Relationships among the climate-relevant gases during the Southern Ocean bloom season.

The ocean plays an essential role in regulating the sources and sinks of climate-relevant gases, like CO2, N2O and dimethyl sulfide (DMS), thus influencing global climate change. Although the Southern Ocean is known to be a strong carbon sink, a significant DMS source and possibly a large source of N2O, our understanding of the interaction among these climate-relevant gases and their potential impacts on climate change is still insufficient in the Southern Ocean. Herein, we analyzed parameters, including surface water pCO2, dissolved inorganic carbon (DIC), alkalinity (TA), DMS and N2O in the water column, collected during the austral summer of 2015-2016 in the 32nd Chinese Antarctic Research Expedition (CHINARE) at the tip of Antarctic Peninsula. A positive correlation between DMS and pCO2 (indicated by deficit of DIC, ∆DIC, refer to values in 100 m) was observed in waters above 75 m, whereas no correlation between N2O saturation anomaly (SA) and DMS, ∆DIC was found. In the area with stable stratification with phytoplankton bloom, significant DMS source and strong CO2 uptake with weak N2O emission were observed. Conversely, strong mixing or upwelling area was shown to be a strong marine CO2 source and significant N2O release with weak DMS source.

Mixing state and distribution of iodine-containing particles in Arctic Ocean during summertime.

Iodine chemistry plays a key role in ozone destruction and new aerosol formation in the marine boundary layer (MBL), especially in polar regions. We investigated iodine-containing particles (0.2-2 µm) in the Arctic Ocean using a ship-based single particle aerosol mass spectrometer from July to August 2017. Seven main particle types were identified: dust, biomass combustion particles, sea salt, organic S, aromatics, hydrocarbon-like compounds, and amines. The number fraction of iodine-containing particles was higher inside the Arctic Circle (>65°N) than outside (55-65°N). According to the air mass back trajectories, the latitudinal distribution of iodine-containing particles can be mainly attributed to iodine emissions from the sea ice edge region. Diurnal trends were found, especially during the second half of cruise, with peak iodine-containing particle number fractions during low-light conditions and relatively low number fractions at midday. These results imply that solar radiation plays a significant role in modulating particulate iodine in the Arctic atmosphere.

Latitudinal Distribution of Gaseous Elemental Mercury in Tropical Western Pacific: The Role of the Doldrums and the ITCZ.

The role of the tropical western Pacific in the latitudinal distribution of atmospheric mercury is still unclear. In this study, we conducted continuous measurements of gaseous elemental mercury (GEM) in the marine boundary layer (MBL) along a large latitudinal transect (∼60° S to ∼30° N) of the western Pacific, accompanied by measurements of dissolved gaseous mercury (DGM) in the surface seawater. We found that the GEM latitudinal gradient is the most significant in the tropical western Pacific, which to some extent might be attributed to the impact of the doldrums and the Intertropical Convergence Zone (ITCZ) in this area. For the doldrums, calm weather may delay the transport of GEM, facilitating its accumulation in the tropical western Pacific. Furthermore, the regional transport, and low O3 and sea-salt aerosol levels in this area which would not favor the oxidation of GEM in the MBL, would intensify the accumulation of GEM in the tropical western Pacific. For the ITCZ, the vast wet deposition of Hg would drive elevated DGM in the surface seawater, which can increase the evasion flux and may further influence the spatial distribution of GEM. This study provides insight into the role of the tropical western Pacific in the regional atmospheric mercury cycle.

Dry-deposition of inorganic and organic nitrogen aerosols in Xiamen Bay: Fluxes, sources, and biogeochemical significance.

Increased dry deposition of nitrogen aerosols (aerosol-N) as a result of anthropogenic emissions has caused large negative impacts on marine ecosystems. We monitored the number concentrations and sizes of inorganic nitrogen aerosols (aerosol-IN: NH4+ and NO3-) and organic nitrogen aerosols (aerosol-ON: methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, and triethylamine) by single-particle aerosol mass spectrometry (SPAMS) during the warm season (WS) and cold season (CS) of 2013 and 2015 in Xiamen Bay. The mean hourly number concentration of aerosol-IN (874/h) overwhelmed that of aerosol-ON (103/h), accounting for 83.9 ± 16.1% of aerosol-N. More than 90% of aerosol-N was concentrated in the condensation mode (0.1-0.5 µm) and droplet mode (0.5-2.0 µm). Aerosol-IN was the main contributor (80.1-94.2%) to aerosol-N deposition. New production potentially supported by the ocean's external nitrogen supply provided aerosol-N input of 11.51-11.96 g C m-2 yr-1, which contributed 17.5-18.2% of total new production in the southern East China Sea. Four potential sources of aerosol-N were identified based on the results of positive matrix factorization analysis, including secondary formation (F1), biogenic source (F2), sea spray, soil dust, biomass burning (F3), and anthropogenic sources (F4). Aerosol-N concentrations in Xiamen Bay were mainly affected by the ocean air masses during the WS and inland air masses during the CS. The percentages of aerosol-N at each backward trajectory cluster showed that the inland air masses brought more aerosol-IN emitted from biomass burning, soil dust, and secondary formation sources, whereas the ocean air masses brought more aerosol-ON emitted from a marine biogenic source into Xiamen Bay. This study provides an example of determining the number concentrations and sizes of IN and ON in aerosols by SPAMS, and helps us further understand the dry deposition and sources of IN and ON in aerosols in Xiamen Bay.

Non-ignorable contribution of anthropogenic source to aerosols in Arctic Ocean.

Arctic Ocean (AO) atmospheric aerosols, which are a factor influencing regional and global climate, have been greatly influenced by an increase in anthropogenic sources. To identify the impact of anthropogenic sources on regional aerosols in the AO and middle and low latitudes (MLO), a single-particle aerosol mass spectrometer was used to count and size aerosols with diameters less than 2.5 µm (PM2.5) and determine their chemical composition. The mean hourly count of PM2.5 aerosols was 1639/h in the AO, which was 57.1% lower than that in the MLO. Na_MSA, sulfate, and Na_rich were three major components, which accounted for 74.3% of PM2.5 aerosols in the AO. The size distribution of PM2.5 aerosols was unimodal, peaking between 0.42 µm and 1.64 µm. A source apportionment method for single aerosol particles in the Arctic was established using positive matrix factorization (PMF) combined with backward air mass trajectory and principal component analysis (PCA). Three potential sources of aerosols were identified: marine sources; anthropogenic sources; and secondary formation. The largest contribution to aerosols in the AO was from marine sources, accounting for 50.6%. This source was 20.4% higher in the AO than that in the MLO. Secondary formation contributed 19.8% and 36.5% to aerosols in the AO and MLO, respectively. However, the contribution of anthropogenic sources to aerosols was 29.6% in the AO, and this was 3.7% lower than that in the MLO. Our study provides a useful method for identifying sources of aerosols in the Arctic, and the results showed that although marine sources were the largest contributors to aerosols in the AO, the contribution of anthropogenic sources could not be ignored.

Effect of sea ice retreat on marine aerosol emissions in the Southern Ocean, Antarctica.

Sea ice retreat in the polar region is expected to increase the emissions of sea salt aerosols and biogenic gases, which may significantly impact the climate by increasing cloud condensation nuclei (CCN) population and changing solar radiation. In this study, aerosol compositions were measured at high-time-resolution (1 h) with an in-situ gas and aerosol composition monitoring system in polynya regions of the Southern Ocean (SO) to access the effects of sea ice concentrations on the sea salt aerosol (SSA) and secondary biogenic aerosol (SBA) in the SO. SSA emissions increased by more than 30% as sea ice concentration decreased from 85% to 29%. However, SSA emissions did not increase monotonically as the sea ice concentration decreased. The highest SSA concentration occurred in drifting sea ice region. Sea ice melting increased SBA concentrations by enhancing the air-sea exchanges of SBA precursor gases and the release of algae from sea ice. Positive correlations between SSA and wind speed were present in different sea ice regions, while SBA didn't reveal an obvious correlation with wind speed in the SO. The impact of wind speed on the SSA emissions were very different, Higher slope value of 41.83 and 35.81 were present in the DSI and SIF region, while the value was only about 16.74 in the SIC region. The results extended the knowledge of the effect of future sea ice retreat on marine aerosol emissions and potential climate changes in the polar region.

[Distribution Characteristics and Sources of Metal Elements in Rainwater in Xiamen].

Forty-one metal elements, including rare earth elements and the lead isotope ratio in rain water in Xiamen were measured by inductively coupled plasma mass spectrometry. Sources of metal elements were identified by combined enrichment factor, isotope analysis, and positive matrix factorization analysis. The results showed that the concentration sequence of total metal elements in rainwater in Xiamen was winter-suburban (213.964 µg·L-1) > winter-urban (176.357 µg·L-1) > summer-suburban (75.401 µg·L-1). There were seasonal and regional differences in the content of rare earth elements, and their standardized distribution patterns were inconsistent with each potential source, indicating that their sources were relatively complex. Enrichment factor analysis showed that Ni, Cu, Zn, and Cd were significantly affected by human sources, whereas Be, Ti, V, Mn, Cr, Co, Ga, Rb, Y, Cs, rare earth elements, Th, and U were mainly affected by natural sources. The result of Pb-isotopic-analysis showed that Pb in rainwater was significantly affected by coal sources with a contribution rate of 63.67%, and soil parent material, garbage incineration, motor vehicle exhaust, and cement dust with a contribution rate of 36.33%. The result of positive matrix factorization combined with the enrichment factor and isotope method showed that the metal elements in rainwater were affected by coal burning, natural sources, industry, and traffic.

Significant Underestimation of Gaseous Methanesulfonic Acid (MSA) over Southern Ocean.

Methanesulfonic acid (MSA), derived from the oxidation of dimethylsulfide (DMS), has a significant impact on biogenic sulfur cycle and climate. Gaseous MSA (MSAg) has been often ignored in previous studies due to its quick conversion to particulate MSA (MSAp) and low concentrations. MSAg, MSAp, and nss-SO42- were observed simultaneously for the first time with high-time-resolution (1 h) in the Southern Ocean (SO). The mean MSAg level reached up to 3.3 ± 1.6 pptv, ranging from ∼24.5 pptv in the SO, contributing to 31% ± 3% to the total MSA (MSAT). A reduction of the MSA to nss-SO42- ratios by about 30% was obtained when MSAg was not accounted for in the calculation, indicating that MSAg was very important in the assessment of the biogenic sulfur contributions in the atmosphere. Mass ratios of MSA to nss-SO42- increased first and then decreased with the temperature from -10 to 5 °C, with a maximum value at the temperature of -3 °C. Positive correlations between MSAg to MSAT ratios and temperature were presented, when the temperature was higher than 5 °C. This study highlights the importance of MSAg for understanding the atmospheric DMS oxidation mechanism and extends the knowledge of MSA formation in the marine atmosphere.

Nitrogen isotope composition of ammonium in PM2.5 in the Xiamen, China: impact of non-agricultural ammonia.

Since NH3 is a significant precursor to ammonium in PM2.5 and contributes significantly to atmospheric nitrogen deposition but largely remains unregulated in China, the insight into the source of NH3 emissions by the isotopic investigation is important in controlling NH3 emissions. In this study, atmospheric concentrations of NH3 and water-soluble ion composition in PM2.5 as well as nitrogen isotope ratios in NH4+ (δ15N-NH4+) in Xiamen, China, were measured. Results showed that average NH3 concentration for the five sites in Xiamen was 7.9 µg m-3 with distinct higher values in the warm season and lower values in the cold season, and PM2.5 concentration for the two sites (urban and suburban) was 59.2 µg m-3 with lowest values in summer. In the PM2.5, NH4+ concentrations were much lower than NH3 and showed a stronger positive correlation with NO3- than that with SO42- suggesting the formation of NH4NO3 and equilibrium between NH3 and NH4+. Although the concentrations of NH3 at the urban site were significantly higher than those at the suburban site, no significant spatial difference in NH4+ and δ15N-NH4+ was obtained. The distinct heavier δ15N-NH4+ values in summer than in other seasons correlated well with the equilibrium isotopic effects between NH3 and NH4+ which depend on temperature. The initial δ15N-NH3 values were in the range of waste treatment (- 25.42‰) and fossil fuel combustion (- 2.5‰) after accounting for the isotope fractionation. The stable isotope mixing model showed that fossil fuel-related NH3 emissions (fossil fuel combustion and NH3 slip) contributed more than 70% to aerosol NH4+. This finding suggested that the reduction of NH3 emissions from urban transportation and coal combustion should be a priority in the abatement of PM2.5 pollution in Xiamen.

Size Distribution and Depolarization Properties of Aerosol Particles over the Northwest Pacific and Arctic Ocean from Shipborne Measurements during an R/V Xuelong Cruise.

Atmospheric aerosols over polar regions have attracted considerable attention for their pivotal effects on climate change. In this study, temporospatial variations in single-particle-based depolarization ratios (δ: s-polarized component divided by the total backward scattering intensity) were studied over the Northwest Pacific and the Arctic Ocean using an optical particle counter with a depolarization module. The δ value of aerosols was 0.06 ± 0.01 for the entire observation period, 61 ± 10% lower than the observations for coastal Japan (0.12 ± 0.02) ( Pan et al. Atmos. Chem. Phys. 2016 , 16 , 9863 - 9873 ) and inland China (0.19 ± 0.02) ( Tian et al. Atmos. Chem. Phys. 2018 , 18 , 18203 - 18217 ) in summer. The volume concentration showed two dominant size modes at 0.9 and 2 µm. The supermicrometer particles were mostly related to sea-salt aerosols with a δ value of 0.09 over marine polar areas, ∼22% larger than in the low-latitude region because of differences in chemical composition and dry air conditions. The δ values for fine particles (<1 µm) were 0.05 ± 0.1, 50% lower than inland anthropogenic pollutants, mainly because of the complex mixtures of submicrometer sea salts. High particle concentrations in the Arctic Ocean could mostly be attributed to the strong marine emission of sea salt associated with deep oceanic cyclones, whereas long-range transport pollutants from the continent were among the primary causes of high particle concentrations in the Northwest Pacific region.

Effect of air masses motion on the rapid change of aerosols in marine atmosphere.

The impact of air masses motion on marine aerosol properties was investigated using an on-board single particle mass spectrometer (SPAMS) deployed for the determination of single particle size resolved chemical composition over Southeast China Sea. Two aerosol blooms (E1 and E2) were observed during the cruise. High average particle number count occurred in E1 (7320), followed by E2 (5850), which was more than 100-150 times of the average particle number count during normal periods. Particles were classified as four major sources, including continental source, shipping source, marine source, and transport source based on the mass spectral similarity. Transport source was identified as those particles with high particle number count occurred only during aerosol bloom period. Three sub-types of EC-Ca, OC-Ca, and Al-rich were classified as transport source. EC-Ca was the dominant particles of the transport source, accounting for more than 70% of the total particles in aerosol bloom events. A uni-modal size distribution in the size range of 0.1-2.0 µm was observed during normal period, while a bimodal distribution with a tiny mode (<0.3 µm) and a coarse mode between 0.4 and 0.6 µm was present during aerosol bloom. The variation of aerosol source is consistent with air masses back trajectories, for the reason that most of the long-range air trajectories are from the ocean, while short air trajectories originate in the continental regions, which means that air masses have a significant impact on the aerosol physical-chemical properties along their tracks.

Impact of marine and continental sources on aerosol characteristics using an on-board SPAMS over southeast sea, China.

The chemical composition of atmospheric aerosols was characterized using an on-board single particle aerosol mass spectrometer (SPAMS) over the Southeast China Sea. High-time-resolution observation of marine aerosols was carried out to clarify the source of aerosols and the interaction of marine and continental aerosols. Atmospheric aerosols were determined by the interaction of continental and marine sources over coastal area. Aerosols from continental sources flux into sea surfaces through deposition or diffusion, which results in the rapid decrease of continental aerosols. Five main subtypes of carbonaceous particles are identified as C_Al-Si, C_V-Ni, C_S, C_K, and C_secondary to clarify the impact of marine and continental sources on atmospheric aerosols. High fraction of C_Al-Si and C_secondary is present over XA (Xiamen anchorage), accounting for 23.8% and 18.6% of total carbonaceous particles. Contrarily, the relative percentage of C_S increases as the distance from land to sea increases. The influence of continental aerosols declines, while the contribution of marine aerosols increases as the distance from land to sea increases. Air masses in XA, LSA (land to sea area), SLA (sea to land area), and SA (sea area) were all from ocean during the observation period, resulting in low relative fraction of continental aerosols in SLA, SA, and LSA. High-time-resolution measurement is useful to understand aerosol source types and the impact of marine and continental sources on marine atmosphere aerosols.

Pollutants identification of ambient aerosols by two types of aerosol mass spectrometers over southeast coastal area, China.

Two different aerosol mass spectrometers, Aerodyne Aerosol Mass Spectrometer (AMS) and Single Particle Aerosol Mass Spectrometer (SPAMS) were deployed to identify the aerosol pollutants over Xiamen, representing the coastal urban area. Five obvious processes were classified during the whole observation period. Organics and sulfate were the dominant components in ambient aerosols over Xiamen. Most of the particles were in the size range of 0.2-1.0µm, accounting for over 97% of the total particles measured by both instruments. Organics, as well as sulfate, measured by AMS were in good correlation with measured by SPAMS. However, high concentration of NH4+ was obtained by AMS, while extremely low value of NH4+ was detected by SPAMS. Contrarily, high particle number counts of NO3- and Cl- were given by SPAMS while low concentrations of NO3- and Cl- were measured by AMS. The variations of POA and SOA obtained from SPAMS during event 1 and event 2 were in accordance with the analysis of HOA and OOA given by AMS, suggesting that both of AMS and SPAMS can well identify the organic clusters of aerosol particles. Overestimate or underestimate of the aerosol sources and acidity would be present in some circumstances when the measurement results were used to analyze the aerosol properties, because of the detection loss of some species for both instruments.

[Marine Aerosol Using On-board Aerosol Mass Spectrometry].

Marine aerosols were measured in real-time by an on-board signal particle aerosol mass spectrometer(SPAMS) over the Southeast China Sea. The chemical compositions and size distribution characteristics of aerosol particles were obtained, and the sources and ion spectra were analyzed. The results showed that particle number concentration decreased with the distance apart from the coastal area. In the coastal area, the aerosol compositions were mainly determined by the emissions of industry, such as vessel, traffic and coal combustion etc. When it was far from the continent, aerosols were mainly affected by the sea sources. Aerosol particles during the observation period disturbed singly with a peak diameter value of 0.5 µm. Most of the particles were in the size range of 0.2 µm to 0.8 µm. High signal intensity of EC with high K+ intensity in the positive spectrum and HSO4- intensity in negative spectrum was present in the marine aerosol over the coastal area. However, the signals of NO3- and NO2- were absent in the negative spectrum. The signal intensity of EC was weak in the marine aerosol over the sea area far from the coastal area. High signal intensity of Na+ and weak Mg+,Ca+ and NaCl+ signals were present in the positive spectrum, while high signal intensity of MSA-,CN-,O- and HSO4- were present in negative spectrum which was considered to be the special ions spectrum of marine biological sources. It indicated that ambient aerosols over the observation area were influenced not only by the anthropogenic emission sources but also affected by the marine aerosol formation.

Characterization of lead-containing aerosol particles in Xiamen during and after Spring Festival by single-particle aerosol mass spectrometry.

To comparatively analyze lead (Pb)-containing particles during and after the Chinese Spring Festival (SF), real-time single-particle aerosol mass spectrometry (SPAMS) was conducted in Xiamen during February 9-19 and March 4-14, 2013. Pb-containing particles were found in 2.4% and 5.3% of the total particle numbers during and after SF, respectively. Based on the SPAMS mass spectral results, the Pb-containing particles were classified into three major types and 11 subtypes: Pb-rich particles comprising Pb-nitrate, Pb-sulfate and Pb-chloride; K-rich particles comprising K-nitrate, K-sulfate, K-metal, K-carbonaceous, K-phosphate, and K-chloride; and metal particles including Fe-rich and Mn-nitrate particles. During SF, lower contributions of Pb-containing particles were due to the effect of the SF holiday. Firework emissions contributed little to the Pb-containing particles. K-rich particles were a major contribution to Pb-containing particles during SF, accounting for approximately 70% of the total number of Pb-containing particles. After SF, significantly increased Pb-containing particles were observed, coincided with NO2 and SO2, due to increased industrial activities and other anthropogenic activities, and Pb-rich particles increased to approximately 50.3% of the total number of Pb-containing particles. Local industrial emissions and the stagnant meteorological conditions resulted in the higher concentrations of Pb-containing particles in the early morning after SF, especially Pb-nitrate particles. This study provides data on the in-situ monitoring of Pb emissions during and after SF and could be helpful for the mitigation of Pb pollution.

Effect of typhoon on atmospheric aerosol particle pollutants accumulation over Xiamen, China.

Great influence of typhoon on air quality has been confirmed, however, rare data especially high time resolved aerosol particle data could be used to establish the behavior of typhoon on air pollution. A single particle aerosol spectrometer (SPAMS) was employed to characterize the particles with particle number count in high time resolution for two typhoons of Soulik (2013) and Soudelor (2015) with similar tracks. Three periods with five events were classified during the whole observation time, including pre - typhoon (event 1 and event 2), typhoon (event 3 and event 4) and post - typhoon (event 5) based on the meteorological parameters and particle pollutant properties. First pollutant group appeared during pre-typhoon (event 2) with high relative contributions of V - Ni rich particles. Pollution from the ship emissions and accumulated by local processes with stagnant meteorological atmosphere dominated the formation of the pollutant group before typhoon. The second pollutant group was present during typhoon (event 3), while typhoon began to change the local wind direction and increase wind speed. Particle number count reached up to the maximum value. High relative contributions of V - Ni rich and dust particles with low value of NO3(-)/SO4(2-) was observed during this period, indicating that the pollutant group was governed by the combined effect of local pollutant emissions and long-term transports. The analysis of this study sheds a deep insight into understand the relationship between the air pollution and typhoon.

[Separation of PM2.5 from coal combustion with phase change].

The influence of two methods of gas moisture conditioning on removal efficiency of PM2.5 from coal combustion with addition of atomized droplets and steam was investigated. The particles size distribution and number concentration were measured in real time by electrical low pressure impactor (ELPI). The results show that collection efficiency of PM2.5 from coal combustion can be highly improved with steam condensational enlargement. Particle stage collection efficiency increases with the particles, especially for those smaller than 0.3 microm. The separation efficiency can be improved by 60% with the size of particles increasing from 0.03 microm to 0.3 microm for 0.1 kg/m3 of steam addition. The removal efficiency is independent of the gas temperature at the inlet of conditioning chamber for steam addition. But it increases with the gas temperature obviously for atomized droplets addition, which can be improved by 30% with increasing gas temperature from 136 degrees C to 256 degrees C. High removal efficiency of PM2.5 from coal combustion can be obtained with atomized droplets evaporation in hot flue gas except for steam addition.