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文献阅读笔记：Silva-2000-AE

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Dust 气溶胶的单颗粒质谱

Information for the paper

Title: Single particle analysis of suspended soil dust from Southern California

Author: Silva, Philip J.

Year: 2000

Journal: Atmospheric Environment

URL: https://doi.org/10.1016/S1352-2310(99)00338-6

Introduction

  1. The use of bulk analysis techniques inherently complicates the possibility of assessing the contribution of dust particles originating from different soil sources, since all particles are collected and analyzed as an integrated sample.
  2. The purpose of this study is to characterize individual particles resulting from the suspension of soil dust. Data on the size and sets of chemical markers are used for the identication of individual soil dust particles in the atmosphere.

Experimental

  1. During this study, each soil sample was dried in an oven prior to analysis, thus facilitating suspension, which cannot be effectively done when moist. This drying process drives off the volatile components associated with the particles. However, for the ultimate purpose of fingerprinting dust particles in the atmosphere, it is the combination of inorganic components that is most useful.

Results

Particle size distributions

  1. Fig. 1 shows a size histogram for the particles generated by the suspension of a soil sample. This distribution is not corrected for instrumental biasing or sampling efficiencies. The dust particles analyzed exhibit a broad size distribution, measuring from approximately 0.6 to about 3.0 μm in aerodynamic diameter.

Chemical composition

The most common types of soil dust (Positive)

  • Fig. 2 show the laser desorption/ionization (LDI) mass spectra from four individual particles showing representative positive ions common to soil dust.
  • The four spectra shown in Fig. 2 are the most typical types observed from the particles in the soil samples that were analyzed.
  1. San Bernardino Mountains (1.6 μm)
    • Major ions: 23[Na]+, 27[Al]+, 39[K]+, 56[Fe]+
    • Minor ions: 1H+, 16O+
  2. Laguna Beach (1.3 μm)
    • Major ions: 23[Na]+, 24[Mg]+, 39[K]+
    • Major ions: 40[Ca]+, 44[Ca]+, 57[CaOH]+, 66[CaCN]+, 75[CaCl]+, 96[Ca2O]+, 112[(CaO)2H]+
    • This calcium-rich particle type is probably indicative of a calcium carbonate or sulfate particle, as many of the same peaks were observed using laser microprobe mass analysis (LAMMA) in a study of calcium compounds.
  3. Laguna Beach (1.9 μm)
    • Major ions: 23[Na]+, 27[Al]+, 39[K]+, 56[Fe]+
    • Major ions: 24[Mg]+, 25[Mg]+, 26[Mg]+
    • This spectrum is similar to the one in Fig. 2a in that it contains sodium, aluminum, potassium, and iron. However, it also clearly contains peaks due to the three isotopes of magnesium (m/z 24, 25, and 26,) and it consistently lacks the peaks due to hydrogen and oxygen.
    • This combination of peaks is very distinct, and seems to be more indicative of dust from sand sources, rather than fine soils.
  4. Box Springs Mountains (1.6 μm)
    • Major ions: 7[Li]+, 23[Na]+, 27[Al]+, 39[K]+, 56[Fe]+, 40[Ca]+, 57[CaOH]+
    • Minor ions: m/z 156
    • The distinctive feature in this spectrum, however, is a cluster of peaks starting at m/z 156.
    • One possible interpretation is that this cluster is indicative of lanthanide oxides or hydroxides.
    • The first four lanthanides oxides (lanthanum, cerium, praseodymium, and neodymium) have isotopes at similar mass-to-charge to the ones observed in this cluster, and the variability could arise from different relative concentrations of the elements in one particle versus another.

The minor types of soil dust (Positive)

  • Fig. 2 shows the most common types of positive ion mass spectra observed from analysis of soil dust. However, the chemical composition of soil particles shows considerably more variability than these four mass spectra.
  • In Fig. 3, four more positive ion mass spectra are shown that display the diversity of the composition of soil particles. These particles are minor types that are observed from the soil samples analyzed.
  • The chemical heterogeneity observed in soil dust particles is a result of the large number of mineral species that are present in soil, and thus one particle can be enriched with an element that is not observed in another particle.
  1. Yucca Valley (a desert area) (2.1 μm)
    • Major ions: 23[Na]+, 27[Al]+, 39[K]+, 56[Fe]+
    • Major ions: 48[Ti]+, 64[TiO]+
    • Minor ions: 93[Nb]+, 109[NbO]+
    • Two peaks are also observed at m/z 93 and 109, probably corresponding to the presence of niniobium and niobium oxide.Since niobium has only one isotope, this assignment is not definitive, however peaks separated by 16 Daltons typically indicate the presence of a metal and its oxide. These peaks are observed in 1% of the soil particles analyzed from the Yucca Valley sample.
  2. San Bernardino Mountain (2.3 μm)
    • Major ions: 23[Na]+, 27[Al]+, 39[K]+, 54[Fe]+, 56[Fe]+
    • Minor ions: 55[Mn]+, 206[Pb]+, 207[Pb]+, 208[Pb]+
    • Peaks due to two other elements are also observed, m/z 55, corresponding to manganese, and three peaks at m/z 206, 207, and 208, representing the three most abundant isotopes of lead.
    • Manganese and lead are observed in particles generated from all five soil samples studied, although they are detected less frequently than the more common cations, such as sodium, aluminum, potassium, calcium, and iron.
  3. Yucca Valley (2.0 μm)
    • Major ions: 23[Na]+, 27[Al]+, 39[K]+, 41[K]+, 55[Mn]+, 56[Fe]+
    • Major ions: 138[Ba]+
  4. Yucca Valley (2.8 μm)
    • Major ions: 27[Al]+, 39[K]+, 40[Ca]+
    • Major ions: 90[Zr]+, 94[Zr]+, 106[ZrO]+, 110[ZrO]+
    • Likewise, Fig. 3d shows zirconium and zirconium oxide peaks; both elements are observed in particles from several soil samples, although typically in < 1% of all the particles.

Negative ion mass spectra

  • The negative ion mass spectra of particles from soil dust are dominated by the presence of silicon-oxide clusters. Negative ion mass spectra can also provide information about other oxygen-containing ions, such as nitrate, sulfate, phosphate, as well as halides.
  1. Box Springs Mountains (1.5 μm)
    • Major ions: 1[H]-, 16[O]-, 17[OH]-
    • Major ions: 59[AlO2]-, 60[SiO2]-, 76[SiO3]-, 119[AlSiO4]-, 179[AlSiO4SiO2]-
    • Minor ions: 26[CN]-, 60[CO3]-
  2. Soil particle (1.6 μm)
    • Major ions: 1[H]-, 16[O]-, 17[OH]-
    • Major ions: 60[SiO2]-, 76[SiO3]-, 119[AlSiO4]-
    • Major ions: 63[PO2]-, 79[PO3]-
    • Major ions: 12[C]-, 26[CN]-, 60[CO3]-, 35[Cl]-
    • The presence of an intense peak at m/z 12 (C-), is indicative of carbon containing compounds. The presence of either carbonate ion or organic compounds may produce this peak.
  3. Laguna Beach sand (1.8 μm)
    • Major ions: 16[O]-, 17[OH]-, 19[F]-, 12[C]-, 35[Cl]-
    • Major ions: 59[AlO2]-, 76[SiO3]-, 119[AlSiO4]-, 179[AlSiO4SiO2]-
    • Major ions: 63[PO2]-, 79[PO3]-
    • In this spectrum, a high intensity peak at m/z 19 (F-) is also observed. This peak is present more frequently and with higher intensity in particles from the Laguna Beach sample than any other.
  4. San Bernardino Mountain (2.7 μm)
    • Major ions: 1[H]-, 16[O]-, 17[OH]-
    • Major ions: 26[CN]-, 35[Cl]-, 46[NO2]-, 63[PO2]-, 76[SiO3]-
    • Major ions: 86[ 54FeO2]-, 88[ 56FeO2]-
    • In addition, the figure shows the presence of peaks at m/z 86 and 88. These peaks match the isotopic ratios of iron (54Fe and 56Fe), and are most likely due to FeO2- . The presence of iron oxide clusters is observed frequently in the mass spectra of single soil dust particles.

Summary

  1. Sodium, magnesium, aluminum, potassium, calcium, and iron are the most common positive ions observed in the mass spectra.
  2. Common negative ions observed include aluminum, silicon, phosphorous, and nitrogen oxides.
  3. The presence of CN- in over 70% of the spectra from several samples most likely indicates organic species containing carbon-nitrogen bonds rather than the cyanide ion.

Atmospheric aerosol analysis

  1. Type 1 (1.5 μm) (Positive)
    • Major ions: 23[Na]+, 27[Al]+, 39[K]+, 56[Fe]+
    • Minor ions: 1H+, 16O+
    • The spectrum is remarkably similar to the one shown in Fig. 2a (San Bernardino Mountains, 1.6 μm).
    • This particle type is by far the most common soil dust particle observed in ambient particle samples in Riverside.
  2. Type 2 (1.6 μm) (Positive)
    • Major ions: 23[Na]+, 40[Ca]+, 44[Ca]+, 56[CaO]+, 96[Ca2O]+, 112[(CaO)2H]+
    • This mass spectrum is similar to the one in Fig. 2b (Laguna Beach Sand, 1.3 μm), although with fewer clusters present.
  3. Type 3 (1.9 μm) (Negative)
    • Major ions: 16[O]-, 17[OH]-, 26[CN]-, 35[Cl]-
    • Major ions: 63[PO2]-, 79[PO3]-
    • Major ions: 76[SiO3]-, 119[AlSiO4]-, 179[AlSiO4SiO2]-
    • Major ions: 46[NO2]-, 62[NO3]-
  4. Type 4 (1.1 μm) (Negative)
    • Major ions: 1[H]-, 16[O]-, 17[OH]-, 12[C]-, 26[CN]-, 35[Cl]-
    • Major ions: 63[PO2]-, 79[PO3]-
    • Major ions: 76[SiO3]-, 119[AlSiO4]-, 179[AlSiO4SiO2]-
    • Major ions: 46[NO2]-, 62[NO3]-
    • Both of these negative ion spectra contain very intense peaks due to nitrogen oxides (46[NO2]- and 62[NO3]-). The large intensity of these peaks indicates that these mineral particles may have served as a sink for gas-phase nitrogen species such as NOx and nitric acid, as models have previously indicated.

总结与启发

  1. 一般来说，悬浮尘产生的颗粒粒径较大 (> 1 μm).
  2. Dust 颗粒物正离子谱图离子：
    • 主要参考离子1: sodium (23[Na]+), aluminum (27[Al]+), potassium (39[K]+), iron (54[Fe]+, 56[Fe]+)
    • 主要参考离子2: calcium clusters, 40/44[Ca]+, 57[CaOH]+, 66[CaCN]+, 75[CaCl]+, 96[Ca2O]+, 112[(CaO)2H]+
    • 次要参考离子1: lithium (7[Li]+), magnesium (24/25/26[Mg]+), manganese (55[Mn]+), lead (206/207/208[Pb]+), barium (138[Ba]+)
    • 次要参考离子2: zirconium (90/94[Zr]+), zirconium oxide (106/110[ZrO]+)
    • 次要参考离子3: titanium (48[Ti]+), titanium oxide (64[TiO]+)
    • 次要参考离子4: niobium (93[Nb]+), niobium oxide (109[NbO]+)
    • 次要参考离子4: 1H+, 16O+
  3. Dust 颗粒物负离子谱图离子：
    • 主要参考离子1: hydrogen (1[H]-), oxygen (16[O]-), hydroxide (17[OH]-)
    • 主要参考离子2: silicate clusters，76[SiO3]-, 119[AlSiO4]-, 179[AlSiO4SiO2]-
    • 主要参考离子3: aluminum (59[AlO2]-), phosphate (63[PO2]-, 79[PO3]-), 35[Cl]-
    • 次要参考离子4: nitrogen oxides, 26[CN]-, 46[NO2]-, 62[NO3]-
    • 次要参考离子1: iron oxide (86/88[ 54/56FeO2]-)
  4. 26[CN]- 离子的出现有两种解释，一是来源于存在碳氮键的有机物，二是来源于氰化物。结合谱图中的一些碳质离子（12[C]-，60[CO3]-），作者倾向于是前者。
  5. 实际大气中观测到的矿物颗粒质谱图中，硝酸盐离子的信号强度较强，表明这些颗粒可能已作为气相氮物质（如氮氧化物和硝酸）的汇。

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