Plume Chemistry Research Articles

The climate impact of ship NO<sub>x</sub> emissions: an improved estimate accounting for plume chemistry

Abstract. Nitrogen oxide (NOx) emissions from maritime shipping produce ozone (O3) and hydroxyl radicals (OH), which in turn destroy methane (CH4). The balance between this warming (due to O3) and cooling (due to CH4) determines the net effect of ship NOx on climate. Previous estimates of the chemical impact and radiative forcing (RF) of ship NOx have generally assumed that plumes of ship exhaust are instantly diluted into model grid cells spanning hundreds of kilometers, even though this is known to produce biased results. Here we improve the parametric representation of exhaust-gas chemistry developed in the GEOS-Chem chemical transport model (CTM) to provide the first estimate of RF from shipping that accounts for sub-grid-scale ship plume chemistry. The CTM now calculates O3 production and CH4 loss both within and outside the exhaust plumes and also accounts for the effect of wind speed. With the improved modeling of plumes, ship NOx perturbations are smaller than suggested by the ensemble of past global modeling studies, but if we assume instant dilution of ship NOx on the grid scale, the CTM reproduces previous model results. Our best estimates of the RF components from increasing ship NOx emissions by 1 Tg(N) yr−1 are smaller than that given in the past literature: + 3.4 ± 0.85 mW m−2 (1σ confidence interval) from the short-lived ozone increase, −5.7 ± 1.3 mW m−2 from the CH4 decrease, and −1.7 ± 0.7 mW m−2 from the long-lived O3 decrease that accompanies the CH4 change. The resulting net RF is −4.0 ± 2.0 mW m−2 for emissions of 1 Tg(N) yr−1. Due to non-linearity in O3 production as a function of background NOx, RF from large changes in ship NOx emissions, such as the increase since preindustrial times, is about 20% larger than this RF value for small marginal emission changes. Using sensitivity tests in one CTM, we quantify sources of uncertainty in the RF components and causes of the ±30% spread in past model results; the main source of uncertainty is the composition of the background atmosphere in the CTM, which is driven by model formulation (±10 to 20%) and the plausible range of anthropogenic emissions (±10%).

Quantitative measurements and modeling of industrial formaldehyde emissions in the Greater Houston area during campaigns in 2009 and 2011

AbstractA sensitive Mobile differential optical absorption spectroscopy (DOAS) system with real‐time evaluation capability and HCHO detection limit of 3 ppb over 100 m has been developed. The system was operated together with a Solar Occultation Flux system for large‐scale vertical flux measurements of HCHO, NO2, SO2, and VOCs in the Houston‐Galveston‐Brazoria area during two studies, in 2009 (Study of Houston Atmospheric Radical Precursors campaign) and in 2011 (Air Quality Research Program study). Both in 2009 and 2011, HCHO plumes from five separate local sources in Texas City, Mont Belvieu, and Houston Ship Channel (HSC) were repeatedly detected using Mobile DOAS with emissions varying between 6 and 40 kg/h. In many cases significant alkene emissions were detected simultaneously with the HCHO plumes. Furthermore, in 2011 two additional sources were observed in Texas City and in HSC, with 10 kg/h and 31 kg/h HCHO, respectively. A plume chemistry model was applied to 13 cases to investigate whether the detected HCHO was emitted directly from the industries or was produced by photochemical degradation of VOCs. The model results showed that on average 90% of the detected HCHO was of primary origin and the photochemical production contributed more than 10% in only three cases. Based on the repeatability, it is likely that the most significant HCHO sources in the area are included in this study with an overall emission of 120 kg/h. On a regional scale, this emission is small compared to the secondary HCHO formed from oxidation of reactive VOCs emitted from the same industries, estimated to be an order of magnitude higher.

First satellite detection of volcanic OClO after the eruption of Puyehue‐Cordón Caulle

AbstractVolcanoes release large amounts of halogen species such as HCl and HBr, which can be converted into reactive halogens by heterogeneous photochemical reactions that are currently not fully characterized. Here we report on the first satellite detection of volcanic chlorine dioxide (OClO). Measurements were performed using the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography instrument for the ash‐laden plume emitted after the 2011 eruption of Puyehue‐Cordón Caulle in Chile. We also identified volcanic BrO using the Ozone Monitoring Instrument, as well as enhanced HCl in data of the Microwave Limb Sounder instrument. These observations suggest that OClO was formed in the plume by the ClO + BrO reaction in presence of a large excess of ClO. The present satellite data set could help better understand reactive halogen chemistry in volcanic plumes and its impact on atmospheric composition.

Reductions in aircraft particulate emissions due to the use of Fischer–Tropsch fuels

Abstract. The use of alternative fuels for aviation is likely to increase due to concerns over fuel security, price stability, and the sustainability of fuel sources. Concurrent reductions in particulate emissions from these alternative fuels are expected because of changes in fuel composition including reduced sulfur and aromatic content. The NASA Alternative Aviation Fuel Experiment (AAFEX) was conducted in January–February 2009 to investigate the effects of synthetic fuels on gas-phase and particulate emissions. Standard petroleum JP-8 fuel, pure synthetic fuels produced from natural gas and coal feedstocks using the Fischer–Tropsch (FT) process, and 50% blends of both fuels were tested in the CFM-56 engines on a DC-8 aircraft. To examine plume chemistry and particle evolution with time, samples were drawn from inlet probes positioned 1, 30, and 145 m downstream of the aircraft engines. No significant alteration to engine performance was measured when burning the alternative fuels. However, leaks in the aircraft fuel system were detected when operated with the pure FT fuels as a result of the absence of aromatic compounds in the fuel. Dramatic reductions in soot emissions were measured for both the pure FT fuels (reductions in mass of 86% averaged over all powers) and blended fuels (66%) relative to the JP-8 baseline with the largest reductions at idle conditions. At 7% power, this corresponds to a reduction from 7.6 mg kg−1 for JP-8 to 1.2 mg kg−1 for the natural gas FT fuel. At full power, soot emissions were reduced from 103 to 24 mg kg−1 (JP-8 and natural gas FT, respectively). The alternative fuels also produced smaller soot (e.g., at 85% power, volume mean diameters were reduced from 78 nm for JP-8 to 51 nm for the natural gas FT fuel), which may reduce their ability to act as cloud condensation nuclei (CCN). The reductions in particulate emissions are expected for all alternative fuels with similar reductions in fuel sulfur and aromatic content regardless of the feedstock. As the plume cools downwind of the engine, nucleation-mode aerosols form. For the pure FT fuels, reductions (94% averaged over all powers) in downwind particle number emissions were similar to those measured at the exhaust plane (84%). However, the blended fuels had less of a reduction (reductions of 30–44%) than initially measured (64%). The likely explanation is that the reduced soot emissions in the blended fuel exhaust plume results in promotion of new particle formation microphysics, rather than coating on pre-existing soot particles, which is dominant in the JP-8 exhaust plume. Downwind particle volume emissions were reduced for both the pure (79 and 86% reductions) and blended FT fuels (36 and 46%) due to the large reductions in soot emissions. In addition, the alternative fuels had reduced particulate sulfate production (near zero for FT fuels) due to decreased fuel sulfur content. To study the formation of volatile aerosols (defined as any aerosol formed as the plume ages) in more detail, tests were performed at varying ambient temperatures (−4 to 20 °C). At idle, particle number and volume emissions were reduced linearly with increasing ambient temperature, with best fit slopes corresponding to −8 × 1014 particles (kg fuel)−1 °C−1 for particle number emissions and −10 mm3 (kg fuel)−1 °C−1 for particle volume emissions. The temperature dependency of aerosol formation can have large effects on local air quality surrounding airports in cold regions. Aircraft-produced aerosols in these regions will be much larger than levels expected based solely on measurements made directly at the engine exit plane. The majority (90% at idle) of the volatile aerosol mass formed as nucleation-mode aerosols, with a smaller fraction as a soot coating. Conversion efficiencies of up to 2.8% were measured for the partitioning of gas-phase precursors (unburned hydrocarbons and SO2) to form volatile aerosols. Highest conversion efficiencies were measured at 45% power.

Implementation and application of sub-grid-scale plume treatment in the latest version of EPA’s third-generation air quality model, CMAQ 5.01

The Community Multiscale Air Quality (CMAQ) modeling system Version 5.0 (CMAQv5.0) was released by the U.S. Environmental Protection Agency (EPA) in February 2012, with an interim release (v5.01) in July 2012. Because CMAQ is a community model, the EPA encourages the development of proven alternative science treatments by external scientists and developers that can be incorporated as part of an official CMAQ release. This paper describes the implementation, evaluation, and testing of a plume-in-grid (PinG) module in CMAQ 5.01. The PinG module, also referred to as Advanced Plume Treatment (APT), provides the capability of resolving sub-grid-scale processes, such as the transport and chemistry of point-source plumes, in a grid model. The new PinG module in CMAQ 5.01 is applied and evaluated for two 15-day summer and winter periods in 2005 to the eastern United States, and the results are compared with those from the base CMAQ 5.01. Eighteen large point sources of NOx in the eastern United States were selected for explicit plume treatment with APT in the PinG simulation. The results show that overall model performance is negligibly affected when PinG treatment is included. However, the PinG model predicts significantly different contributions of the 18 sources to pollutant concentrations and deposition downwind of the point sources compared to the base model.Implications: This study describes the incorporation of a plume-in-grid (PinG) capability within the latest version of the EPA grid model, CMAQ. The capability addresses the inherent limitation of the grid model to resolve processes, such as the evolution of point-source plumes, which occur at scales much smaller than the grid resolution. The base grid model and the PinG version predict different source contributions to ozone and PM2.5 concentrations that need to be considered when source attribution studies are conducted to determine the impacts of large point sources on downwind concentrations and deposition of primary and secondary pollutants.

Geochemical evidence of magma intrusion inferred from diffuse CO2 emissions and fumarole plume chemistry: the 2010–2011 volcanic unrest at Taal Volcano, Philippines

We report herein significant increases in the diffuse CO2 emission through the lake and soils of the Taal Volcano Main Crater (Philippines), during a volcano-seismic unrest period in April 2010–June 2011. Monitoring of CO2 emissions from the Taal Main Crater Lake and soils in the fumarole areas started in 2008 with a collaborative project between ITER and PHIVOLCS. In August 2010, the total diffuse CO2 emission from the Taal Main Crater Lake increased almost three times from a previously measured baseline emission value ∼1,000 t day−1 to 2,716 ± 54 t day−1. This increase occurred during anomalous seismic activity which started in April 2010. The highest CO2 emission value in the crater lake was measured in March 2011 at 4,670 ± 159 t day−1 when the volcano was still showing signs of unrest. Significant changes in the CO2/SO2, CO2/H2O, and SO2/H2S ratios in the fumarole gases suggest the occurrence of a magmatic injection several weeks before the onset of the volcano-seismic unrest period. These observed changes in the CO2 emission rate and the fumarole gas composition as the result of magmatic activity were likely caused by magma moving from a deep reservoir to a shallow reservoir.

Vibrational emission analysis of the CN molecules in laser-induced breakdown spectroscopy of organic compounds

Laser-induced breakdown spectroscopy (LIBS) of organic materials is based on the analysis of atomic and ionic emission lines and on a few molecular bands, the most important being the CN violet system and the C2 Swan system. This paper is focused in molecular emission of LIBS plasmas based on the CN (B2Σ–X2Σ) band, one of the strongest emissions appearing in all carbon materials when analyzed in air atmosphere. An analysis of this band with sufficient spectral resolution provides a great deal of information on the molecule, which has revealed that valuable information can be obtained from the plume chemistry and dynamics affecting the excitation mechanisms of the molecules. The vibrational emission of this molecular band has been investigated to establish the dependence of this emission on the molecular structure of the materials. The paper shows that excitation/emission phenomena of molecular species observed in the plume depend strongly on the time interval selected and on the irradiance deposited on the sample surface. Precise time resolved LIBS measurements are needed for the observation of distinctive CN emission. For the organic compounds studied, larger differences in the behavior of the vibrational emission occur at early stages after plasma ignition. Since molecular emission is generally more complex than that involving atomic emission, local plasma conditions as well as plume chemistry may induce changes in vibrational emission of molecules. As a consequence, alterations in the distribution of the emissions occur in terms of relative intensities, being sensitive to the molecular structure of every single material.

Modeling and Validation of Ku-Band Signal Attenuation Through Rocket Plumes

Communications to and from a launch vehicle during ascent are of critical importance to the success of rocket-launch operations. During ascent, the rocket’s exhaust plume causes significant interference in the radio communications between the vehicle and ground station. This paper presents an improved line of sight: a lower-collision-frequency microwave signal attenuation model based on the plume chemistry, microwave path, and the cross section for momentum transfer. The proposed model considers the combustion products in the exhaust plume, ambient air entrainment downstream of the nozzle, and a plasma attenuation model to estimate the total radio-frequency signal attenuation. The proposed model is benchmarked against measurements of signal attenuation through an exhaust plume in the 12.4 to 18 GHz frequency range.

Wildland fire emissions, carbon, and climate: Plume rise, atmospheric transport, and chemistry processes

This paper provides an overview and summary of the current state of knowledge regarding critical atmospheric processes that affect the distribution and concentrations of greenhouse gases and aerosols emitted from wildland fires or produced through subsequent chemical reactions in the atmosphere. These critical atmospheric processes include the dynamics of plume rise, chemical reactions involving smoke plume constituents, the long-range transport of smoke plumes, and the potential transport of gases and aerosols from wildland fires into the stratosphere. In the area of plume-rise dynamics, synthesis information is provided on (1) the relevance of plume height for assessing impacts of gases and aerosol from wildland fires on the climate system, (2) recent scientific advances in understanding the role of multiple updraft cores in plume behavior, and (3) some of the current modeling tools and remote sensing monitoring techniques available for predicting and measuring smoke plume heights. In the area of atmospheric chemistry associated with wildland fire emissions, synthesis information is provided on what is currently known about the atmospheric fate of wildland fire smoke-plume constituents and the relationship of their atmospheric chemistry to radiative forcing. Synthesis information related to long-range atmospheric transport of wildland fire emissions is presented and summarizes many of the recent published observational and modeling studies that provide clear evidence of intercontinental, continental, and regional transport of North American fire emissions, including black carbon, to locations far-removed from the fire-event locations. Recent studies are also highlighted that examined the significance of troposphere-stratosphere exchange processes, which can result in the transport of greenhouse gases and aerosols from North American wildland fires into the stratosphere where they can remain for very long periods of time and alter the radiative balance and typical chemical reactions that occur there. Finally, specific research gaps and needs related to plume dynamics, atmospheric transport and deposition processes, and the atmospheric chemistry of wildland fire emissions are identified and discussed.

Comparison of Constant and Transient‐Source Zones on Simulated Contaminant Plume Evolution in Groundwater: Implications for Hydrogeological Risk Assessment

AbstractContaminant fate and transport models used for hydrogeological risk assessment commonly include an assumed constant source concentration to predict downgradient concentrations in groundwater. This assumption is unrealistic in many cases where nonaqueous phase liquids (NAPLs) are the contaminant source. In this study the effect of a constant and transient (declining) source term on contaminant plume chemistry and groundwater impacts predicted by a hydrogeological risk assessment model is investigated for the release of dissolved phase constituents from an unleaded petroleum fuel light nonaqueous phase liquid (LNAPL). Two transient source models were developed: a mass balance model and an exponential decay model. Both use Raoult's Law to describe the aqueous phase partitioning and depletion of organic compounds from a multicomponent LNAPL source to groundwater. The models were used to estimate the changing LNAPL composition and effective aqueous solubility of six common constituents (benzene, toluene, ethylbenzene, xylene, methyl‐tert‐butyl‐ether, and tert‐amyl‐methyl‐ether) in a representative unleaded petroleum fuel. The predicted source concentrations were then compared with groundwater quality data from a contaminated site. The source concentrations estimated from these models were propagated into a hydrogeological risk assessment model using the Remedial Targets Worksheet v3.1 developed by the Environment Agency of England and Wales. Different groundwater impacts and associated estimates of risk were predicted between the constant and transient source simulations. These are illustrated using simple calculations and established risk assessment methods. The constant‐source model predicted higher contaminant concentrations at the compliance point, which also persisted over a much longer duration. Consequently, there was a greater requirement for remedial action estimated using the hydrogeological model in scenarios that assumed a constant‐source. This could result in unnecessary remedial action in cases where no unacceptable risk is predicted when a more representative description of a declining source is used.

SO2photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism

Natural climate variation, such as that caused by volcanoes, is the basis for identifying anthropogenic climate change. However, knowledge of the history of volcanic activity is inadequate, particularly concerning the explosivity of specific events. Some material is deposited in ice cores, but the concentration of glacial sulfate does not distinguish between tropospheric and stratospheric eruptions. Stable sulfur isotope abundances contain additional information, and recent studies show a correlation between volcanic plumes that reach the stratosphere and mass-independent anomalies in sulfur isotopes in glacial sulfate. We describe a mechanism, photoexcitation of SO2, that links the two, yielding a useful metric of the explosivity of historic volcanic events. A plume model of S(IV) to S(VI) conversion was constructed including photochemistry, entrainment of background air, and sulfate deposition. Isotopologue-specific photoexcitation rates were calculated based on the UV absorption cross-sections of (32)SO2, (33)SO2, (34)SO2, and (36)SO2 from 250 to 320 nm. The model shows that UV photoexcitation is enhanced with altitude, whereas mass-dependent oxidation, such as SO2 + OH, is suppressed by in situ plume chemistry, allowing the production and preservation of a mass-independent sulfur isotope anomaly in the sulfate product. The model accounts for the amplitude, phases, and time development of Δ(33)S/δ(34)S and Δ(36)S/Δ(33)S found in glacial samples. We are able to identify the process controlling mass-independent sulfur isotope anomalies in the modern atmosphere. This mechanism is the basis of identifying the magnitude of historic volcanic events.

The effect of coal-fired power-plant SO<sub>2</sub> and NO<sub>x</sub> control technologies on aerosol nucleation in the source plumes

Abstract. Nucleation in coal-fired power-plant plumes can greatly contribute to particle number concentrations near source regions. The changing emissions rates of SO2 and NOx due to pollution-control technologies over recent decades may have had a significant effect on aerosol formation and growth in the plumes with ultimate implications for climate and human health. We use the System for Atmospheric Modeling (SAM) large-eddy simulation model with the TwO-Moment Aerosol Sectional (TOMAS) microphysics algorithm to model the nucleation in plumes of coal-fired plants. We test a range of cases with varying emissions to simulate the implementation of emissions-control technologies between 1997 and 2010. We start by simulating the W. A. Parish power plant (near Houston, TX) during this time period, when NOx emissions were reduced by ~90% and SO2 emissions decreased by ~30%. Increases in plume OH (due to the reduced NOx) produced enhanced SO2 oxidation and an order-of-magnitude increase in particle nucleation in the plume despite the reduction in SO2 emissions. These results suggest that NOx emissions could strongly regulate particle nucleation and growth in power-plant plumes. Next, we test a range of cases with varying emissions to simulate the implementation of SO2 and NOx emissions-control technologies. Particle formation generally increases with SO2 emission, while NOx shows two different regimes: increasing particle formation with increasing NOx under low-NOx emissions and decreasing particle formation with increasing NOx under high-NOx emissions. Next, we compare model results with airborne measurements made in the W. A. Parish power-plant plume in 2000 and 2006, confirming the importance of NOx emissions on new particle formation and highlighting the substantial effect of background aerosol loadings on this process (the more polluted background of the 2006 case caused more than an order-of-magnitude reduction in particle formation in the plume compared to the cleaner test day in 2000). Finally, we calculate particle-formation statistics of 330 coal-fired power plants in the US in 1997 and 2010, and the model results show a median decrease of 19% in particle formation rates from 1997 to 2010 (whereas the W. A. Parish case study showed an increase). Thus, the US power plants, on average, show a different result than was found for the W. A. Parish plant specifically, and it shows that the strong NOx controls (90% reduction) implemented at the W. A. Parish plant (with relatively weak SO2 emissions reductions, 30%) are not representative of most power plants in the US during the past 15 yr. These results suggest that there may be important climate implications of power-plant controls due to changes in plume chemistry and microphysics, but the magnitude and sign of the aerosol changes depend greatly on the relative reductions in NOx and SO2 emissions in each plant. More extensive plume measurements for a range of emissions of SO2 and NOx and in varying background aerosol conditions are needed, however, to better quantify these effects.

Development and initial application of a sub-grid scale plume treatment in a state-of-the-art online Multi-scale Air Quality and Weather Prediction Model

Traditional Eulerian air quality models are unable to accurately simulate sub-grid scale processes, such as the near-source transport and chemistry of point source plumes, because they assume instantaneous mixing of the emitted pollutants within the grid cell containing the release, and neglect the turbulent segregation effects that limit the near-source mixing of emitted pollutants with the background atmosphere (e.g., Kramm and Meixner, 2000). Observations by Dlugi et al. (2010) show that the segregation of chemically reactive species can slow effective second-order reaction rates by as much as 15%, due to inhomogeneous mixing of the reactants. This limitation of traditional grid models applies to both “off-line” models, in which externally derived meteorology is used to drive the chemistry model, and newer “on-line” models, such as the Weather Research and Forecasting model with Chemistry (WRF/Chem), that simulate the emissions, transport, mixing, and chemical transformation of trace gases and aerosols simultaneously with the meteorology. While a number of approaches have been used in the past to address this limitation, the approach that has been most effectively used in operational models is the plume-in-grid (PinG) approach, in which a reactive plume model is embedded within the grid model to resolve sub-grid scale plumes. This paper describes the implementation of such a PinG treatment in WRF/Chem, based on a similar extension to the U.S. EPA Community Multi-scale Air Quality (CMAQ) model. The treatment, referred to as Advanced Plume Treatment, has been tested in CMAQ over more than a decade and has been used successfully in both episodic and long-term applications for assessing point source contributions to ozone and particulate matter. This paper presents the application of the PinG version of WRF/Chem for a three-day episode in July 2001, including a model performance evaluation and comparison of model results with and without PinG treatment. The results from the model application show that overall model performance is only slightly affected when the PinG treatment is used, although there are some generally small improvements, with the PinG treatment showing a 5% lower bias in predicting ozone concentrations, and 3% lower bias in sulfate predictions. However, the predicted spatial patterns of ozone and PM2.5 concentrations from the two simulations show both large decreases of up to 40 ppb ozone and 14 μg m−3 PM2.5, and increases of up to 80 ppb ozone and 33 μg m−3 PM2.5 as a result of using the PinG treatment. These differences are attributed to both direct effects of the PinG treatment (i.e., differences in dispersion, transport and chemistry of point source emissions) and indirect effects (i.e., impacts of air quality changes on meteorology).

Electrochemical sensing of volcanic gases

We report here the development and application of a compact “geochemical nose” incorporating electrochemical sensors for gas measurements in volcanic plumes. A novel element of the instrument design is the arrangement of the sensors in a parallel array that enables near-simultaneous exposure and fast response. Data analysis methods were developed that utilise the multi-sensor output currents to extract gas mixing ratio abundances and eliminate cross-sensitivities. Use of filter methods is demonstrated to remove baseline drift or instrument noise. We introduce a new approach for analysis of measurements from sensors that have a slower response time (e.g. HCl), and apply this model to estimate HCl/SO2 ratios. We deployed the sensor system at Aso volcano, Japan, detecting emissions from its fumarole field hot crater lake, and a mixed plume. We measured SO2, H2S, CO and HCl, ranging in abundance from ~102–104ppbv. Neither NO2 nor Cl2 were detected. For the fumarolic gases, molar ratios were measured as follows: H2S/SO2 is ~0.15, H2/SO2 ~0.25, CO/SO2 ~0.02, HCl/SO2 ~0.1. The crater lake plume's H2S/SO2 is ~0.03. The compositions are discussed in terms of degassing equilibria and plume chemistry. Our instrument design represents a cost-effective, low-power and highly portable system that can be readily adapted for operational surveillance of volcanic gases.

Microphysical simulations of sulfur burdens from stratospheric sulfur geoengineering

Abstract. Recent microphysical studies suggest that geoengineering by continuous stratospheric injection of SO2 gas may be limited by the growth of the aerosols. We study the efficacy of SO2, H2SO4 and aerosol injections on aerosol mass and optical depth using a three-dimensional general circulation model with sulfur chemistry and sectional aerosol microphysics (WACCM/CARMA). We find increasing injection rates of SO2 in a narrow band around the equator to have limited efficacy while broadening the injecting zone as well as injecting particles instead of SO2 gas increases the sulfate burden for a given injection rate, in agreement with previous work. We find that injecting H2SO4 gas instead of SO2 does not discernibly alter sulfate size or mass, in contrast with a previous study using a plume model with a microphysical model. However, the physics and chemistry in aircraft plumes, which are smaller than climate model grid cells, need to be more carefully considered. We also find significant perturbations to tropospheric aerosol for all injections studied, particularly in the upper troposphere and near the poles, where sulfate burden increases by up to 100 times. This enhanced burden could have implications for tropospheric radiative forcing and chemistry. These results highlight the need to mitigate greenhouse gas emissions rather than attempt to cool the planet through geoengineering, and to further study geoengineering before it can be seriously considered as a climate intervention option.

Hyperspectral Earth Observation from IASI: Five Years of Accomplishments

The Infrared Atmospheric Sounding Interferometer (IASI) forms the main infrared sounding component of the European Organisation for the Exploitation of Meteorological Satellites's (EUMETSAT's) Meteorological Operation (MetOp)-A satellite (Klaes et al. 2007), which was launched in October 2006. This article presents the results of the first 4 yr of the operational IASI mission. The performance of the instrument is shown to be exceptional in terms of calibration and stability. The quality of the data has allowed the rapid use of the observations in operational numerical weather prediction (NWP) and the development of new products for atmospheric chemistry and climate studies, some of which were unexpected before launch. The assimilation of IASI observations in NWP models provides a significant forecast impact; in most cases the impact has been shown to be at least as large as for any previous instrument. In atmospheric chemistry, global distributions of gases, such as ozone and carbon monoxide, can be produced in near–real time, and short-lived species, such as ammonia or methanol, can be mapped, allowing the identification of new sources. The data have also shown the ability to track the location and chemistry of gaseous plumes and particles associated with volcanic eruptions and fires, providing valuable data for air quality monitoring and aircraft safety. IASI also contributes to the establishment of robust long-term data records of several essential climate variables. The suite of products being developed from IASI continues to expand as the data are investigated, and further impacts are expected from increased use of the data in NWP and climate studies in the coming years. The instrument has set a high standard for future operational hyperspectral infrared sounders and has demonstrated that such instruments have a vital role in the global observing system.

Airborne and ground-based measurements of the trace gases and particles emitted by prescribed fires in the United States

Abstract. We have measured emission factors for 19 trace gas species and particulate matter (PM2.5) from 14 prescribed fires in chaparral and oak savanna in the southwestern US, as well as conifer forest understory in the southeastern US and Sierra Nevada mountains of California. These are likely the most extensive emission factor field measurements for temperate biomass burning to date and the only published emission factors for temperate oak savanna fuels. This study helps to close the gap in emissions data available for temperate zone fires relative to tropical biomass burning. We present the first field measurements of the biomass burning emissions of glycolaldehyde, a possible precursor for aqueous phase secondary organic aerosol formation. We also measured the emissions of phenol, another aqueous phase secondary organic aerosol precursor. Our data confirm previous observations that urban deposition can impact the NOx emission factors and thus subsequent plume chemistry. For two fires, we measured both the emissions in the convective smoke plume from our airborne platform and the unlofted residual smoldering combustion emissions with our ground-based platform. The smoke from residual smoldering combustion was characterized by emission factors for hydrocarbon and oxygenated organic species that were up to ten times higher than in the lofted plume, including high 1,3-butadiene and isoprene concentrations which were not observed in the lofted plume. This should be considered in modeling the air quality impacts for smoke that disperses at ground level. We also show that the often ignored unlofted emissions can significantly impact estimates of total emissions. Preliminary evidence suggests large emissions of monoterpenes in the residual smoldering smoke. These data should lead to an improved capacity to model the impacts of biomass burning in similar temperate ecosystems.

Accounting for non-linear chemistry of ship plumes in the GEOS-Chem global chemistry transport model

Abstract. We present a computationally efficient approach to account for the non-linear chemistry occurring during the dispersion of ship exhaust plumes in a global 3-D model of atmospheric chemistry (GEOS-Chem). We use a plume-in-grid formulation where ship emissions age chemically for 5 h before being released in the global model grid. Besides reducing the original ship NOx emissions in GEOS-Chem, our approach also releases the secondary compounds ozone and HNO3, produced during the 5 h after the original emissions, into the model. We applied our improved method and also the widely used "instant dilution" approach to a 1-yr GEOS-Chem simulation of global tropospheric ozone-NOx-VOC-aerosol chemistry. We also ran simulations with the standard model (emitting 10 molecules O3 and 1 molecule HNO3 per ship NOx molecule), and a model without any ship emissions at all. The model without any ship emissions simulates up to 0.1 ppbv (or 50%) lower NOx concentrations over the North Atlantic in July than our improved GEOS-Chem model. "Instant dilution" overestimates NOx concentrations by 0.1 ppbv (50%) and ozone by 3–5 ppbv (10–25%), compared to our improved model over this region. These conclusions are supported by comparing simulated and observed NOx and ozone concentrations in the lower troposphere over the Pacific Ocean. The comparisons show that the improved GEOS-Chem model simulates NOx concentrations in between the instant dilution model and the model without ship emissions, which results in lower O3 concentrations than the instant dilution model. The relative differences in simulated NOx and ozone between our improved approach and instant dilution are smallest over strongly polluted seas (e.g. North Sea), suggesting that accounting for in-plume chemistry is most relevant for pristine marine areas.

Investigation of chlorine radical chemistry in the Eyjafjallajökull volcanic plume using observed depletions in non-methane hydrocarbons

As part of the effort to understand volcanic plume composition and chemistry during the eruption of the Icelandic volcano Eyjafjallajkull, the CARIBIC atmospheric observatory was deployed for three special science flights aboard a Lufthansa passenger aircraft. Measurements made during these flights included the collection of whole air samples, which were analyzed for non-methane hydrocarbons (NMHCs). Hydrocarbon concentrations in plume samples were found to be reduced to levels below background, with relative depletions characteristic of reaction with chlorine radicals (Cl). Recent observations of halogen oxides in volcanic plumes provide evidence for halogen radical chemistry, but quantitative data for free halogen radical concentrations in volcanic plumes were absent. Here we present the first observation-based calculations of Cl radical concentrations in volcanic plumes, estimated from observed NMHC depletions. Inferred Cl concentrations were between 1.3 × 10 and 6.6 × 10 Cl cm. The relationship between NMHC variability and local lifetimes was used to investigate the ratio between OH and Cl within the plume, with [OH]/[Cl] estimated to be ∼37. Copyright 2011 by the American Geophysical Union.

In situ measurements of tropospheric volcanic plumes in Ecuador and Colombia during TC4

A NASA DC-8 research aircraft penetrated tropospheric gas and aerosol plumes sourced from active volcanoes in Ecuador and Colombia during the Tropical Composition, Cloud and Climate Coupling (TC^4) mission in July–August 2007. The likely source volcanoes were Tungurahua (Ecuador) and Nevado del Huila (Colombia). The TC^4 data provide rare insight into the chemistry of volcanic plumes in the tropical troposphere and permit a comparison of SO_2 column amounts measured by the Ozone Monitoring Instrument (OMI) on the Aura satellite with in situ SO_2 measurements. Elevated concentrations of SO_2, sulfate aerosol, and particles were measured by DC-8 instrumentation in volcanic outflow at altitudes of 3–6 km. Estimated plume ages range from ~2 h at Huila to ~22–48 h downwind of Ecuador. The plumes contained sulfate-rich accumulation mode particles that were variably neutralized and often highly acidic. A significant fraction of supermicron volcanic ash was evident in one plume. In-plume O_3 concentrations were ~70%–80% of ambient levels downwind of Ecuador, but data are insufficient to ascribe this to O_3 depletion via reactive halogen chemistry. The TC^4 data record rapid cloud processing of the Huila volcanic plume involving aqueous-phase oxidation of SO_2 by H_2O_2, but overall the data suggest average in-plume SO_2 to sulfate conversion rates of ~1%–2% h^(−1). SO_2 column amounts measured in the Tungurahua plume (~0.1–0.2 Dobson units) are commensurate with average SO_2 columns retrieved from OMI measurements in the volcanic outflow region in July 2007. The TC^4 data set provides further evidence of the impact of volcanic emissions on tropospheric acidity and oxidizing capacity.