Showing papers in "Tellus B in 2011"

Amount and timing of permafrost carbon release in response to climate warming

Abstract: The thaw and release of carbon currently frozen in permafrost will increase atmospheric CO 2 concentrations and amplify surface warming to initiate a positive permafrost carbon feedback (PCF) on climate. We use surface weather from three global climate models based on the moderate warming, A1B Intergovernmental Panel on Climate Change emissions scenario and the SiBCASA land surface model to estimate the strength and timing of the PCF and associated uncertainty. By 2200, we predict a 29–59% decrease in permafrost area and a 53–97 cm increase in active layer thickness. By 2200, the PCF strength in terms of cumulative permafrost carbon flux to the atmosphere is 190 ± 64 Gt C. This estimate may be low because it does not account for amplified surface warming due to the PCF itself and excludes some discontinuous permafrost regions where SiBCASA did not simulate permafrost. We predict that the PCF will change the arctic from a carbon sink to a source after the mid-2020s and is strong enough to cancel 42–88% of the total global land sink. The thaw and decay of permafrost carbon is irreversible and accounting for the PCF will require larger reductions in fossil fuel emissions to reach a target atmospheric CO 2 concentration. DOI: 10.1111/j.1600-0889.2011.00527.x

Characterization of Saharan dust, marine aerosols and mixtures of biomass-burning aerosols and dust by means of multi-wavelength depolarization and Raman lidar measurements during SAMUM 2

Abstract: The particle linear depolarization ratio δ p of Saharan dust, marine aerosols and mixtures of biomass-burning aerosols from southern West Africa and Saharan dust was determined at three wavelengths with three lidar systems during the SAharan Mineral dUst experiMent 2 at the airport of Praia, Cape Verde, between 22 January and 9 February 2008. The lidar ratio S p of these major types of tropospheric aerosols was analysed at two wavelengths. For Saharan dust, we find wavelength dependent mean particle linear depolarization ratios δ p of 0.24–0.27 at 355 nm, 0.29–0.31 at 532 nm and 0.36–0.40 at 710 nm, and wavelength independent mean lidar ratios S p of 48–70 sr. Mixtures of biomass-burning aerosols and dust show wavelength independent values of δ p and S p between 0.12–0.23 and 57–98 sr, respectively. The mean values of marine aerosols range independent of wavelength for δ p from 0.01 to 0.03 and for S p from 14 to 24 sr. DOI: 10.1111/j.1600-0889.2011.00556.x

Saharan Mineral Dust Experiments SAMUM-1 and SAMUM-2 : what have we learned?

Abstract: Two comprehensive field campaigns were conducted in 2006 and 2008 in the framework of the Saharan Mineral Dust Experiment (SAMUM) project. The relationship between chemical composition, shape morphology, size distribution and optical effects of the dust particles was investigated. The impact of Saharan dust on radiative transfer and the feedback of radiative effects upon dust emission and aerosol transport were studied. Field observations (ground-based, airborne and remote sensing) and modelling results were compared within a variety of dust closure experiments with a strong focus on vertical profiling. For the first time, multiwavelength Raman/polarization lidars and an airborne high spectral resolution lidar were involved in major dust field campaigns and provided profiles of the volume extinction coefficient of the particles at ambient conditions (for the full dust size distribution), of particle-shape-sensitive optical properties at several wavelengths, and a clear separation of dust and smoke profiles allowing for an estimation of the single-scattering albedo of the biomass-burning aerosol. SAMUM–1 took place in southern Morocco close to the Saharan desert in the summer of 2006, whereas SAMUM–2 was conducted in Cape Verde in the outflow region of desert dust and biomass-burning smoke from western Africa in the winter of 2008. This paper gives an overview of the SAMUM concept, strategy and goals, provides snapshots (highlights) of SAMUM–2 observations and modelling efforts, summarizes main findings of SAMUM–1 and SAMUM–2 and finally presents a list of remaining problems and unsolved questions.

Processes affecting isotopes in precipitation of an arid region

Abstract: The isotopic composition of precipitation has been measured in samples simultaneously collected during individual precipitation events at two neighbouring high-altitude stations (Houxia at 2100 m a.s.l. and Gaoshan at 3545 m a.s.l.) in the Tianshan Mts., northwest China. The observed changes of δ 18 O( δ 2 H) and deuterium excess with surface air temperature, altitude and season have been evaluated to derive information on the effects of subcloud evaporation and moisture recycling on the formation of precipitation and its isotopic composition under arid climatic conditions. Consulting the long-term monthly averages of ‘d’ excess and temperature of the nearest GNIP station Wulumuqi, a striking similarity was found with the results of the two high-altitude stations concerning the relation between ‘d’ excess and temperature. The ‘d’ excess‐temperature plot of the Wulumuqi data shows an hysteresis effect which appears to signify seasonal changes in the interplay between subcloud evaporation and moisture recycling. Finally, for the first time a negative altitude gradient of the d excess has been found for all stations including two more GNIP stations in northwest China but far away from the study area. This ‘inverse altitude effect’ may manifest a decrease of the recycled fraction in air moisture with altitude.

Monthly, global emissions of carbon dioxide from fossil fuel consumption

Abstract: This paper examines available data, develops a strategy and presents a monthly, global time series of fossil-fuel carbon dioxide emissions for the years 1950–2006. This monthly time series was constructed from detailed study of monthly data from the 21 countries that account for approximately 80% of global total emissions. These data were then used in a Monte Carlo approach to proxy for all remaining countries. The proportional-proxy methodology estimates by fuel group the fraction of annual emissions emitted in each country and month. Emissions from solid, liquid and gas fuels are explicitly modelled by the proportional-proxy method. The primary conclusion from this study is the global monthly time series is statistically significantly different from a uniform distribution throughout the year. Uncertainty analysis of the data presented show that the proportional-proxy method used faithfully reproduces monthly patterns in the data and the global monthly pattern of emissions is relatively insensitive to the exact proxy assignments used. The data and results presented here should lead to a better understanding of global and regional carbon cycles, especially when the mass data are combined with the stable carbon isotope data in atmospheric transport models. DOI: 10.1111/j.1600-0889.2011.00530.x

Electron microscopy of particles collected at Praia, Cape Verde, during the Saharan Mineral Dust Experiment: particle chemistry, shape, mixing state and complex refractive index

Abstract: A large field experiment of the Saharan Mineral Dust Experiment (SAMUM) was performed in Praia, Cape Verde, in January and February 2008. The aerosol at Praia is a superposition of mineral dust, sea-salt, sulphates and soot. Particles smaller than 500 nm are mainly mineral dust, mineral dust–sulphate mixtures, sulphates and soot–sulphate mixtures. Particles larger then 2.5 μm consist of mineral dust, sea-salt and few mineral dust–sulphate mixtures. A transition range exists in between. The major internal mixtures are mineral dust–sulphate and soot–sulphate. Mineral dust–sea-salt mixtures occur occasionally, mineral dust–soot mixtures were not observed. The aspect ratio was 1.3–1.4 for dry particles smaller than 500 nm and 1.6–1.7 for larger ones. Parameterizations are given for dry and humid state. Although the real part of the refractive index showed low variation (1.55–1.58 at 532 nm), a multi-modal imaginary part was detected as function of particle size, reflecting the complex composition. Soot mainly influences the absorption for wavelengths longer than the haematite absorption edge, whereas for shorter wavelengths dust is dominating. The refractive index of the aerosol depends on the source region of the mineral dust and on the presence/absence of a marine component. DOI: 10.1111/j.1600-0889.2011.00550.x

Profiling of Saharan dust and biomass‐burning smoke with multiwavelength polarization Raman lidar at Cape Verde

Abstract: Extensive lidar measurements of Saharan dust and biomass-burning smoke were performed with one airborne and three ground-based instruments in the framework of the second part of the SAharan Mineral dUst experiMent (SAMUM-2a) during January and February of 2008 at Cape Verde. Further lidar observations with one system only were conducted during May and June of 2008 (SAMUM-2b). The active measurements were supported by Sun photometer observations. During winter, layers of mineral dust from the Sahara and biomass-burning smoke from southern West Africa pass Cape Verde on their way to South America while pure dust layers cross the Atlantic on their way to the Caribbean during summer. The mean 500-nm aerosol optical thickness (AOT) observed during SAMUM-2a was 0.35 ± 0.18. SAMUM-2a observations showed transport of pure dust within the lowermost 1.5 km of the atmospheric column. In the height range from 1.5 to 5.0 km, mixed dust/smoke layers with mean lidar ratios of 67 ± 14 sr at 355 and 532 nm, respectively, prevailed. Within these layers, wavelength-independent linear particle depolarization ratios of 0.12–0.18 at 355, 532, and 710 nm indicate a large contribution (30–70%) of mineral dust to the measured optical properties. Angstrom exponents for backscatter and extinction of around 0.7 support this finding. Mean extinction coefficients in the height range between 2 and 4 km were 66 ± 6 Mm -1 at 355 nm and 48 ± 5 Mm -1 at 532 nm. Comparisons with airborne high-spectral-resolution lidar observations show good agreement within the elevated layers. 3–5 km deep dust layers where observed during SAMUM-2b. These layers showed optical properties similar to the ones of SAMUM-1 in Morocco with a mean 500-nm AOT of 0.4 ± 0.2. Dust extinction coefficients were about 80 ± 6 Mm -1 at 355 and 532 nm. Dust lidar ratios were 53 ± 10 sr at 355 and 532 nm, respectively. Dust depolarization ratios showed an increase with wavelength from 0.31 ± 0.10 at 532 nm to 0.37 ± 0.07 at 710 nm. DOI: 10.1111/j.1600-0889.2011.00548.x

Sea ice contribution to the air-sea CO2 exchange in the Arctic and Southern oceans

Abstract: Although salt rejection from sea ice is a key process in deep-water formation in ice-covered seas, the concurrent rejection of CO 2 and the subsequent effect on air–sea CO 2 exchange have received little attention. We review the mechanisms by which sea ice directly and indirectly controls the air–sea CO 2 exchange and use recent measurements of inorganic carbon compounds in bulk sea ice to estimate that oceanic CO 2 uptake during the seasonal cycle of sea-ice growth and decay in ice-covered oceanic regions equals almost half of the net atmospheric CO 2 uptake in ice-free polar seas. This sea-ice driven CO 2 uptake has not been considered so far in estimates of global oceanic CO 2 uptake. Net CO 2 uptake in sea-ice–covered oceans can be driven by; (1) rejection during sea–ice formation and sinking of CO 2 -rich brine into intermediate and abyssal oceanic water masses, (2) blocking of air–sea CO 2 exchange during winter, and (3) release of CO 2 -depleted melt water with excess total alkalinity during sea-ice decay and (4) biological CO 2 drawdown during primary production in sea ice and surface oceanic waters. DOI: 10.1111/j.1600-0889.2011.00571.x

Microphysical and optical properties of dust and tropical biomass burning aerosol layers in the Cape Verde region—an overview of the airborne in situ and lidar measurements during SAMUM‐2

Abstract: In the framework of the Saharan Mineral Dust Experiment (SAMUM) airborne High Spectral Resolution Lidar and in situ measurements of the particle size, aerosol mixing state and absorption coefficient were conducted. Here, the properties of mineral dust and tropical biomass burning layers in the Cape Verde region in January/February 2008 are investigated and compared with the properties of fresh dust observed in May/June 2006 close the Sahara. In the Cape Verde area, we found a complex stratification with dust layers covering the altitude range below 2 km and biomass burning layers aloft. The aerosol type of the individual layers was classified based on depolarization and lidar ratios and, in addition, on in situ measured Angstrom exponents of absorption a ap . The dust layers had a depth of 1.3 ± 0.4 km and showed a median a ap of 3.95. The median effective diameter D eff was 2.5 μm and the dust layers over Cape Verde yielded clear signals of aging: large particles were depleted due to gravitational settling and the accumulation mode diameter was shifted towards larger sizes as a result of coagulation. The tropical biomass layers had a depth of 2.0 ± 1.1 km and were characterized by a median a ap of 1.34. They always contained a certain amount of large dust particles and showed a median D eff of 1.1 μm and a fine mode D eff , fine of 0.33. The dust and biomass burning layers had a median aerosol optical depth (AOD) of 0.23 and 0.09, respectively. The median contributions to the AOD of the total atmospheric column below 10 km were 75 and 37%, respectively. DOI: 10.1111/j.1600-0889.2011.00566.x

Characterization and sources of aerosol particles over the southeastern Tibetan Plateau during the Southeast Asia biomass-burning season

Abstract: The Tibetan Plateau is one of the highest regions in the world, exerting profound influence on the large-scale atmospheric circulation of Asia and the global climate. Here we report ambient concentrations of black carbon (BC), aerosol mass (PM 2.5 and PM 10 ) and associated carbonaceous species and water-soluble inorganic ions from a remote mountain site in the southeastern part of the Tibetan Plateau during spring, in order to characterize the major sources contributing to the ambient aerosol in the background atmosphere of Southeast Asia. Significant build-up of aerosol and BC concentrations was observed during a dry period, accompanied by the occurrence of fires and transport of pollution from the nearby regions of Southeast Asia and the northern part of the Indian Peninsula. The concentrations of BC, PM 2.5 and PM 10 mass reached maximum hourly values of 1470 ng m -3 , 107 and 117 μg m -3 , respectively. Organic carbon (OC), elemental carbon (EC) and sulfate were the predominant aerosol components. OC showed strong correlations with EC ( R 2 = 0.93 for PM 2.5 and 0.74 for PM 10 ) and non-sea-salt potassium, especially in fine aerosol ( R 2 = 0.95). In addition, the relative change rates of K + against OC reached characteristically high values, highlighting the important contributions of biomass-burning smoke. DOI: 10.1111/j.1600-0889.2010.00512.x

Modelling lidar‐relevant optical properties of complex mineral dust aerosols

Abstract: We model lidar-relevant optical properties of mineral dust aerosols and compare the modelling results with optical properties derived from lidar measurements during the SAMUM field campaigns. The Discrete Dipole Approximation is used for optical modelling of single particles. For modelling of ensemble properties, the desert aerosol type of the OPAC aerosol dataset is extended by mixtures of absorbing and non-absorbing irregularly shaped mineral dust particles. Absorbing and non-absorbing particles are mixed to mimic the natural mineralogical inhomogeneity of dust particles. A sensitivity study reveals that the mineralogical inhomogeneity is critical for the lidar ratio at short wavelengths; it has to be considered for agreement with the observed wavelength dependence of the lidar ratio. The amount of particles with low aspect ratios (about 1.4 and lower) affects the lidar ratio at any lidar wavelength; their amount has to be low for agreement with SAMUM observations. Irregularly shaped dust particles with typical refractive indices, in general, have higher linear depolarization ratios than corresponding spheroids, and improve the agreement with the observations. DOI: 10.1111/j.1600-0889.2011.00559.x

Optical and microphysical properties of smoke over Cape Verde inferred from multiwavelength lidar measurements

Abstract: Lidar measurements of mixed dust/smoke plumes over the tropical Atlantic ocean were carried out during the winter campaign of SAMUM-2 at Cape Verde. Profiles of backscatter and extinction coefficients, lidar ratios, and Angstr¨ exponents related to pure biomass-burning aerosol from southern West Africa were extracted from these observations. Furthermore, these findings were used as input for an inversion algorithm to retrieve microphysical properties of pure smoke. Seven measurement days were found suitable for the procedure of aerosol-type separation and successive inversion of optical data that describe biomass-burning smoke. We inferred high smoke lidar ratios of 87 ± 17 sr at 355 nm and 79 ± 17 sr at 532 nm. Smoke lidar ratios and Angstr¨ om exponents are higher compared to the ones for the dust/smoke mixture. These numbers indicate higher absorption and smaller sizes for pure smoke particles compared to the dust/smoke mixture. Inversion of the smoke data set results in mean effective radii of 0.22 ± 0.08 µm with individual results varying between 0.10 and 0.36 µm. The single-scattering albedo for pure biomass-burning smoke was found to vary between 0.63 and 0.89 with a very low mean value of 0.75 ± 0.07. This is in good agreement with findings of airborne in situ measurements which showed values of 0.77 ± 0.03. Effective radii from the inversion were similar to the ones found for the fine mode of the in situ size distributions.

Ground-based off-line aerosol measurements at Praia, Cape Verde, during the Saharan Mineral Dust Experiment: microphysical properties and mineralogy

Abstract: A large field experiment of the Saharan Mineral Dust Experiment (SAMUM) was performed in Praia, Cape Verde, in January and February 2008. This work reports on the aerosol mass concentrations, size distributions and mineralogical composition of the aerosol arriving at Praia. Three dust periods were recorded during the measurements, divided by transitional periods and embedded in maritime-influenced situations. The total suspended particle mass/PM 10 /PM 2.5 were 250/180/74 μg/m 3 on average for the first dust period (17–21 January) and 250/230/83 μg/m 3 for the second (24–26 January). The third period (28 January to 2 February) was the most intensive with 410/340/130 μg/m 3 . Four modes were identified in the size distribution. The first mode (50–70 nm) and partly the second (700–1100 nm) can be regarded as of marine origin, but some dust contributes to the latter. The third mode (2–4 μm) is dominated by advected dust, while the intermittently occurring fourth mode (15–70 μm) may have a local contribution. The dust consisted of kaolinite (dust/maritime period: 35%wt./25%wt.), K-feldspar (20%wt./25%wt.), illite (14%wt./10%wt.), quartz (11%wt./8%wt.), smectites (6%wt./4%wt.), plagioclase (6%wt./1%wt.), gypsum (4%wt./7%wt.), halite (2%wt./17%wt.) and calcite (2%wt./3%wt.). DOI: 10.1111/j.1600-0889.2011.00546.x

Separating remote fetch and local mixing influences on vertical radon measurements in the lower atmosphere

Abstract: Two-point radon gradients provide a direct, unambiguous measure of near-surface atmospheric mixing. A 31-month data set of hourly radon measurements at 2 and 50 m is used to characterize the seasonality and diurnal variability of radon concentrations and gradients at a site near Sydney. Vertical differencing allows separation of remote (fetch-related) effects on measured radon concentrations from those due to diurnal variations in the strength and extent of vertical mixing. Diurnal composites, grouped according to the maximum nocturnal radon gradient ( ΔC max ), reveal strong connections between radon, wind, temperature and mixing depth on subdiurnal timescales. Comparison of the bulk Richardson Number ( Ri B ) and the turbulence kinetic energy (TKE) with the radon-derived bulk diffusivity ( K B ) helps to elucidate the relationship between thermal stability, turbulence intensity and the resultant mixing. On nights with large ΔC max , K B and TKE levels are low and Ri B is well above the ‘critical’ value. Conversely, when ΔC max is small, K B and TKE levels are high and Ri B is near zero. For intermediate ΔC max , however, Ri B remains small whereas TKE and K B both indicate significantly reduced mixing. The relationship between stability and turbulence is therefore non-linear, with even mildly stable conditions being sufficient to suppress mixing. DOI: 10.1111/j.1600-0889.2011.00565.x

Gas diffusion through columnar laboratory sea ice: Implications for mixed-layer ventilation of CO2 in the seasonal ice zone

Abstract: Gas diffusion through the porous microstructure of sea ice represents a pathway for ocean‐atmosphere exchange and for transport of biogenic gases produced within sea ice. We report on the experimental determination of the bulk gas diffusion coefficients, D, for oxygen (O2) and sulphur hexafluoride (SF6) through columnar sea ice under constant ice thickness conditions for ice surface temperatures between − 4a nd−12 ◦C. Profiles of SF6 through the ice indicate decreasinggasconcentrationfromtheice/waterinterfacetotheice/airinterface,withevidenceforsolubilitypartitioning between gas-filled and liquid-filled pore spaces. On average, DSF6 was 1.3 × 10 −4 cm 2 s −1 (±40%) and DO2 was 3.9 × 10 −5 cm 2 s −1 (±41%). The preferential partitioning of SF6 to the gas phase, which is the dominant diffusion pathway produced the greater rate of SF6 diffusion. Comparing these estimates of D with an existing estimate of the air‐sea gas transfer through leads indicates that ventilation of the mixed layer by diffusion through sea ice may be negligible, compared to air‐sea gas exchange through fractures in the ice pack, even when the fraction of open water is less than 1%.

The relationship between peak warming and cumulative CO2 emissions, and its use to quantify vulnerabilities in the carbon-climate-human system

Abstract: Interactions between the carbon cycle, climate and human societies are subject to several major vulnerabilities, broadly defined as factors contributing to the risk of harm from human-induced climate change. We assess five vulnerabilities: (1) effects of increasing CO 2 on the partition of anthropogenic carbon between atmospheric, land and ocean reservoirs; (2) effects of climate change (quantified by temperature) on CO 2 fluxes; (3) uncertainty in climate sensitivity; (4) non-CO 2 radiative forcing and (5) anthropogenic CO 2 emissions. Our analysis uses a physically based expression for T p ( Q p ), the peak warming T p associated with a cumulative anthropogenic CO 2 emission Q p to the time of peak warming. The approximations in this expression are evaluated using a non-linear box model of the carbon–climate system, forced with capped emissions trajectories described by an analytic form satisfying integral and smoothness constraints. The first four vulnerabilities appear as parameters that influence T p ( Q p ), whereas the last appears through the independent variable. In terms of likely implications for T p ( Q p ), the decreasing order of the first four vulnerabilities is: uncertainties in climate sensitivity, effects of non-CO 2 radiative forcing, effects of climate change on CO 2 fluxes and effects of increasing CO 2 on the partition of anthropogenic carbon. DOI: 10.1111/j.1600-0889.2010.00521.x

Spatial and temporal patterns of CO 2 and CH 4 fluxes in China's croplands in response to multifactor environmental changes

Abstract: The spatial and temporal patterns of CO2 and CH4 fluxes in China’s croplands were investigated and attributed to multifactor environmental changes using the agricultural module of the Dynamic Land Ecosystem Model (DLEM), a highly integrated process-based ecosystem model. During 1980‐2005 modelled results indicated that China’s croplands acted as a carbon sink with an average carbon sequestration rate of 33.4TgCyr −1 (1 Tg = 10 12 g). Both the highest net CO2 uptake rate and the largest CH4 emission rate were found in southeast region of China’s croplands. Of primary influences were land-cover and land-use change, atmospheric CO2 and nitrogen deposition, which accounted for 76%, 42% and 17% of the total carbon sequestration in China’s croplands during the study period, respectively. The total carbon losses due to elevated ozone and climate variability/change were equivalent to 27% and 9% of the total carbon sequestration, respectively. Our further analysis indicated that nitrogen fertilizer application accounted for 60% of total national carbon uptake in cropland, whereas changes in paddy field areas mainly determined the variability of CH4 emissions. Our results suggest that improving air quality by means such as reducing ozone concentration and optimizing agronomic practices can enhance carbon sequestration capacity of China’s croplands.

Characterization of new particle and secondary aerosol formation during summertime in Beijing, China

Abstract: Size-resolved aerosol number and mass concentrations and the mixing ratios of O 3 and various trace gases were continuously measured at an urban station before and during the Beijing Olympic and Paralympic Games (5 June to 22 September, 2008). 23 new particle formation (NPF) events were identified; these usually were associated with changes in wind direction and/or rising concentrations of gas-phase precursors or after precipitation events. Most of the NPF events started in the morning and continued to noon as particles in the nucleation mode grew into the Aitken mode. From noon to midnight, the aerosols grew into the accumulation mode through condensation and coagulation. Ozone showed a gradual rise starting around 10:00 local time, reached its peak around 15:00 and then declined as the organics increased. The dominant new particle species were organics (40–75% of PM 1 ) and sulphate; nitrate and ammonium were more minor contributors. DOI: 10.1111/j.1600-0889.2011.00533.x

Optical properties of aerosol mixtures derived from sun-sky radiometry during SAMUM-2

Abstract: The SAMUM-2 experiment took place in the Cape Verde islands in January–February 2008. The colocated ground-based and airborne instruments allow the study of desert dust optical and microphysical properties in a closure experiment. The Meteorological Institute of the University of Munich deployed one sun-sky photometer and two tropospheric lidar systems. A travelling AERONET-Cimel sun-sky radiometer was also deployed. During the measurement period the aerosol scenario over Cape Verde mostly consisted of a dust layer below 2 km and a smoke-dust layer above 2–4 km a.s.l. The Saharan dust arrived at the site from the NE, whereas the smoke originated in the African equatorial region. This paper describes the main results of the Sun photometer observations, supported by lidar information. An analysis of the variations in the aerosol optical depth (AOD) in the range 340–1550 nm, the Angstrom exponent, volume size distributions and single scattering albedo is presented. The aerosol mixtures are analysed by means of the fine mode fraction of the AOD provided by the sun-sky inversion data and the Spectral Deconvolution Algorithm. The mean AOD (500 nm) was 0.31, with associated low Angstrom exponent of 0.46. Several types of events were detected within the data set, with prevalence of dust or mixtures as characterized by the Angstrom exponents of extinction and absorption and the fine mode fraction. Aerosol properties derived from sunphotometry were compared to in situ measurements of size distribution, effective radius and single scattering albedo. DOI: 10.1111/j.1600-0889.2011.00573.x

Levoglucosan enhancement in ambient aerosol during springtime transport events of biomass burning smoke to Southeast China

Abstract: An intensive field experiment was conducted at an urban and a rural site in Hong Kong to identify the influence of biomass burning emissions transported from distinct regions on ambient aerosol in coastal southeast China. Water-soluble ionic and carbonaceous species, specifically the biomass burning tracer levoglucosan, were analysed. Elevated levoglucosan concentrations with maxima of 91.5 and 133.7 ng m -3 and overall average concentrations of 30 and 36 ng m -3 were observed at the rural and urban sites, respectively. By combining the analysed meteorological data, backward trajectories, fire counts and Aerosol Index from the Earth Probe satellite, southwest China and the northern Philippines, together with the southeast China coast, were identified for the first time as source regions of the transported biomass burning particles at the surface level in rural Hong Kong. Occasional levoglucosan enhancements observed at urban Hong Kong were attributed to local incense and joss paper burning during the Ching-Ming festival period. The contributions of transported biomass burning emissions, especially from the northern Philippines, were estimated to account for 7.5% and 2.9% of OC and PM 2.5 , respectively. DOI: 10.1111/j.1600-0889.2010.00515.x

Elemental carbon deposition to Svalbard snow from Norwegian settlements and long-range transport

Abstract: The impact on snow pack albedo from local elemental carbon (EC) sources in Svalbard has been investigated for the winter of 2008. Highly elevated EC concentrations in the snow are observed around t ...

Particle chemical properties in the vertical column based on aircraft observations in the vicinity of Cape Verde Islands

Abstract: During the second Saharan Mineral Dust Experiment (SAMUM-2) field campaign, particles with geometric diameters ( d ) between ∼0.1 and 25 μm were collected on board of the Deutsches Zentrum fur Luft- und Raumfahrt (German Aerospace Center, DLR) Falcon aircraft. Size, chemical composition and mixing state of aerosols sampled (spatially and vertically resolved) along the West African coastline and in the Cape Verde Islands region were determined by electron microscopy. A pronounced layer structure of biomass-burning aerosol and desert dust was present for all days during the sampling period from 23 January to 6 February. The aerosol composition of the small particles ( d 0.5 μm) were dominated by silicates. In the Cape Verde Islands region mineral dust is well mixed. The determination of source regions by elemental or mineralogical composition was generally not possible, except for air masses which were transported over the Gulf of Guinea. The real part of the refractive index showed little variation. In contrast, the imaginary part strongly depended on the abundance of soot (biomass-burning aerosol) and haematite (mineral dust). DOI: 10.1111/j.1600-0889.2011.00553.x

Spatiotemporal variability of biogenic terpenoid emissions in Pearl River Delta, China, with high-resolution land-cover and meteorological data

Abstract: This study intended to provide 4-km gridded, hourly, year-long, regional estimates of terpenoid emissions in the Pearl River Delta (PRD), China. It combined Thematic Mapper images and local-survey data to characterize plant functional types, and used observed emission potential of biogenic volatile organic compounds (BVOC) from local plant species and high-resolution meteorological outputs from the MM5 model to constrain the MEGAN BVOC-emission model. The estimated annual emissions for isoprene, monoterpene and sesquiterpene are 95.55 × 10 6 kg C, 117.35 × 10 6 kg C and 9.77 × 10 6 kg C, respectively. The results show strong variabilities of terpenoid emissions spanning diurnal and seasonal time scales, which are mainly distributed in the remote areas (with more vegetation and less economic development) in PRD. Using MODIS PFTs data reduced terpenoid emissions by 27% in remote areas. Using MEGAN-model default emission factors led to a 24% increase in BVOC emission. The model errors of temperature and radiation in MM5 output were used to assess impacts of uncertainties in meteorological forcing on emissions: increasing (decreasing) temperature and downward shortwave radiation produces more (less) terpenoid emissions for July and January. Strong temporal variability of terpenoid emissions leads to enhanced ozone formation during midday in rural areas where the anthropogenic VOC emissions are limited. DOI: 10.1111/j.1600-0889.2010.00523.x

Dust mobilization and aerosol transport from West Africa to Cape Verde—a meteorological overview of SAMUM–2

Abstract: The second field campaign of the SAharan Mineral dUst experiMent (SAMUM-2) was performed between 15 January and 14 February 2008 at the airport of Praia, Cape Verde, and provided valuable information to study the westward transport of Saharan dust and the mixing with biomass-burning smoke and sea-salt aerosol. Here lidar, meteorological, and particle measurements at Praia, together with operational analyses, trajectories, and satellite and synoptic station data are used to give an overview of the meteorological conditions and to place other SAMUM-2 measurements into a large-scale context. It is demonstrated that wintertime dust conditions at Cape Verde are closely related to the movement and intensification of mid-latitude high-pressure systems and the associated pressure gradients at their southern flanks. These cause dust emission over Mauritania, Mali, and Niger, and subsequent westward transport to Cape Verde within about 1–5 d. Dust emissions often peak around midday, suggesting a relation to daytime mixing of momentum from nocturnal low-level jets to the surface. The dust layer over Cape Verde is usually restricted to the lowest 1.5 km of the atmosphere. During periods with near-surface wind speeds about 5.5 m s -1 , a maritime aerosol layer develops which often mixes with dust from above. On most days, the middle levels up to about 5 km additionally contain smoke that can be traced back to sources in southern West Africa. Above this layer, clean air masses are transported to Cape Verde with the westerly flow at the southern side of the subtropical jet. The penetration of extra-tropical disturbances to low latitudes can bring troposphere-deep westerly flow and unusually clean conditions to the region. DOI: 10.1111/j.1600-0889.2011.00544.x

Evolution of natural and anthropogenic fluxes of atmospheric CO 2 from 1957 to 2003

Abstract: An analysis is carried out of the longest available records of atmospheric CO 2 and its 13 C/ 12 C ratio from the Scripps Institution of Oceanography network of fixed stations, augmented by data in the 1950s and 1960s from ships and ice floes. Using regression analysis, we separate the interhemispheric gradients of CO 2 and 13 C/ 12 C into: (1) a stationary (possibly natural) component that is constant with time, and (2) a time-evolving component that increases in proportion to fossil fuel emissions. Inverse calculations using an atmospheric transport model are used to interpret the components of the gradients in terms of land and ocean sinks. The stationary gradients in CO 2 and 13 C/ 12 C are both satisfactorily explained by ocean processes, including an ocean carbon loop that transports 0.5 PgC yr -1 southwards in the ocean balanced by an atmospheric return flow. A stationary northern land sink appears to be ruled out unless its effect on the gradient has been offset by a strong rectifier effect, which seems doubtful. A growing northern land sink is not ruled out, but has an uncertain magnitude (0.3–1.7 PgC yr -1 centred on year 2003) dependent on the rate at which CO 2 from fossil fuel burning is dispersed vertically and between hemispheres. DOI: 10.1111/j.1600-0889.2010.00507.x

Regional modelling of Saharan dust and biomass-burning smoke Part I: Model description and evaluation

Abstract: The spatio-temporal evolution of the Saharan dust and biomass-burning plume during the SAMUM-2 field campaign in January and February 2008 is simulated at 28 km horizontal resolution with the regional model-system COSMOMUSCAT. The model performance is thoroughly tested using routine ground-based and space-borne remote sensing and local field measurements. Good agreement with the observations is found in many cases regarding transport patterns, aerosol optical thicknesses and the ratio of dust to smoke aerosol. The model also captures major features of the complex aerosol layering. Nevertheless, discrepancies in the modelled aerosol distribution occur, which are analysed in detail. The dry synoptic dynamics controlling dust uplift and transport during the dry season are well described by the model, but surface wind peaks associated with the breakdown of nocturnal low-level jets are not always reproduced. Thus, a strong dust outbreak is underestimated. While dust emission modelling is a priori more challenging, since strength and placement of dust sources depend on on-line computed winds, considerable inaccuracies also arise in observation-based estimates of biomass-burning emissions. They are caused by cloud and spatial errors of satellite fire products and uncertainties in fire emission parameters, and can lead to unrealistic model results of smoke transport.

Spectral particle absorption coefficients, single scattering albedos and imaginary parts of refractive indices from ground based in situ measurements at Cape Verde Island during SAMUM-2

Abstract: During the SAMUM-2 experiment, spectral absorption coefficients, single scattering albedos and imaginary parts of refractive indices of mineral dust particles were investigated at the Cape Verde Islands. Main absorbing constituents of airborne samples were mineral dust and soot. PM10 spectral absorption coefficients were measured using a Spectral Optical Absorption Photometer (SOAP) covering the wavelength range from 300 to 960 nm with a resolution of 25 nm. From SOAP, also information on the particle scattering coefficients could be retrieved. Spectral single scattering albedos were obtained in the wavelength range from 350 to 960 nm. Imaginary parts of the refractive index were inferred from measured particle number size distributions and absorption coefficients using Mie scattering theory. Imaginary parts for a dust case were 0.012, 0.0047 and 0.0019 at the wavelengths 450, 550 and 950 nm, respectively, and the single scattering albedos were 0.91, 0.96 and 0.98 at the same wavelengths. During a marine case, the imaginary parts of the refractive indices were 0.0045, 0.0040 and 0.0036 and single scattering albedos were 0.93, 0.95 and 0.96 at the wavelengths given above. DOI: 10.1111/j.1600-0889.2011.00572.x

Mixing of mineral dust with urban pollution aerosol over Dakar (Senegal): impact on dust physico-chemical and radiative properties

Abstract: In the framework of the Saharan Mineral Dust Experiment (SAMUM) in 2008, the mixing of the urban pollution plume of Dakar (Senegal) with mineral dust was studied in detail using the German research aircraft Falcon which was equipped with a nadir-looking high spectral resolution lidar (HSRL) and extensive aerosol in situ instrumentation. The mineral dust layer as well as the urban pollution plume were probed remotely by the HSRL and in situ. Back trajectory analyses were used to attribute aerosol samples to source regions. We found that the emission from the region of Dakar increased the aerosol optical depth (532 nm) from approximately 0.30 over sea and over land east of Dakar to 0.35 in the city outflow. In the urban area, local black carbon (BC) emissions, or soot respectively, contributed more than 75% to aerosol absorption at 530 nm. In the dust layer, the single-scattering albedo at 530 nm was 0.96 − 0.99, whereas we found a value of 0.908 ± 0.018 for the aerosol dominated by urban pollution. After 6 h of transport over the North Atlantic, the externally mixed mode of secondary aerosol particles had almost completely vanished, whereas the BC agglomerates (soot) were still externally mixed with mineral dust particles.

Air–sea flux of CO2 in arctic coastal waters influenced by glacial melt water and sea ice

Abstract: Annual air–sea exchange of CO 2 in Young Sound, NE Greenland was estimated using p CO 2 surface-water measurements during summer (2006–2009) and during an ice-covered winter 2008. All surface p CO 2 values were below atmospheric levels indicating an uptake of atmospheric CO 2 . During sea ice formation, dissolved inorganic carbon (DIC) content is reduced causing sea ice to be under saturated in CO 2 . Approximately 1% of the DIC forced out of growing sea ice was released into the atmosphere while the remaining 99% was exported to the underlying water column. Sea ice covered the fjord 9 months a year and thereby efficiently blocked air–sea CO 2 exchange. During sea ice melt, dissolution of CaCO 3 combined with primary production and strong stratification of the water column acted to lower surface-water p CO 2 levels in the fjord. Also, a large input of glacial melt water containing geochemically reactive carbonate minerals may contribute to the low surface-water p CO 2 levels. The average annual uptake of atmospheric CO 2 was estimated at 2.7 mol CO 2 m -2 yr -1 or 32 g C m -2 yr -1 for the study area, which is lower than estimates from the Greenland Sea. Variability in duration of sea ice cover caused significant year-to-year variation in annual gas exchange. DOI: 10.1111/j.1600-0889.2011.00540.x

Continuous 25-yr aerosol records at coastal Antarctica - I: inter-annual variability of ionic compounds and links to climate indices

Abstract: The aerosol climatology at the coastal Antarctic Neumayer Station (NM) was investigated based on continuous, 25-yr long observations of biogenic sulphur components (methanesulfonate and non–sea salt sulphate), sea salt and nitrate. Although significant long-term trends could only be detected for nitrate (−3.6 ± 2.5% per year between 1983 and 1993 and +4.0 ± 3.2% per year from 1993–2007), non-harmonic periodicities between 2 and 5 yr were typical for all species. Dedicated time series analyses revealed that relations to sea ice extent and various circulation indices are weak at best or not significant. In particular, no consistent link between sea ice extent and sea salt loadings was evident suggesting only a rather local relevance of the NM sea salt record. Nevertheless, a higher Southern Annular Mode index tended to entail a lower biogenic sulphur signal. In examining the spatial uniformity of the NM findings we contrasted them to respective 17 yr records from the coastal Dumont d’Urville Station. We found similar long-term trends for nitrate, indicating an Antarctic-wide but not identifiable atmospheric signal, although any significant impact of solar activity or pollution could be ruled out. No inter-site variability on the multiannual scale was evident for the other ionic compounds. DOI: 10.1111/j.1600-0889.2011.00542.x