
experienced during the two cruises, we used the techniques of Luo et al. (2016) to classify the 2015 marine aerosol samples into three types (namely,
sea-fog-modified aerosol (orange triangles) collected in the ECSs, dust
aerosol (pink circles) and background aerosol (black squares) sampled in
the NWPO; Fig. 1) based on the meteorological conditions (Fig. S2),
concentrations of aluminium (data not shown) and the lidar browse images
from NASA (Fig. S3). Compared with the ECSs, which were strongly influenced
by anthropogenic emissions, the NWPO (open ocean) was relatively clear.
Hereafter, we define “background aerosol” as aerosol collected in the NWPO
without influence from dust and sea fog during the investigation period.
To examine the relationships between the isotopic compositions of WSON in
marine aerosol and DON in SSW, we collected SSW at a depth of 5 m (sampling
locations are shown in Fig. 1b as open blue circles) using Niskin bottles
during the 2015 cruise. The SSW samples were filtered using a 0.22 µm
MILLEX®-GP filter and kept frozen at -20 ∘C in 50 mL
450 ∘C pre-combusted brown glass tubes until analysis.
Chemical analysesNO3- and NH4+ in marine aerosol
The marine aerosol samples were extracted in Milli-Q water (with specific
resistivity of 18.2 MΩ cm-1) following Luo et al. (2016). The
aerosol extracts were analysed using an ion chromatograph (model ICS-1100
for anions and model ICS-900 for cations) equipped with a conductivity
detector (ASRS-ULTRA) and suppressor (ASRS-300 for the ICS-1100 and CSRS-300
for the ICS-900). The precision was better than 5 % for all ionic species.
Details of the analytical processes can be found in Hsu et al. (2014). Only
five of the aerosol samples contained detectable
NO2-, and these accounted for < 1 % of the WSTN. A total of eight filters of the same type as those used
to collect samples were taken as blanks. Before storage, the blank filter
was placed on the filter holder, then the filter holder with the blank
filter was subsequently installed in the TSP sampler on the top of the ship
under the vacuum motor power-off for 5 min, after which the blank filter was
retrieved. All blank filters and aerosol samples were stored at -20 ∘C during the sampling periods and underwent the same extraction
procedures. The data presented here have been corrected for blanks.
NO3- in SSW
The SSW NO3- concentration was measured
using a chemiluminescence method (Braman and Hendrix, 1989). Briefly, the
solution containing NO3- was injected
into a heated solution of acidic Vanadium (III), in which the
NO3- was reduced to nitric oxide (NO)
to be measured by a NOx analyser (MODEL T200U, Teledyne Technologies
Incorporated, USA). Working standards were injected after every 10 samples.
The relative standard deviation for the standard replicate was < 5 %. The concentration of NO2- in the
SSW was below the 0.1 µmol L-1 detection limit throughout the
cruise, as reported previously (Adornato et al., 2005).
WSTN in marine aerosol and total dissolved nitrogen in SSW
Aerosol WSTN and SSW total dissolved nitrogen (TDN, i.e.
NO3-+ NH4++ DON) were measured using the alkaline
potassium persulfate oxidation method to convert WSTN and TDN to NO3-
(Luo et al., 2016; Knapp et al., 2005). The NO3- content of the
digested solution was then measured via chemiluminescent detection (Braman
and Hendrix, 1989). To verify the WSTN and TDN oxidation efficiency,
N-containing organic and inorganic compound standards (specifically, glycine,
urea, ethylene diamine tetraacetic acid and ammonium sulfate) were prepared
in solution at a concentration of 800 µM of
N for oxidation analysis. The recoveries of the
N-containing compound standards under oxidation by alkaline potassium
persulfate were within 95–105 % (n= 6).
Stable nitrogen isotope
The δ15N-NO3- was analysed
using the denitrifier method described by Sigman et al. (2001) and Casciotti
et al. (2002), which has been widely used to analyse the δ15N
in NO3- in aerosol, rainwater and seawater (Buffam and McGlathery, 2003; Hastings et al., 2003; Sigman et al., 2005; Altieri et al., 2013; Gobel et al.,
2013), as well as that in
NO3- in solutions digested with
alkaline potassium persulfate (Knapp et al., 2005, 2010, 2011, 2012). Detailed stable nitrogen isotope analysis
procedures can be found in Archana et al. (2016) and Yang et al. (2014).
Briefly, NO3- was reduced to N2O
by the denitrifying bacteria Pseudomonas aureofaciens (ATCC 13985); then, the stable nitrogen
isotope of N2O was analysed using a GasBench II connected to a
continuous flow isotope ratio mass spectrometer (IRMS, Thermo Delta V
Advantage). Two international standards, namely USGS34 and IAEA-N3
(Böhlke et al., 2003), and two NO3-
laboratory working standards were used to verify instrument stability. After
the WSTN and TDN were oxidized to NO3-,
the δ15N-WSTN and δ15N-TDN were analysed using the
same procedures employed for NO3-. The
pooled standard deviations for replicates were ±0.2, ±0.5 and ±0.5 ‰ for δ15N-NO3-, δ15N-WSTN
and δ15N-TDN, respectively.
Data analysis
The concentrations of WSON in marine aerosol, which could not be measured
directly (as mentioned previously), were calculated using the following
equation:
[WSON]=[WSTN]-[NO3-]-[NH4+],
where [WSON], [WSTN], [NO3-] and
[NH4+] are the molar concentrations
(nmol N m-3) of the given water-soluble nitrogen species in marine
aerosol. The calculated WSON was subject to relatively large and variable
uncertainties by error propagation since
[NO3-] and
[NH4+] were generally much higher than
WSON concentrations in most observations. Such error propagation was a
common and unavoidable problem (Mace and Duce, 2002; Cornell et al., 2003;
Cape et al., 2011; Lesworth et al., 2010; Zamora et al., 2011). In previous
studies, data points with high relative uncertainties were excluded
(> 100 %, Lesworth et al., 2010; Zamora et al., 2011) and the
negative values were taken as zero (Mace and Duce, 2002; Cornell et al.,
2003; Violaki et al., 2015). Following previous studies, we excluded both
the negative data and those with high relative uncertainties to reduce the
uncertainty of mean WSON.
Reduced nitrogen (RN, i.e. NH4++
WSON) and the δ15N-RN in the aerosol were calculated via mass
balance:
[RN]=[WSTN]-[NO3-],δ15N-RN=(δ15N-WSTN×[WSTN]-δ15N-NO3-×[NO3-])/[RN],
where [WSTN] and [NO3-] are the molar
concentrations (nmol N m-3) of the given water-soluble nitrogen species
in the marine aerosol. The average propagated standard error for RN was
9 % for both 2014 and 2015, and the propagated error for the calculation of
δ15N-RN was ±0.6 ‰.
Similar to aerosol WSON, the SSW DON concentration and δ15N-DON
were calculated using the following equations:
[DON]=[TDN]-[NO3-],δ15N-DON=(δ15N-TDN×[TDN]-δ15N-NO3-×[NO3-])/[DON],
where [TDN] and [NO3-] are the molar
concentrations (µmol N L-1) of the given species in SSW. The
standard error propagated through the DON calculation was 5.3 %. Since the
average [NH4+] in SSW at the selected
sites during the 2015 cruise (12 sites and 23 samples) was 0.05 µM,
which is much less than DON at µM level,
[NH4+] was neglected in Eqs. (4) and (5). Unfortunately, most of the NO3-
concentrations in the SSW samples were < 0.5 µmol L-1,
which is too low for the measurement of δ15N-NO3-. We attempted to
evaluate the interference from nitrate in the δ15N-DON
calculations. For all the SSW samples on average,
NO3- comprised 5.7 % of the total
NO3- plus DON; the δ15N-NO3- in SSW ranged from
+8.2 to +16.4 ‰ in our measurements, and the bias of
the calculated δ15N-DON varied from +0.5 to
+0.9 ‰ .
The dry deposition nitrogen fluxes were calculated as follows:
F=Ci×Vi,
where Ci is the concentration of a given water-soluble nitrogen species
in the aerosol, and Vi is the given dry deposition velocity of the
given nitrogen species. In addition to particle size, Vi was controlled by
the meteorological conditions (wind speed and relative humidity; Duce et
al., 1991; Hoppel et al., 2002) and underlying surface (smooth or rough;
Piskunov, 2009). The Vi simulated by the model varied from 0.01 to 10 cm s-1
under wind speeds from 5 to 30 m s-1 and particle size from
0.1 to 100 µm (Hoppel et al., 2002). In our observations, wind speed
ranged from 0.1 to 18 m s-1, with relative humidity ranging from 40 to
100 % (for 2014 data, see Luo et al. (2016) and for 2015 data see Fig. S2), which was variable, thus prohibiting an accurate deposition estimate.
Moreover, we did not obtain information about the size distribution.
Previous studies showed that most of the
NO3- is distributed in supermicron size
(ranging from 1 to 10 µm) in marine aerosol, with a small fraction in
submicron size (ranging from 0.1 to 1 µm). However,
NH4+ is mainly distributed in submicron
size and only partly in supermicron size (Nakamura et al., 2005; Baker et
al., 2010; Jung et al., 2013), except in coastal areas with mixed pollution
and marine aerosols, where NH4+ was
present in the coarse mode and NO3- in
the fine mode (Yeatman et al., 2001). In our case, the weather conditions,
such as fog and dust, further affected the size distribution of aerosol Nr (Mori et al., 2003; Yao and Zhang, 2012; Hsu et al., 2014). Therefore, in
this study, the deposition velocities of water-soluble nitrogen species were
set to 2 cm s-1 for NO3-, 0.1 cm s-1 for NH4+ and 1.0 cm s-1
for WSON, which have also been widely used to estimate the marine aerosol Nr dry deposition (Nakamura et al., 2005; Jung et al., 2013; Luo et al., 2016).
However, bearing in mind, that any use of fixed deposition velocities to
calculate the depositional flux of aerosol Nr may cause under- or
over-estimation.
Concentrations of aerosol WSTN (a, b),
NH4+ (c, d),
NO3- (e, f) and WSON
(g, h) with longitude for the 2014 and 2015 cruises. The orange open
triangles denote sea-fog-modified aerosol in the ECSs, the pink circles
denote dust aerosol, and the black open squares denote background aerosol in
the NWPO. The error bars in (g) and (h) were the uncertainties of WSON
caused by error propagation during the calculation.
Results and discussionSpatial and temporal variations of water-soluble nitrogen species in the
aerosol
Overall, significant logarithmic decreases occurred from the shore seaward
for all water-soluble nitrogen species and WSTN in both 2014 and 2015 (Fig. 2). The seaward gradient was caused primarily by continental emissions
influenced by sea fog (Luo et al., 2016); thus, concentrations were high in
the ECSs (orange triangles in Fig. 2) and low offshore in the NWPO
background aerosol (black squares in Fig. 2). Dust aerosol (pink circles in
Fig. 2) appeared sporadically in the NWPO and generally featured higher
NH4+ and
NO3- (but not WSON) values (Table 1 and Fig. 2).
The measured WSTN concentrations in TSP varied from 21 to 2411 nmol m-3 (Table 1 and Fig. 2a and b), lower than those in PM10 sampled during
spring in Xi'an, China (which ranged from 786 to 3000 nmol m-3; Wang et
al., 2013), but higher than those in TSP sampled in Sapporo, Japan (which
ranged from 20.9 to 108.6 nmol m-3; Pavuluri et al., 2015); Okinawa
Island (which ranged from 5 to 216 nmol m-3; Kunwar and Kawamura,
2014); and the North Pacific (which ranged from 1.4 to 64.3 nmol m-3 in
May–July; Hoque et al., 2015). This wide range of aerosol WSTN content
illustrates the influence of the distance between sampling locations and
emission sources (Matsumoto et al., 2014), seasonality (Kunwar and Kawamura,
2014) and meteorological conditions, such as sea fog (Luo et al., 2016).
Concentration ranges and means for WSTN, NH4+, NO3-,
WSON and RN in aerosols.
The concentrations of marine aerosol WSTN in the ECSs ranged from 444 to
2411 nmol m-3 in 2014 (with a volume-weighted mean of
1136 nmol m-3) and from 92.9 to 1195 nmol m-3 in 2015 (with a
volume-weighted mean of 287 nmol m-3), which were clearly higher than
those in dust aerosol (with volume-weighted means of 242 nmol m-3 in
2014 and 154 nmol m-3 in 2015) and background aerosol (with
volume-weighted means of 85.6 nmol m-3 in 2014 and
42.3 nmol m-3 in 2015) collected in the NWPO (Table 1). The air mass
backward trajectories (see Fig. S5 for 2015 and Luo et al. (2016) for 2014)
reveal that the high aerosol water-soluble nitrogen species in the ECSs arose
from anthropogenic Nr emissions from eastern China (Gu et al., 2012). In
addition, frequent formation of sea fog in the ECSs in spring (Zhang et al.,
2009) may also enrich the amount of water-soluble nitrogen in
sea-fog-modified aerosol via chemical processing (Luo et al., 2016). The much
higher concentrations of water-soluble
nitrogen species in the ECSs marine aerosol (compared to that in the NWPO
aerosol) indicate that continental and/or anthropogenic Nr strongly affected the marine
aerosol. The amounts of
sea-salt ions (such as Na+) in the ECSs aerosols sampled in both 2014
(123 ± 98 nmol m-3; Luo et al., 2016) and 2015
(151 ± 164 nmol m-3; Luo et al., unpublished data) were higher
than those in land aerosol sampled during spring
(23 ± 7.8 nmol m-3 in Beijing; Zhang et al., 2013), which
implies that those aerosols sampled in the ECSs were also significantly
influenced by sea salt. Thus, we define the aerosol collected by ship over
the ECSs as marine aerosol.
Box plots for spring concentrations of aerosol
NH4+(a),
NO3-(b) and WSON (c) in the ECSs (the
orange boxes denote sea-fog-modified aerosol) and NWPO (the pink boxes
denote dust aerosol and the black boxes denote background aerosol), and
summer aerosol (the blue box denotes
NH4+ and
NO3- from Miyazaki et al. (2011) and
Jung et al. (2013) and the WSON from Miyazaki et al., 2011). The large
boxes represented the interquartile range from the 25th to 75th percentile,
the line inside the box indicates the median value, and the whiskers extend
upward to the 90th and downward to the 10th percentiles. Significant differences at the p < 0.05 level between different
years are marked with coloured uppercase letters.
In the NWPO, higher WSTN values were observed in dust aerosol than in
background aerosol in both 2014 and 2015; the dust aerosol WSTN consisted
predominantly of NH4+ and
NO3- rather than WSON (Table 1, pink
circles in Fig. 2), which implies that dust can carry more
NH4+ and
NO3- during long-range transport from
East Asia to the NWPO during the Asian winter monsoon in spring. The air
mass back trajectories of those dust aerosols arose mainly from high-Nr
regions, as evidenced by dust plumes captured by lidar browse images from
NASA (Fig. S3 for 2015 and Luo et al., 2016 for 2014).
Aerosol δ15N-NO3- (a, b) and δ15N-WSTN (c, d) in the ECSs (the orange open triangles denote for
sea-fog-modified aerosol), and in the NWPO (the pink open circles denote
dust aerosol and the black open squares denote background aerosol) with
longitude during the 2014 and 2015 cruise, respectively.
In our observations, the concentrations of
NH4+ and
NO3- were higher in all aerosols in
2014 than they were in 2015 (Fig. 3a and b; Table 1). The difference
between the two years was caused by a stronger Asian winter monsoon in 2014.
Additionally, the cruise in 2014 (17 March to 22 April) occurred during a
period of intensive fossil fuel combustion for heat supply in northern
China; in contrast, the 2015 cruise started on 30 March and finished on 3
May, during a decrease in heating demand. The influence of heating on
aerosol emissions can be seen in the atmospheric aerosol optical depth over
heat-generating areas in China; for example, Xiao et al. (2015) reported
that the aerosol optical depth was 5 times higher during heat generation
periods than during non-generation periods. The consistent variations between
heat supply in northern China and higher
NO3- in marine aerosol sampled in 2014
than 2015 underscore the influence of anthropogenic NOx emissions on
marine aerosol NO3-. Our spring
observations in 2014 and 2015 showed average concentrations of
NH4+ and
NO3- in background aerosol (black boxes
in Fig. 3a and b; Table 1) higher than the average concentrations (3.5 ± 3.3 nmol m-3 for NH4+ and
2.1 ± 1.5 nmol m-3 for NO3-)
reported in the western Pacific Ocean in summer (blue boxes in Fig. 3a and b, data from Miyazaki et al., 2011 and Jung et al., 2013), which suggests
the far-reaching influence of anthropogenic emissions during the monsoon
transition. Moreover, concentrations of
NH4+ and
NO3- were higher in 2014 due to the
stronger Asian winter monsoon, which further supports the idea that the
monsoon exerts an important role in annual and seasonal variations in marine
aerosol Nr via atmospheric long-range transport.
Ranges and means for stable nitrogen isotopes of WSTN,
NO3- and RN in aerosols.
Unlike NH4+ and
NO3-, WSON concentrations in the
background aerosol sampled in the NWPO in 2014 (average = 12.2 ± 6.3 nmol m-3)
were similar to those in 2015 (average = 13.3 ± 8.5 nmol m-3; black boxes in Fig. 3c). In the open ocean, apart from
terrestrial and anthropogenic WSON long-range transport (Mace et al., 2003;
Lesworth et al., 2010), the ocean itself is the most likely source of marine
aerosol WSON. For instance, in situ observations in the subtropical North
Atlantic found that aerosol WSON had strong positive relationships with
surface ocean primary productivity and wind speed (Altieri et al., 2016).
Another study in the South Atlantic Ocean showed that the WSON in marine
aerosol associated with high SSW chlorophyll a was 9 times higher than that
associated with low SSW chlorophyll a (Violaki et al., 2015). In our
observations, the WSON in the background aerosol (black bar in Fig. 3c) was
significantly higher in spring than in summer (blue bar in Fig. 3c), which
is consistent with the higher SSW chlorophyll a concentration over the NWPO
in spring relative to that in summer (Fig. S6). However, the sources of
marine aerosol WSON are a complex mixture composed of primary marine organic
N and secondary N-containing organic aerosol. Biogenic organic material in
SSW can be injected into the atmosphere to form an ice cloud via bubble
bursting at the atmosphere–ocean interface (Wilson et al., 2015); this is
probably the primary WSON aerosol source. Volatile organic compounds emitted
from the surface ocean can react with NOx and NHx in the
atmosphere to form secondary N-containing organic aerosol (Fischer et al.,
2014; Liu et al., 2015).
Scatter plots of δ15N-WSTN against the
NH4+/ WSTN ratio in (a) aerosol sampled
in the ECSs, (b) dust aerosol and (c) background aerosol collected in the
NWPO. Scatter plots of aerosol δ15N-WSTN against the WSON / WSTN
ratio in the (d) ECSs, (e) dust aerosol and (f) background aerosol in the
NWPO. The solid and open symbols indicate aerosol sampled in 2014 and 2015,
respectively.
Isotopic composition of nitrogen species
Aerosol δ15N-NO3- values
over the ECSs and NWPO in 2014 and 2015 ranged from -9.2 to
+10.2 ‰ (Table 2 and Fig. 4a and b). All the observed
δ15N-NO3- values fell
within the ranges previously reported for atmospheric δ15N-NO3- over land (Elliott et
al., 2009; Fang et al., 2011; Felix and Elliott, 2014) and in the marine
boundary layer (Hastings et al.,
2003; Morin et al., 2009; Altieri et al., 2013; Gobel et al., 2013; Savarino et al., 2013). The mass-weighted mean
aerosol δ15N-NO3- values
in 2014 (+1.6 ‰ in the ECSs, -1.1 ‰ for dust aerosol and -2.6 ‰ for background aerosol
sampled in the NWPO) were similar to those in 2015
(+1.9 ‰ in the ECSs, -3.8 ‰ for
dust aerosol and -1.1 ‰ for background aerosol sampled
in the NWPO; Table 2) for all the aerosols, suggesting that the aerosol
NO3- arose from similar origins and
atmospheric chemical pathways in both 2014 and 2015.
The δ15N-WSTN values for all the aerosols ranged from -10.7 to
+5.6 ‰ (Table 2, Fig. 4c and d), which is consistent
with the δ15N-WSTN ranges reported in precipitation, namely
-4.2 to +12.3 ‰ in the Baltic Sea (Rolff et al.,
2008); -8 to +8 ‰ in Bermuda (Knapp et al., 2010);
-4.9 to +3.2 ‰ in a forest in southern China (Koba et
al., 2012); and -12.1 to +2.9 ‰ in Cheju, Korea (Lee
et al., 2012). In contrast, our results were lower than the δ15N-WSTN in TSP sampled in Sapporo, Japan (+12.2 to
+39.1 ‰ ; Pavuluri et al., 2015) and the Sapporo Forest
(+9.0 to +26.0 ‰; Miyazaki et al., 2014). These
authors attributed higher isotopic values to biogenic sources, nitrogenous
aerosol ageing and fossil fuel combustion. However, WSTN is, in fact,
composed of various nitrogen species, and the relative proportions of
NH4+,
NO3- and WSON to WSTN, coupled with
their isotopic compositions (i.e. δ15N-NH4+, δ15N-NO3- and δ15N-WSON), jointly mediate variations in aerosol δ15N-WSTN (where δ15N-WSTN ⋅ [WSTN] =δ15N-NO3-⋅ [NO3-] +δ15N-NH4+⋅ [NH4+] +δ15N-WSON ⋅ [WSON]). Taking our study as an example, the
inconsistent trends in both the positive relationships between δ15N-WSTN and δ15N-NO3- in the ECSs aerosols and
NWPO background aerosols (Fig. S7a and c) and the negative relationship
between δ15N-WSTN and the
NO3- concentration (Fig. S7d and f)
imply that the δ15N of other species
(NH4+ and WSON) in WSTN affected the
δ15N-WSTN.
(a)δ15N-DON (open circles) and δ15N-NO3- (black squares), and (b) concentrations of DON (open circles) and
NO3- (black squares) in SSW with
longitude during the 2015 cruise.
The δ15N-WSTN values in 2014 (-10.7 to
+1.0 ‰) were lower than those in 2015 (-5.6 to
+5.6 ‰; Table 2), whereas the
NH4+/ WSTN ratios were higher in 2014
than in 2015 (Table 1) for all aerosol types. The negative linear
relationships between NH4+/ WSTN and
δ15N-WSTN for all aerosol types (Fig. 5a–c) may be
attributed to higher proportions of
NH4+ in WSTN and negative δ15N-NH4+ values, which originated
from the anthropogenic and marine emissions (Yeatman et
al., 2001; Jickells, 2003; Altieri et al., 2014; Koba et al., 2012; Xiao et al., 2012; Liu et al., 2014). In fact, low δ15N-NH4+ values have been
reported in precipitation in many places, such as Beijing (-33.0 to
+14.0 ‰ with an arithmetic mean of
-10.8 ‰; Liu et al., 2014); Guiyang City in
south-western China (-38.0 to +5.0 ‰ with an average of
-15.9 ‰; Xiao et al., 2012); Gwangju, Korea (-15.9 to
+2.9 ‰ with volume-weighted means of
-6.0 ‰ in 2007 and -6.8 ‰ in 2008;
Lee et al., 2012); and a forest in southern China (-18.0 to
+0.0 ‰ with a concentration-weighted mean of
-7.7 ‰; Koba et al., 2012). Low atmospheric δ15N-NH4+ has also been associated
with marine air masses (e.g. -8 to -5 ‰, Jickells et
al. 2003; -9 ± 8 ‰, Yeatman et al., 2001; and
-4.1 ± 2.6 ‰, Altieri et al., 2014). Together,
this low atmospheric average δ15N-NH4+ (-15.9 to
-4.1 ‰) supports our findings of higher
NH4+/ WSTN and lower δ15N-WSTN in aerosol.
There were positive linear relationships between the WSON / WSTN ratio and
δ15N-WSTN for all the aerosols types (Fig. 5d–f).
This implies that the aerosol δ15N-WSON may be positive. The
WSON in the marine aerosol either originated from terrestrial long-range
transport or the DON from SSW and N-containing secondary organic marine
aerosol as discussed in Sect. 3.1. Terrestrial aerosol δ15N-WSON was reported in a wide range (-15.0 to
+14.7 ‰) with mean values from -3.7 to
+5.0 ‰, and δ15N-WSON in marine aerosol
with more positive δ15N (Fig. S1). In addition, our own
observations for δ15N-DON in SSW showed positive δ15N in the ECSs (varying from +5.1 to +12.9 ‰,
with an average of +7.9 ± 2.3 ‰) and NWPO
(ranging from +1.9 to +11.6 ‰, with an average of
+5.7 ± 2.0 ‰; Fig. 6a). At the same time, DON
concentration in our observations ranged from 4.4 to 11.8 µmol L-1 (Fig. 6b), which is within the DON concentration range reported
in global SSW (Li et al., 2009; Van Engeland et al., 2010; Knapp et al., 2011; Letscher et al., 2013;
Lønborg et al., 2015). This high DON
concentration in SSW may be ejected into the atmosphere during
bubble-bursting (Wilson et al., 2015).
To better clarify the sources of aerosol WSON, we removed the aerosol
NO3- and its δ15N effect
from the WSTN and its δ15N-WSTN, respectively, by mass balance.
The remaining NH4+ and WSON was defined
as reduced nitrogen (RN =NH4++ WSON). The δ15N-RN ranged from -11.8 to
+7.4 ‰ for all aerosol types in both 2014 and 2015
(Table 2), which is consistent with the reported δ15N-RN in
precipitation (-12.6 to +7.8 ‰) collected in Bermuda,
in the Atlantic Ocean (Knapp et al., 2010). The negative relationships
between δ15N-RN and NH4+
concentration (Fig. S8a, S8b and S8c), as well as between δ15N-RN and
the ratios of NH4+/ RN (Fig. S8d–f) for all aerosol types, further support the low values of δ15N-NH4+ in marine aerosol. Three
important endmembers, compiled from atmospheric δ15N-NH4+ (-15.9 to -4.1 ‰, green bars in Fig. 7) and continental δ15N-WSON (-3.7 to +5.0 ‰, grey bars) versus the
δ15N-DON observed in SSW in our cruise (+7.9 ± 2.3 ‰ in the ECSs
and +5.7 ± 2.0 ‰ in the NWPO, red dots with error bars), were added
to Figure 7 to facilitate discussion. Note that nearly all the aerosol
δ15N-RN values in 2014 were lower than those in 2015, which may
be attributed to higher NH4+
concentrations in 2014 than in 2015 (Table 1). Moreover, higher values of
δ15N-RN can be seen with higher WSON / RN ratios for all aerosol
types in Fig. 7. The high values of δ15N in continental WSON
and marine DON in SSW may cause these positive relationships. Thus, although
higher WSON / RN values accompany higher δ15N-RN, we may
still not conclude a significant DON in SSW contribution to aerosol WSON. In
the open ocean, to some extent, background aerosol WSON was more likely
influenced by DON in surface seawater, judging by nitrogen isotopic
information.
Note that some data points collected in 2015 for the open-ocean case in Fig. 7b and c fell outside the mixing field, deviating toward higher δ15N-RN values; these high δ15N-RN values may be
attributable to δ15N fractionation and 15N enrichment in
the WSON during processes such as secondary N-containing organic aerosol
formation by the reaction of NHx or NOx with organic aerosol
(Fischer et al., 2014; Liu et al., 2015), complex atmospheric chemical
reactions (i.e. the photolysis of organic nitrogen into ammonium; Paulot et
al., 2015), the aerosol WSON ageing process and in-cloud scavenging (Altieri et
al., 2016). More studies are needed to explore nitrogen transformation
processes, especially those focusing on secondary N-containing organic
aerosol in the atmosphere from an isotopic perspective.
Scatter plots of aerosol δ15N-RN against the WSON / RN
ratio in the (a) ECSs, (b) dust aerosol in the NWPO and (c) background
aerosol in the NWPO. The green bar indicates the sources of anthropogenic,
terrestrial and oceanic δ15N-NH4+, the grey bar indicates
the sources of terrestrial and anthropogenic δ15N-WSON, and the
red bar indicates the δ15N-DON in SSW.
Dry deposition fluxes of water-soluble nitrogen species.
NH4+ (µmol N m-2 d-1)NO3- (µmol N m-2 d-1)WSON (µmol N m-2 d-1)RangeMeanaMeanbRangeMeanaMeanbRangeMeanaMeanbECSs (sea fog)201419.7–67.238.137.8277–193192695134–44614714620152.2–48.710.99.852.1–4121611515.9–338.998.572.5NWPO (dust)20148.2–14.111.911.9136–25017217014.614.614.620151.8–12.45.05.360.0–21898.81019.5–69.730.229.1NWPO (Bgd.)20141.4–21.14.74.511.0–28744.643.32.7–23.410.59.920150.6–2.61.41.34.9–60.621.923.14.4–34.811.511.6
a Arithmetic mean. b Volume-weighted mean.
Dry deposition of aerosol
NO3--N (a, b),
NH4+-N (c, d) and WSON-N (e, f)
in the ECSs (orange open triangles) and in the NWPO (pink open circles for
dust aerosol and black open squares for background aerosol) along longitude
during the 2014 and 2015 cruise, respectively.
Nr dry deposition and its biogeochemical role
The dry deposition of aerosol NH4+,
NO3- and WSON is summarized in Table 3.
The calculated depositional fluxes of water-soluble nitrogen species in the
ECSs were significantly higher than those in the NWPO (Fig. 8). The averaged
dry depositional fluxes of NH4+ and
NO3- in 2014 were 2 to 5 times higher
than those in 2015 for all aerosol types (Table 3). The dry depositional
fluxes of NH4+ and
NO3- in dust aerosol were clearly
higher than those in background aerosol in the NWPO (Table 3, Fig. 8a–d). Comparisons of these dry fluxes with other similar studies and
estimations of the contribution of atmospheric Nr deposition to primary
production in the NWPO are discussed in Luo et al. (2016), specifically for
2014; here, we focus on the influence of atmospheric Nr deposition on
the nitrogen cycle in the ocean.
The influences of atmospheric Nr deposition on the marine
nitrogen cycle are obvious over long timescales. For example, by analysing
concentrations of NO3- and phosphorus in seawater over the NWPO from
1980 to 2010, Kim et al. (2011) reported that the higher N / P ratio in
the upper ocean (in contrast to the deep ocean) in the NWPO was caused
primarily by the accumulation of atmospheric anthropogenic Nr
deposition. Another recent study found higher atmospheric anthropogenic
Nr deposition to be associated with lower δ15N in
surface sediment over the NWPO (Kim et al., 2017), the authors also posited
that atmospheric anthropogenic Nr deposition can reach as far
down as the deep ocean through biological action and lower the δ15N
in surface sediment. The atmospheric δ15N values for water-soluble
nitrogen species in our observations (Table 2) are lower than the
δ15N-NO3- in deep ocean water (+5.6 ‰;
unpublished data from Kao); thus, it is possible that atmospheric
δ15N-Nr can lower δ15N-NO3- in the
thermocline, as mentioned in previous studies (Knapp et al., 2010; Yang et al., 2014). However, it is hard to quantify the
contribution of atmospheric δ15N-Nr to δ15N-NO3- in the thermocline from the perspective of 15N for
the following reasons: first, there are large spatial and temporal
uncertainties in the dry and wet depositional fluxes of atmospheric
Nr. For example, the dry depositional fluxes of NH4+ and
NO3- (23.1–43.3 µmol N m-2 d-1; Table 3) in our
observations are significantly higher than those in summer
(4.9 µmol N m-2 d-1; Jung et al., 2013). Moreover,
according to a previous study, wet Nr deposition is 2–3 times
higher than dry deposition (Jung et al., 2013), and Nr wet deposition in spring over the NWPO is
unknown. Second, the δ15N of N fixation (-2 to 0 ‰;
summarized by Knapp et al., 2010) is similar to the atmospheric
δ15N-Nr (Table 2), but the fluxes of N fixation in the
global ocean also vary considerably both spatially and temporally (Mulholland
and Bernhardt, 2005; Needoba et al., 2007; Karl et al., 1997). Third,
15N fractionation occurs in the complicated marine nitrogen cycle (Knapp
et al., 2005, 2010, 2011, 2012), which hampers the use of 15N in
estimating the influence of atmospheric deposition Nr on marine
δ15N under our limited current understanding.
Conclusions
Concentrations of water-soluble total nitrogen, nitrate and ammonium, as well as the stable nitrogen
isotopes of δ15N-WSTN and δ15N-NO3-, were measured in marine
aerosols sampled between the ECSs and the NWPO in spring 2014 and 2015.
Dissolved organic nitrogen and δ15N-DON were also analysed
in SSW, collected at a depth of 5 m along the cruise route in the spring of
2015. The highest concentrations of water-soluble nitrogen species were
found in aerosol sampled in the ECSs, which suggests significant influence
from anthropogenic emissions on aerosol Nr. The higher
NO3- and
NH4+ in all aerosol types in 2014
(relative to 2015) may be attributed to the stronger Asian winter monsoon in
2014, as well as the intensity of residential heating in spring in northern
China.
Negative linear relationships were found between the
NH4+/ WSTN ratios and δ15N-WSTN for all aerosol types. In contrast, positive linear
relationships were observed between the WSON / WSTN ratios and δ15N-WSTN. The distinctive nitrogen species compositions and isotopic
compositions suggest that aerosol δ15N-WSTN values were
mediated synergistically by NO3-,
NH4+ and WSON in our observations.
Meanwhile, our isotope mixing model indicates that DON in SSW is likely to
be a source of primary WSON in aerosol, especially over the open ocean. Many
uncertainties remain concerning Nr in the marine boundary layer and SSW, let
alone Nr exchange at the atmosphere–ocean interface; further study of Nr exchange between the lower atmosphere and upper ocean is needed in the
future.
Data availability
The underlying data for this study have
been reposited at the PANGAEA database Data Publisher for Earth &
Environmental Science
(https://doi.pangaea.de/10.1594/PANGAEA.889124, Luo et al., 2018).
The supplement related to this article is available online at: https://doi.org/10.5194/acp-18-6207-2018-supplement.
Competing interests
The authors declare that they have no conflict of
interest.
Acknowledgements
This research was funded by the National Natural Science Foundation of China
(NSFC U1305233), Major State Basic Research Development Program of China (973
program) (no. 2014CB953702 and 2015CB954003), National Natural Science
Foundation Committee and Hong Kong Research Grants Council Joint Foundation
(NSFC-RGC 41561164019), National Natural Science Foundation of China (NSFC
41763001), Doctoral Scientific Research Foundation of East China University
of Technology (no. DHBK2016105), Science and technology project of the
Jiangxi Provincial Department of Education (no. GJJ160580), and Scientific
Research Foundation of the East China University of Technology for the
Science and Technology Innovation Team (no. DHKT2015101). The MEL (State Key
Laboratory of Marine Environmental Science) publication number for this paper
is no. 2017209. Edited by: Maria Cristina Facchini Reviewed
by: two anonymous referees
ReferencesAdornato, L. R., Kaltenbacher, E. A., Villareal, T. A., and Byrne, R. H.:
Continuous in situ determinations of nitrite at nanomolar concentrations,
Deep-Sea Res. Pt. I, 52, 543–551,
10.1016/j.dsr.2004.11.008, 2005.Altieri, K. E., Hastings, M. G., Gobel, A. R., Peters, A. J., and Sigman, D.
M.: Isotopic composition of rainwater nitrate at Bermuda: The influence of
air mass source and chemistry in the marine boundary layer, J.
Geophys. Res.-Atmos., 118, 304–311, 10.1002/jgrd.50829,
2013.Altieri, K. E., Hastings, M. G., Peters, A. J., Oleynik, S., and Sigman, D.
M.: Isotopic evidence for a marine ammonium source in rainwater at Bermuda,
Global Biogeochem. Cy., 28, 1066–1080, 10.1002/2014gb004809, 2014.Altieri, K. E., Fawcett, S. E., Peters, A. J., Sigman, D. M., and Hastings,
M. G.: Marine biogenic source of atmospheric organic nitrogen in the
subtropical North Atlantic, P. Natl. Acad. Sci. USA, 113, 925–930, 10.1073/pnas.1516847113,
2016.
Archana, A., Luo L., Kao S. J., Thibodeau, B., and Baker, D. M.: Variations
in nitrate isotope composition of wastewater effluents by treatment type in
Hong Kong, Mar. Pollut. Bull., 111, 143–152, 2016.Baker, A., Lesworth, T., Adams, C., Jickells, T., and Ganzeveld, L.:
Estimation of atmospheric nutrient inputs to the Atlantic Ocean from
50∘ N to 50∘ S based on large-scale field
sampling: fixed nitrogen and dry deposition of phosphorus, Global
Biogeochem. Cy., 24, GB3006, 10.1029/2009GB003634, 2010.
Böhlke, J., Mroczkowski, S., and Coplen, T.: Oxygen isotopes in nitrate:
New reference materials for 18O: 17O: 16O measurements and observations on
nitrate-water equilibration, Rapid Commun. Mass Sp., 17,
1835–1846, 2003.
Braman, R. S. and Hendrix, S. A.: Nanogram nitrite and nitrate
determination in environmental and biological materials by vanadium (III)
reduction with chemiluminescence detection, Anal. Chem., 61,
2715–2718, 1989.
Buffam, I. and McGlathery, K. J.: Effect of ultraviolet light on dissolved
nitrogen transformations in coastal lagoon water, Limnology
Oceanogr., 48, 723–734, 2003.Cape, J. N., Cornell, S. E., Jickells, T. D., and Nemitz, E.: Organic
nitrogen in the atmosphere – Where does it come from? A review of sources
and methods, Atmos. Res., 102, 30–48,
10.1016/j.atmosres.2011.07.009, 2011.
Casciotti, K., Sigman, D., Hastings, M. G., Böhlke, J., and Hilkert, A.:
Measurement of the oxygen isotopic composition of nitrate in seawater and
freshwater using the denitrifier method, Anal. Chemi., 74,
4905–4912, 2002.
Cornell, S., Randell, A., and Jickells, T.: Atmospheric inputs of dissolved
organic nitrogen to the oceans, Nature, 376, 243–246, 1995.
Cornell, S. E., Jickells, T. D., Cape, J. N., Rowland, A. P., and Duce, R.
A.: Organic nitrogen deposition on land and coastal environments: a review of
methods and data, Atmos. Environ., 37, 2173–2191, 2003.
Doney, S. C.: The growing human footprint on coastal and open-ocean
biogeochemistry, Science, 328, 1512–1516, 2010.
Duce, R., Unni, C., Ray, B., Prospero, J., and Merrill, J.: Long-rangeatmosp
heric transport of soil dust from Asia to the tropical NorthPacific:
temporal variability, Science, 209, 1522–1524, 1980.
Duce, R., Liss, P., Merrill, J., Atlas, E., Buat-Menard, P., Hicks, B.,
Miller, J., Prospero, J., Arimoto, R., and Church, T.: The atmospheric input
of trace species to the world ocean, Global Biogeochem. Cy., 5, 193–259,
1991.Duce, R., LaRoche, J., Altieri, K., Arrigo, K. R., Baker, A. R., Capone, D.
G., Cornell, S., Dentener, F., Galloway, J., Ganeshram, R. S., Geider, R.
J., Jickells, T., Kuypers, M. M., Langlois, R., Liss, P. S., Liu, S. M.,
Middelburg, J. J., Moore,
C. M., Nickovic, S., Oschlies, A., Pedersen, T., Prospero, J., Schlitzer,
R., Seitzinger, S., Sorensen, L. L., Uematsu, M., Ulloa, O., Voss, M., Ward,
B., and Zamora, L.: Impacts of atmospheric anthropogenic nitrogen on the
open ocean, Science,
320, 893–897, 10.1126/science.1150369, 2008.Elliott, E. M., Kendall, C., Boyer, E. W., Burns, D. A., Lear, G. G., Golden,
H. E., Harlin, K., Bytnerowicz, A., Butler, T. J., and Glatz, R.: Dual
nitrate isotopes in dry deposition: Utility for partitioning NOx source
contributions to landscape nitrogen deposition, J. Geophys. Res., 114,
G04020, 10.1029/2008jg000889, 2009.
Erisman, J. W., Hensen, A., de Vries, W., Kros, H., van de Wal, 95 T., de
Winter, W., Wien, J., van Elswijk, M., Maat, M., and Sanders, K.: The
nitrogen decision support system: NitroGenius, Energy research Centre of the
Netherlands ECN, Petten, 2002.Fang, Y. T., Koba, K., Wang, X. M., Wen, D. Z., Li, J., Takebayashi, Y., Liu,
X. Y., and Yoh, M.: Anthropogenic imprints on nitrogen and oxygen isotopic
composition of precipitation nitrate in a nitrogen-polluted city in southern
China, Atmos. Chem. Phys., 11, 1313–1325,
10.5194/acp-11-1313-2011, 2011.
Felix, J. D. and Elliott, E. M.: Isotopic composition of passively
collected nitrogen dioxide emissions: Vehicle, soil and livestock source
signatures, Atmos. Environ., 92, 359–366, 2014.Felix, J. D., Elliott, E. M., and Shaw, S. L.: Nitrogen isotopic composition
of coal-fired power plant NOx: influence of emission controls and
implications for global emission inventories, Environ. Sci. Technol., 46, 3528–3535, 10.1021/es203355v, 2012.Fischer, E. V., Jacob, D. J., Yantosca, R. M., Sulprizio, M. P., Millet, D.
B., Mao, J., Paulot, F., Singh, H. B., Roiger, A., Ries, L., Talbot, R. W.,
Dzepina, K., and Pandey Deolal, S.: Atmospheric peroxyacetyl nitrate (PAN): a
global budget and source attribution, Atmos. Chem. Phys., 14, 2679–2698,
10.5194/acp-14-2679-2014, 2014.Freyer, H.: Seasonal trends of NH4+ and NO3- nitrogen isotope composition
in rain collected at Jülich, Germany, Tellus A, 30, 83–92, 10.1111/j.2153-3490.1978.tb00820.x , 1978.
Gobel, A. R., Altieri, K. E., Peters, A. J., Hastings, M. G., and Sigman, D.
M.: Insights into anthropogenic nitrogen deposition to the North Atlantic
investigated using the isotopic composition of aerosol and rainwater
nitrate, Geophys. Res. Lett., 40, 5977–5982, 2013.
Gu, B., Ge, Y., Ren, Y., Xu, B., Luo, W., Jiang, H., Gu, B., and Chang J.:
Atmospheric reactive nitrogen in China: sources, recent trends, and damage
costs, Environ. Sci. Technol., 46, 9420–9427, 2012.Hastings, M. G., Sigman, D. M., and Lipschultz, F.: Isotopic evidence for
source changes of nitrate in rain at Bermuda, J. Geophys. Res.-Atmos., 108,
D244790, 10.1029/2003JD003789, 2003.Heaton, T. H. E.: 15N14N ratios of nitrate and ammonium in rain at Pretoria,
South Africa, Atmos. Environ., 21, 843–852, 1987.Hoppel, W., Frick, G., and Fitzgerald, J.: Surface source function for
sea-salt aerosol and aerosol dry deposition to the ocean surface, J.
Geophys. Res.-Atmos., 107, AAC7.1–AAC7.17, 10.1029/2001JD002014, 2002.Hoque, M., Kawamura, K., Seki, O., and Hoshi, N.: Spatial distributions of
dicarboxylic acids, ω-oxoacids, pyruvic acid and α-dicarbonyls in the remote marine aerosols over the North Pacific, Mar.
Chem., 172, 1–11, 10.1016/j.marchem.2015.03.003, 2015.
Hsu, S. C., Lee, C. S. L., Huh, C. A., Shaheen, R., Lin, F. J., Liu, S. C.,
Liang, M. C., and Tao, J.: Ammonium deficiency caused by heterogeneous
reactions during a super Asian dust episode, J. Geophys. Res.-Atmos., 119, 6803–6817, 2014.
Jickells, T. D., Kelly, S. D., Baker, A. R., Biswas, K., Dennis, P. F.,
Spokes, L. J., Witt, M., and Yeatman, S. G.: Isotopic evidence for a marine
ammonia source, Geophys. Res. Lett., 30, 359–376, 2003.Jung, J., Furutani, H., Uematsu, M., Kim, S., and Yoon, S.: Atmospheric
inorganic nitrogen input via dry, wet, and sea fog deposition to the
subarctic western North Pacific Ocean, Atmos. Chem. Phys., 13, 411–428,
10.5194/acp-13-411-2013, 2013.Kanakidou, M., Duce, R. A., Prospero, J. M., Baker, A. R., Benitez-Nelson,
C., and Dentener, F. J.: Atmospheric fluxes of organic N and P to the global
ocean, Global Biogeochem. Cy., 26, GB3026, 10.1029/2011GB004277,
2012.
Kang, C.-H., Kim, W.-H., Ko, H.-J., and Hong, S.-B.: Asian dust effects on
total suspended particulate (TSP) compositions at Gosanin Jeju Island,
Korea, Atmos. Res., 94, 345–355, 2009.
Karl, D., Letelier, R., Tupas, L., Dore, J., Christian, J., and Hebel, D.:
The role of nitrogen fixation in biogeochemical cycling in the subtropical
North Pacific Ocean, Nature, 388, 533–538, 1997.Kelly, S. D., Stein, C., and Jickells, T. D.: Carbon and nitrogen isotopic
analysis of atmospheric organic matter, Atmos. Environ., 39,
6007–6011, 10.1016/j.atmosenv.2005.05.030, 2005.Kim, T. W., Lee, K., Najjar, R. G., Jeong, H. D., and Jeong, H. J.:
Increasing N abundance in the northwestern Pacific Ocean due to atmospheric
nitrogen deposition, Science, 334, 505–509, 10.1126/science.1206583,
2011.Knapp, A. N., Sigman, D. M., and Lipschultz, F.: N isotopic composition of
dissolved organic nitrogen and nitrate at the Bermuda Atlantic Time-series
Study site, Global Biogeochem. Cy., 19, 10.1029/2004GB002320,
2005.Knapp, A. N., Hastings, M. G., Sigman, D. M., Lipschultz, F., and Galloway,
J. N.: The flux and isotopic composition of reduced and total nitrogen in
Bermuda rain, Mar. Chem., 120, 83–89,
10.1016/j.marchem.2008.08.007, 2010.Knapp, A. N., Sigman, D. M., Lipschultz, F., Kustka, A. B., and Capone, D.
G.: Interbasin isotopic correspondence between upper-ocean bulk DON and
subsurface nitrate and its implications for marine nitrogen cycling, Global
Biogeochem. Cy., 25, GB4004, 10.1029/2010GB003878, 2011.
Knapp, A. N., Sigman, D. M., Kustka, A. B., Sañudo-Wilhelmy, S. A., and
Capone, D. G.: The distinct nitrogen isotopic compositions of low and high
molecular weight marine DON, Mar. Chem., 136, 24–33, 2012.Koba, K., Fang, Y., Mo, J., Zhang, W., Lu, X., Liu, L., Zhang, T.,
Takebayashi, Y., Toyoda, S., Yoshida, N., Suzuki, K., Yoh, M., and Senoo, K.:
The15N natural abundance of the N lost from an N-saturated subtropical
forest in southern China, J. Geophys. Res.-Biogeo., 117, G02015,
10.1029/2010jg001615, 2012.Kunwar, B. and Kawamura, K.: One-year observations of carbonaceous and
nitrogenous components and major ions in the aerosols from subtropical
Okinawa Island, an outflow region of Asian dusts, Atmos. Chem. Phys., 14,
1819–1836, 10.5194/acp-14-1819-2014, 2014.Lee, K.-S., Lee, D.-S., Lim, S.-S., Kwak, J.-H., Jeon, B.-J., Lee, S.-I.,
Lee, S.-M., and Choi, W.-J.: Nitrogen isotope ratios of dissolved organic
nitrogen in wet precipitation in a metropolis surrounded by agricultural
areas in southern Korea, Agr. Ecosyst. Environ., 159,
161–169, 10.1016/j.agee.2012.07.010, 2012.Lesworth, T., Baker, A. R., and Jickells, T.: Aerosol organic nitrogen over
the remote Atlantic Ocean, Atmos. Environ., 44, 1887–1893,
10.1016/j.atmosenv.2010.02.021, 2010.
Letscher, R. T., Hansell, D. A., Carlson, C. A., Lumpkin, R., and Knapp, A.
N.: Dissolved organic nitrogen in the global surface ocean: Distribution and
fate, Global Biogeochem. Cy., 27, 141–153, 2013.Li, J., Glibert, P. M., Zhou, M., Lu, S., and Lu, D.: Relationships between
nitrogen and phosphorus forms and ratios and the development of
dinoflagellate blooms in the East China Sea, Mar. Ecol. Prog. Ser.,
383, 11–26, 10.3354/meps07975, 2009.Liu, D., Fang, Y., Tu, Y., and Pan, Y.: Chemical method for nitrogen
isotopic analysis of ammonium at natural abundance, Anal. Chem., 86,
3787–3792, 10.1021/ac403756u, 2014.Liu, Y., Liggio, J., Staebler, R., and Li, S.-M.: Reactive uptake of ammonia
to secondary organic aerosols: kinetics of organonitrogen formation, Atmos.
Chem. Phys., 15, 13569–13584, 10.5194/acp-15-13569-2015,
2015.
Lønborg, C., Yokokawa, T., Herndl, G. J., and Álvarez-Salgado, X. A.:
Production and degradation of fluorescent dissolved organic matter in
surface waters of the eastern north Atlantic ocean, Deep-Sea Res. Pt. I, 96, 28–37, 2015.Luo, L., Yao, X. H., Gao, H. W., Hsu, S. C., Li, J. W., and Kao, S. J.:
Nitrogen speciation in various types of aerosols in spring over the
northwestern Pacific Ocean, Atmos. Chem. Phys., 16, 325–341,
10.5194/acp-16-325-2016, 2016.Luo, L., Kao, S.-J., Bao, H., Xiao, H., Xiao, H., Yao, X., Gao, H., Li, J.,
and Lu, Y.: Nitrogen in marine aerosol and surface seawater over the
Northwest Pacific Ocean in spring,
https://doi.pangaea.de/10.1594/PANGAEA.889124, last access: 27 April
2018
Mace, K. A. and Duce, R. A.: On the use of UV photo-oxidation for the determination
of total nitrogen in rainwater and water-extracted atmospheric aerosol,
Atmos. Environ., 36, 5937–5946, 2002.Mace, K. A., Kubilay, N., and Duce, R. A.: Organic nitrogen in rain and
aerosol in the eastern Mediterranean atmosphere: an association with
atmospheric dust, J. Geophys. Res.-Atmos., 108,
4320, 10.1029/2002JD002997, 2003Matsumoto, K., Yamamoto, Y., Kobayashi, H., Kaneyasu, N., and Nakano, T.:
Water-soluble organic nitrogen in the ambient aerosols and its contribution
to the dry deposition of fixed nitrogen species in Japan, Atmos.
Environ., 95, 334–343, 10.1016/j.atmosenv.2014.06.037, 2014.Miyazaki, Y., Kawamura, K., Jung, J., Furutani, H., and Uematsu, M.:
Latitudinal distributions of organic nitrogen and organic carbon in marine
aerosols over the western North Pacific, Atmos. Chem. Phys., 11, 3037–3049,
10.5194/acp-11-3037-2011, 2011.Miyazaki, Y., Fu, P., Ono, K., Tachibana, E., and Kawamura, K.: Seasonal
cycles of water-soluble organic nitrogen aerosols in a deciduous broadleaf
forest in northern Japan, J. Geophys. Res.-Atmos., 119,
1440–1454, 10.1002/2013jd020713, 2014.
Mori, I., Nishikawa, M., Tanimura, T., and Quan, H.: Change in size
distribution and chemical composition of kosa (Asian dust) aerosol during
long-range transport, Atmos. Environ., 37, 4253–4263, 2003.Morin, S., Savarino, J., Frey, M. M., Domine, F., Jacobi, H. W., Kaleschke,
L., and Martins, J. M. F.: Comprehensive isotopic composition of atmospheric
nitrate in the Atlantic Ocean boundary layer from 65∘ S to
79∘ N, J. Geophys. Res., 114, D05303, 10.1029/2008jd010696,
2009.Mulholland, M. R. and Bernhardt, P. W.: The effect of growth rate,
phosphorus concentration, and temperature on N2 fixation, carbon fixation,
and nitrogen release in continuous cultures of Trichodesmium IMS101, Limnol.
Oceanogr, 50, 839–849, 2005.
Nakamura, T., Matsumoto, K., and Uematsu, M.: Chemical characteristics of aerosols
transported from Asia to the East China Sea: an evaluation of anthropogenic
combined nitrogen deposition in autumn, Atmos. Environ.,
39, 1749–1758, 2005.
Needoba, J. A., Foster, R. A., Sakamoto, C., Zehr, J. P., and Johnson, K.
S.: Nitrogen fixation by unicellular diazotrophic cyanobacteria in the
temperate oligotrophic North Pacific Ocean, Limnol. Oceanogr., 52,
1317–1327, 2007.Paulot, F., Jacob, D. J., Johnson, M. T., Bell, T. G., Baker, A. R., Keene,
W. C., Lima, I. D., Doney, S. C., and Stock, C. A.: Global oceanic emission
of ammonia: Constraints from seawater and atmospheric observations, Global
Biogeochem. Cy., 29, 1165–1178, 10.1002/2015gb005106, 2015.Pavuluri, C. M., Kawamura, K., and Fu, P. Q.: Atmospheric chemistry of
nitrogenous aerosols in northeastern Asia: biological sources and secondary
formation, Atmos. Chem. Phys., 15, 9883–9896,
10.5194/acp-15-9883-2015, 2015.
Piskunov, V. N.: Parameterization of aerosol dry deposition velocities onto
smooth and rough surfaces, J. Aero. Sci., 40, 664–679,
2009.Rolff, C., Elmgren, R., and Voss, M.: Deposition of nitrogen and phosphorus
on the Baltic Sea: seasonal patterns and nitrogen isotope composition,
Biogeosciences, 5, 1657–1667, 10.5194/bg-5-1657-2008, 2008.Russell, K. M., Galloway, J. N., Macko, S. A., Moody, J. L., and Scudlark,
J. R.: Sources of nitrogen in wet deposition to the Chesapeake Bay region,
Atmos. Environ., 32, 2453–2465, 10.1016/S1352-2310(98)00044-2,
1998.Savarino, J., Morin, S., Erbland, J., Grannec, F., Patey, M. D., Vicars, W.,
Alexander, B., and Achterberg, E. P.: Isotopic composition of atmospheric
nitrate in a tropical marine boundary layer, P. Natl.
Acad. Sci. USA, 110, 17668–17673,
10.1073/pnas.1216639110, 2013.Sigman, D., Casciotti, K., Andreani, M., Barford, C., Galanter, M., and
Böhlke, J.: A bacterial method for the nitrogen isotopic analysis of
nitrate in seawater and freshwater, Anal. Chem., 73, 4145–4153,
10.1021/ac010088e, 2001.Sigman, D. M., Granger, J., DiFiore, P. J., Lehmann, M. M., Ho, R., Cane, G.,
and van Geen, A.: Coupled nitrogen and oxygen isotope measurements of nitrate
along the eastern North Pacific margin, Global Biogeochem. Cy., 19, GB4022,
10.1029/2005gb002458, 2005.Van Engeland, T., Soetaert, K., Knuijt, A., Laane, R., and Middelburg, J.:
Dissolved organic nitrogen dynamics in the North Sea: A time series
analysis, Estuarine, Coastal and Shelf Science, 89, 31–42,
10.1016/j.ecss.2010.05.009, 2010.Violaki, K., Sciare, J., Williams, J., Baker, A. R., Martino, M., and
Mihalopoulos, N.: Atmospheric water-soluble organic nitrogen (WSON) over
marine environments: a global perspective, Biogeosciences, 12, 3131–3140,
10.5194/bg-12-3131-2015, 2015.Walters, W. W., Goodwin, S. R., and Michalski, G.: Nitrogen Stable Isotope
Composition (δ15N) of Vehicle Emitted NOx, Environ. Sci.
Technol., 49, 2278–2285, 10.1021/es505580v, 2015.
Wang, B., Clemens, S. C., Liu, P.: Contrasting the Indian and East Asian
monsoons: implications on geologic timescales, Mar Geol.,
201, 5–21, 2003.Wang, G. H., Zhou, B. H., Cheng, C. L., Cao, J. J., Li, J. J., Meng, J. J.,
Tao, J., Zhang, R. J., and Fu, P. Q.: Impact of Gobi desert dust on aerosol
chemistry of Xi'an, inland China during spring 2009: differences in
composition and size distribution between the urban ground surface and the
mountain atmosphere, Atmos. Chem. Phys., 13, 819–835,
10.5194/acp-13-819-2013, 2013.Wilson, T. W., Ladino, L. A., Alpert, P. A., Breckels, M. N., Brooks, I. M.,
Browse, J., Burrows, S. M., Carslaw, K. S., Huffman, J. A., Judd, C.,
Kilthau, W. P., Mason, R. H., McFiggans, G., Miller, L. A., Najera, J. J.,
Polishchuk, E., Rae, S., Schiller, C. L., Si, M., Temprado, J. V., Whale, T.
F., Wong, J. P., Wurl, O., Yakobi-Hancock, J. D., Abbatt, J. P., Aller, J.
Y., Bertram, A. K., Knopf, D. A., and Murray, B. J.: A marine biogenic
source of atmospheric ice-nucleating particles, Nature, 525, 234–238,
10.1038/nature14986, 2015.Wozniak, A. S., Willoughby, A. S., Gurganus, S. C., and Hatcher, P. G.:
Distinguishing molecular characteristics of aerosol water soluble organic
matter from the 2011 trans-North Atlantic US GEOTRACES cruise, Atmos. Chem.
Phys., 14, 8419–8434, 10.5194/acp-14-8419-2014, 2014.Xiao, H.-W., Xiao, H.-Y., Long, A.-M., and Wang, Y.-L.: Who controls the
monthly variations of NH4+ nitrogen isotope composition in precipitation?,
Atmos. Environ., 54, 201–206, 10.1016/j.atmosenv.2012.02.035,
2012.Xiao, Q., Ma, Z., Li, S., and Liu, Y.: The impact of winter heating on air
pollution in China, PloS one, 10, e011731,
10.1371/journal.pone.0117311, 2015.Yang, J.-Y. T., Hsu, S.-C., Dai, M. H., Hsiao, S. S.-Y., and Kao, S.-J.:
Isotopic composition of water-soluble nitrate in bulk atmospheric deposition
at Dongsha Island: sources and implications of external N supply to the
northern South China Sea, Biogeosciences, 11, 1833–1846,
10.5194/bg-11-1833-2014, 2014.Yang, Y. Q., Wang, J. Z., Niu T., Zhou, C., Chen, M., and Liu, J.: The
Variability of Spring Sand-Dust Storm Frequency in Northeast Asia from 1980
to 2011. J. Meteorol. Res.-PRC, 27, 119–127, 2013.
Yao, X. H. and Zhang, L.: Supermicron modes of ammonium ions related to fog
in rural atmosphere, Atmos. Chem. Phys., 12, 11165–11178,
10.5194/acp-12-11165-2012, 2012.Yeatman, S., Spokes, L., Dennis, P., and Jickells, T.: Comparisons of
aerosol nitrogen isotopic composition at two polluted coastal sites,
Atmos. Environ., 35, 1307–1320, 10.1016/S1352-2310(00)00408-8,
2001.Zamora, L. M., Prospero, J. M., and Hansell, D. A.: Organic nitrogen in aerosols and
precipitation at Barbados and Miami: Implications regarding sources,
transport and deposition to the western subtropical North Atlantic, J. Geophys. Res.-Atmos., 116,
D20309, 10.1029/2011JD015660, 2011.Zhang, R., Jing, J., Tao, J., Hsu, S.-C., Wang, G., Cao, J., Lee, C. S. L.,
Zhu, L., Chen, Z., Zhao, Y., and Shen, Z.: Chemical characterization and
source apportionment of PM2.5 in Beijing: seasonal perspective, Atmos. Chem.
Phys., 13, 7053–7074, 10.5194/acp-13-7053-2013, 2013.Zhang, S.-P., Xie, S.-P., Liu, Q.-Y., Yang, Y.-Q., Wang, X.-G., and Ren,
Z.-P.: Seasonal variations of Yellow Sea fog: observations and Mechanisms,
J. Climate, 22, 6758–6772, 10.1175/2009jcli2806.1, 2009.