Search

The optical properties (light scattering and absorption) of soot particles depend on soot size and index of refraction, but also on the soot complex morphology and the internal mixing with other material at the single particle level. For example, freshly emitted (nascent) soot particles can interact with other materials in the atmosphere, materials that can condense on soot and coat it. This coating can affect the soot optical properties by refracting light, or by changing the soot aggregate structure. A common approach to studying the effect of coating on soot optical properties is to measure absorption and scattering values in ambient air and then measure them again after removing the coating using a thermodenuder. In this approach, it is assumed that: 1) Most of the coating material is removed; 2) charred organic coating does not add to the refractory carbon; 3) oxidation of soot is negligible; and 4) the pre-existing core soot structure is left unaltered despite potential oxidation of the core at elevated temperature. In this study, we investigate the validity of the last assumption, by studying the effect of thermodenuding on the structure of nascent soot. To this end, we analyze the morphological properties of laboratory generated nascent soot, before and after thermodenuding. Our investigation shows that there is only minor restructuring of nascent soot by thermodenuding.

NASA's Orbiting Carbon Observatory-2 (OCO-2) has been measuring carbon dioxide column-averaged dry air mole fractions, XCO2, in the Earth’s atmosphere for almost two years. In this paper, we describe the comparisons between the OCO-2 version 7Br retrievals and XCO2 estimates from OCO-2's primary ground-based validation network: the Total Carbon Column Observing Network (TCCON). The OCO-2 XCO2 retrievals, after bias correction, agree well globally with the TCCON for nadir, glint, and target observations, with median differences less than 0.5 ppm and RMS differences typically below 1.5 ppm. Target observations over TCCON stations correlate best with the TCCON data (R2 = 0.83) on a global scale. At local scales, the target comparisons reveal residual biases likely related to surface properties and aerosol scattering. It is thus crucial to continue measurement comparisons with TCCON to monitor and evaluate the OCO-2 XCO2 data quality throughout its mission.

Forests soak up 25% of the carbon dioxide (CO2) emitted by anthropogenic fossil energy use (10 Gt C y-1), moderating its atmospheric accumulation. How this terrestrial CO2 uptake will evolve with climate change in the 21st Century is largely unknown. Rainforests are the most active ecosystems, with the Amazon basin storing 120 Gt C as biomass and exchanging 18 Gt C y-1 of CO2 via photosynthesis and respiration and fixing carbon at 2-3 kg C m-2 y-1. Furthermore, the intense hydrologic and carbon cycles are tightly coupled in the Amazon where about half of the water is recycled by evapotranspiration and the other half imported from the ocean by Northeasterly trade winds. Climate models predict a drying in the Amazon with reduced carbon uptake while observationally guided assessments indicate sustained uptake. We set out to resolve this huge discrepancy in the size and sign of the future Amazon carbon cycle by performing the first simultaneous regional-scale high-frequency measurements of atmospheric CO2, H2O, HOD, CH4, N2O, and CO at the T3 site in Manacupuru, Brazil, as part of DOE's GoAmazon 2014/15 project. Our data will be used to inform and develop DOE's Community Land Model (CLM) on the tropical carbon-water couplingsmore » at the appropriate grid scale (10-50 km). Our measurements will also validate the CO2 data from Japan's Greenhouse gases Observing Satellite (GOSAT) and NASA's Orbiting Carbon Observatory (OCO)-2 satellite (launched in July, 2014). Our data addresses these science questions: 1. How does ecosystem heterogeneity and climate variability influence the rainforest carbon cycle? 2. How well do current tropical ecosystem models simulate the observed regional carbon cycle? 3. Does nitrogen deposition (from the Manaus, Brazil, plume) enhance rainforest carbon uptake?« less

This slide deals with the following: Affordable artificial neural network and mini-sensor system to locate and quantify methane leaks on a well pad; ARPA-e project schematic for monitoring methane leaks

Wildfires are important contributors to atmospheric aerosols and a large source of emissions that impact regional air quality and global climate. In this study, the regional and nearfield influences of wildfire emissions on ambient aerosol concentration and chemical properties in the Pacific Northwest region of the United States were studied using real-time measurements from a fixed ground site located in Central Oregon at the Mt. Bachelor Observatory (∼2700 m a.s.l.) as well as near their sources using an aircraft. The regional characteristics of biomass burning aerosols were found to depend strongly on the modified combustion efficiency (MCE), an index of the combustion processes of a fire. Organic aerosol emissions had negative correlations with MCE, whereas the oxidation state of organic aerosol increased with MCE and plume aging. The relationships between the aerosol properties and MCE were consistent between fresh emissions (∼1 h old) and emissions sampled after atmospheric transport (6-45 h), suggesting that biomass burning organic aerosol concentration and chemical properties were strongly influenced by combustion processes at the source and conserved to a significant extent during regional transport. These results suggest that MCE can be a useful metric for describing aerosol properties of wildfire emissions and their impacts on regional air quality and global climate.

We demonstrate the use of compact solar-tracking Fourier transform spectrometers (Bruker EM27/SUN) for differential measurements of the column-averaged dry-air mole fractions of CH4 and CO2 within urban areas. Using Allan variance analysis, we show that the differential column measurement has a precision of 0.1 ‰ for XCO2 and XCH4 using an optimum integration time of 10 min, which corresponds to standard deviations of 0.04 ppm, and 0.2 ppb, respectively. The sensor system is very stable over time and after relocation across the continent. We report tests of the differential column measurement, and its sensitivity to emission sources, by measuring the downwind minus upwind column gradient ΔXCH4 across dairy farms in the Chino California area and using the data to verify emissions reported in the literature. Spatial column gradient ratios ΔXCH4/ΔXCO2 were observed across Pasadena within the Los Angeles basin, indicating values consistent with regional emission ratios from the literature. Our precise, rapid measurements allow us to determine significant short-term variations (5–10 minutes) of ΔXCO2 and ΔXCH4, and to show that they represent atmospheric phenomena. Overall, this study helps establish a range of new applications for compact solar-viewing Fourier transform spectrometers. By accurately measuring the small differences in integrated column amounts across local and regional sources, we directly observe the mass loading of the atmosphere due to the influence of emissions in the intervening locale. The inference of the source strength is much more direct than inversion modeling using only surface concentrations, and less subject to errors associated with small-scale transport phenomena.

Wildfires contribute significantly to global soot emissions, yet their aerosol formation mechanisms and resulting particle properties are poorly understood and parameterized in climate models. The conventional view holds that soot is formed via the cluster-dilute aggregation mechanism in wildfires and emitted as aggregates with fractal dimension Df ≈ 1.8 mobility diameter Dm ≤ 1 μm, and aerodynamic diameter Da ≤ 300 nm. Here we report the ubiquitous presence of soot superaggregates (SAs) in the outflow from a major wildfire in India. SAs are porous, low-density aggregates of cluster-dilute aggregates with characteristic Df ≈ 2.6, Dm > 1 μm, and Da ≤ 300 nm that form via the cluster-dense aggregation mechanism. We present additional observations of soot SAs in wildfire smoke-laden air masses over Northern California, New Mexico, and Mexico City. We estimate that SAs contribute, per unit optical depth, up to 35% less atmospheric warming than freshly-emitted (Df ≈ 1.8) aggregates, and ≈90% more warming than the volume-equivalent spherical soot particles simulated in climate models.

Scientific Reports 4: Article number: 5508; 10.1038/srep05508 published online: July012014; updated: March102016 The original version of this Article contained an error in the Abstract. “We estimate that SAs contribute, per unit optical depth, up to 35% less atmospheric warming than freshly-emitted (Df ≈ 1.8) aggregates, and ≈90% more warming than the volume-equivalent spherical soot particles simulated in climate models.” now reads: “At 550 nm wavelength, we estimate that SAs contribute, per unit optical depth, up to 35% less atmospheric warming than freshly-emitted (Df ≈ 1.8) aggregates, and ≈90% more warming than the volume-equivalent spherical soot particles simulated in climate models.” Additionally, the original version of this Article contained an error in the Methods section. “The parameter β is the up-scatter fraction, which is a function of asymmetry parameter g as follows:” now reads: “The parameter β is the up-scatter fraction, which is a function of asymmetry parameter g using the Henyey-Greenstein phase function as follows:” These errors have been corrected in the HTML version of the Article but have not been corrected in the PDF version of the Article.

Consistent validation of satellite CO2 estimates is a prerequisite for using multiple satellite CO2 measurements for joint flux inversion, and for establishing an accurate long-term atmospheric CO2 data record. Harmonizing satellite CO2 measurements is particularly important since the differences in instruments, observing geometries, sampling strategies, etc. imbue different measurement characteristics in the various satellite CO2 data products. We focus on validating model and satellite observation attributes that impact flux estimates and CO2 assimilation, including accurate error estimates, correlated and random errors, overall biases, biases by season and latitude, the impact of coincidence criteria, validation of seasonal cycle phase and amplitude, yearly growth, and daily variability. We evaluate dry-air mole fraction (XCO2) for Greenhouse gases Observing SATellite (GOSAT) (Atmospheric CO2 Observations from Space, ACOS b3.5) and SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) (Bremen Optimal Estimation DOAS, BESD v2.00.08) as well as the CarbonTracker (CT2013b) simulated CO2 mole fraction fields and the Monitoring Atmospheric Composition and Climate (MACC) CO2 inversion system (v13.1) and compare these to Total Carbon Column Observing Network (TCCON) observations (GGG2012/2014). We find standard deviations of 0.9, 0.9, 1.7, and 2.1 ppm vs. TCCON for CT2013b, MACC, GOSAT, and SCIAMACHY, respectively, with the single observation errors 1.9 and 0.9 times the predicted errors for GOSAT and SCIAMACHY, respectively. We quantify how satellite error drops with data averaging by interpreting according to error2 = a2 + b2/n (with n being the number of observations averaged, a the systematic (correlated) errors, and b the random (uncorrelated) errors). a and b are estimated by satellites, coincidence criteria, and hemisphere. Biases at individual stations have year-to-year variability of ∼ 0.3 ppm, with biases larger than the TCCON-predicted bias uncertainty of 0.4 ppm at many stations. We find that GOSAT and CT2013b underpredict the seasonal cycle amplitude in the Northern Hemisphere (NH) between 46 and 53° N, MACC overpredicts between 26 and 37° N, and CT2013b underpredicts the seasonal cycle amplitude in the Southern Hemisphere (SH). The seasonal cycle phase indicates whether a data set or model lags another data set in time. We find that the GOSAT measurements improve the seasonal cycle phase substantially over the prior while SCIAMACHY measurements improve the phase significantly for just two of seven sites. The models reproduce the measured seasonal cycle phase well except for at Lauder_125HR (CT2013b) and Darwin (MACC). We compare the variability within 1 day between TCCON and models in JJA; there is correlation between 0.2 and 0.8 in the NH, with models showing 10–50 % the variability of TCCON at different stations and CT2013b showing more variability than MACC. This paper highlights findings that provide inputs to estimate flux errors in model assimilations, and places where models and satellites need further investigation, e.g., the SH for models and 45–67° N for GOSAT and CT2013b.

An Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed during the Carbonaceous Aerosols and Radiative Effects Study (CARES) that took place in northern California in June 2010. We present results obtained at Cool (denoted as the T1 site of the project) in the foothills of the Sierra Nevada Mountains, where intense biogenic emissions are periodically mixed with urban outflow transported by daytime southwesterly winds from the Sacramento metropolitan area. During this study, the average mass loading of submicrometer particles (PM1) was 3.0 μg m−3, dominated by organics (80%) and sulfate (9.9%). The organic aerosol (OA) had a nominal formula of C1H1.38N0.004OM0.44, thus an average organic mass-to-carbon (OM/OC) ratio of 1.70. Two distinct oxygenated OA factors were identified via Positive matrix factorization (PMF) of the high-resolution mass spectra of organics. The more oxidized MO-OOA (O/C = 0.54) was interpreted as a surrogate for secondary OA (SOA) influenced by biogenic emissions whereas the less oxidized LO-OOA (O/C = 0.42) was found to represent SOA formed in photochemically processed urban emissions. LO-OOA correlated strongly with ozone and MO-OOA correlated well with two 1st generation isoprene oxidation products (methacrolein and methyl vinyl ketone), indicating that both SOAs were relatively fresh. A hydrocarbon like OA (HOA) factor was also identified, representing primary emissions mainly due to local traffic. On average, SOA (= MO-OOA + LO-OOA) accounted for 91% of the total OA mass and 72% of the PM1 mass observed at Cool. Twenty three periods of urban plumes from T0 (Sacramento) to T1 (Cool) were identified using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). The average PM1 mass loading was considerably higher in urban plumes than in air masses dominated by biogenic SOA. The change in OA mass relative to CO (ΔOA/ΔCO) varied in the range of 5-196 μg m−3 ppm−1, reflecting large variability in SOA production. The highest ΔOA/ΔCO was reached when air masses were dominated by anthropogenic emissions in the presence of a high concentration of biogenic volatile organic compounds (BVOCs). This ratio, which was 97 μg m−3 ppm−1 on average, was much higher than when urban plumes arrived in a low BVOC environment (~36 μg m−3 ppm−1) or during other periods dominated by biogenic SOA (35 μg m−3 ppm−1). These results demonstrate that SOA formation is enhanced when anthropogenic emissions interact with biogenic precursors.

Substantial uncertainties still exist in the scientific understanding of the possible interactions between urban and natural (biogenic) emissions in the production and transformation of atmospheric aerosol and the resulting impact on climate change. The US Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program's Carbonaceous Aerosol and Radiative Effects Study (CARES) carried out in June 2010 in Central Valley, California, was a comprehensive effort designed to improve this understanding. The primary objective of the field study was to investigate the evolution of secondary organic and black carbon aerosols and their climate-related properties in the Sacramento urban plume as it was routinely transported into the forested Sierra Nevada foothills area. Urban aerosols and trace gases experienced significant physical and chemical transformations as they mixed with the reactive biogenic hydrocarbons emitted from the forest. Two heavily-instrumented ground sites – one within the Sacramento urban area and another about 40 km to the northeast in the foothills area – were set up to characterize the evolution of meteorological variables, trace gases, aerosol precursors, aerosol size, composition, and climate-related properties in freshly polluted and "aged" urban air. On selected days, the DOE G-1 aircraft was deployed to make similar measurements upwind and across the evolving Sacramento plume in the morning and again in the afternoon. The NASA B-200 aircraft, carrying remote sensing instruments, was also deployed to characterize the vertical and horizontal distribution of aerosols and aerosol optical properties within and around the plume. This overview provides: (a) the scientific background and motivation for the study, (b) the operational and logistical information pertinent to the execution of the study, (c) an overview of key observations and initial findings from the aircraft and ground-based sampling platforms, and (d) a roadmap of planned data analyses and focused modeling efforts that will facilitate the integration of new knowledge into improved representations of key aerosol processes and properties in climate models., United States. Dept. of Energy. Atmospheric System Research Program (Contract DE-AC06-76RLO 1830), United States. National Oceanic and Atmospheric Administration, United States. National Aeronautics and Space Administration. HQ Science Mission Directorate Radiation Sciences Program, United States. National Aeronautics and Space Administration. CALIPSO Program, United States. Dept. of Energy. Atmospheric Radiation Measurement Program (Interagency Agreement No. DE-AI02-05ER63985)

This paper examines the effects of two largely contrasting aerosol emissions scenarios on regional climate using National Center for Atmospheric Research Community Climate System Model version 3: (1) increasing the anthropogenic aerosols over China and India by a factor of three and (2) reducing the global anthropogenic aerosols by a factor of 10. Dynamic footprints of the increased Asian aerosols with monthly variations are obtained from Model for OZone And Related chemical Tracers simulations. Increasing Asian aerosol emissions would result in cooling and reduction of precipitation over China and India, with large warming over the USA and southern Canada in winter and cooling in summer. Additionally, large changes in rainfall rate are identified over the tropical regions. In contrast, reducing the global aerosol emissions by a factor of 10 would significantly warm the atmosphere especially over the polluted land areas of both hemispheres. Increases in rainfall over polluted land areas are also noted. Deepening of the Aleutian low and weakening of the Icelandic low in winter are noted in the 500-mb geopotential height under both scenarios suggesting a strengthening of the North Pacific storm track and weakening of the North Atlantic Oscillation. The polar regions of winter hemisphere are subject to large changes in the 500-mb geopotential height. Teleconnection patterns associated with ENSO play important roles in causing large changes in surface air temperature and rainfall far away from the source regions of the altered aerosol concentrations. Copyright © 2009 Royal Meteorological Society

Transport of aerosols in pollution plumes from the mainland Asian continent was observed in situ at Jeju, South Korea during the Cheju Asian Brown Cloud Plume-Asian Monsoon Experiment (CAPMEX) field campaign throughout August and September 2008 using a 3-laser photoacoustic spectrometer (PASS-3), chemical filter analysis, and size distributions. The PASS-3 directly measures the effects of morphology (e.g. coatings) on light absorption that traditional filter-based instruments are unable to address. Transport of mixed sulfate, carbonaceous, and nitrate aerosols from various Asian pollution plumes to Jeju accounted for 74% of the deployment days, showing large variations in their measured chemical and optical properties. Analysis of eight distinct episodes, spanning wide ranges of chemical composition, optical properties, and source regions, reveals that episodes with higher organic carbon (OC)/sulfate (SO42−) and nitrate (NO3−)/SO42− composition ratios exhibit lower single scatter albedo at shorter wavelengths (ω405). We infer complex refractive indices (n–ik) as a function of wavelength for the high, intermediate, and low OC/SO42− pollution episodes by using the observed particle size distributions and the measured optical properties. The smallest mean particle diameter corresponds to the high OC/SO42− aerosol episode. The imaginary part of the refractive index (k) is greater for the high OC/SO42− episode at all wavelengths. A distinct, sharp increase in k at short wavelength implies enhanced light absorption by OC, which accounts for 50% of the light absorption at 405 nm, in the high OC/SO42− episode. Idealized analysis indicates increased absorption at 781 nm by factors greater than 3 relative to denuded black carbon in the laboratory. We hypothesize that coatings of black carbon cores are the mechanism of this enhancement. This implies that climate warming and atmospheric heating rates from black carbon particles can be significantly larger than have been estimated previously. The results of this study demonstrate ways in which atmospheric processing and mixing can amplify particle light absorption for carbonaceous aerosol, significantly at short wavelength, underscoring the need to understand and predict chemical composition effects on optical properties to accurately estimate the climate radiative forcing by mixed carbonaceous aerosols.

We introduce a method for deriving aerosol spectral radiative forcing, along with single scattering albedo, asymmetry parameter and surface albedo from airborne vertical profile measurements of shortwave spectral irradiance and spectral aerosol optical thickness. The new method complements the traditional, direct measurement of aerosol radiative forcing efficiency from horizontal flight legs below gradients of aerosol optical thickness, and is particularly useful over heterogeneous land surfaces or for homogeneous aerosol layers where the horizontal gradient method is impractical. Using data collected by the Solar Spectral Flux Radiometer (SSFR) and the Ames Airborne Tracking Sunphotometer (AATS-14) during the MILAGRO (Megacity Initiative: Local and Global Research Observations) experiment, we validate an over-ocean spectral aerosol forcing efficiency from the new method by comparing with the traditional method. Retrieved over-land aerosol optical properties are compared with in-situ measurements and AERONET retrievals. The spectral forcing efficiencies over ocean and land are remarkably similar, and agree with results from other field experiments.

This paper examines the impact of tripled anthropogenic emissions from China and India over the base level (gaseous species and carbonaceous aerosols for 2000) on air quality over the U.S. using the WRF/Chem (Weather Research and Forecasting – Chemistry) model at 1° resolution. WRF/Chem is a state-of-the-science, fully coupled chemistry and meteorology system suitable for simulating the transport and dispersion of pollutants and their impacts. The analyses in this work were focused on MAM (March, April and May). The simulations indicate an extensive area of elevated pollutant concentrations spanning from the Arabian Sea to the Northern Pacific and to the Northern Atlantic. MAM mean contributions from the tripled Asian emissions over the U.S. are found to be: 6–12 ppbv for CO, 1.0–2.5 ppbv for O3, and 0.6–1.6 μg m−3 for PM2.5 on a daily basis.

We report the direct observation of laboratory production of spherical, carbonaceous particles – "tar balls" – from smoldering combustion of two commonly occurring dry mid-latitude fuels. Real-time measurements of spectrally varying absorption Ångström coefficients (AAC) indicate that a class of light absorbing organic carbon (OC) with wavelength dependent imaginary part of its refractive index – optically defined as "brown carbon" – is an important component of tar balls. The spectrum of the imaginary parts of their complex refractive indices can be described with a Lorentzian-like model with an effective resonance wavelength in the ultraviolet (UV) spectral region. Sensitivity calculations for aerosols containing traditional OC (no absorption at visible and UV wavelengths) and brown carbon suggest that accounting for near-UV absorption by brown carbon leads to an increase in aerosol radiative forcing efficiency and increased light absorption. Since particles from smoldering combustion account for nearly three-fourths of the total carbonaceous aerosol mass emitted globally, inclusion of the optical properties of tar balls into radiative forcing models has significance for the Earth's radiation budget, optical remote sensing, and understanding of anomalous UV absorption in the troposphere.

A single particle soot photometer (SP2) uses an intense laser to heat individual aerosol particles of refractory black carbon (rBC) to vaporization, causing them to emit detectable amounts of thermal radiation that are used to quantify rBC mass. This approach is well suited for the detection of the majority of rBC mass loading in the ambient atmosphere, which occurs primarily in the accumulation mode (∼ 1–300 fg-rBC/particle). In addition to operator choices about instrument parameters, SP2 detection of rBC number and/or mass can be limited by the physical process inherent in the SP2 detection technique — namely at small rBC mass or low laser intensities, particles fail to heat to vaporization, a requirement for proper detection. In this study, the SP2's ability to correctly detect and count individual flame-generated soot particles was measured at different laser intensities for different rBC particle masses. The flame-generated soot aerosol used for testing was optionally prepared with coatings of organ...

An inter-comparison study of instruments designed to measure the microphysical and optical properties of soot particles was completed. The following mass-based instruments were tested: Couette Centrifugal Particle Mass Analyzer (CPMA), Time-of-Flight Aerosol Mass Spectrometer—Scanning Mobility Particle Sizer (AMS-SMPS), Single Particle Soot Photometer (SP2), Soot Particle-Aerosol Mass Spectrometer (SP-AMS) and Photoelectric Aerosol Sensor (PAS2000CE). Optical instruments measured absorption (photoacoustic, interferometric, and filter-based), scattering (in situ), and extinction (light attenuation within an optical cavity). The study covered an experimental matrix consisting of 318 runs that systematically tested the performance of instruments across a range of parameters including: fuel equivalence ratio (1.8 ≤ φ ≤ 5), particle shape (mass-mobility exponent ( D fm ), 2.0 ≤ D fm ≤ 3.0), particle mobility size (30 ≤ d m ≤ 300 nm), black carbon mass (0.07 ≤ m BC ≤ 4.2 fg) and particle chemical composition. I...

Aerosols influence climate directly by scattering and absorbing radiation and indirectly through their influence on cloud microphysical and dynamical properties. The Intergovernmental Panel on Climate Change (IPCC) concluded that the global radiative forcing due to aerosols is large and in general cools the planet. But the uncertainties in these estimates are also large due to our poor understanding of many of the important processes related to aerosols and clouds. To address this uncertainty an integrated strategy for addressing issues related to aerosols and aerosol processes was proposed. Using this conceptual framework, the Cumulus Humilis Aerosol Processing Study (CHAPS) is a stage 1 activity, that is, a detailed process study. The specific focus of CHAPS was to provide concurrent observations of the chemical composition of the activated [particles that are currently serving as cloud condensation nuclei (CCN)] and nonactivated aerosols, the scattering and extinction profiles, and detailed aerosol and droplet size spectra in the vicinity of Oklahoma City, Oklahoma, during June 2007. Numerous campaigns have examined aerosol properties downwind from large pollution sources, including the Megacity Initiative: Local and Global Research Observations (MILAGRO) campaign and the two of the three Aerosol Characterization Experiments, ACE-2 and ACE-Asia. Other studies conducted near citiesmore » have examined changes in both aerosols and clouds downwind of urban areas. For example wintertime stratiform clouds associated with the urban plumes of Denver, Colorado, and Kansas City, Missouri, have a larger number concentration and smaller median volume diameter of droplets than clouds that had not been affected by the urban plume. Likewise, a decrease in precipitation in polluted regions along the Front Range of the Rocky Mountains was discovered. In a modeling study, it was found that precipitation downwind of urban areas may be influenced by changes in aerosols as well as the convergence pattern caused by the city. Recently, the New England Air Quality Study (NEAQS), and the 2004 International Consortium for Atmospheric Research on Transport and Transformation, which were conducted during the summer of 2004, examined the transport of pollutants and aerosols eastward from New England over the Atlantic Ocean. The Texas Air Quality Study/Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS/GoMACCS) also looked at relationships between clouds and aerosols in polluted conditions around Houston, Texas. In contrast to these recent studies near large or very dirty cities, CHAPS was conducted near a moderately sized city that is representative of a large number of cities around the United States. CHAPS was also one of the first times that a Aerodyne aerosol mass spectrometer was used in conjunction with a counterflow virtual impactor (CVI) inlet on an aircraft. The AMS provides information on the nonrefractory (i.e., materials that are chemically and physically unstable at high temperatures) composition of aerosols, while the CVI uses a counterflow relative to the main incoming airstream to exclude small droplets and nonactivated particles from the inlet, allowing only larger cloud droplets to enter the inlet. The combination of the CVI and AMS allow the examination of the chemical composition of the dried aerosol kernel from the cloud droplets. A key objective of the U.S. Department of Energy's (DOE)'s Atmospheric Sciences Program (ASP) is to improve the understanding of aerosol radiative effects on climate. This objective encompasses not only clear sky observations but also studies relating the effects of both aerosols on clouds and clouds on aerosols - in particular, how clouds affect the chemical and optical properties of aerosols. The latter was the science driver in the design of CHAPS. The measurement strategy for CHAPS was intended to provide measurements relevant to four questions associated with the aerosol radiative forcing issues of interest to the ASP: (1) How do the below-cloud and above-cloud aerosol optical and cloud nucleating properties downwind of a typical North American city differ from the optical and nucleating properties of aerosols in air unperturbed by urban emissions? Our interest is in the differences in the radiative properties, chemical composition, hygroscopic properties, and size distributions below and above cloud, and upwind and downwind of such a city. (2) How does the distribution of aerosol extinction vary in relation to the proximity to individual clouds and fields of clouds and why? (3) What are the differences, in terms of both size distributions and chemical composition, between activated aerosols within the urban plume and those outside the urban plume? (4) To what extent can models with state-of-the-art cloud parameterizations capture the statistical features of the below-above-cloud aerosols?« less

This work compares the WRF/Chem (Weather Research and Forecasting – Chemistry) simulated O3 concentrations in the Mexico City Metropolitan Area (MCMA) with measurements from the ground-based RAMA network during the MILAGRO (Megacity Initiative: Local and Global Research Observations) period. The model resolves the observations reasonably well in terms of diurnal cycle and mean magnitude as reflected by high correlation coefficients and low root-mean-square errors. Stations located in the center of the MCMA generally exhibit higher correlation coefficients and lower model biases than those stations located in the peripheral of the MCMA. Large temporal variations in the observed and simulated O3 concentrations are noted from station to station during the MILAGRO period. Sensitivity analyses of O3 concentrations to changes in NOx and VOC emissions rates suggest that O3 production in the MCMA is VOC-sensitive, and VOC-emissions reduction appears to be an effective strategy for reducing high surface O3 concentrations in the MCMA.

Black carbon (BC) and light-absorbing organic carbon (brown carbon, BrC) play key roles in warming the atmosphere, but the magnitude of their effects remains highly uncertain. Theoretical modelling and laboratory experiments demonstrate that coatings on BC can enhance BC's light absorption, therefore many climate models simply assume enhanced BC absorption by a factor of ∼1.5. However, recent field observations show negligible absorption enhancement, implying models may overestimate BC's warming. Here we report direct evidence of substantial field-measured BC absorption enhancement, with the magnitude strongly depending on BC coating amount. Increases in BC coating result from a combination of changing sources and photochemical aging processes. When the influence of BrC is accounted for, observationally constrained model calculations of the BC absorption enhancement can be reconciled with the observations. We conclude that the influence of coatings on BC absorption should be treated as a source and regionally specific parameter in climate models., Uncertainties in the absorptive properties of black and brown carbon particles limit our understanding of their warming potential. Following an extensive field campaign, Liu et al. report that the magnitude of warming is dependent on particle coatings, which vary due to source and photochemical aging.

This report discusses the ghgas IC project which when applied, allows for an evaluation of LANL's HIGRAD model which can be used to create atmospheric simulations.

Atmospheric models are compared in collaboration with LANL and the University of Michigan to understand emissions and the condition of the atmosphere from a model perspective.

The potential for carbon dioxide (CO2) sequestration via engineered chemical sinks is investigated using a three dimensional chemical transport model (CTM). Meteorological and chemical constraints for flat or vertical systems that would absorb CO2 from the atmosphere, as well as an example chemical system of calcium hydroxide (Ca(OH)2) proposed by Elliott et al. [Compensation of atmospheric CO2 buildup through engineered chemical sinkage, Geophys. Res. Lett. 28 (2001) 1235] are reviewed. The CTM examines land based deposition sinks, with 4°×5° latitude/longitude resolution at various locations, and deposition velocities (v). A maximum uptake of ∼20 Gton (1015 g) C yr−1 is attainable with v>5 cm s−1 at a mid-latitude site. The atmospheric increase of CO2 (3 Gton yr−1) can be balanced by an engineered sink with an area of no more than 75,000 km2 at v of 1 cm s−1. By building the sink upwards or splitting this area into narrow elements can reduce the active area by more than an order of magnitude as discussed in Dubey et al. [31].

The Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics & Nitrogen (BEACHON) project seeks to understand the feedbacks and inter-relationships between hydrology, biogenic emissions, carbon assimilation, aerosol properties, clouds and associated feedbacks within water-limited ecosystems. The Manitou Experimental Forest Observatory (MEFO) was established in 2008 by the National Center for Atmospheric Research to address many of the BEACHON research objectives, and it now provides a fixed field site with significant infrastructure. MEFO is a mountainous, semi-arid ponderosa pine-dominated forest site that is normally dominated by clean continental air but is periodically influenced by anthropogenic sources from Colorado Front Range cities. This article summarizes the past and ongoing research activities at the site, and highlights some of the significant findings that have resulted from these measurements. These activities include - soil property measurements; - hydrological studies; - measurements of high-frequency turbulence parameters; - eddy covariance flux measurements of water, energy, aerosols and carbon dioxide through the canopy; - determination of biogenic and anthropogenic volatile organic compound emissions and their influence on regional atmospheric chemistry; - aerosol number and mass distributions; - chemical speciation of aerosol particles; - characterization of ice and cloud condensation nuclei; - trace gas measurements; and - model simulations using coupled chemistry and meteorology. In addition to various long-term continuous measurements, three focused measurement campaigns with state-of-the-art instrumentation have taken place since the site was established, and two of these studies are the subjects of this special issue: BEACHON-ROCS (Rocky Mountain Organic Carbon Study, 2010) and BEACHON-RoMBAS (Rocky Mountain Biogenic Aerosol Study, 2011).

Wildfires contribute significantly to global soot emissions, yet their aerosol formation mechanisms and resulting particle properties are poorly understood and parameterized in climate models. The conventional view holds that soot is formed via the cluster-dilute aggregation mechanism in wildfires and emitted as aggregates with fractal dimension D(sub f) approximately equals 1.8 mobility diameter D(sub m) (is) less than or equal to 1 micron, and aerodynamic diameter D(sub a) (is) less than or equal to 300 nm. Here we report the ubiquitous presence of soot superaggregates (SAs) in the outflow from a major wildfire in India. SAs are porous, low-density aggregates of cluster-dilute aggregates with characteristic D(sub f) approximately equals 2.6,D(sub m) (is) greater than 1 micron, and D(sub a) is less than or equal to 300 nm that form via the cluster-dense aggregation mechanism.We present additional observations of soot SAs in wildfire smoke-laden air masses over Northern California, New Mexico, and Mexico City. We estimate that SAs contribute, per unit optical depth, up to 35% less atmospheric warming than freshly-emitted (D(sub f) approximately equals 1.8) aggregates, and approximately equals 90% more warming than the volume-equivalent spherical soot particles simulated in climate models.

At Trinidad, California we observed elevated CO2 concentrations and concomitant lowered O2 levels coincident with forest fires 70 km distant (from 10/8/99 to 10/21/99). The precision of our O2 data, ±1 µmol O2/mol dry air, revealed the reduction of atmospheric oxygen resulting from the combustion of biomass, and the stoichiometric ratios (−O2/CO2) of the wildfire emissions. Estimates of daily −O2/CO2 ratios were obtained by regression of CO2 against corresponding O2 data (R² 0.86 to 0.96). Daily −O2/CO2 ratios changed from 1.15 to 1.41 on a particularly smoky day that coincided with elevated levels of CH4 and increased CH4/CO2 ratios. The change to a higher ratio during smoky conditions illustrates the association between changing emissions and −O2/CO2 ratios, possibly due to changing wildfire dynamics.

Retrieval of background carbon dioxide into regional chemical extractors would counter anthropogenic inputs in a manner friendly to established industries. We demonstrate via atmospheric transport/scaling calculations that for idealized flat removal units, global coverage could be less than two hundred thousand square kilometers. The disrupted area drops to a small fraction of this with engineering into the vertical to bypass laminarity. Fence structures and artificial roughness elements can both be conceived. Sink thermodynamics are analyzed by taking calcium hydroxide as a sample reactant. Energy costs could be minimized at near the endothermicity of binding reversal. In the calcium case the value is 25 kcal mole−1, as against a fuel carbon content of 150 in the same units. Aqueous kinetics are less than favorable for the hydroxide, but misting could counteract slow liquid phase transfer. Properties of superior scrubbers are outlined.

The reaction of OH with NO2 is central to atmospheric chemistry, and its dynamics can be constrained by studying the kinetics of isotopically labeled 18OH with NO2. This labeling opens an isotopic ...

Effects of recommended rate parameter changes in the NASA JPL-2000 evaluation from JPL-94 values on local ozone concentrations in a 2-D model are predicted using local sensitivity analysis results from the LLNL 2-D diurnally averaged model. Ozone decreases of 5% in the middle stratosphere and 10% increases near the tropopause and upper troposphere are indicated. Altered NOx kinetics are largely responsible for these changes, and increased model NOx levels and ozone depletion from stratospheric aircraft are also expected according to sensitivity analysis. Effects of specific changes, such as the nitric acid formation rate, are examined. New error bars on rate parameters in the evaluation are propagated by the sensitivity coefficients to derive revised kinetics uncertainties for the model ozone calculations at several altitudes, latitudes, and seasons. Middle-upper stratospheric ozone uncertainties of 12% from the catalytic photochemistry are indicated, increasing in the lower stratosphere.

Compared to measurements, atmospheric models have overestimated [ClO]/[HCl] and [ClONO2]/[HCl] in the upper and middle stratosphere, respectively, and consequently have predicted lower [O3] than observed. It is believed that a minor branch that produces HCl from the OH + ClO reaction can account for these discrepancies. Recent laboratory studies have indicated a 5 ( 2% yield for this channel. 1 By performing box model sensitivity analysis calculations using the output from the LLNL-2D diurnally averaged stratospheric model, we quantitatively confirm that this reaction is the most prominent contributor to the model [ClO]/ [HCl] and [ClONO2]/[HCl] uncertainties in the upper stratosphere and that it is most effective in increasing [O3] at higher latitudes during winter. Using theoretical methods, we examine the OH + ClO reaction mechanism, in which an initially energized HOOCl* complex is formed that can dissociate to HO2 + Cl (major) or HCl + O2( 1 ¢) (minor) products, redissociate to reactants, or be collisionally stabilized. Multichannel RRKM calculations guided by ab initio electronic structure calculations and the available kinetic data are presented. We show that the four-center transition state (TS3) for HCl production must lie at least 2 kcal/ mol below the reactants for the HCl yield to exceed 5%. Our ab initio relative energy of -2.3 ( 3 kcal/mol for TS3 demonstrates that this minor HCl channel is mechanistically feasible. We also predict small pressure, temperature, and H/D isotopic dependencies for the minor channel yield and insignificant rates of complex stabilization under atmospheric conditions.

Box model sensitivity-uncertainty calculations for O3 depletion from supersonic aircraft emissions were performed at the most perturbed locale using localized outputs of the LLNL 2-D diurnally averaged assessment model. Processes controlling N2O5, catalytic O3 loss steps O+NO2 and HO2+O3, HOx sink reactions OH+ HNO3/HNO4, and the O+O2 recombination that forms O3 are identified as the dominant photochemical uncertainty sources. Guided by local sensitivities, 2-D model runs were repeated with 9 targeted input parameters altered to 1/3 of their l-σ uncertainties to put error-bounds on the predicted O3 change. Results indicate these kinetic errors can cause the predicted local O3 loss of 1.5% to be uncertain by up to 3% in regions of large aircraft NOx injection.

We present data for the rate constant of the reaction NO2 + OH → HONO2 in nitrogen from 2 to 600 torr at 300 K. This is the first application of our high-pressure flow technique to a pressure-dependent reaction. The pressure range in this experiment overlaps the ranges covered by traditional discharge flow studies and flash photolysis studies, allowing exploration of the transition between the low-pressure and intermediate pressure regimes. The measured rate constants are in excellent agreement with previously published values; however, current recommendations systematically overestimate the room temperature rate constant by between 10 and 30% in the pressure range 20-700 torr. A reanalysis of all available data yields a new recommendation in good agreement with most of the data over the entire observational pressure range. This analysis includes an explicit treatment of the collisional efficiencies of different bath gases and includes the extreme broadening of the pressure falloff curve caused by the very strong HO-NO2 bond. We also report room temperature results for the reaction NO + OH over a more limited pressure range (4 to 75 torr). Our data agree with the currently recommended rate constants over this range.

Gas-phase hydrogen (H) abstractions from molecules by free radicals have been studied extensively. They form the simplest class of elementary reactions and also play a key role in atmospheric chemistry and so are the centerpiece of models of reactivity. Despite intense scrutiny, two fundamental mechanistic issues remain unresolved: (1) Do H abstractions proceed directly or indirectly? (2) Do thermodynamic or electronic interactions determine their reaction barrier? The thermoneutral identity reaction, OH + H2O → H2O + OH, provides an excellent opportunity to answer these questions. Several theoretically predicted H2O−HO complexes raise the possibility of an indirect mechanism, while no thermodynamic forcing influences the reaction barrier. To examine the various reactivity models, the isotopic scrambling reactions 18OH + H216O → H218O + 16OH and 16OD + H216O → H16OD + 16OH are studied in a high-pressure flow reactor. The measured rate constants are (2.3 ± 1.0) × 10-13 exp[−(2100 ± 250)/T] cm3 molecule-1 ...

Biomass burning is one of the largest sources of carbonaceous aerosols in the atmosphere, significantly affecting earth’s radiation budget and climate. Tar balls, abundant in biomass burning smoke, absorb sunlight and have highly variable optical properties, typically not accounted for in climate models. Here we analyse single biomass burning particles from the Las Conchas fire (New Mexico, 2011) using electron microscopy. We show that the relative abundance of tar balls (80%) is 10 times greater than soot particles (8%). We also report two distinct types of tar balls; one less oxidized than the other. Furthermore, the mixing of soot particles with other material affects their optical, chemical and physical properties. We quantify the morphology of soot particles and classify them into four categories: ~50% are embedded (heavily coated), ~34% are partly coated, ~12% have inclusions and~4% are bare. Inclusion of these observations should improve climate model performances., Biomass burning is a major source of carbonaceous particles, including tar balls and soot, that affect earth’s climate. Studying a wildfire plume, this work identifies two types of tar balls and classifies soot according to its mixing state with implications for the calculation of aerosol radiative forcing.

Ground-based aerosol measurements made in June 2010 within Sacramento urban area (site T0) and at a 40-km downwind location (site T1) in the forested Sierra Nevada foothills area are used to investigate the evolution of multispectral optical properties as the urban aerosols aged and interacted with biogenic emissions. Along with black carbon and non-refractory aerosol mass and composition observations, spectral absorptio (βabs), scattering (βsca), and extinction (βext) coefficients for wavelengths ranging from 355 to 1064 nm were measured at both sites using photoacoustic (PA) instruments with integrating nephelometers and using cavity ring-down (CRD) instruments. The daytime average Ångström exponent of absorption (AEA) was ~1.6 for the wavelength pair 405 and 870 nm at T0, while it was ~1.8 for the wavelength pair 355 and 870 nm at T1, indicating a modest wavelength-dependent enhancement of absorption at both sites throughout the study. The measured and Mie theory calculations of multispectral βsca showed good correlation (R2=0.85–0.94). The average contribution of supermicron aerosol (mainly composed of sea salt particles advected in from the Pacific Ocean) to the total scattering coefficient ranged from less than 20% at 405 nm to greater than 80% at 1064 nm. From 22 to 28 June, secondary organic aerosol mass increased significantly at both sites due to increased biogenic emissions coupled with intense photochemical activity and air mass recirculation in the area. During this period, the short wavelength scattering coefficients at both sites gradually increased due to increase in the size of submicron aerosols. At the same time, BC mass-normalized absorption cross-section (MAC) values for ultraviolet wavelengths at T1 increased by ~60% compared to the relatively less aged urban emissions at the T0 site. In contrast, the average MAC values for 870 nm wavelength were identical at both sites. These results suggest formation of moderately brown secondary organic aerosols formed in biogenically-influenced urban air.

In situ laser-induced fluorescence measurements of atmospheric OH are susceptible to interference from laser generated OH, particularly in the troposphere. To quantify this interference we implement the addition of perfluoropropene, C_3F_6, for the chemical removal of OH from the ambient air. The removal rate of OH by C_3F_6 is determined in the laboratory using the discharge flow technique. Over the temperature range 249 to 296 K the rate constant is (6.0±0.8) × 10^(−13) exp[(370±40)/T] cm^³ molecule^(−1) s^(−1), independent of pressure. In situ measurements using C_3F_6 addition are performed in both aircraft-borne and ground-based experiments. These studies show that laser excitation of the ^²Σ^+(v=1)← ^²Π(v=0) transition (282 nm) at high pulse repetition rates and low peak power can provide reliable and sensitive measurements of tropospheric OH.

Carbonaceous aerosols including organic carbon and black carbon have significant implications for both climate and air quality. In the current global climate or chemical transport models, a fixed hydrophobic-to-hydrophilic conversion lifetime for carbonaceous aerosol (τ) is generally assumed, which is usually around one day. We have implemented a new detailed aging scheme for carbonaceous aerosols in a chemical transport model (GEOS-Chem) to account for both the chemical oxidation and the physical condensation-coagulation effects, where τ is affected by local atmospheric environment including atmospheric concentrations of water vapor, ozone, hydroxyl radical and sulfuric acid. The updated τ exhibits large spatial and temporal variations with the global average (up to 11 km altitude) calculated to be 2.6 days. The chemical aging effects are found to be strongest over the tropical regions driven by the low ozone concentrations and high humidity there. The τ resulted from chemical aging generally decreases with altitude due to increases in ozone concentration and decreases in humidity. The condensation-coagulation effects are found to be most important for the high-latitude areas, in particular the polar regions, where the τ values are calculated to be up to 15 days. When both the chemical aging and condensation-coagulation effects are considered, the total atmospheric burdens and global average lifetimes of BC, black carbon, (OC, organic carbon) are calculated to increase by 9% (3%) compared to the control simulation, with considerable enhancements of BC and OC concentrations in the Southern Hemisphere. Model evaluations against data from multiple datasets show that the updated aging scheme improves model simulations of carbonaceous aerosols for some regions, especially for the remote areas in the Northern Hemisphere. The improvement helps explain the persistent low model bias for carbonaceous aerosols in the Northern Hemisphere reported in literature. Further model sensitivity simulations focusing on the continental outflow of carbonaceous aerosols demonstrate that previous studies using the old aging scheme could have significantly underestimated the intercontinental transport of carbonaceous aerosols.

[1] The Greenland δ18O ice core record is used as a proxy for Greenland surface air temperatures and to interpret Atlantic Multidecadal Oscillation (AMO) variability. An analysis of annual δ18O data from six Arctic ice cores (five from Greenland and one from Canada's Ellesmere Island) suggests a significant AMO spatial and temporal variability within a recent period of 660 years. A dominant AMO periodicity near 20 years is clearly observed in the southern (Dye3 site) and the central (GISP2, Crete and Milcent) regions of Greenland. This 20-year variability is, however, significantly reduced in the northern (Camp Century and Agassiz Ice Cap) region, likely due to a larger distance from the Atlantic Ocean, and a much lower snow accumulation. A longer time scale AMO component of 45–65 years, which has been seen clearly in the 20th century SST data, is detected only in central Greenland ice cores. We find a significant difference between the AMO cycles during the Little Ice Age (LIA) and the Medieval Warm Period (MWP). The LIA was dominated by a ∼20 year AMO cycle with no other decadal or multidecadal scale variability above the noise level. However, during the preceding MWP the 20 year cycle was replaced by a longer scale cycle centered near a period of 43 years with a further 11.5 year periodicity. An analysis of two coupled atmosphere-ocean general circulation models control runs (UK Met Office HadCM3 and NOAA GFDL CM2.1) agree with the shorter and longer time-scales of Atlantic Meridional Overturning Circulation (AMOC) and temperature fluctuations with periodicities close to those observed. However, the geographic variability of these periodicities indicated by ice core data is not captured in model simulations.

We describe the synoptic and regional-scale meteorological conditions that affected the transport and mixing of trace gases and aerosols in the vicinity of Sacramento, California during June 2010 when the Carbonaceous Aerosol and Radiative Effects Study (CARES) was conducted. The meteorological measurements collected by various instruments deployed during the campaign and the performance of the chemistry version of the Weather Research and Forecasting model (WRF-Chem) are both discussed. WRF-Chem was run daily during the campaign to forecast the spatial and temporal variation of carbon monoxide emitted from 20 anthropogenic source regions in California to guide aircraft sampling. The model is shown to reproduce the overall circulations and boundary-layer characteristics in the region, although errors in the upslope wind speed and boundary-layer depth contribute to differences in the observed and simulated carbon monoxide. Thermally-driven upslope flows that transported pollutants from Sacramento over the foothills of the Sierra Nevada occurred every afternoon, except during three periods when the passage of mid-tropospheric troughs disrupted the regional-scale flow patterns. The meteorological conditions after the passage of the third trough were the most favorable for photochemistry and likely formation of secondary organic aerosols. Meteorological measurements and model forecasts indicate that the Sacramento pollutant plume was likely transported over a downwind site that collected trace gas and aerosol measurements during 23 time periods; however, direct transport occurred during only eight of these periods. The model also showed that emissions from the San Francisco Bay area transported by intrusions of marine air contributed a large fraction of the carbon monoxide in the vicinity of Sacramento, suggesting that this source likely affects local chemistry. Contributions from other sources of pollutants, such as those in the Sacramento Valley and San Joaquin Valley, were relatively low. Aerosol layering in the free troposphere was observed during the morning by an airborne Lidar. WRF-Chem forecasts showed that mountain venting processes contributed to aged pollutants aloft in the valley atmosphere that are then entrained into the growing boundary layer the subsequent day.

We present simulations of the 20th century Arctic temperature anomaly from the second generation Canadian Earth System Model (CanESM2). The new model couples together an atmosphere-ocean general circulation model, a land-vegetation model and terrestrial and oceanic interactive carbon cycle. It simulates well the observed 20th century Arctic temperature variability that includes the early and late 20th century warming periods and the intervening 1940–1970 period of substantial cooling. The addition of the land-vegetation model and the terrestrial and oceanic interactive carbon cycle to the coupled atmosphere-ocean model improves the agreement with observations from 1900–1970, however, it increases the overestimate of the post 1970 warming. In contrast the older generation coupled atmosphere-ocean general circulation models Canadian CanCM3 and NCAR/LANL CCSM3, used in the IPCC 2007 climate change assessment report, overestimate the rate of the 20th century Arctic warming by factor of two to three and they are unable to reproduce the observed 20th century Arctic climate variability.

[1] Using five ice core data sets combined into a single time series, we provide for the first time strong observational evidence for two distinct time scales of Arctic temperature fluctuation that are interpreted as variability associated with the Atlantic Multidecadal Oscillation (AMO). The dominant and the only statistically significant multidecadal signal has a time scale of about 20 years. The longer multidecadal variability of 45–85 years is not well defined and none of the time scales in this band is statistically significant. We compare these observed temperature fluctuations with results of coupled climate model simulations (HadCM3 and GFDL CM2.1). Both the 20–25 year and a variable longer AMO time scale are prominent in the models' long control runs. This periodicity supports our conjecture that the observed ice core fluctuations are a signature of the AMO. The robustness of this short time scale period in both observations and model simulations has implications for understanding the dominant AMO mechanisms in climate.

Compared with other industrial processes, carbon capture and storage (CCS) will have an unusual impact on atmospheric composition by reducing the CO 2 released from fossil-fuel combustion plants, but not reducing the associated O 2 loss. CO 2 that leaks into the air from below-ground CCS sites will also be unusual in lacking the O 2 deficit normally associated with typical land CO 2 sources, such as from combustion or ecosystem exchanges. CCS may also produce distinct isotopic changes in atmospheric CO 2 . Using simple models and calculations, we estimate the impact of CCS or leakage on regional atmospheric composition. We also estimate the possible impact on global atmospheric composition, assuming that the technology is widely adopted. Because of its unique signature, CCS may be especially amenable to monitoring, both regionally and globally, using atmospheric observing systems. Measurements of the O 2 /N 2 ratio and the CO 2 concentration in the proximity of a CCS site may allow detection of point leaks of the order of 1000 ton CO 2 yr −1 from a CCS reservoir up to 1 km from the source. Measurements of O 2 /N 2 and CO 2 in background air from a global network may allow quantification of global and hemispheric capture rates from CCS to the order of ±0.4 Pg C yr −1 .

A comprehensive dataset of microphysical and radiative properties of aerosols and clouds in the boundary layer in the vicinity of Barrow, Alaska, was collected in April 2008 during the Indirect and Semi-Direct Aerosol Campaign (ISDAC). ISDAC's primary aim was to examine the effects of aerosols, including those generated by Asian wildfires, on clouds that contain both liquid and ice. ISDAC utilized the Atmospheric Radiation Measurement Pro- gram's permanent observational facilities at Barrow and specially deployed instruments measuring aerosol, ice fog, precipitation, and radiation. The National Research Council of Canada Convair-580 flew 27 sorties and collected data using an unprecedented 41 stateof- the-art cloud and aerosol instruments for more than 100 h on 12 different days. Aerosol compositions, including fresh and processed sea salt, biomassburning particles, organics, and sulfates mixed with organics, varied between flights. Observations in a dense arctic haze on 19 April and above, within, and below the single-layer stratocumulus on 8 and 26 April are enabling a process-oriented understanding of how aerosols affect arctic clouds. Inhomogeneities in reflectivity, a close coupling of upward and downward Doppler motion, and a nearly constant ice profile in the single-layer stratocumulus suggests that vertical mixing is responsible for its longevity observed during ISDAC. Data acquired in cirrus on flights between Barrow and Fairbanks, Alaska, are improving the understanding of the performance of cloud probes in ice. Ultimately, ISDAC data will improve the representation of cloud and aerosol processes in models covering a variety of spatial and temporal scales, and determine the extent to which surface measurements can provide retrievals of aerosols, clouds, precipitation, and radiative heating.

Publisher Summary This chapter provides an overview of the current CO2 adsorption technologies with various solid adsorbents. Aqueous and dry processes have different CO2 sorption characteristics. In aqueous sorption, CO2 is dissolved into the solvent. In solid sorption, CO2 molecules are chemisorbed to the sorbents by strong chemical bonds, or physisorbed by weaker intermolecular bonds resulting from the interactions between sorbent and CO2 molecules. For the evaluation of the CO2 sorption activity with respect to the separation process, two principal modes of adsorption are used that include physical and chemical. Physical adsorption, physisorption, of molecules involves relatively weak intermolecular forces. These forces include dispersion, dipolar or van der Waal interactions between the adsorbent surface, and the adsorbate CO2 molecules. Chemical adsorption, also known as chemisorption, on solid materials is achieved by substantial sharing of electrons between the surface of adsorbent and adsorbate to create a covalent or ionic bond. Thus, chemical adsorption may not be fully reversible, and could require high energy for regeneration. As carbon dioxide molecules are adsorbed on the surface of the adsorbent through valence bonds, they form a monolayer. The chemisorption energy between the gas molecules and adsorbents can vary significantly depending on the bond strength between adsorbent and adsorbate species.

Understanding the phase relationship between climate changes in the Arctic and Antarctic regions is essential for our understanding of the dynamics of the Earth's climate system. In this paper we show that the 20th century detrended Arctic and Antarctic temperatures vary in anti-phase seesaw pattern - when the Arctic warms the Antarctica cools and visa versa. This is the first time that a bi-polar seesaw pattern has been identified in the 20th century Arctic and Antarctic temperature records. The Arctic (Antarctic) detrended temperatures are highly correlated (anti-correlated) with the Atlantic Multi-decadal Oscillation (AMO) index suggesting the Atlantic Ocean as a possible link between the climate variability of the Arctic and Antarctic regions. Recent accelerated warming of the Arctic results from a positive reinforcement of the linear warming trend (due to an increasing concentration of greenhouse gases and other possible forcings) by the warming phase of the multidecadal climate variability (due to fluctuations of the Atlantic Ocean circulation).

The article of record as published may be located at http://dx.doi.org/10.1029/2008JD011699. In situ cloud condensation nuclei (CCN) measurements were obtained in the boundary layer over Houston, Texas, during the 2006 Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS) campaign onboard the CIRPAS Twin Otter. Polluted air masses in and out of cloudy regions were sampled for a total of 22 flights, with CCN measurements obtained for 17 of these flights. In this paper, we focus on CCN closure during two flights, within and downwind of the Houston regional plume and over the Houston Ship Channel. During both flights, air was sampled with particle concentrations exceeding 25,000 cm 3 and CCN concentrations exceeding 10,000 cm 3. CCN closure is evaluated by comparing measured concentrations with those predicted on the basis of measured aerosol size distributions and aerosol mass spectrometer particle composition. Different assumptions concerning the internally mixed chemical composition result in average CCN overprediction ranging from 3% to 36% (based on a linear fit). It is hypothesized that the externally mixed fraction of the aerosol contributes much of the CCN closure scatter, while the internally mixed fraction largely controls the overprediction bias. On the basis of the droplet sizes of activated CCN, organics do not seem to impact, on average, the CCN activation kinetics.