Lawrence Layman | Desert Research Institute (original) (raw)

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Papers by Lawrence Layman

A nebulizer for generating aerosol having small droplet sizes and high efficiency at low sample i... more A nebulizer for generating aerosol having small droplet sizes and high efficiency at low sample introduction rates. The nebulizer has a cylindrical gas permeable active surface. A sleeve is disposed around the cylinder and gas is provided from the sleeve to the interior of the cylinder formed by the active surface. In operation, a liquid is provided to the inside

Isotopes in Environmental and Health Studies, 2013

2013): Comparison of water isotope-ratio determinations using two cavity ringdown instruments and... more 2013): Comparison of water isotope-ratio determinations using two cavity ringdown instruments and classical mass spectrometry in continuous ice-core analysis, Isotopes in Environmental and Health Studies,

We present the WD2014 chronology for the upper part (0–2850 m; 31.2 ka BP) of the West Antarctic ... more We present the WD2014 chronology for the upper part (0–2850 m; 31.2 ka BP) of the West Antarctic Ice Sheet (WAIS) Divide (WD) ice core. The chronology is based on counting of annual layers observed in the chemical, dust and electrical conductivity records. These layers are caused by seasonal changes in the source, transport, and deposi-tion of aerosols. The measurements were interpreted manually and with the aid of two automated methods. We validated the chronology by comparing to two high-accuracy, absolutely dated chronologies. For the Holocene, the cos-mogenic isotope records of 10 Be from WAIS Divide and 14 C for IntCal13 demonstrated that WD2014 was consistently accurate to better than 0.5 % of the age. For the glacial period, comparisons to the Hulu Cave chronology demonstrated that WD2014 had an accuracy of better than 1 % of the age at three abrupt climate change events between 27 and 31 ka. WD2014 has consistently younger ages than Green-land ice core chronologies during most of the Holocene. For

Climate of the Past, 2015

The West Antarctic Ice Sheet Divide (WAIS Divide, WD) ice core is a newly drilled, high-accumulat... more The West Antarctic Ice Sheet Divide (WAIS Divide, WD) ice core is a newly drilled, high-accumulation deep ice core that provides Antarctic climate records of the past ∼ 68 ka at unprecedented temporal resolution. The upper 2850 m (back to 31.2 ka BP) have been dated using annual-layer counting. Here we present a chronology for the deep part of the core (67.8-31.2 ka BP), which is based on stratigraphic matching to annual-layer-counted Greenland ice cores using globally well-mixed atmospheric methane. We calculate the WD gas age-ice age difference ( age) using a combination of firn densification modeling, ice-flow modeling, and a data set of δ 15 N-N 2 , a proxy for past firn column thickness. The largest age at WD occurs during the Last Glacial Maximum, and is 525 ± 120 years. Internally consistent solutions can be found only when assuming little to no influence of impurity content on densification rates, contrary to a recently proposed hypothesis. We synchronize the WD chronology to a linearly scaled version of the layer-counted Greenland Ice Core Chronology (GICC05), which brings the age of Dansgaard-Oeschger (DO) events into agreement with the U / Th absolutely dated Hulu Cave speleothem record. The small age at WD provides valuable opportunities to investigate the timing of atmospheric greenhouse gas variations relative to Antarctic climate, as well as the interhemispheric phasing of the "bipolar seesaw".

Previous studies of line widths and shapes of spectral lines emitted from the inductively coupled... more Previous studies of line widths and shapes of spectral lines emitted from the inductively coupled plasmas (ICP) have concentrated on plasmas sustained in pure argon [1]. For the present study, we used the Los Alamos Fourier transform spectrometer to estimate line widths and line shapes of Fe I lines emitted from helium and argon-nitrogen ICP discharges. The effect of gas composition and plasma operating conditions on widths and shapes of the spectral lines were examined. Line widths and line shapes of Fe lines were compared with those of argon and helium for Ar ICP and He ICP discharges. Results were used to calculate Doppler temperatures and electron number densities of the cited plasmas.

Journal of Geophysical Research: Atmospheres, 2014

The sources and transport pathways of aerosol species in Antarctica remain uncertain, partly due ... more The sources and transport pathways of aerosol species in Antarctica remain uncertain, partly due to limited seasonally resolved data from the harsh environment. Here, we examine the seasonal cycles of major ions in three high-accumulation West Antarctic ice cores for new information regarding the origin of aerosol species. A new method for continuous acidity measurement in ice cores is exploited to provide a comprehensive, charge-balance approach to assessing the major non-sea-salt (nss) species. The average nss-anion composition is 41% sulfate (SO 4 2À ), 36% nitrate (NO 3 À ), 15% excess-chloride (ExCl À ), and 8% methanesulfonic acid (MSA). Approximately 2% of the acid-anion content is neutralized by ammonium (NH 4 + ), and the remainder is balanced by the acidity (Acy ≈ H + À HCO 3 À ). The annual cycle of NO 3 À shows a primary peak in summer and a secondary peak in late winter/spring that are consistent with previous air and snow studies in Antarctica. The origin of these peaks remains uncertain, however, and is an area of active research. A high correlation between NH 4 + and black carbon (BC) suggests that a major source of NH 4 + is midlatitude biomass burning rather than marine biomass decay, as previously assumed. The annual peak in excess chloride (ExCl À ) coincides with the late-winter maximum in sea ice extent. Wintertime ExCl À is correlated with offshore sea ice concentrations and inversely correlated with temperature from nearby Byrd station. These observations suggest that the winter peak in ExCl À is an expression of fractionated sea-salt aerosol and that sea ice is therefore a major source of sea-salt aerosol in the region.

Journal of Geophysical Research: Atmospheres, 2013

Nature Climate Change, 2014

Spectrochimica Acta Part B: Atomic Spectroscopy, 1994

Intensities and widths of atomic spectral lines of He, H, and Fe, excited in an atmosphericpressu... more Intensities and widths of atomic spectral lines of He, H, and Fe, excited in an atmosphericpressure helium inductively coupled plasma (He ICP) were measured with a high-resolution Fourier transform spectrometer. These data along with measured intensities of rotational bands, such as B*P: + XX: of N; and A%+ + XTI, of OH, were used to estimate excitation, rotational, and Doppler temperatures, and electron number densities. Similar to an Ar ICP, the widths of Fe lines ranged from 3 to 4 pm. The line widths of H and He lines in the spectra from a dry He ICP generally were larger than those observed from a wet plasma. The line-width data for H were used to evaluate electron number densities in wet and dry He ICP discharges. The excitation temperature of He ICP was dependent upon the energy levels of the selected thermometric species. The rotational temperatures measured from OH (3000 K) and N; (2200 K) were substantially different from those of an Ar ICY. The presence of water in the aerosol resulted in an increase in the excitation temperature of the He ICP, similar to the trend observed earlier for the Ar ICP. The implications of these results in He ICP spectrochemical analysis are discussed. 1081 1082 MINGXIANG CAI et al.

Spectrochimica Acta Part B: Atomic Spectroscopy, 1990

The high-resolution Fourier transform spectrometer (FIX) of the Los Alamos National Laboratory wa... more The high-resolution Fourier transform spectrometer (FIX) of the Los Alamos National Laboratory was used for diagnostic studies of Ar-N, ICP discharges, High-resolution FIS data were obtained to: (a) conduct analysis of line widths and line shapes for Fe lines to ascertain contributions from the Gaussian and Lore&an components; (b) to calculate the Doppler or translational temperatures of emitting species by using the half width of the Gaussian component; and (c) to determine excitation temperatures based on the relative intensities of many spectral lines. The effect of gas composition and plasma operating ~nditions on line widths, Doppler and excitation temperatures were examined.

Reconstruction of past changes in Arctic sea ice extent may be critical for understanding its fut... more Reconstruction of past changes in Arctic sea ice extent may be critical for understanding its future
15 evolution. Methanesulphonate (MSA) and bromine concentrations preserved in ice cores have both
16 been proposed as indicators of past sea ice conditions. In this study, two ice cores from central and NE
17 Greenland were analysed at sub-annual resolution for MSA (𝐶𝐻#𝑆𝑂#𝐻) and bromine, covering the time
18 period 1750-2010. We examine correlations between ice core MSA and the HadISST1 ICE sea ice
19 dataset and consult back-trajectories to infer the likely source regions. A strong correlation between the
20 low frequency MSA and bromine records during preindustrial times indicates that both chemical species
21 are likely linked to processes occurring on or near sea ice in the same source regions. The positive
22 correlation between ice core MSA and bromine persists until the mid-20th century, when the acidity of
23 Greenland ice begins to increase markedly due to increased fossil fuel emissions. After that time, MSA
24 levels decrease as a result of declining sea ice extent but bromine levels increase. We consider several
25 possible explanations and ultimately suggest that increased acidity, specifically nitric acid, of snow on
26 sea ice stimulates the release of reactive Br from sea ice, resulting in increased transport and deposition
27 on the Greenland ice sheet.

A nebulizer for generating aerosol having small droplet sizes and high efficiency at low sample i... more A nebulizer for generating aerosol having small droplet sizes and high efficiency at low sample introduction rates. The nebulizer has a cylindrical gas permeable active surface. A sleeve is disposed around the cylinder and gas is provided from the sleeve to the interior of the cylinder formed by the active surface. In operation, a liquid is provided to the inside

Isotopes in Environmental and Health Studies, 2013

2013): Comparison of water isotope-ratio determinations using two cavity ringdown instruments and... more 2013): Comparison of water isotope-ratio determinations using two cavity ringdown instruments and classical mass spectrometry in continuous ice-core analysis, Isotopes in Environmental and Health Studies,

We present the WD2014 chronology for the upper part (0–2850 m; 31.2 ka BP) of the West Antarctic ... more We present the WD2014 chronology for the upper part (0–2850 m; 31.2 ka BP) of the West Antarctic Ice Sheet (WAIS) Divide (WD) ice core. The chronology is based on counting of annual layers observed in the chemical, dust and electrical conductivity records. These layers are caused by seasonal changes in the source, transport, and deposi-tion of aerosols. The measurements were interpreted manually and with the aid of two automated methods. We validated the chronology by comparing to two high-accuracy, absolutely dated chronologies. For the Holocene, the cos-mogenic isotope records of 10 Be from WAIS Divide and 14 C for IntCal13 demonstrated that WD2014 was consistently accurate to better than 0.5 % of the age. For the glacial period, comparisons to the Hulu Cave chronology demonstrated that WD2014 had an accuracy of better than 1 % of the age at three abrupt climate change events between 27 and 31 ka. WD2014 has consistently younger ages than Green-land ice core chronologies during most of the Holocene. For

Climate of the Past, 2015

The West Antarctic Ice Sheet Divide (WAIS Divide, WD) ice core is a newly drilled, high-accumulat... more The West Antarctic Ice Sheet Divide (WAIS Divide, WD) ice core is a newly drilled, high-accumulation deep ice core that provides Antarctic climate records of the past ∼ 68 ka at unprecedented temporal resolution. The upper 2850 m (back to 31.2 ka BP) have been dated using annual-layer counting. Here we present a chronology for the deep part of the core (67.8-31.2 ka BP), which is based on stratigraphic matching to annual-layer-counted Greenland ice cores using globally well-mixed atmospheric methane. We calculate the WD gas age-ice age difference ( age) using a combination of firn densification modeling, ice-flow modeling, and a data set of δ 15 N-N 2 , a proxy for past firn column thickness. The largest age at WD occurs during the Last Glacial Maximum, and is 525 ± 120 years. Internally consistent solutions can be found only when assuming little to no influence of impurity content on densification rates, contrary to a recently proposed hypothesis. We synchronize the WD chronology to a linearly scaled version of the layer-counted Greenland Ice Core Chronology (GICC05), which brings the age of Dansgaard-Oeschger (DO) events into agreement with the U / Th absolutely dated Hulu Cave speleothem record. The small age at WD provides valuable opportunities to investigate the timing of atmospheric greenhouse gas variations relative to Antarctic climate, as well as the interhemispheric phasing of the "bipolar seesaw".

Previous studies of line widths and shapes of spectral lines emitted from the inductively coupled... more Previous studies of line widths and shapes of spectral lines emitted from the inductively coupled plasmas (ICP) have concentrated on plasmas sustained in pure argon [1]. For the present study, we used the Los Alamos Fourier transform spectrometer to estimate line widths and line shapes of Fe I lines emitted from helium and argon-nitrogen ICP discharges. The effect of gas composition and plasma operating conditions on widths and shapes of the spectral lines were examined. Line widths and line shapes of Fe lines were compared with those of argon and helium for Ar ICP and He ICP discharges. Results were used to calculate Doppler temperatures and electron number densities of the cited plasmas.

Journal of Geophysical Research: Atmospheres, 2014

The sources and transport pathways of aerosol species in Antarctica remain uncertain, partly due ... more The sources and transport pathways of aerosol species in Antarctica remain uncertain, partly due to limited seasonally resolved data from the harsh environment. Here, we examine the seasonal cycles of major ions in three high-accumulation West Antarctic ice cores for new information regarding the origin of aerosol species. A new method for continuous acidity measurement in ice cores is exploited to provide a comprehensive, charge-balance approach to assessing the major non-sea-salt (nss) species. The average nss-anion composition is 41% sulfate (SO 4 2À ), 36% nitrate (NO 3 À ), 15% excess-chloride (ExCl À ), and 8% methanesulfonic acid (MSA). Approximately 2% of the acid-anion content is neutralized by ammonium (NH 4 + ), and the remainder is balanced by the acidity (Acy ≈ H + À HCO 3 À ). The annual cycle of NO 3 À shows a primary peak in summer and a secondary peak in late winter/spring that are consistent with previous air and snow studies in Antarctica. The origin of these peaks remains uncertain, however, and is an area of active research. A high correlation between NH 4 + and black carbon (BC) suggests that a major source of NH 4 + is midlatitude biomass burning rather than marine biomass decay, as previously assumed. The annual peak in excess chloride (ExCl À ) coincides with the late-winter maximum in sea ice extent. Wintertime ExCl À is correlated with offshore sea ice concentrations and inversely correlated with temperature from nearby Byrd station. These observations suggest that the winter peak in ExCl À is an expression of fractionated sea-salt aerosol and that sea ice is therefore a major source of sea-salt aerosol in the region.

Journal of Geophysical Research: Atmospheres, 2013

Nature Climate Change, 2014

Spectrochimica Acta Part B: Atomic Spectroscopy, 1994

Intensities and widths of atomic spectral lines of He, H, and Fe, excited in an atmosphericpressu... more Intensities and widths of atomic spectral lines of He, H, and Fe, excited in an atmosphericpressure helium inductively coupled plasma (He ICP) were measured with a high-resolution Fourier transform spectrometer. These data along with measured intensities of rotational bands, such as B*P: + XX: of N; and A%+ + XTI, of OH, were used to estimate excitation, rotational, and Doppler temperatures, and electron number densities. Similar to an Ar ICP, the widths of Fe lines ranged from 3 to 4 pm. The line widths of H and He lines in the spectra from a dry He ICP generally were larger than those observed from a wet plasma. The line-width data for H were used to evaluate electron number densities in wet and dry He ICP discharges. The excitation temperature of He ICP was dependent upon the energy levels of the selected thermometric species. The rotational temperatures measured from OH (3000 K) and N; (2200 K) were substantially different from those of an Ar ICY. The presence of water in the aerosol resulted in an increase in the excitation temperature of the He ICP, similar to the trend observed earlier for the Ar ICP. The implications of these results in He ICP spectrochemical analysis are discussed. 1081 1082 MINGXIANG CAI et al.

Spectrochimica Acta Part B: Atomic Spectroscopy, 1990

The high-resolution Fourier transform spectrometer (FIX) of the Los Alamos National Laboratory wa... more The high-resolution Fourier transform spectrometer (FIX) of the Los Alamos National Laboratory was used for diagnostic studies of Ar-N, ICP discharges, High-resolution FIS data were obtained to: (a) conduct analysis of line widths and line shapes for Fe lines to ascertain contributions from the Gaussian and Lore&an components; (b) to calculate the Doppler or translational temperatures of emitting species by using the half width of the Gaussian component; and (c) to determine excitation temperatures based on the relative intensities of many spectral lines. The effect of gas composition and plasma operating ~nditions on line widths, Doppler and excitation temperatures were examined.

Reconstruction of past changes in Arctic sea ice extent may be critical for understanding its fut... more Reconstruction of past changes in Arctic sea ice extent may be critical for understanding its future
15 evolution. Methanesulphonate (MSA) and bromine concentrations preserved in ice cores have both
16 been proposed as indicators of past sea ice conditions. In this study, two ice cores from central and NE
17 Greenland were analysed at sub-annual resolution for MSA (𝐶𝐻#𝑆𝑂#𝐻) and bromine, covering the time
18 period 1750-2010. We examine correlations between ice core MSA and the HadISST1 ICE sea ice
19 dataset and consult back-trajectories to infer the likely source regions. A strong correlation between the
20 low frequency MSA and bromine records during preindustrial times indicates that both chemical species
21 are likely linked to processes occurring on or near sea ice in the same source regions. The positive
22 correlation between ice core MSA and bromine persists until the mid-20th century, when the acidity of
23 Greenland ice begins to increase markedly due to increased fossil fuel emissions. After that time, MSA
24 levels decrease as a result of declining sea ice extent but bromine levels increase. We consider several
25 possible explanations and ultimately suggest that increased acidity, specifically nitric acid, of snow on
26 sea ice stimulates the release of reactive Br from sea ice, resulting in increased transport and deposition
27 on the Greenland ice sheet.