48 research outputs found
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Contribution of particulate nitrate to airborne measurements of total reactive nitrogen
Simultaneous measurements of speciated, total reactive nitrogen (NOy) and particulate NO3 (particle diameter <1.3 μm) were made on board the NASA P-3B aircraft over the western Pacific in February-April 2001 during the Transport and Chemical Evolution over the Pacific (TRACE-P) experiment. Gas-phase and particulate NOy was measured using a gold tube catalytic converter. For the interpretation of particulate NOy, conversion efficiencies of particulate NH4NO3, KNO3, NaNO3, and Ca(NO3)2 were measured in the laboratory. Only NH4NO3 showed quantitative conversion, and its conversion efficiency was as high as that for HNO3. NOy measured on board the aircraft was found to be systematically higher by 10-30% than the sum of the individual NOy gas components (Σ(NOy)i) at 0-4 km. Particulate NO3- concentrations measured by a particle-into-liquid sampler (PILS) were nearly equal to NOy - Σ(NOy)i under low-dust-loading conditions. The PILS data showed that the majority of the particulate NO3- was in the form of NH4NO3 under these conditions, suggesting that NH4NO3 particles were quantitatively converted to detectable NO by the NOy converter, consistent with the laboratory experiments. The contribution of particulate NO3- to NOy was most important at 0-2 km, where NO3- constituted 10-30% of NOy during TRACE-P. On average, the amounts of particulate NO3- and gas-phase HNO3 were comparable in this region. Copyright 2005 by the American Geophysical Union
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Synoptic-scale transport of reactive nitrogen over the western Pacific in spring
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Impacts of biomass burning in Southeast Asia on ozone and reactive nitrogen over the western Pacific in spring
Aircraft measurements of ozone (O3) and its precursors (reactive nitrogen, CO, nonmethane hydrocarbons) were made over the western Pacific during the Transport and Chemical Evolution Over the Pacific (TRACE-P) campaign, which was conducted during February-April 2001. Biomass burning activity was high over Southeast Asia (SEA) during this period (dry season), and convective activity over SEA frequently transported air from the boundary layer to the free troposphere, followed by eastward transport to the sampling region over the western Pacific south of 30°N. This data set allows for systematic investigations of the chemical and physical processes in the outflow from SEA. Methyl chloride (CH3Cl) and CO are chosen as primary and secondary tracers, respectively, to gauge the degree of the impact of emissions of trace species from biomass burning. Biomass burning is found to be a major source of reactive nitrogen (NO x, PAN, HNO3, and nitrate) and O3 in this region from correlations of these species with the tracers. Changes in the abundance of reactive nitrogen during upward transport are quantified from the altitude change of the slopes of the correlations of these species with CO. NOx decreased with altitude due to its oxidation to HNO3. On the other hand, PAN was conserved during transport from the lower to the middle troposphere, consistent with its low water solubility and chemical stability at low temperatures. Large losses of HNO3 and nitrate, which are highly water soluble, occurred in the free troposphere, most likely due to wet removal by precipitation. This has been shown to be the major pathway of NOy loss in the middle troposphere. Increases in the mixing ratios of O3 and its precursors due to biomass burning in SEA are estimated using the tracers. Enhancements of CO and total reactive nitrogen (NOy), which are directly emitted from biomass burning, were largest at 2-4 km. At this altitude the increases in NOy and O3 were 810 parts per trillion by volume (pptv) and 26 parts per billion by volume (ppbv) above their background values of 240 pptv and 31 ppbv, respectively. The slope of the O3-CO correlation in biomass burning plumes was similar to those observed in fire plumes in northern Australia, Africa, and Canada. The O3 production efficiency (OPE) derived from the O3-CO slope and NOx/CO emission ratio (ER) is shown to be positively correlated with the C2H4 /NOx ER, indicating that the C2H4/NO x ER is a critical parameter in determining the OPE. Comparison of the net O3 flux across the western Pacific region and total O3 production due to biomass burning in SEA suggests that about 70% of O3 produced was transported to the western Pacific. Copyright 2004 by the American Geophysical Union
Organic Constituents on the Surfaces of Aerosol Particles from Southern Finland, Amazonia, and California Studied by Vibrational Sum Frequency Generation
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Open-path, quantum cascade-laser-based sensor for high-resolution atmospheric ammonia measurements
We demonstrate a compact, open-path, quantum cascade-laser-based atmospheric
ammonia sensor operating at 9.06 μm for high-sensitivity, high
temporal resolution, ground-based measurements. Atmospheric ammonia
(NH3) is a gas-phase precursor to fine particulate matter, with
implications for air quality and climate change. Currently, NH3 sensing
challenges have led to a lack of widespread in situ measurements. Our
open-path sensor configuration minimizes sampling artifacts associated with
NH3 surface adsorption onto inlet tubing and reduced pressure sampling
cells, as well as condensed-phase partitioning ambiguities. Multi-harmonic
wavelength modulation spectroscopy allows for selective and sensitive
detection of atmospheric pressure-broadened absorption features. An in-line
ethylene reference cell provides real-time calibration (±20%
accuracy) and normalization for instrument drift under rapidly changing field
conditions. The sensor has a sensitivity and noise-equivalent limit
(1σ) of 0.15 ppbv NH3 at 10 Hz, a mass of ~ 5 kg and
consumes ~ 50 W of electrical power. The total uncertainty in NH3
measurements is 0.20 ppbv NH3 ± 10%, based on a
spectroscopic calibration method. Field performance of this open-path
NH3 sensor is demonstrated, with 10 Hz time resolution and a large
dynamic response for in situ NH3 measurements. This sensor provides the
capabilities for improved in situ gas-phase NH3 sensing relevant for
emission source characterization and flux measurements
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Clarifying the Dominant Sources and Mechanisms of Cirrus Cloud Formation
Analysis of the thermal-mechanical redox stability of Nb2TiO7 and Nb1.33Ti0.67O4 for SOFC application
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Aircraft measurements of BrO, IO, glyoxal, NO<sub>2</sub>, H<sub>2</sub>O, O<sub>2</sub>–O<sub>2</sub> and aerosol extinction profiles in the tropics: comparison with aircraft-/ship-based in situ and lidar measurements
Tropospheric chemistry of halogens and organic carbon over tropical oceans
modifies ozone and atmospheric aerosols, yet atmospheric models remain
largely untested for lack of vertically resolved measurements of bromine
monoxide (BrO), iodine monoxide (IO) and small oxygenated hydrocarbons like
glyoxal (CHOCHO) in the tropical troposphere. BrO, IO, glyoxal, nitrogen
dioxide (NO<sub>2</sub>), water vapor (H<sub>2</sub>O) and O<sub>2</sub>–O<sub>2</sub> collision
complexes (O<sub>4</sub>) were measured by the University of Colorado Airborne Multi-AXis Differential
Optical Absorption Spectroscopy (CU AMAX-DOAS) instrument, aerosol
extinction by high spectral resolution lidar (HSRL), in situ aerosol size
distributions by an ultra high sensitivity aerosol spectrometer (UHSAS) and
in situ H<sub>2</sub>O by vertical-cavity surface-emitting laser (VCSEL) hygrometer. Data are presented from two research flights (RF12, RF17) aboard
the National Science Foundation/National Center for Atmospheric
Research Gulfstream V aircraft over the tropical Eastern Pacific Ocean (tEPO) as
part of the "Tropical Ocean tRoposphere Exchange of Reactive halogens and
Oxygenated hydrocarbons" (TORERO) project (January/February 2012). We assess the
accuracy of O<sub>4</sub> slant column density (SCD) measurements in the presence
and absence of aerosols. Our O<sub>4</sub>-inferred aerosol extinction
profiles at 477 nm agree within 6% with HSRL in the boundary layer and
closely resemble the renormalized profile shape of Mie calculations
constrained by UHSAS at low (sub-Rayleigh) aerosol extinction in the free
troposphere. CU AMAX-DOAS provides a flexible choice of geometry, which we
exploit to minimize the SCD in the reference spectrum (SCD<sub>REF</sub>, maximize
signal-to-noise ratio) and to test the robustness of BrO, IO and glyoxal
differential SCDs. The RF12 case study was conducted in pristine marine and
free tropospheric air. The RF17 case study was conducted above the NOAA RV <i>Ka'imimoana</i> (TORERO cruise, KA-12-01) and provides independent validation
data from ship-based in situ cavity-enhanced DOAS and MAX-DOAS. Inside the
marine boundary layer (MBL) no BrO was detected (smaller than 0.5 pptv), and
0.2–0.55 pptv IO and 32–36 pptv glyoxal were observed. The near-surface
concentrations agree within 30% (IO) and 10% (glyoxal) between ship
and aircraft. The BrO concentration strongly increased with altitude to 3.0 pptv at 14.5 km (RF12, 9.1 to 8.6° N; 101.2 to 97.4° W).
At 14.5 km, 5–10 pptv NO<sub>2</sub> agree with model predictions and demonstrate
good control over separating tropospheric from stratospheric absorbers
(NO<sub>2</sub> and BrO). Our profile retrievals have 12–20 degrees of freedom
(DoF) and up to 500 m vertical resolution. The tropospheric BrO vertical column density (VCD) was 1.5 × 10<sup>13</sup> molec cm<sup>−2</sup> (RF12)
and at least 0.5 × 10<sup>13</sup> molec cm<sup>−2</sup> (RF17, 0–10 km, lower limit). Tropospheric IO VCDs correspond to
2.1 × 10<sup>12</sup> molec cm<sup>−2</sup> (RF12) and 2.5 × 10<sup>12</sup> molec cm<sup>−2</sup>
(RF17) and glyoxal VCDs of 2.6 × 10<sup>14</sup> molec cm<sup>−2</sup> (RF12) and 2.7 × 10<sup>14</sup> molec cm<sup>−2</sup> (RF17).
Surprisingly, essentially all BrO as well as
the dominant IO and glyoxal VCD fraction was located above 2 km (IO:
58 ± 5%, 0.1–0.2 pptv; glyoxal: 52 ± 5%, 3–20 pptv). To our
knowledge there are no previous vertically resolved measurements of BrO and
glyoxal from aircraft in the tropical free troposphere. The atmospheric
implications are briefly discussed. Future studies are necessary to better
understand the sources and impacts of free tropospheric halogens and
oxygenated hydrocarbons on tropospheric ozone, aerosols, mercury oxidation
and the oxidation capacity of the atmosphere
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Contribution of particulate nitrate to airborne measurements of total reactive nitrogen
Simultaneous measurements of speciated, total reactive nitrogen (NOy) and particulate NO3 (particle diameter <1.3 μm) were made on board the NASA P-3B aircraft over the western Pacific in February-April 2001 during the Transport and Chemical Evolution over the Pacific (TRACE-P) experiment. Gas-phase and particulate NOy was measured using a gold tube catalytic converter. For the interpretation of particulate NOy, conversion efficiencies of particulate NH4NO3, KNO3, NaNO3, and Ca(NO3)2 were measured in the laboratory. Only NH4NO3 showed quantitative conversion, and its conversion efficiency was as high as that for HNO3. NOy measured on board the aircraft was found to be systematically higher by 10-30% than the sum of the individual NOy gas components (Σ(NOy)i) at 0-4 km. Particulate NO3- concentrations measured by a particle-into-liquid sampler (PILS) were nearly equal to NOy - Σ(NOy)i under low-dust-loading conditions. The PILS data showed that the majority of the particulate NO3- was in the form of NH4NO3 under these conditions, suggesting that NH4NO3 particles were quantitatively converted to detectable NO by the NOy converter, consistent with the laboratory experiments. The contribution of particulate NO3- to NOy was most important at 0-2 km, where NO3- constituted 10-30% of NOy during TRACE-P. On average, the amounts of particulate NO3- and gas-phase HNO3 were comparable in this region. Copyright 2005 by the American Geophysical Union