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文献阅读笔记：Dall'Osto-2019-ACS

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南极海洋表面和大气共生环境中的烷基胺

Information for the paper

Title: Simultaneous Detection of Alkylamines in the Surface Ocean and Atmosphere of the Antarctic Sympagic Environment

Author: Manuel Dall'Osto

Year: 2019

Journal: ACS Earth and Space Chemistry

URL: https://doi.org/10.1021/acsearthspacechem.9b00028

Introduction

  1. The plankton-derived trace gas dimethylsulfid (DMS) has long been identified as a major source of nonsea-salt sulfate and methanesulfonate in newly formed and aged secondary aerosols, enhancing particle number and mass concentrations.
  2. Alkylamines may comprise a small percentage of marine organic nitrogen but can effectively diffuse across the air−sea interface where they may affect the chemistry of the atmosphere, for example, being one of the few semivolatile compounds that reacts with sulfate and other acidic species in the atmosphere to form aerosol.
  3. The mass spectra of an aerosol population can be defined as the degree of homogeneity in the distribution of the chemical components within it. Thus, an aerosol population can be broadly defined as "internally mixed" when each single particle presents the same chemical composition, which equals the bulk composition, or "externally mixed" when particles of different chemical composition co-occur.
  4. TMA (and other low-molecular weight alkylamines as well) is water-soluble and semivolatile, so it tends to partition between the gas and aerosol phase as dictated by equilibrium thermodynamics. Similar to its inorganic counterpart ammonia/ammonium, TMA tends to increasingly partition to the aerosol as temperature decreases, and aerosol liquid water content (LWC) and acidity increases.

Methodology

  1. We used the ATOFMS (model 3800−100, TSI, Inc.) to collect bipolar mass spectra of individual aerosol particles.
  2. Briefly, some of the main ART-2a clusters were very similar to each other. The main differences were due to the peak area or to the noise level. For example, a problem encountered in the classification of different particle types arises from the miscalibration of some peaks (i.e., while the ATOFMS positive spectra are almost identical between two different classes, the negative one could only differ by a shifting of m/z 1 of spectra or few peaks). Although the reason for this miscalibration is unknown, the issue was solved by merging the two different ART-2a clusters.
  3. N-osmolyte concentration: glycine betaine + choline
  4. Methylamine concentration: monomethylamine + dimethylamine + trimethylamine

Results and Discussion

Water and Melted Sea Ice Measurements

  1. The melted sea ice measurements were carried out 24 h after bubbling, at least after water recirculation for ice melting; as there was no control on gas losses, it is very likely these measurements are underestimates, nevertheless still supporting the idea that sea ice is a source of these chemical compounds (N-osmolyte and methylamine).

Aerosol Chamber Experiments

  1. Mass spectra of particles generated by bubbling melted sea ice were compared with those produced by bubbling surface seawater. ... Here, we expanded the analysis by running ART-2a on the combined seawater and melted sea ice aerosol chamber data set (approximately 7000 single particle mass spectra).
  2. We already reported that ATOFMS single-particle information on the mixing state revealed that 21% of the sea ice-derived particles were an internal mixture of sea salt with organic nitrogen and carbon, versus only 5% in seawater spray.
  3. The primary aerosol chamber ATOFMS measurements revealed unique organic nitrogen features in the mass spectra of individual particles, named "OC-CHN" (organic carbon-amines), "OC-CHN-NaCl" (organic carbon-amines-sodium chloride), "NaCl-OC-CHN" (sodium chloride-organic carbon-amines), and "Ca-OC-CHN" (calcium-organic carbon-amines), altogether accounting for about 5——21% of the ATOFMS particles classified during aerosol chamber experiments (depending on the water type bubbled).
  4. All particles were internally mixed with Na (m/z 23), Mg (m/z 24), K (m/z 39), and Cl (m/z 35), consistent with the expectation that they were internally mixed with sea salt in sea spray. Peaks at m/z −111 and −129 were attributed to [NaCl2(H2O)]− and [NaCl2(H2O)2]−, respectively. The presence of water in pure sea-salt particles was confirmed by the presence of peaks at m/z −16 [O]−, −17 [OH]−, −46 [Na2]−, 62 [Na2O]+, and 63 [Na2OH]+.
  5. The negative ion mass spectrum shows prominent peaks at m/z −26 [CN]− and m/z −42 [CNO]−, indicating that all particle types presented were internally mixed with organo-nitrogen species.
  6. The ATOFMS single particle mass spectra collected during the primary aerosol chamber experiments revealed that all the amine-containing particles were internally mixed with sea spray, although larger supermicron particles showed stronger influence of sea spray and likely other Ca-rich components.

OC-CHN (Organic Carbon-Amines)

  1. However, in this study we detected TMA in primary-generated aerosol particles; furthermore, the analysis of water samples also revealed the presence of TMA, and compounds that could readily produce TMA (e.g., glycine betaine).
  2. This ATOFMS OC-CHN particle type also presents peaks at m/z 27 [C2H3]+ and m/z 43 [(CH3)CO]+ usually associated with oxidized organic aerosol.
  3. Finally, the unique presence of peaks at m/z −45, −59, and −71 are likely to be due to the formate [CHO2]−, acetate [C2H3O2]−, and propionate [C3H5O2]− ions, respectively.
  4. In summary, particle type OC-CHN was characerized by the highest amount of organic peaks both in the positive and negative mass spectra, and distributed in the smallest size bins at about 0.5 μm.

OC-CHN-NaCl (Organic Carbon-Amines-Sodium Chloride)

  1. Relative to the previous one, this type shows a presence of a peak at m/z 81 [Na2Cl], usually considered as a marker for NaCl.

NaCl-ON−CHN (Sodium Chloride-Organic Carbon-Amines)

  1. Major peaks can be seen for sea spray due to [Na2Cl]+ (m/z 81 and 83) and [NaCl2]− (m/z −93, −95, and −97), respectively, in the positive and negative mass spectra.
  2. This was confirmed by the larger average size distributions (Figure S1) where supermicron particles were present.

Ca-OC-CHN (Calcium-Organic Carbon-Amines)

  1. In the positive spectra, strong peaks associated with calcium (m/z 40 [Ca]+, 56 [CaO]+, 57 [CaOH]+, and 96 [Ca2O]+) were present.
  2. These particles were, on average, the largest submicron organic nitrogen-containing particles detected in this study.
  3. The enrichment of calcium may be possibly related to marine polymeric gels, which are produced by phytoplankton and sea ice alga secretions and can be transferred by bubble bursting from the air−sea interface into the polar atmosphere.
  4. These biopolymers are interbridged with divalent cations (Ca2+ and Mg2+) to which other organic compounds, such as proteins and lipids, are readily bound, resulting in a gel-like consistency.
  5. A subset of coarser particles contained alkylamines internally mixed with calcium, which could originate from algae or other biological samples in the form of particulate organic matter such as marine polymeric gels.

Aerosol Ambient Data.

  1. It is worth noting that the majority of the ambient ATOFMS spectra contained a main peak at m/z 114, which may be assigned to dipropylamine or tripropylamine. This peak was not seen in ATOFMS positive mass spectra from the generated primary aerosols reported. The marker ion at m/z 114 has previously been demonstrated to be preserved in particles that contain amine salts and which have been subjected to photo-oxidation. Further studies are needed to understand more about the origin of the peak at m/z 114 and why it was not seen in aerosol tank experiments. It is likely that unknown photo-oxidative processes could be converting ON primary species into the ambient atmosphere ones responsible for the peak at m/z 114.
  2. In the negative mass spectra, peaks due to oxalate (m/z −89, [(C2O4H)H]−) and to a lesser extent sulfate (m/z −97 [SO4]2−) could be seen. The small peak at m/z 179 is attributed to the oxalic acid dimer [(C2O4H)2H]−, which is commonly observed in the spectra of oxalic acid standards. This supports the fact that the peak at m/z −89 can be predominantly attributed to oxalic acid.
  3. In our ambient aerosols study, about a fourth of the detected and analyzed particles collected in Antarctic air masses over a period of about 40 days contained alkylamines. Most of them (75−89%) were externally mixed with sea spray and likely were of secondary origin.
  4. They also demonstrate that a flux of low molecular weight alkyl amines from seawater to the atmospheric gas phase and subsequent condensation onto acidic submicron particles is possible over the Weddell Sea, and in fact will only partition to the most acidic of submicron particles (ultrafines).

Organic Nitrogen Sources in the Antarctic Region

  1. In the marine environment, low molecular weight aliphatic amines usually have gas-phase concentrations that are about 2 orders of magnitude lower than that of ammonia (NH3); however, these species are more basic than NH3, which makes them better suited to neutralize strong acids like sulfuric and methanesulfonic and stabilize molecular clusters that may lead to new particle formation.
  2. Our study points to sea ice and surrounding microbiota being an important and overlooked contributor to aerosols through emissions of volatile and nonvolatile organic nitrogen, including alkylamines.

总结与启发

  1. 作者把表面海水和融化的海冰气溶胶化，通过 ATOFMS 检测发现，约 21% 海冰-气溶胶内部混有海盐、有机氮和含碳物质，而海水喷雾则只有 5%。从海水-融化海冰的气溶胶颗粒物（一次源）中提取出含有机氮颗粒物并分为四类，OC-CHN, OC-CHN-NaCl, NaCl-OC-CHN, 以及 Ca-OC-CHN。这些气溶胶中含有 TMA 等烷基胺，表明这些海水、海冰可能是大气中烷基胺的一个来源。Ca-OC-CHN 类气溶胶中含有钙物质，作者认为这些钙物质与海洋聚合物凝胶有关，这些凝胶可能来浮游植物和藻类等。
  2. 从大气中直接检测到的颗粒物中，约有 1/4 的颗粒物含有烷基胺，这 1/4 的颗粒物中的大部分（75%-89%）与海洋喷雾外部混合，可能是二次形成。大气颗粒物中，检测到了 m/z 114 峰，但是在海水-融化海冰的气溶胶中并未发现该信号，作者认为含有胺盐的颗粒物经光氧化后才会产生 m/z 114。大气颗粒物中还检测到草酸（m/z -89, -179），草酸通常来源于液相氧化过程。此外，从大气中直接检测的气溶胶中，作者并未提到是否检测到这类Ca-OC-CHN。
  3. 作者对海水海冰气溶胶的描述较为详细，但是对大气中直接检测颗粒物的描述过于简略。作者提到约有 1/4 的大气颗粒物含有烷基胺，但是却只展示并描述了其中 1 个（不是一类）含烷基胺颗粒物的质谱图。个人认为至少应当把大气中含烷基胺的众多颗粒物的平均质谱图给出，如果能像海水海冰气溶胶那样进行分类展示就更好了。

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