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This paper aims at characterising the impact of the atmospheric variability on the aerosol burden and residence time in the Arctic region. For this purpose, a global simulation using an emissions inventory from the year 2000 is performed for the period 2000-2005. The model thus describes a 6-yr evolution of sulphate, black carbon (BC) and mineral dust, whose variability is driven by the atmosphere only. Our simulation is validated, thanks to comparisons with surface observations. The aerosol residence time takes minimum values in fall: 4 d for sulphate and 8 d for BC and dust. It takes maximum values in June: 10 d for sulphate and 16 d for BC and dust. However, from one spring to another, it can vary by about 50% for sulphate, 40% for BC and 100% for dust, depending on the atmospheric variability. In June, sulphate, BC and dust burden averaged over the Arctic region reach respectively maximums of 1.9 mg[S]m-2, 0.2 mgm-2 and 6mgm-2, characteristic of the so-called Arctic haze. From one year to another, these values can vary by 20% for sulphate, 10% for BC and 60% for dust. [ABSTRACT FROM AUTHOR]

Response function models are often used to represent the behaviour of complex, high order global carbon cycle (GCC) and climate models in applications which require short model run times. Although apparently black-box, these response function models need not necessarily be entirely opaque, but instead may also convey useful insights into the properties of the parent model or process. By exploiting a transfer function (TF) framework to analyse the Lenton GCC model, this paper attempts to demonstrate that response function representations of GCC models can sometimes also provide structural information on the parent model from which they are identified and calibrated. We take a fifth-order TF identified from the impulse response of the Lenton model atmospheric burden, and decompose this to show how it can be re-expresses in a generic five-box form in sympathy with the structure of the parent model. [ABSTRACT FROM AUTHOR]

The spatial and temporal gradients in atmospheric CO2 contain signatures of carbon fluxes, and as part of inverse studies, these signatures have been combined with atmospheric models to infer carbon sources and sinks. However, such studies have yet to yield finer-scale, regional fluxes over the continent that can be linked to ecosystem processes and ground-based observations. The reasons for this gap are twofold: lack of atmospheric observations over the continent and model deficiencies in interpreting such observations. This paper describes a series of intensive atmospheric sampling field programmes designed as pilot experiments to bridge the observational gap over the continent and to help test and develop models to interpret these observations. We summarize recent results emerging from this work, outlining the role of the intensive atmospheric programmes in collecting CO2 data in both the vertical and horizontal dimensions. These data: (1) quantitatively establish the spatial variability of CO2 and the associated errors from neglecting this variability in models; (2) directly measure regional carbon fluxes from airmass-following experiments and (3) challenge models to reduce and account for uncertainties in atmospheric transport. We conclude with a look towards the future, outlining ways in which intensive atmospheric sampling can contribute towards advancing carbon science. [ABSTRACT FROM AUTHOR]

The lack of a firm relationship between wind speed (U10) and gas transfer velocity (k) is considered to be one of the factors that hinders accurate quantification of interannual variations of ocean–atmosphere CO2 fluxes. In this paper the interannual variations ofkof using four differentk– U10 parametrizations are examined using wind speed data from the NCEP/NCAR reanalysis project. The extent to which interannual variations are faithfully reproduced in the NCEP/NCAR data is also investigated. This is carried out through comparison with QuikSCAT data. Compared with 4 yr of QuikSCAT data, NCEP/NCAR data reproduce interannualkvariations, although the absolute magnitude ofkis underestimated. Interannualkvariation shows great sensitivity to selection ofk– U10 parametrization, and in the Westerlies it changes by a factor of three depending onk– U10 parametrization. Use of monthly mean winds speeds leads to overestimation of interannualkvariations compared withkvariations computed using 6-hourly wind speeds and the appropriatek– U10 parametrization. Even though the effect of changingk– U10 parametrization is large enough to be an issue that needs to be considered when computing interannual air–sea CO2 flux variations through combining estimates ofkwith data for the air–sea CO2 gradient, it is not sufficient to bridge the gap between such estimates and estimates based on analyses of atmospheric oxygen, CO2 andδ13C data. Finally it is shown that the ambiguity in the relationship between wind speed andkintroduces an uncertainty in interannual flux variations comparable to a bias of interannualΔ pCO2 variations of at most±5μatm. [ABSTRACT FROM AUTHOR]

abstract This paper presents the results of a simulation with a mechanistic terrestrial ecosystem model, focusing on the atmosphere–biosphere exchange and stable isotope composition of carbon. The simulation was performed from 1953 to 1999 on the basis of observed climate data and atmospheric carbon dioxide (CO2 ) concentration and stable carbon isotope ratio (δ13 C). The model, termed Sim-CYCLE, captures carbon dynamics from photosynthetic assimilation to microbial decomposition, including seasonal and interannual variability. Photosynthetic discrimination effect on δ13 C was considered at three levels: (1) leaf-level fractionation, (2) canopy-level CO2 recycling and (3) continent-level C3 /C4 pattern. The 47-yr simulation estimated that the average gross CO2 flux was 121 Pg C yr-1 , and that the average photosynthetic δ13 C discrimination coefficient (Δ) was 18.2%. A sensitivity analysis indicated that the estimated Δ depends heavily on the parameterization of stomatal conductance and C3 /C4 composition. In spite of their small biomass, C4 plants contributed considerably to the biospheric productivity and belowground carbon supply. The estimated net CO2 and isotopic exchange of the terrestrial ecosystems corresponded, at least qualitatively, with observed atmospheric CO2 and its δ13 C seasonal patterns in the Northern Hemisphere. The gross CO2 fluxes of photosynthesis and respiration indicated a wide range of interannual variability, which was in a sufficient magnitude to induce anomalies in the atmospheric CO2 growth rate. The estimated Δ showed a wide range of latitudinal and longitudinal variations and seasonal oscillation, but little interannual change. However, during the 47-yr period, the estimated δ13 C of carbon pools decreased by 0.3%, while the δ13 C of atmospheric CO2 decreased by 0.7%. These results carry implications for the application of a top-down approach, i.e. the double-deconvolution method, to inferring the global terrestrial CO2 budget. [ABSTRACT FROM AUTHOR]

The spatial and temporal gradients in atmospheric CO2 contain signatures of carbon fluxes, and as part of inverse studies, these signatures have been combined with atmospheric models to infer carbon sources and sinks. However, such studies have yet to yield finer-scale, regional fluxes over the continent that can be linked to ecosystem processes and ground-based observations. The reasons for this gap are twofold: lack of atmospheric observations over the continent and model deficiencies in interpreting such observations. This paper describes a series of intensive atmospheric sampling field programmes designed as pilot experiments to bridge the observational gap over the continent and to help test and develop models to interpret these observations. We summarize recent results emerging from this work, outlining the role of the intensive atmospheric programmes in collecting CO2 data in both the vertical and horizontal dimensions. These data: (1) quantitatively establish the spatial variability of CO2 and the associated errors from neglecting this variability in models; (2) directly measure regional carbon fluxes from airmass-following experiments and (3) challenge models to reduce and account for uncertainties in atmospheric transport. We conclude with a look towards the future, outlining ways in which intensive atmospheric sampling can contribute towards advancing carbon science. [ABSTRACT FROM AUTHOR]

ABSTRACT We apply methods from extreme value theory to identify extreme events in high (termed EHOs) and low (termed ELOs) total ozone and to describe the distribution tails (i.e. very high and very low values) of five long-term European ground-based total ozone time series. The influence of these extreme events on observed mean values, long-term trends and changes is analysed. The results show a decrease in EHOs and an increase in ELOs during the last decades, and establish that the observed downward trend in column ozone during the 1970-1990s is strongly dominated by changes in the frequency of extreme events. Furthermore, it is shown that clear 'fingerprints' of atmospheric dynamics (NAO, ENSO) and chemistry [ozone depleting substances (ODSs), polar vortex ozone loss] can be found in the frequency distribution of ozone extremes, even if no attribution is possible from standard metrics (e.g. annual mean values). The analysis complements earlier analysis for the world's longest total ozone record at Arosa, Switzerland, confirming and revealing the strong influence of atmospheric dynamics on observed ozone changes. The results provide clear evidence that in addition to ODS, volcanic eruptions and strong/moderate ENSO and NAO events had significant influence on column ozone in the European sector. [ABSTRACT FROM AUTHOR]

BSTRACT The trends of terrestrial carbon exchange and their mechanistic drivers are key components in understanding how carbon reservoirs will respond to climate change. Here we show trends in seasonal non-fossil land-atmosphere carbon exchange from 1980 to 2008 using atmospheric CO [ABSTRACT FROM AUTHOR]

Measurements of H at the high-altitude site of Jungfraujoch, Switzerland are reported upon for the period of August, 2005-November, 2009. The time series consists of measurements that are primarily representative of free tropospheric background conditions. Highest background H mixing ratios were observed in May, while the lowest were observed in November. The mean seasonal H peak-to-trough amplitude of 21 parts per billion (ppb, 10 dry air mixing ratio) at Jungfraujoch was considerably less than at other stations at similar latitudes and the seasonal minimum in November was comparatively delayed. These differences are primarily attributed to a dampening and delay of the surface soil sink signal during its vertical propagation to the free troposphere. Excess (mixing ratio minus corresponding baseline value) H (ΔH) and excess CO (ΔCO) displayed no significant correlation. This lacking correlation is attributed to H removal by soil during transport to Jungfraujoch, thereby significantly altering the ΔH/ΔCO ratio from traffic combustion sources, which is the largest source of anthropogenic H influencing measurements at Jungfraujoch. [ABSTRACT FROM AUTHOR]

Human conversion of natural ecosystems to croplands modifies not only the exchange of water and energy between the surface and the atmosphere, but also carbon fluxes. To investigate the impacts of crops on carbon fluxes and resulting atmospheric CO concentrations in the mid-continent region of the United States, we coupled a crop-specific phenology and physiology scheme for corn, soybean and wheat to the coupled ecosystem-atmosphere model SiB3-RAMS. Using SiBcrop-RAMS improved carbon fluxes at the local scale and had regional impacts, decreasing the spring uptake and increasing the summer uptake over the mid-continent. The altered fluxes changed the mid-continent atmospheric CO concentration field at 120 m compared to simulations without crops: concentrations increased in May and decreased >20 ppm during July and August, summer diurnal cycle amplitudes increased, synoptic variability correlations improved and the gradient across the mid-continent region increased. These effects combined to reduce the squared differences between the model and high-precision tower CO concentrations by 20%. Synoptic transport of the large-scale N-S gradient caused significant day-to-day variability in concentration differences measured between the towers. This simulation study shows that carbon exchange between crops and the atmosphere significantly impacts regional CO fluxes and concentrations. [ABSTRACT FROM AUTHOR]

Global high-precision atmospheric Δ14CO2 records covering the last two decades are presented, and evaluated in terms of changing (radio)carbon sources and sinks, using the coarse-grid carbon cycle model GRACE. Dedicated simulations of global trends and interhemispheric differences with respect to atmospheric CO2 as well as δ13CO2 and Δ14CO2, are shown to be in good agreement with the available observations (1940–2008). While until the 1990s the decreasing trend of Δ14CO2 was governed by equilibration of the atmospheric bomb 14C perturbation with the oceans and terrestrial biosphere, the largest perturbation today are emissions of 14C-free fossil fuel CO2. This source presently depletes global atmospheric Δ14CO2 by 12–14‰ yr−1, which is partially compensated by 14CO2 release from the biosphere, industrial 14C emissions and natural 14C production. Fossil fuel emissions also drive the changing north–south gradient, showing lower Δ14C in the northern hemisphere only since 2002. The fossil fuel-induced north–south (and also troposphere–stratosphere) Δ14CO2 gradient today also drives the tropospheric Δ14CO2 seasonality through variations of air mass exchange between these atmospheric compartments. Neither the observed temporal trend nor the Δ14CO2 north–south gradient may constrain global fossil fuel CO2 emissions to better than 25%, due to large uncertainties in other components of the (radio)carbon cycle. [ABSTRACT FROM AUTHOR]

Atmospheric N2O concentration was observed in the Pacific for the period 1991–2006, using commercial container ships sailing between Japan and North America and between Japan and Australia or New Zealand. The N2O concentration showed a secular increase and interannual variations at all sampling locations, but a seasonal cycle was detectable only at northern high latitudes. The annual mean N2O concentration showed little longitudinal variations (within ± 0.3 ppb) in the northern Pacific, but showed a clear north-south gradient of about 0.8 ppb, with higher values in the Northern Hemisphere. The annual mean N2O was also characterized by especially high values at 30°N due to strong local N2O emissions and by a steep latitudinal decrease from the equator to 20°S due to the suppression of interhemispheric exchange of air by the South Pacific Convergence Zone. The N2O growth rate showed an interannual variation with a period of about 3 yr (high-values in 1999 and 2000), with a delayed eastward and poleward phase propagation in the northern and western Pacific, respectively. The interannual variations of the N2O growth rate and soil water showed a good correlation, suggesting that the N2O emission from soils have an important causative role in the atmospheric N2O variation. [ABSTRACT FROM AUTHOR]

Long-term measurements of fluxes of sensible heat ( H), latent heat ( LE) and carbon dioxide ( Fc) were made from December 2005 to August 2006 over an urban landscape in Helsinki, Finland using the direct micrometeorological eddy covariance technique. Three distinguished sectors of land-use cover (vegetation, roads and buildings) allowed comparisons of fluxes over different urban surfaces. The normalized standard deviation of wind and scalars as a function of atmospheric stability were typical for rough surfaces, as were turbulence spectra and cospectra. Footprint analysis was performed by a boundary-layer one and half-order closure model allowing for discrimination of surface and canopy sinks/sources and complex topography. Fluxes were analysed as average diurnal courses over winter, spring and summer periods. H exceeded LE reaching 300 W m–2 over urban and road surfaces in the summer and it was close to 100 W m–2 in the winter. LE was highest in the summer over vegetation cover attaining 150 W m–2. The emission rate of CO2 was high over road sector [20 μmol (m2s)–1][Correction added after online publication 16 Oct 2007: 30 μmol changed to 20 μmol] while in the vegetation sector it remained below 5 μmol (m2s)–1 and at summertime reached even −10 μmol(m2 s)−1[Correction added after online publication 16 Oct 2007: wording of sentence altered]. Effluxes from soil measured by chambers were 1–3 μmol (m2s)−1. Fc correlated with traffic density and a background non-vehicle flux was 1 μmol (m2s)−1[Correction added after online publication 16 Oct 2007: 2 μmol changed to 1 μmol]. [ABSTRACT FROM AUTHOR]

A technique called extended mosaic (EM) was designed to allow the subgrid scale interactions between the land surface and the atmosphere to extend vertically. EM addresses a limitation of previously existing techniques, and has been shown to have an important impact on the simulated climate in global models. The present work focuses on an observational validation of the climate characteristics of a general circulation model using EM, based on a set of 10-yr simulations with each of EM and the standard mosaic technique (M), driven by climatological sea surface temperatures. Model simulations using EM show improvements in many aspects of the mid-latitude climate and in wintertime air temperature over Alaska and Western Canada and in the pattern of the Australian monsoon precipitation over land. An example of a degradation in the EM simulation is the temperature over southern South America in wintertime. [ABSTRACT FROM AUTHOR]

The Models-3 Community Multi-scale Air Quality modeling system (CMAQ) coupled with the Regional Atmospheric Modeling System (RAMS) is used to analyse the geographical and the seasonal characteristics of nitrate aerosol (ANO3) concentration distributions over East Asia. Three-dimensional concentrations in January, March, April, July and October of 2001 are simulated, and for the evaluation of model performances, the simulated values of wind direction, wind speed, temperature, specific humidity, nitric oxide (NO), nitrogen oxide (NO2), ANO3 and ammonium aerosol (ANH4) are compared with the observational data obtained onboard the P-3B aircraft during its four consecutive flights over the South China Sea, the East China Sea, the Yellow Sea and the water areas to the east of Japan conducted on 13, 17, 18 and 21 March 2001. The observed data are 5-min averaged and the model results with a 1-hour temporal resolution are interpolated to the aircraft location and time using trilinear interpolation. Comparison shows that the observed values exhibit strong temporo-spatial variations, and the model reproduces these variations reasonably well. The simulated values of wind direction, wind speed, temperature and specific humidity are generally in good agreement with the observed ones, their correlation coefficients reach 0.66, 0.94, 0.99 and 0.96, respectively. Comparison also shows that the average mixing ratios of modelled and observed NO, NO2, ANO3 and ANH4 agree reasonably well with each other, the correlation coefficient for ANO3 and ANH4 are larger than 0.8, but the simulated standard deviations are smaller than the observed one, and the correlation coefficient for NO and NO2 are 0.48 and 0.44. Analysis of horizontal distributions of monthly averaged ANO3 concentrations in the boundary layer indicates that the ANO3 mixing ratios have noticeable differences among the four seasons. Generally the concentrations are high in the winter, spring and fall and low in the summer, and seasonal variations are typically strongest over China and Japan. Highest concentrations are found over eastern China where emissions of nitrogen oxides and ammonia are high and long-range transport may cause elevated concentrations in remote areas under favourable meteorological conditions, but the seasonal variation in the ANO3 concentrations is heavily influenced by the changes in precipitation and temperature. [ABSTRACT FROM AUTHOR]

The Integrated Deposition Model (IDEM) was improved by incorporating a novel multilayer biochemical dry deposition module for gases. The aerosol and base cation deposition module was adopted from IDEM. For evaluation of primary and ecosystem productivity, carbon respiration schemes were included. The resulting Framework for Atmosphere-Canopy Exchange Modelling (FACEM) was then evaluated by the case studies presented here. First, results for deposition of SO x, NO y and NH x were compared with site observations, showing correlations of up to . Applicability for grid deposition calculations for these compounds was then evaluated for Europe. The model was clearly able to reproduce the elevated deposition near the important emission areas in Europe. Next, we compared the modelled CO2 fluxes with measurements from 26 European sites. Correlations of up to indicate good performance. To evaluate grid performance, the 2003 European heat wave was studied in a final case study, resulting in convincing correspondence with the observed productivity anomalies. [ABSTRACT FROM AUTHOR]

The sensible and latent heat fluxes, representatives of the physical exchange processes of energy and water between land and air, are the two crucial variables controlling the surface energy partitioning related to temperature and humidity. The net primary production (NPP), the major carbon flux exchange between vegetation and atmosphere, is of great importance for the terrestrial ecosystem carbon cycle. The fluxes are simulated by a two-way coupled model, Atmosphere-Vegetation Interaction Model-Global Ocean-Atmosphere-Land System Model (AVIM-GOALS) in which the surface physical and physiological processes are coupled with general circulation model (GCM), and the global spatial and temporal variation of the fluxes is studied. The simulated terrestrial surface physical fluxes are consistent with the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA40) in the global distribution, but the magnitudes are generally 20–40 W/m2 underestimated. The annual NPP agrees well with the International Geosphere Biosphere Programme (IGBP) NPP data except for the lower value in northern high latitudes. The surface physical fluxes, leaf area index (LAI) and NPP of the global mid-latitudes, especially between 30 °N–50 °N, show great variation in annual oscillation amplitudes. And all physical and biological fields in northern mid-latitudes have the largest seasonality with a high statistical significance of 99.9%. The seasonality of surface physical fluxes, LAI and NPP are highly correlated with each other. The meridional three-peak pattern of seasonal change emerges in northern mid-latitudes, which indicates the interaction of topographical gradient variation of surface fluxes and vegetation phenology on these three latitudinal belts. [ABSTRACT FROM AUTHOR]

The impact of increasing levels of carbon dioxide on stomatal conductance and surface ozone levels was investigated using a global three-dimensional general circulation model (GCM) coupled to an interactive land surface scheme and a chemistry model. Pre-industrial, present day and doubled present day levels of carbon dioxide were used. This approach was used to examine the sensitivity of modelled surface ozone levels to changes in stomatal conductance via dry deposition. A doubled level of carbon dioxide was found to increase surface ozone levels by between 2 and 8 ppb in all four seasons owing to reduced dry deposition fluxes, although the location and extent of the changes were very different between each season. No change in levels of nitrogen oxides (NO and NO2) was modelled. A similar experiment to examine the same effect on modelled pre-industrial ozone levels showed that the ozone levels over Europe were only slightly smaller (by 1–1.5 ppb) when the CO2 level was decreased from 369 ppm to 280 ppm. [ABSTRACT FROM AUTHOR]

The standard approach to predicting climate change, assessing its impacts and planning mitigation strategies tends to be compartmentalized, leading to inadequate or incomplete advice for climate policy. Climate models used for future global warming predictions and attribution of past changes generally consider only global climate drivers, ignoring local drivers, such as land use change and urban effects. Impacts studies are generally carried out in isolation from each other and hence ignore interactions between different impacts sectors, such as hydrology, natural ecosystems and agriculture. Feedbacks from impacts to climate change, which often involve land ecosystem-atmosphere interactions, are often neglected. This can result in representations of global changes that are at best inconsistent and at worst completely misleading. Moreover, a number of climate change mitigation strategies, such as carbon sequestration and biofuels involve changes in land ecosystems. In addition to affecting climate through the exchange of carbon with the atmosphere, these land ecosystem changes may affect climate change or its impacts through a variety of additional processes, such as surface albedo change or changes in the surface moisture budget. Failure to account for these may have consequences that are potentially at odds with the aims of climate change mitigation. [ABSTRACT FROM AUTHOR]

During the period of July 8–13, 2002, we collected vertical profiles by aircraft of meteorological variables and atmospheric CO2 over the OBS (old black spruce) site located in Boreal Ecosystem Research and Monitoring Sites in Northern Saskatchewan, Canada. We have used the data from the morning and afternoon flights to calculate the regional daily afternoon CO2 flux for the days July 8–11. These daily fluxes were then compared to those obtained by the boundary layer budget method and by the eddy covariance measurements on the tower at the OBS site. We identified the importance of changes in the CO2 concentration by advection to the flux estimates. In addition, we provide arguments to suggest that subseasonal temporal averaging might not, at least in some cases, eliminate advective bias contribution to the flux estimates. Because the advective influence is large and highly directional, even on seasonal and interannual timescales, it is advisable that flux estimates based on CO2 concentration change at a site contain dynamic description of an air parcel transport history. [ABSTRACT FROM AUTHOR]

Atmospheric CO2 inversion studies infer surface sources and sinks from observations and models. These studies usually require determination of the fossil fuel component of the observation, which can be estimated using anthropogenic tracers such as CO. The objective of this study is to demonstrate a new CO tracer method that accounts for overlapping forest fire and photochemical CO influences, and to quantify several aspects of the uncertainty in the CO tracer technique. Photochemistry model results and observations from the International Consortium for Atmospheric Research on Transport and Transformation experiment are used to quantify changes in the fossil fuel CO2 prediction from the CO tracer method with and without the inclusion of CO from biomass burning and photochemistry. Although the chemical sources and sinks tend to offset each other, there are regions where the chemical reactions change fossil fuel CO2 predictions by up to ±4 ppm. Including biomass burning lowers fossil fuel CO2 by an average of 12 ppm in plumes heavily influenced by long-range transport of forest fire CO. An alternate fossil fuel CO2 calculation is done in a power plant plume using SO2 as a tracer, giving a change in 20 ppm from the CO method, indicative of uncertainty in the assumed CO:CO2 ratio. [ABSTRACT FROM AUTHOR]

Oceanic anthropogenic CO2 uptake will decrease both the pH and the aragonite saturation state (Ωarag) of seawater leading to an oceanic acidification. However, the factors controlling future changes in pH and Ωarag are independent and will respond differently to oceanic climate change feedbacks such as ocean warming, circulation and biological changes. We examine the sensitivity of these two CO2-related parameters to climate change feedbacks within a coupled atmosphere-ocean model. The ocean warming feedback was found to dominate the climate change responses in the surface ocean. Although surface pH is projected to decrease relatively uniformly by about 0.3 by the year 2100, we find pH to be insensitive to climate change feedbacks, whereas Ωarag is buffered by ∼15%. Ocean carbonate chemistry creates a situation whereby the direct pH changes due to ocean warming are almost cancelled by the pH changes associated with dissolved inorganic carbon concentrations changes via a reduction in CO2 solubility from ocean warming. We show that the small climate change feedback on future surface ocean pH is independent to the amount of ocean warming. Our analysis therefore implies that future projections of surface ocean acidification only need to consider future atmospheric CO2 levels, not climate change induced modifications in the ocean. [ABSTRACT FROM AUTHOR]

We have devised a new search algorithm for secondary particle formation events, or ‘nucleation events’ in data sets of atmospheric particle size distributions. The search algorithm is simple and based on the investigation of 18 integral parameters of the particle size distribution, three of which were found to be most relevant for identifying nucleation events. The algorithm is tested using long-term size distribution data sets of high-size resolution observed at Melpitz, Hohenpeissenberg, and Leipzig, Germany, and Beijing, China, thereby covering a wide range of clean and polluted conditions. By specifying the particular training sets, the method can be used by other researchers with different data sets or different research goals. The same search approach could be applied to identify and analyze other systematic changes in size distribution such as during frontal passages or sand storms. As an example application of the new algorithm, the 50 strongest nucleation events (‘bananas’) at each of the four sites are analyzed statistically in terms of average changes of integral parameters of the particle size distribution. [ABSTRACT FROM AUTHOR]

A three-dimensional Chemistry Transport Model was used to study the meteorologically induced interannual variability and trends in deposition of sulphur and nitrogen as well as concentrations of surface ozone (O3), nitrogen dioxide (NO2) and particulate matter (PM) and its constituents over Europe during 1958–2001. The model was coupled to the meteorological reanalysis ERA40, produced at the European Centre for Medium-range Weather Forecasts. Emissions and boundary conditions of chemical compounds and PM were kept constant at present levels. The average European interannual variation, due to meteorological variability, ranges from 3% for O3, 5% for NO2, 9% for PM, 6–9% for dry deposition, to about 20% for wet deposition of sulphur and nitrogen. For the period 1979–2001 the trend in ozone, due to climate variability is increasing in central and southwestern Europe and decreasing in northeastern Europe, the trend in NO2 is approximately opposite. The trend in PM is positive in eastern Europe. There are negative trends in wet deposition in southwestern and central Europe and positive trends in dry deposition overall. A bias in ERA40 precipitation could be partly responsible for the trends. The variation and trends need to be considered when interpreting measurements and designing measurement campaigns. [ABSTRACT FROM AUTHOR]

Measurements of changes in the atmospheric O2/N2 ratio have typically relied on compressed air derived from high-pressure tanks as the reference material against which atmospheric changes are assessed. The validity of this procedure is examined here in the context of the history of 18 O2/N2 reference tanks compared over a 12-yr time-frame. By considering differences in tank sizes, material types, and by performing additional tests, the long-term stability of the delivered gas is evaluated with respect to surface reactions, leakage, regulator effects, and thermal diffusion and gravimetric fractionation. Results are also reported for the stability of CO2 in these tanks. The results emphasize the importance of orienting tanks horizontally within a thermally insulated enclosure to reduce thermal and gravimetric fractionation of both O2/N2 and CO2 concentrations, and they emphasize the importance of avoiding elastomeric O-rings at the head-valve base. With the procedures documented here, the long-term drift in O2/N2 appears to be zero to within approximately ±0.4 per meg yr−1, which projects to an uncertainty of ±0.16 Pg C yr−1 (1σ) in O2-based global carbon budgets. [ABSTRACT FROM AUTHOR]

The CSIRO biosphere model has been coupled to an atmosphere model and a simulation has been performed for the 20th century. Both biosphere and atmosphere are forced with global CO2 concentration and the atmosphere is also forced with prescribed sea surface temperatures. The simulation follows the C4MIP Phase 1 protocol. We assess the model simulation using atmospheric CO2 data. Mauna Loa growth rate is well simulated from 1980 but overestimated before that time. The interannual variations in growth rate are reasonably reproduced. Seasonal cycles are underestimated in northern mid-latitudes and are out of phase in the southern hemisphere. The north–south gradient of annual mean CO2 is substantially overestimated due to a northern hemisphere net biosphere source and a southern tropical sink. Diurnal cycles at three northern hemisphere locations are larger than observed in many months, most likely due to larger respiration than observed. [ABSTRACT FROM AUTHOR]

Carbon cycle feedbacks will have a direct effect on anthropogenic emissions required to stabilize CO2 in the atmosphere. In this study, I used an intermediate complexity coupled climate-carbon model to quantify allowable CO2 emissions for a series of scenarios leading to CO2 stabilization at levels between 350 and 1000 ppmv. For all scenarios, global temperature did not stabilize over the next several centuries, but rather continued to increase well beyond the point of CO2 stabilization. Furthermore, neither long-term climate change, nor total allowable CO2 emissions, were sensitive to the shape of the CO2 stabilization profile, but only to the final stabilization level. For the 550-stabilization scenario, positive carbon cycle-climate feedbacks required a reduction of annual CO2 emissions throughout the simulation, with a maximum reduction of 2.3 GtC/yr occurring at 2050. Total emissions over the 21st century were 20% lower than those derived from an equivalent simulation without feedbacks. In two additional runs with varied climate sensitivities, emissions consistent with 550-stabilization were reduced by between 190 and 540 GtC over the next 400 yr relative to the no-feedbacks run. Allowable emissions were further reduced in all cases if CO2 increases did not affect future vegetation productivity, as this removed an otherwise important negative feedback on atmospheric CO2. [ABSTRACT FROM AUTHOR]

We derive regional-scale (∼104 km2) CO2 flux estimates for summer 2004 in the northeast United States and southern Quebec by assimilating extensive data into a receptor-oriented model-data fusion framework. Surface fluxes are specified using the Vegetation Photosynthesis and Respiration Model (VPRM), a simple, readily optimized biosphere model driven by satellite data, AmeriFlux eddy covariance measurements and meteorological fields. The surface flux model is coupled to a Lagrangian atmospheric adjoint model, the Stochastic Time-Inverted Lagrangian Transport Model (STILT) that links point observations to upwind sources with high spatiotemporal resolution. Analysis of CO2 concentration data from the NOAA-ESRL tall tower at Argyle, ME and from extensive aircraft surveys, shows that the STILT–VPRM framework successfully links model flux fields to regionally representative atmospheric CO2 data, providing a bridge between ‘bottom-up’ and ‘top-down’ methods for estimating regional CO2 budgets on timescales from hourly to monthly. The surface flux model, with initial calibration to eddy covariance data, produces an excellent a priori condition for inversion studies constrained by atmospheric concentration data. Exploratory optimization studies show that data from several sites in a region are needed to constrain model parameters for all major vegetation types, because the atmosphere commingles the influence of regional vegetation types, and even high-resolution meteorological analysis cannot disentangle the associated contributions. Airborne data are critical to help define uncertainty within the optimization framework, showing for example, that in summertime CO2 concentration at Argyle (107 m) is ∼0.6 ppm lower than the mean in the planetary boundary layer. [ABSTRACT FROM AUTHOR]

Stable isotopes of CO2 contain unique information on the biological and physical processes that exchange CO2 between terrestrial ecosystems and the atmosphere. Ecosystem exchange of carbon isotopes with the atmosphere is correlated diurnally and seasonally with the planetary boundary layer (PBL) dynamics. The strength of this kind of covariation affects the vertical gradient of δ13C and thus the global δ13C distribution pattern. We need to understand the various processes involved in transport/diffusion of carbon isotope ratio in the PBL and between the PBL and the biosphere and the troposphere. In this study, we employ a one-dimensional vertical diffusion/transport atmospheric model (VDS), coupled to an ecosystem isotope model (BEPS-EASS) to simulate dynamics of 13CO2 in the PBL over a boreal forest region in the vicinity of the Fraserdale (FRD) tower (49°52′29.9″N, 81°34′12.3″W) in northern Ontario, Canada. The data from intensive campaigns during the growing season in 1999 at this site are used for model validation in the surface layer. The model performance, overall, is satisfactory in simulating the measured data over the whole course of the growing season. We examine the interaction of the biosphere and the atmosphere through the PBL with respect to δ13C on diurnal and seasonal scales. The simulated annual mean vertical gradient of δ13C in the PBL in the vicinity of the FRD tower was about 0.25‰ in 1999. The δ13C vertical gradient exhibited strong diurnal (29%) and seasonal (71%) variations that do not exactly mimic those of CO2. Most of the vertical gradient (96.5%±) resulted from covariation between ecosystem exchange of carbon isotopes and the PBL dynamics, while the rest (3.5%±) was contributed by isotopic disequilibrium between respiration and photosynthesis. This disequilibrium effect on δ13C of CO2 dynamics in PBL, moreover, was confined to the near surface layers (less than 350 m). [ABSTRACT FROM AUTHOR]

Two approximations to convective transport have been implemented in an offline chemistry transport model (CTM) to explore the impact on calculated atmospheric CO2 distributions. Global CO2 in the year 2000 is simulated using the CTM driven by assimilated meteorological fields from the NASA's Goddard Earth Observation System Data Assimilation System, Version 4 (GEOS-4). The model simulates atmospheric CO2 by adopting the same CO2 emission inventory and dynamical modules as described in Kawa et al. (convective transport scheme denoted as Conv1). Conv1 approximates the convective transport by using the bulk convective mass fluxes to redistribute trace gases. The alternate approximation, Conv2, partitions fluxes into updraft and downdraft, as well as into entrainment and detrainment, and has potential to yield a more realistic simulation of vertical redistribution through deep convection. Replacing Conv1 by Conv2 results in an overestimate of CO2 over biospheric sink regions. The largest discrepancies result in a CO2 difference of about 7.8 ppm in the July NH boreal forest, which is about 30% of the CO2 seasonality for that area. These differences are compared to those produced by emission scenario variations constrained by the framework of Intergovernmental Panel on Climate Change (IPCC) to account for possible land use change and residual terrestrial CO2 sink. It is shown that the overestimated CO2 driven by Conv2 can be offset by introducing these supplemental emissions. [ABSTRACT FROM AUTHOR]

The sources and sinks of important climatic trace gases such as carbon dioxide (CO2) are often deduced from spatial and temporal variations in atmospheric concentrations. Reducing uncertainties in our understanding of the contemporary carbon budget and its underlying dynamics, however, requires significantly denser observations globally than is practical with in situ measurements. Space-based measurements appear technically feasible but require innovations in data analysis approaches. We develop a variational data assimilation scheme to estimate surface CO2 fluxes at fine time/space scales from such dense atmospheric data. Global flux estimates at a daily time step and model-grid spatial resolution ( here) are rapidly achieved after only a few dozen minimization steps. We quantify the flux errors from existing, planned and hypothetical surface and space-borne observing systems. Simulations show that the planned NASA Orbital Carbon Observatory (OCO) satellite should provide significant additional information beyond that from existing and proposed in situ observations. Improvements in data assimilation techniques and in mechanistic process models are both needed to fully exploit the emerging global carbon observing system. [ABSTRACT FROM AUTHOR]

Atmospheric CO2 measurements show strong synoptic variability. To understand the contribution of the synoptic signals on atmospheric CO2 inversion, we simulate the cases of biospheric fluxes with and without synoptic variations (referred to as ‘Synoptic’ and ‘Reference’, respectively) using an atmospheric transport model, and then perform inversion analyses with these biospheric CO2 concentration fields. Results show the monthly and annually averaged CO2 concentration anomalies (Synoptic–Reference) are functions of the distance from the continental biospheric source regions. Remote sites (like Mauna Loa) show averaged monthly amplitude of ∼0.2 ppm, while continental sites show averaged monthly amplitudes of 1–2 ppm with maximum monthly amplitudes up to 7 ppm. Spatial scales of these monthly mean synoptic anomaly patterns may exceed 1000 km. These CO2 concentration patterns are the results of the interaction of the synoptic CO2 flux field and atmospheric transport, and may be referred to as the synoptic Rectifier Effect. Inversion CO2 fluxes for 1992–1995 are obtained using biospheric background fields with and without synoptic biospheric flux variations. The maximum magnitude differences in estimated monthly flux for land and ocean regions are ∼0.4 and ∼0.2 GtC month−1, respectively. The average land sink increases by 0.19 GtC yr−1 while the average ocean sink decreases by 0.30 GtC yr−1. [ABSTRACT FROM AUTHOR]

The air–sea gas transfer velocity is an important determinant of the exchange of gases, including CO2, between the atmosphere and ocean, but the magnitude of the transfer velocity and what factors control it remains poorly known. Here, we use oceanic and atmospheric observations of 14C and 13C to constrain the global mean gas transfer velocity as well as the exponent of its wind speed dependence, utilizing the distinct signatures left by the air–sea exchange of 14CO2 and 13CO2. While the atmosphere and ocean inventories of 14CO2 and 13CO2 constrain the mean gas transfer velocity, the latitudinal pattern in the atmospheric and oceanic 14C and 13C distributions contain information about the wind speed dependence. We computed the uptake of bomb 14C by the ocean for different transfer velocity patterns using pulse response functions from an ocean general circulation model, and evaluated the match between the predicted bomb 14C concentrations and observationally based estimates for the 1970s–1990s. Using a wind speed climatology based on satellite measurements, we solved either for the best-fit global relationship between gas exchange and mean wind speed or for the mean gas transfer velocity over each of 11 ocean regions. We also compared the predicted consequences of different gas exchange relationships on the rate of change and interhemisphere gradient of 14C in atmospheric CO2 with tree-ring and atmospheric measurements. Our results suggest that globally, the dependence of the air–sea gas transfer velocity on wind speed is close to linear, with an exponent of 0.5 ± 0.4, and that the global mean gas transfer velocity at a Schmidt number of 660 is 20 ± 3 cm/hr, similar to the results of previous analyses. We find that the air–sea flux of 13C estimated from atmosphere and ocean observations also suggests a lower than quadratic dependence of gas exchange on wind speed. [ABSTRACT FROM AUTHOR]

Tropospheric ozone (O3), carbon monoxide (CO), total reactive nitrogen (NO y) and aerosols (PM2.5 and PM10) were measured on the southeastern Tibetan Plateau at Tengchong (25.01°N, 98.3°E, 1960 m a.s.l.) in Southwest China, where observational data is scarce, during a field campaign of the TAPTO-China (Transport of Air Pollutants and Tropospheric O3 over China) in the spring of 2004. Fire maps derived from satellite data and backward air trajectories were used to trace the source regions and transport pathways of pollution. Ozone, CO, NO y, PM10 and PM2.5 had average concentrations of 26 ± 8 ppb, 179 ± 91 ppb, 2.7 ± 1.2 ppb and 34 ± 23 and 28 ± 19 μg/m3, respectively. The measured O3 level is low when compared with those reported for similar longitudinal sites in Southeast (SE) Asia and northeastern Tibetan Plateau in Northwest China suggesting that there exist complex O3 variations in the Tibetan Plateau and its neighbouring SE Asian region. High levels of pollution with hourly averages of O3, CO, NO y, PM10 and PM2.5 concentrations up to 59, 678 and 7.7 ppb and 158 and 137 μg/m3, respectively, were observed. The increase of pollutants in the lower troposphere was caused by regional built-up and transport of pollution from active fire regions of the SE Asia subcontinent and from northern South Asia. Our results showed that pollution transport from SE Asia and South Asia had relatively stronger impacts than that from Central and South China on the abundance of O3, trace gases and aerosols in the background atmosphere of the Tibetan Plateau of Southwest China. [ABSTRACT FROM AUTHOR]

Smoothing splines have been used extensively in the analysis of gas concentration data from bubbles in ice cores. Since the fit is a linear projection of the data, propagation of data uncertainty through the fitting process is formally straightforward and, as we demonstrate, readily achievable from pre-existing spline-fitting procedures. The uncertainty propagation can be extended to determining both uncertainties in derivatives and uncertainties in quantities that reflect rates of input to the atmosphere. As an example, we apply the technique to 1000 yr of methane data from a Law Dome ice core. [ABSTRACT FROM AUTHOR]

Transmission electron microscopy photographs of airborne particles are compared with those of particles found in the surface microlayer of the open water between ice floes in the central Arctic Ocean in summer. The similarity in morphology, physical properties, X-ray spectra and a chemical reaction of the numerous aggregates and their building blocks predominantly smaller than 70 nm diameter, and of bacteria and other micro-organisms found in both, strongly suggests that the airborne particles were ejected from the water by bursting bubbles. The shape of the size distribution of aggregates in the air is very similar to that in the water, each with a well-defined Aitken mode but shifted towards smaller sizes. Diffuse electron-transparent material joining and surrounding the heat resistant and non-hygroscopic particulates in both the air and water is shown to have properties consistent with the exopolymer secretions (EPS) of microalgae and bacteria in the water. EPS are highly surface-active, highly hydrated molecules that can spontaneously assemble into gels. They are broken down by ultraviolet light or acidification. These properties provide an explanation for the different resistance to dehydration of bacteria from air and water samples when subjected to a vacuum, and the apparent absence of sea salt on airborne bacteria and aggregates. The difference in size distribution between the air and water samples is also explained. The role of EPS and particulate matter from the open lead surface microlayer in the production of the airborne Aitken mode particles and cloud condensation nuclei is examined and concluded to be very important. [ABSTRACT FROM AUTHOR]

In TransCom-3 (Level 1), atmospheric CO2 measurements from 76 monitoring stations for the period 1992–1996 and 16 atmospheric transport models were used to constrain annual mean CO2 fluxes over 11 land and 11 ocean regions. The tower measurements of atmospheric CO2 from Fraserdale, a continental site in northern Ontario, Canada are now available and processed for use in the TransCom-3 inverse modelling framework. In this short study, we show that by including this set of continental CO2 data, the estimated flux for the North American boreal region becomes nearly zero, a reduction of about 0.26 Pg C yr−1 from the previous estimate. The uncertainty of the estimated flux for this region is also reduced by ∼30%. All transport models show negative changes for boreal North America, with the strongest responses shown by NIRE, NIES, CSU and SKYHI. Furthermore, models showing a strong response in boreal North America tend to show strong sensitivity in middle- and high-latitude Asian regions. [ABSTRACT FROM AUTHOR]

Model-predicted atmospheric concentrations of222Rn based on two different222Rn source terms have been compared with observations in the lower troposphere. One simulation used a globally uniform222Rn source term from ice-free land surfaces of 1 atom cm−2 s−1; the other assumed a northwards-decreasing source term (linear decrease from 1 atom cm−2 s−1 at 30°N to 0.2 atom cm−2 s−1 at 70°N). Zero emissions were assigned to oceans. The northwards-decreasing source term improved predictions at four out of six stations north of 50°N, reducing the mean prediction/observation ratio from 2.8 to 0.87. In the latitudinal band between 30°N and 50°N, the northwards-decreasing source term resulted in systematic under-prediction of atmospheric222Rn, whereas the uniform source term provided predictions close to observations. Predictions based on the northwards-decreasing source term were significantlybetter than those based on the uniform source term for an averaged vertical222Rn profile around 44°N, but were not for one around 38°N. The results indicate that a northwards-decreasing source term could be a more realistic representation of actual222Rn emissions than a uniform 1 atom cm−2 s−1 source term. However, the decrease in222Rn source strength with increasing latitude might not begin at 30°N but somewhat further north. This hypothesis should be investigated through model-independent means. [ABSTRACT FROM AUTHOR]

Extensive aerosol and trace gas measurements were conducted at Ny-Ålesund (Svalbard) before and after Arctic sunrise in 2001 (NICE Dark and Light intensive campaigns) in order to study the possible role of aerosols in the renoxification mechanism. This study reports aerosol physical measurements over a continuous 3-month period. Arctic and sub-Arctic air masses dominated the measurement period and were characterized by low number (and 590 cm−3 respectively) and surface area (and 28μm2 cm−3) concentrations (measured range) except for two Arctic haze events with high concentrations in springtime (and∼ 125μm2 cm−3). Excluding these events, aerosol volatility measurements indicated no significant variation in the volatile (∼0.40), semi-volatile (∼0.32) or refractory (∼0.28) volume fractions which are commonly attributed to H2SO4,and soot/dust/sea-salt aerosol. [ABSTRACT FROM AUTHOR]

Measurements of the partial pressure of CO2 in surface seawaterwere made in the Southern Ocean south of Australia during four cruises in January to February 1969, December 1983 to January 1984, December 1994 to January 1995 and January 2002. The spatial distribution offor the four cruises showed the same pattern north of the Sub-Antarctic Front (SAF), while year-to-year changes were noted south of the SAF. We evaluated the long-term trend of therepresentative of the zone between oceanographic fronts by taking into account changes in the seasonal variation inand the long-term increase of the sea-surface temperature (SST) of the Southern Hemisphere. The observed growth rate ofwas 0.7± 0.1μatm yr−1 at its minimum, which was observed at the SST of 15°C north of the Subtropical Front (STF), 1.0± 0.5μatm yr−1 in the Sub-Antarctic Zone (SAZ) between STF and SAF, 1.5± 0.4μatm yr−1 in the Polar Frontal Zone (PFZ) between SAF and the Polar Front (PF) and 1.8± 0.2μatm yr−1 in the Polar Zone (PZ) between PF and 62°S, determined as the northern edge of the Seasonal Sea Ice Zone (SSIZ) on the basis of surface salinity and satellite images. These increases were caused by the uptake of anthropogenic CO2 as well as variations in the thermodynamic temperature effect, ocean transport and biological activity. In the SSIZ between 62 and 66.5°S, we could not clearly evaluate the long-term trend ofdue to the remarkable CO2 drawdown due to biological activity in January 2002. The relatively low growth rates ofclose to the STF and in the SAZ are probably associated with the formation of Subtropical Mode Water and Sub-Antarctic Mode Water in their respective zones. Between the north of the STF and the PZ, the growth rate of total dissolved inorganic carbon was calculated to be about 0.5–0.8μmol kg−1 yr−1 via the buffer factor. [ABSTRACT FROM AUTHOR]

Deposition of water-insoluble dust was measured in winter snow deposited at Murododaira (2450 m) on the western flank of Mount Tateyama in central Japan. An analysis of temporal variation in atmospheric aerosol concentration, incremental snow height and concentration of dust in the snow cover suggests that wet deposition is the major process in forming thicker dust layers in the snow cover at Mount Tateyama. Dust layers in the snow cover contain Ca-rich materials typically found in Asian dust (Kosa) particles. Volume size distributions of dust particles in the snow showed single and bi-modal structures having volume median diameters from 6–21 μm. Dust profiles in snow cover over the last 6 yr reveal frequent sporadic high dust concentrations in spring and large year-to-year variations in the amount deposited. The average amount of dust deposition (7.7 g m−2) from winter to spring at the site was close to the long-term averages of annual flux obtained from sea sediment near Japan, implying that dusty precipitation in spring contributes to annual deposition of aeolian mineral dust. [ABSTRACT FROM AUTHOR]

We present an evaluation of the representation of subgrid scale transport in the new multiscale global chemistry and transport model MOCAGE. The approach is an off-line computation of vertical mass fluxes due to convective and turbulent processes, using only large-scale variables archived in meteorological analyses. Radon is a naturally emitted gas with a radioactive half-life of 3.8 days and is a useful tracer of tropospheric transport processes. A 1-yr (1999) simulation of atmospheric radon concentration has been performed, using 6-hourly meteorological analyses for the forcings. Two different mass flux convection schemes have been tested: a simplified version of the scheme and Kain–Fritsch–Bechtold ( ). We compare model outputs with observations at different time and space scales, showing good overall results. A new interpretation is given to the more contrasted results obtained in Antarctica, as for other models. The state-of-the-art representation of synoptic scale activity around Antarctica is markedly worse than in other parts of the world, both due to oversimplifications of the seasonal evolution of the extent of sea ice, and to the scarcity of observations. Twelve-hourly simulated concentrations are evaluated at two sites for 1999. At Amsterdam Island results are satisfactory: correlation between observed and modelled concentrations is of the order of 0.5. The model reproduces well “radonic storm” events. At the coastal site of Mace Head in Ireland, simulations are available at two different horizontal resolutions. The correlation between observations and the model is of the order of 0.7. This result is mainly determined by the synoptic scale context, even though local-scale circulations such as breezes interfere on occasions. Finally, it appears that the off-line approach in MOCAGE for subgrid transport is a practical one for chemistry and transport multiscale modelling. [ABSTRACT FROM AUTHOR]

A series of sensitivity studies were performed with a spectral radiative transfer model using aerosol data from the Global Aerosol Data Set (GADS, data available at ) in order to investigate and quantify the relative role of key climatic parameters on clear-sky ultraviolet–visible direct aerosol radiative forcing at the top of the atmosphere (TOA), within the atmosphere and at the Earth's surface. The model results show that relative humidity and aerosol single-scattering albedo are the most important climatic parameters that determine aerosol forcing at the TOA and at the Earth's surface and atmosphere, respectively. Relative humidity exerts a non-linear positive radiative effect, i.e. increasing humidity amplifies the magnitude of the forcing in the atmosphere and at the surface. Our model sensitivity studies show that increasing relative humidity by 10%, in relative terms, increases the aerosol forcing by factors of 1.42 at the TOA, 1.02 in the atmosphere and 1.17 at the surface. An increase in aerosol single-scattering albedo by 10%, in relative terms, increased the aerosol forcing at the TOA by 1.29, while it decreased the forcing in the atmosphere and at the surface by factors of 0.2 and 0.69, respectively. Our results show that an increase in relative humidity enhances the planetary cooling effect of aerosols (increased reflection of solar radiation to space) over oceans and low-albedo land areas, whilst over polar regions and highly reflecting land surfaces the warming effect of aerosols changes to a cooling effect. Thus, global warming and an associated increase in relative humidity would lead to enhanced aerosol cooling worldwide. The sensitivity results also demonstrate that an increase in surface albedo due to, for example, a reduction in land vegetation cover, would lead to enhanced atmospheric warming by aerosols leading to a reduction in cloud formation and enhancement of the desertification process. On the contrary, a decrease in surface albedo over polar regions due to, for example, ice-melting associated with global warming, would reduce the planetary warming effect of aerosols over polar areas. Aerosol forcing is found to be quite sensitive to cloud cover, as well as to aerosol optical thickness and the asymmetry parameter, and to the wavelength dependence of the aerosol optical properties. [ABSTRACT FROM AUTHOR]

We examine the atmospheric budget of CO2 at temperate continental sites in the Northern Hemisphere. On a monthly time scale both surface exchange and atmospheric transport are important in determining the rate of change of CO2 mixing ratio at these sites. Vertical differences between the atmospheric boundary layer and free troposphere over the continent are generally greater than large-scale zonal gradients such as the difference between the free troposphere over the continent and the marine boundary layer. Therefore, as a first approximation we parametrize atmospheric transport as a vertical exchange term related to the vertical gradient of CO2 and the mean vertical velocity from the NCEP Reanalysis model. Horizontal advection is assumed to be negligible in our simple analysis. We then calculate the net surface exchange of CO2 from CO2 mixing ratio measurements at four tower sites. The results provide estimates of the surface exchange that are representative of a regional scale (i.e. ∼106 km2). Comparison with direct, local-scale (eddy covariance) measurements of net exchange with the ecosystems around the towers are reasonable after accounting for anthropogenic CO2 emissions within the larger area represented by the mixing ratio data. A network of tower sites and frequent aircraft vertical profiles, separated by several hundred kilometres, where CO2 is accurately measured would provide data to estimate horizontal and vertical advection and hence provide a means to derive net CO2 fluxes on a regional scale. At present CO2 mixing ratios are measured with sufficient accuracy relative to global reference gas standards at only a few continental sites. The results also confirm that flux measurements from carefully sited towers capture seasonal variations representative of large regions, and that the midday CO2 mixing ratios sampled in the atmospheric surface layer similarly capture regional and seasonal variability in the continental CO2 budget. [ABSTRACT FROM AUTHOR]

Tropospheric ozone (O3) profiles over the east China coast at LinAn (30.30°N, 119.75°E) were measured by electrochemical concentration cell ozonesondes in the spring of 2001. The measurement revealed that extremely high O3 with mixing ratios up to 1200 ppbv sometimes penetrated deeply into 8.5–16 km above sea level as a result of lowering of the tropopause across the East Asia strong subtropical jet stream. In addition, high O3 in the 75–150 ppbv range penetrated into the upper and middle troposphere following the extreme O3 regimes and caused an overall high O3 mixing ratio in these regions. The occurrence of the high O3 regimes followed the propagation of dry air with low relative humidity and high potential vorticity suggesting that the O3 is of stratospheric origin. High O3 episodes with O3 mixing ratios in the 75–100 ppbv range were observed in the lower troposphere and especially in the boundary layer. Trajectory analysis suggested that the O3-rich air masses had passed through the industrialized and urbanized zones of the Pearl River Delta region of south China, northeast China coast and Yangtze River Delta region of east China. The O3 is probably of anthropogenic origin resulting from photochemical formation from pollutants emitted from these regions. Our analysis thus revealed that over the east China coast at LinAn, stratospheric O3 is still the predominant source of O3 in the middle and upper troposphere, while anthropogenic sources caused a high O3 pollution episode in the boundary layer. [ABSTRACT FROM AUTHOR]

ABSTRACT We have developed an instrument for making continuous, field-based, part-per-million (ppm) level measurements of atmospheric oxygen concentration, and have implemented it on research cruises in the equatorial Pacific and Southern Oceans. The instrument detects changes in oxygen by the absorption of vacuum ultraviolet (VUV) radiation as it passes through a flowing gas stream, and has a precision comparable to existing laboratory techniques. Here we describe the VUV instrument and present atmospheric O[sub 2] and CO[sub 2] data collected from the NOAA ship Ka'imimoana in the equatorial Pacific during April and May of 1998, and from the NSF ship Lawrence M. Gould in the Southern Ocean during October 1998. These data represent the first field-based measurements of atmospheric O[sub 2] , and significant additions to the O[sub 2] datasets in these regions. Our boreal-springtime equatorial measurements reveal significant short-term variations in atmospheric O[sub 2] , resulting from variations in atmospheric mixing relative to the strong interhemispheric gradient. Our austral-springtime Southern Ocean observations confirm the low O[sub 2] concentrations seen in flask samples from this region, allow the separate identification of oceanic and industrial influences on CO[sub 2] , and provide evidence of a Southern Ocean source for CO[sub 2] at this time of year. These shipboard VUV observations do not provide any evidence to support coupled ocean–atmosphere model predictions of a large decreasing atmospheric O[sub 2] gradient between equatorial and high-southern latitudes. [ABSTRACT FROM AUTHOR]

Presents a study which measured aerosol size distributions at the Jungfraujoch High Alpine Research Station. Measurement of ambient and dry size distributions; Analysis of hygroscopic growth factors; Results and discussion.

Focuses on a study which examined the ventilation of chlorofluorocarbons (CFC) in the North Atlantic Ocean. Background on the introduction of CFC trace gas in the atmosphere; Zonal distribution of CFC; Influence of North Atlantic deep waters on CFC concentration.

Focuses on a study which quantified the role of spring biological production for the air-sea carbon dioxide flux in the Western Subarctic Gyre, where the vertical profile of temperature revealed the existence of temperature minimum layer in the North Pacific. Methodology of the study; Results and discussion.

Focuses on a study which described approaches for calculating isotopic discrimination from atmospheric measurements of carbon dioxide and carbon. Information on the traditional 'Keeling plot' two end-member mixing model; Methodology of the study; Results and discussion.