bluuebunny/crossref_metadata_2025 huggingface dataset:
Interpreting the variability of CO2 columns over North America using a chemistry transport model: application to SCIAMACHY data
Authors: Palmer P. I. , Barkley M. P. , Monks P. S.
Published: April 2010

Abstract. We use the GEOS-Chem chemistry transport model to interpret variability of CO2 columns and associated column-averaged volume mixing ratios (CVMRs) observed by the SCIAMACHY satellite instrument during the 2003 North American growing season, accounting for the instrument averaging kernel. Model and observed columns, largely determined by surface topography, averaged on a 2°×2.5° grid, are in excellent agreement (model bias=3%, r>0.9), as expected. Model and observed CVMRs, determined by scaling column CO2 by surface pressure data, are on average within 3% but are only weakly correlated, reflecting a large positive model bias (10–15 ppmv) at 50–70° N during midsummer at the peak of biospheric uptake. GEOS-Chem generally reproduces the magnitude and seasonal cycle of observed CO2 surface VMRs across North America. During midsummer we find that model CVMRs and surface VMRs converge, reflecting the instrument vertical sensitivity and the strong influence of the land biosphere on lower tropospheric CO2 columns. We use model tagged tracers to show that local fluxes largely determine CVMR variability over North America, with the largest individual CVMR contributions (1.1%) from the land biosphere. Fuel sources are relatively constant while biomass burning make a significant contribution only during midsummer. We also show that non-local sources contribute significantly to total CVMRs over North America, with the boreal Asian land biosphere contributing close to 1% in midsummer at high latitudes. We used the monthly-mean Jacobian matrix for North America to illustrate that: 1) North American CVMRs represent a superposition of many weak flux signatures, but differences in flux distributions should permit independent flux estimation; and 2) the atmospheric e-folding lifetimes for many of these flux signatures are 3–4 months, beyond which time they are too well-mixed to interpret.
Twelve years of global observation of formaldehyde in the troposphere using GOME and SCIAMACHY sensors
Authors: De Smedt I. , Müller J.-F. , Stavrakou T. , van der A R. , Eskes H. , Van Roozendael M.
Published: April 2010

Abstract. This work presents global tropospheric formaldehyde columns retrieved from near-UV radiance measurements performed by the GOME instrument onboard ERS-2 since 1995, and by SCIAMACHY, in operation on ENVISAT since the end of 2002. A special effort has been made to ensure the coherence and quality of the CH2O dataset covering the period 1996–2007. Optimised DOAS settings are proposed in order to reduce the impact of two important sources of error in the derivation of slant columns, namely, the polarisation anomaly affecting the SCIAMACHY spectra around 350 nm, and a major absorption band of the O4 collision complex centred near 360 nm. The air mass factors are determined from scattering weights generated using radiative transfer calculation taking into account the cloud fraction, the cloud height and the ground albedo. Vertical profile shapes of CH2O are provided by the global CTM IMAGES based on an up-to-date representation of emissions, atmospheric transport and photochemistry. A comprehensive error analysis is presented. This includes errors on the slant columns retrieval and errors on the air mass factors which are mainly due to uncertainties in the a priori profile and in the cloud properties. The major features of the retrieved formaldehyde column distribution are discussed and compared with previous CH2O datasets over the major emission regions.
New constraints on terrestrial and oceanic sources of atmospheric methanol
Authors: Millet D. B. , Jacob D. J. , Custer T. G. , de Gouw J. A. , Goldstein A. H. , Karl T. , Singh H. B. , Sive B. C. , Talbot R. W. , Warneke C. , Williams J.
Published: April 2010

Abstract. We use a global 3-D chemical transport model (GEOS-Chem) to interpret new aircraft, surface, and oceanic observations of methanol in terms of the constraints that they place on the atmospheric methanol budget. Recent measurements of methanol concentrations in the ocean mixed layer (OML) imply that in situ biological production must be the main methanol source in the OML, dominating over uptake from the atmosphere. It follows that oceanic emission and uptake must be viewed as independent terms in the atmospheric methanol budget. We deduce that the marine biosphere is a large primary source (85 Tg y−1) of methanol to the atmosphere and is also a large sink (101 Tg y−1), comparable in magnitude to atmospheric oxidation by OH (88 Tg y−1). The resulting atmospheric lifetime of methanol in the model is 4.7 days. Aircraft measurements in the North American boundary layer imply that terrestrial plants are a much weaker source than presently thought, likely reflecting an overestimate of broadleaf tree emissions, and this is also generally consistent with surface measurements. We deduce a terrestrial plant source of 80 Tg y−1, comparable in magnitude to the ocean source. The aircraft measurements show a strong correlation with CO (R2=0.51–0.61). We reproduce this correlation in the model with the reduced plant source, which also confirms that the anthropogenic source of methanol must be small. Our reduced plant source also provides a better simulation of methanol observations over tropical South America.
Technical note: A geostatistical fixed-lag Kalman smoother for atmospheric inversions
Authors: Michalak A. M.
Published: April 2010

Abstract. Inverse modeling methods are now commonly used for estimating surface fluxes of carbon dioxide, using atmospheric mass fraction measurements combined with a numerical atmospheric transport model. The geostatistical approach to flux estimation takes advantage of the spatial and/or temporal correlation in fluxes and does not require prior flux estimates. In this work, a geostatistical implementation of a fixed-lag Kalman smoother is developed to improve the computational efficiency of the inverse problem. This method makes it feasible to perform multi-year inversions, at fine resolutions, and with large amounts of data. The new method is applied to the recovery of global gridscale carbon dioxide fluxes for 1997 to 2001 using pseudodata representative of a subset of the NOAA-ESRL Cooperative Air Sampling Network.
Sources of organic carbon in PM1 in Helsinki urban air
Authors: Saarikoski S. , Timonen H. , Saarnio K. , Aurela M. , Järvi L. , Keronen P. , Kerminen V.-M. , Hillamo R.
Published: April 2010

Abstract. A major fraction of fine particle matter consists of organic carbon (OC) but its origin is still inadequately known. In this study the sources of OC were investigated in the northern European urban environment in Helsinki, Finland. Measurements were carried out over one year and they included both filter (PM1) and online methods. From the filter samples OC, elemental carbon (EC), water-soluble OC (WSOC), levoglucosan and major ions were analyzed. Filter data together with the concentrations of inorganic gases were analyzed by Positive matrix factorization (PMF) method in order to find the sources of OC (and WSOC) on an annual as well as on a seasonal basis. In order to study the diurnal variation of sources, OC and EC were measured by a semicontinuous OC/EC analyzer and major ions were determined by a Particle-into-Liquid Sampler coupled to ion chromatographs. According to PMF, OC concentrations were impacted by four sources: biomass combustion, traffic, long-range transport and secondary production. On an annual basis the OC concentration was dominated by secondary organic aerosol (SOA). Its contribution to OC was as high as 64% in summer, which may result besides anthropogenic sources also from the large biogenic VOC emissions in the boreal region. In winter biomass combustion constituted the largest fraction in OC due to domestic wood combustion for heating purposes. Traffic contributed to OC from 15 to 27%. Regarding the diurnal variation, the contribution of traffic was higher from 08:00 to 18:00 on weekdays than on weekends. The contribution of long-range transport to OC was 24% on average. All four sources influenced also on the WSOC concentrations, however, the contribution of SOA was significantly larger to WSOC than to OC.
Three years of greenhouse gas column-averaged dry air mole fractions retrieved from satellite – Part 2: Methane
Authors: Schneising O. , Buchwitz M. , Burrows J. P. , Bovensmann H. , Bergamaschi P. , Peters W.
Published: April 2010

Abstract. Carbon dioxide (CO2) and methane (CH4) are the two most important anthropogenic greenhouse gases. SCIAMACHY on ENVISAT is the first satellite instrument whose measurements are sensitive to concentration changes of the two gases at all altitude levels down to the Earth's surface where the source/sink signals are largest. We have processed three years (2003–2005) of SCIAMACHY near-infrared nadir measurements to simultaneously retrieve vertical columns of CO2 (from the 1.58 μm absorption band), CH4 (1.66 μm) and oxygen (O2 A-band at 0.76 μm) using the scientific retrieval algorithm WFM-DOAS. We show that the latest version of WFM-DOAS, version 1.0, which is used for this study, has been significantly improved with respect to its accuracy compared to the previous versions while essentially maintaining its high processing speed (~1 min per orbit, corresponding to ~6000 single measurements, and per gas on a standard PC). The greenhouse gas columns are converted to dry air column-averaged mole fractions, denoted XCO2 (in ppm) and XCH4 (in ppb), by dividing the greenhouse gas columns by simultaneously retrieved dry air columns. For XCO2 dry air columns are obtained from the retrieved O2 columns. For XCH4 dry air columns are obtained from the retrieved CO2 columns because of better cancellation of light path related errors compared to using O2 columns retrieved from the spectrally distant O2 A-band. Here we focus on a discussion of the XCH4 data set. The XCO2 data set is discussed in a separate paper (Part 1). For 2003 we present detailed comparisons with the TM5 model which has been optimally matched to highly accurate but sparse methane surface observations. After accounting for a systematic low bias of ~2% agreement with TM5 is typically within 1–2%. We investigated to what extent the SCIAMACHY XCH4 is influenced by the variability of atmospheric CO2 using global CO2 fields from NOAA's CO2 assimilation system CarbonTracker. We show that the CO2 corrected and uncorrected XCH4 spatio-temporal pattern are very similar but that agreement with TM5 is better for the CarbonTracker CO2 corrected XCH4. In line with previous studies (e.g., Frankenberg et al., 2005) we find significantly higher methane over the tropics compared to the model. We show that tropical methane is also higher when normalizing the CH4 columns with retrieved O2 columns instead of CO2. Concerning inter-annual variability we find similar methane spatio-temporal pattern for 2003 and 2004. For 2005 the retrieved methane shows significantly higher variability compared to the two previous years, most likely due to somewhat larger noise of the spectral measurements.
Operational climate monitoring from space: the EUMETSAT satellite application facility on climate monitoring (CM-SAF)
Authors: Schulz J. , Albert P. , Behr H.-D. , Caprion D. , Deneke H. , Dewitte S. , Dürr B. , Fuchs P. , Gratzki A. , Hechler P. , Hollmann R. , Johnston S. , Karlsson K.-G. , Manninen T. , Müller R. , Reuter M. , Riihelä A. , Roebeling R. , Selbach N. , Tetzlaff A. , Thomas W. , Werscheck M. , Wolters E. , Zelenka A.
Published: April 2010

Abstract. The Satellite Application Facility on Climate Monitoring (CM-SAF) aims at the provision of satellite-derived geophysical parameter data sets suitable for climate monitoring. CM-SAF provides climatologies for Essential Climate Variables (ECV), as required by the Global Climate Observing System implementation plan in support of the UNFCCC. Several cloud parameters, surface albedo, radiation fluxes at the top of the atmosphere and at the surface as well as atmospheric temperature and humidity products form a sound basis for climate monitoring of the atmosphere. The products are categorized in monitoring data sets obtained in near real time and data sets based on carefully intercalibrated radiances. The CM-SAF products are derived from several instruments on-board operational satellites in geostationary and polar orbit, i.e., the Meteosat and NOAA satellites, respectively. The existing data sets will be continued using data from the instruments on-board the new EUMETSAT Meteorological Operational satellite (MetOP). The products have mostly been validated against several ground-based data sets both in situ and remotely sensed. The accomplished accuracy for products derived in near real time is sufficient to monitor variability on diurnal and seasonal scales. Products based on intercalibrated radiance data can also be used for climate variability analysis up to inter-annual scale. A central goal of the recently started Continuous Development and Operations Phase of the CM-SAF (2007–2012) is to further improve all CM-SAF data sets to a quality level that allows for studies of inter-annual variability.
Analysis of the hygroscopic and volatile properties of ammonium sulphate seeded and un-seeded SOA particles
Authors: Meyer N. K. , Duplissy J. , Gysel M. , Metzger A. , Dommen J. , Weingartner E. , Alfarra M. R. , Fletcher C. , Good N. , McFiggans G. , Jonsson Å. M. , Hallquist M. , Baltensperger U. , Ristovski Z. D.
Published: April 2010

Abstract. The volatile and hygroscopic properties of ammonium sulphate seeded and un-seeded secondary organic aerosol (SOA) derived from the photo-oxidation of atmospherically relevant concentrations of α-pinene were studied. The seed particles were electrospray generated ammonium sulphate ((NH4)2SO4) having diameters of approximately 33 nm with a quasi-mono-disperse size distribution (geometric standard deviation σg=1.3). The volatile and hygroscopic properties of both seeded and unseeded SOA were simultaneously measured with a VH-TDMA (volatility – hygroscopicity tandem differential mobility analyzer). VH-TDMA measurements of unseeded SOA show a decrease in the hygroscopic growth (HGF) factor for increased volatilisation temperatures such that the more volatile compounds appear to be more hygroscopic. This is opposite to the expected preferential evaporation of more volatile but less hygroscopic material, but could also be due to enhanced oligomerisation occurring at the higher temperature in the thermodenuder. In addition, HGF measurements of seeded SOA were measured as a function of time at two relative humidities, below (RH 75%) and above (RH 85%) the deliquescence relative humidity (DRH) of the pure ammonium sulphate seeds. As these measurements were conducted during the onset phase of photo-oxidation, during particle growth, they enabled us to find the dependence of the HGF as a function of the volume fraction of the SOA coating. HGF's measured at RH of 85% showed a continuous decrease as the SOA coating thickness increased. The measured growth factors show good agreements with ZSR predictions indicating that, at these RH values, there are only minor solute-solute interactions. At 75% RH, as the SOA fraction increased, a rapid increase in the HGF was observed indicating that an increasing fraction of the (NH4)2SO4 is subject to a phase transition, going into solution, with an increasing volume fraction of SOA. To our knowledge this is the first time that SOA derived from photo-oxidised α-pinene has been shown to affect the equilibrium water content of inorganic aerosols below their DRH. For SOA volume fractions above ~0.3 the measured growth factor followed roughly parallel to the ZSR prediction based on fully dissolved (NH4)2SO4 although with a small difference that was just larger than the error estimate. Both incomplete dissolution and negative solute-solute interactions could be responsible for the lower HGF observed compared to the ZSR predictions.
Modelling of cirrus clouds – Part 2: Competition of different nucleation mechanisms
Authors: Spichtinger P. , Gierens K. M.
Published: April 2010

Abstract. We study the competition of two different freezing mechanisms (homogeneous and heterogeneous freezing) in the same environment for cold cirrus clouds. To this goal we use the recently developed and validated ice microphysics scheme (Spichtinger and Gierens, 2008, henceforth "Part 1") which distinguishes between ice classes according to their formation process. We investigate cases with purely homogeneous ice formation and compare them with cases where background ice nuclei in varying concentration heterogeneously form ice prior to homogeneous nucleation. We perform additionally a couple of sensitivity studies regarding threshold humidity for heterogeneous freezing, uplift speed, and ambient temperature, and we study the influence of random motions induced by temperature fluctuations in the clouds. We find three types of cloud evolution, homogeneously dominated, heterogeneously dominated, and a mixed type where neither nucleation process dominates. The latter case is prone to long–lasting in–cloud ice supersaturation of the order 30% and more.
Simulation of the climate impact of Mt. Pinatubo eruption using ECHAM5 – Part 1: Sensitivity to the modes of atmospheric circulation and boundary conditions
Authors: Thomas M. A. , Timmreck C. , Giorgetta M. A. , Graf H.-F. , Stenchikov G.
Published: April 2010

Abstract. Large volcanic eruptions and their subsequent climate responses are relatively short-lived perturbations to the climate system. They provide an excellent opportunity to understand the response of the climate system to a global radiative forcing and to assess the ability of our climate models to simulate such large perturbations. The eruption of Mt. Pinatubo in Philippines in June 1991 was one of the strongest volcanic eruptions in the 20th century and this well observed eruption can serve as an important case study to understand the subsequent weather and climate changes. In this paper, the most comprehensive simulations to date of the climate impact of Mt. Pinatubo eruption are carried out with prescribed volcanic aerosols including observed SSTs, QBO and volcanically induced ozone anomalies. This is also the first attempt to include all the known factors for the simulation of such an experiment. Here, the climate response is evaluated under different boundary conditions including one at a time, thereby, investigating the radiative and dynamical responses to individual and combined forcings by observed SSTs, QBO and volcanic effects. Two ensembles of ten members each, for unperturbed and volcanically perturbed conditions were carried out using the middle atmosphere configuration of ECHAM5 model. Our results show that the pure aerosol response in lower stratospheric temperature is insensitive to the boundary conditions in the tropics and does not show some observed features which results from the boundary conditions. To simulate realistically the lower stratospheric temperature response, one must include all the known factors. The pure QBO and ocean responses are simulated consistent with earlier studies. The dynamical response manifested as the winter warming pattern is not simulated in the ensemble mean of the experiments. Our analysis also shows that the response to El Niño conditions is very strong in the model and that it partially masks the effects due to volcanic forcing.
Do atmospheric aerosols form glasses?
Authors: Zobrist B. , Marcolli C. , Pedernera D. A. , Koop T.
Published: April 2010

Abstract. A new process is presented by which water-soluble organics might influence ice nucleation, ice growth, chemical reactions and water uptake of aerosols in the upper troposphere: the formation of glassy aerosol particles. Glasses are disordered amorphous (non-crystalline) solids that form when a liquid is cooled without crystallization until the viscosity increases exponentially and molecular diffusion practically ceases. The glass transition temperatures, Tg, homogeneous ice nucleation temperatures, Thom, and ice melting temperatures, Tm, of various aqueous inorganic, organic and multi-component solutions are investigated with a differential scanning calorimeter. The investigated solutes are: various polyols, glucose, raffinose, levoglucosan, an aromatic compound, sulfuric acid, ammonium bisulphate and mixtures of dicarboxylic acids (M5), of dicarboxylic acids and ammonium sulphate (M5AS), of two polyols, of glucose and ammonium nitrate, and of raffinose and M5AS. The results indicate that aqueous solutions of the investigated inorganic solutes show Tg-values that are too low to be of atmospheric importance. In contrast, aqueous organic and multi-component solutions readily form glasses at low but atmospherically relevant temperatures (≤230 K). To apply the laboratory data to the atmospheric situation, the measured phase transition temperatures were transformed from a concentration to a water activity scale by extrapolating water activities determined between 252 K and 313 K to lower temperatures. The obtained state diagrams reveal that the higher the molar mass of the aqueous organic or multi-component solutes, the higher Tg of their respective solutions at a given water activity. To a lesser extent, Tg also depends on the hydrophilicity of the organic solutes. Therefore, aerosol particles containing larger and more hydrophobic organic molecules (≳150 g mol-1) are more likely to form glasses at intermediate to high relative humidities in the upper troposphere. Our results suggest that the water uptake of aerosols, heterogeneous chemical reactions in aerosol particles, as well as ice nucleation and ice crystal growth can be significantly impeded or even completely inhibited in organic-enriched aerosols at upper tropospheric temperatures with implications for cirrus cloud formation and upper tropospheric relative humidity.
Nitric acid in the stratosphere based on Odin observations from 2001 to 2007 – Part 1: A global climatology
Authors: Urban J. , Pommier M. , Murtagh D. P. , Santee M. L. , Orsolini Y. J.
Published: April 2010

Abstract. The Sub-Millimetre Radiometer (SMR) on board the Odin satellite, launched in February 2001, observes thermal emissions of stratospheric nitric acid (HNO3) originating from the Earth limb in a band centred at 544.6 GHz. Height-resolved measurements of the global distribution of nitric acid in the stratosphere between ~18–45 km (~1.5–60 hPa) were performed approximately on two observation days per week. An HNO3 climatology based on roughly 6 years of observations from August 2001 to December 2007 was created. The study highlights the spatial and seasonal variation of nitric acid in the stratosphere, characterised by a pronounced seasonal cycle at middle and high latitudes with maxima during late fall and minima during spring, strong denitrification in the lower stratosphere of the Antarctic polar vortex during winter (the irreversible removal of NOy by the sedimentation of cloud particles containing HNO3), as well as high quantities of HNO3 formed every winter at high-latitudes in the middle and upper stratosphere. A strong inter-annual variability is observed in particular at high latitudes. A comparison with a stratospheric HNO3 climatology based on UARS/MLS measurements from the 1990s shows a good consistency and agreement of the main morphological features in the potential temperature range ~465 to ~960 K, if the different characteristics of the data sets such as altitude range and resolution are considered.
Nitric acid in the stratosphere based on Odin observations from 2001 to 2007 – Part 2: High-altitude polar enhancements
Authors: Orsolini Y. J. , Urban J. , Murtagh D. P.
Published: April 2010

Abstract. The wintertime abundance of nitric acid (HNO3) in the polar upper stratosphere displays a strong inter-annual variability, and is known to be strongly influenced by energetic particle precipitation, primarily during solar proton events, but also by precipitating electrons in the auroral zone. While wintertime HNO3 enhancements in the polar upper stratosphere had been occasionally observed before, from the ground or from satellite, we present here measurements by the Sub-Millimeter Radiometer instrument aboard the Odin satellite through 6 full annual cycles (2001 to 2007). Major solar proton events, e.g. during November 2001 or the Halloween solar storms of autumn 2003, lead to a two-stage HNO3 enhancement, likely involving different chemical reactions: a fast (about 1 week) in-situ enhancement from the mid to the upper stratosphere is followed by a slower, longer-lasting one, whereby anomalies originating in the upper stratosphere can descend within the polar vortex into the lower stratosphere. We highlight the fact that the actual chemical coupling between the upper and lower atmosphere involves a complex interplay of chemistry, dynamics and energetic particle precipitation.
Intra-community spatial variability of particulate matter size distributions in southern California/Los Angeles
Authors: Krudysz M. , Moore K. , Geller M. , Sioutas C. , Froines J.
Published: April 2010

Abstract. Ultrafine particle (UFP) number concentrations vary significantly on small spatial and temporal scales due to their short atmospheric lifetimes and multiplicity of sources. To determine UFP exposure gradients within a community, simultaneous particle number concentration measurements at a network of sites are necessary. Concurrent particle size distribution measurements aid in identifying UFP sources, while providing data to investigate local scale effects of both photochemical and physical processes on UFP. From April to December 2007, we monitored particle size distributions at 13 sites within 350 m to 11 km of each other in the vicinity of the Ports of Los Angeles and Long Beach using Scanning Mobility Particle Sizers (SMPS). Typically, three SMPS units were simultaneously deployed and rotated among sites at 1–2 week intervals. Total particle number concentration measurements were conducted continuously at all sites. Seasonal and diurnal size distribution patterns are complex, highly dependent on local meteorology, nearby PM sources, and times of day, and cannot be generalized over the study area nor inferred from one or two sampling locations. Spatial variation in particle number size distributions was assessed by calculating the coefficient of divergence (COD) and correlation coefficients (r) between site pairs. Results show an overall inverse relationship between particle size and CODs, implying that number concentrations of smaller particles (<40 nm) differ from site to site, whereas larger particles tend to have similar concentrations at various sampling locations. In addition, variations in r values as a function of particle size are not necessarily consistent with corresponding COD values, indicating that using results from correlation analysis alone may not accurately assess spatial variability.
In-situ ambient quantification of monoterpenes, sesquiterpenes, and related oxygenated compounds during BEARPEX 2007 – implications for gas- and particle-phase chemistry
Authors: Bouvier-Brown N. C. , Goldstein A. H. , Gilman J. B. , Kuster W. C. , de Gouw J. A.
Published: April 2010

Abstract. We quantified ambient mixing ratios of 9 monoterpenes, 6 sesquiterpenes, methyl chavicol, the oxygenated terpene linalool, and nopinone using an in-situ gas chromatograph with a quadrupole mass spectrometer (GC-MS). These measurements were a part of the 2007 Biosphere Effects on AeRosols and Photochemistry EXperiment (BEARPEX) at Blodgett Forest, a ponderosa pine forest in the Sierra Nevada Mountains of California. To our knowledge, these observations represent the first direct in-situ ambient quantification of the sesquiterpenes α-bergamotene, longifolene, α-farnesene, and β-farnesene. From average diurnal mixing ratio profiles, we show that α-farnesene emissions are dependent mainly on temperature whereas α-bergamotene and β-farnesene emissions are temperature- and light-dependent. The amount of sesquiterpene mass quantified above the canopy was small (averaging a total of 3.3 ppt during the day), but nevertheless these compounds contributed 8.5% to the overall ozone reactivity above the canopy. Assuming that the monoterpene-to-sesquiterpene emission rate in the canopy is similar to that observed in branch enclosure studies at the site during comparable weather conditions, and the average yield of aerosol mass from these sesquiterpenes is 10–50%, the amount of sesquiterpene mass reacted within the Blodgett Forest canopy alone accounts for 8–38% of the total organic aerosol mass measured during BEARPEX. The oxygenated monoterpene linalool was also quantified for the first time at Blodgett Forest. The linalool mass contribution was small (9.9 ppt and 0.74 ppt within and above the canopy, respectively), but it contributed 1.2% to the total ozone reactivity above the canopy. Reactive and semi-volatile compounds, especially sesquiterpenes, significantly impact the gas- and particle-phase chemistry of the atmosphere at Blodgett Forest and should be included in both biogenic volatile organic carbon emission and atmospheric chemistry models.
Increasing surface ozone concentrations in the background atmosphere of southern China, 1994–2007
Authors: Wang T. , Wei X. L. , Ding A. J. , Poon C. N. , Lam K. S. , Li Y. S. , Chan L. Y. , Anson M.
Published: April 2010

Abstract. Tropospheric ozone is of great importance with regard to air quality, atmospheric chemistry, and climate change. In this paper we report the first continuous record of surface ozone in the background atmosphere of South China. The data were obtained from 1994 to 2007 at a coastal site in Hong Kong, which is strongly influenced by the outflow of Asian continental air during the winter and the inflow of maritime air from the subtropics in the summer. Overall, the ozone concentration increased by an averaged rate of 0.55 ppbv/yr, with a larger increase in autumn (0.68 ppbv/yr). We also examine the trend in air masses from various source regions in Asia. Using local wind and concurrently measured carbon monoxide (CO) data to filter out local emissions, the mean ozone in air masses from eastern China, using the pooled averaging method, increased by 0.64 ppbv/yr, while ozone levels in other air-mass groups showed a positive trend (0.29–0.67 ppbv/yr) but with lower levels of statistical significance. An examination of the nitrogen dioxide (NO2) column concentration data obtained from GOME and SCIAMACHY reveals an increase in atmospheric NO2 in the three fastest developing coastal regions of China, whereas NO2 in other parts of Asia decreased during the same period. It is believed that the observed increase in background ozone in Hong Kong is primarily due to the increased emissions of NO2 (and possibly volatile organic compounds (VOCs) as well) in the upwind coastal regions of mainland China, which is supported by the observed positive CO trend (5.23 ppbv/yr) at the site. The increase in background ozone contributed two thirds of the annual increase in ''total ozone'' in the downwind urban areas of Hong Kong, suggesting the need to consider distant sources when developing long-term strategies to mitigate local ozone pollution, although short-term strategies should be aimed at sources in Hong Kong and the adjacent Pearl River Delta.
Decadal regional air quality simulations over Europe in present climate: near surface ozone sensitivity to external meteorological forcing
Authors: Katragkou E. , Zanis P. , Tegoulias I. , Melas D. , Krüger B. C. , Huszar P. , Halenka T. , Rauscher S.
Published: April 2010

Abstract. Regional air quality decadal simulations were carried out using the air quality model CAMx driven off-line by the regional climate model RegCM3 for the time slice 1991–2000 using two different datasets of external meteorological forcing to constrain RegCM3: the ERA40 global atmospheric reanalysis dataset and the output from the GCM ECHAM5. The focus of this work is to compare the perfect lateral boundary conditions experiment with the GCM driven control experiment and to investigate how this external meteorological forcing affects near surface ozone. The different RegCM3 meteorological forcings resulted in changes of near surface ozone over Europe ranging between ±5 ppb for winter and summer, while all model parameterizations and anthropogenic emissions remained unchanged. Changes in near surface ozone are induced by changes in meteorological fields and biogenic emissions, which are on-line calculated and meteorology-dependent. The model simulations suggest that the change in solar radiation is the factor that mostly modulates the ozone changes in summer. During winter season it is found that the induced changes in NOx explain about 40% of the ozone variability. The meteorological induced changes in biogenic emissions are quite low for winter with rather small impact on ozone while they are more temperature than radiation dependent. Using multiple regression analysis to associate the changes in near surface ozone with the respective changes in selected meteorological parameters and ozone precursors, an explained variance of 70% in summer and 60% in winter is reproduced.
A new paradigm for intensity modification of tropical cyclones: thermodynamic impact of vertical wind shear on the inflow layer
Authors: Riemer M. , Montgomery M. T. , Nicholls M. E.
Published: April 2010

Abstract. An important roadblock to improved intensity forecasts for tropical cyclones (TCs) is our incomplete understanding of the interaction of a TC with the environmental flow. In this paper we re-visit the classical idealised numerical experiment of tropical cyclones (TCs) in vertical wind shear on an f-plane. We employ a set of simplified model physics – a simple bulk aerodynamic boundary layer scheme and "warm rain" microphysics – to foster better understanding of the dynamics and thermodynamics that govern the modification of TC intensity. A suite of experiments is performed with intense TCs in moderate to strong vertical shear. In all experiments the TC is resilient to shear but significant differences in the intensity evolution occur. The ventilation of the TC core with dry environmental air at mid-levels and the dilution of the upper-level warm core are two prevailing hypotheses for the adverse effect of vertical shear on storm intensity. Here we propose an alternative and arguably more effective mechanism how cooler and drier (lower θe) air – "anti-fuel" for the TC power machine – can enter the core region of the TC. Strong and persistent downdrafts flux low θe air from the lower and middle troposphere into the boundary layer, significantly depressing the θe values in the storm's inflow layer. Air with lower θe values enters the eyewall updrafts, considerably reducing eyewall θe values in the azimuthal mean. When viewed from the perspective of an idealised Carnot-cycle heat engine a decrease of storm intensity can thus be expected. Although the Carnot cycle model is – if at all – only valid for stationary and axisymmetric TCs, a strong correlation between the downward transport of low θe into the boundary layer and the intensity evolution offers further evidence in support of our hypothesis. The downdrafts that flush the inflow layer with low θe air are associated with a quasi-stationary region of convective activity outside the TC's eyewall. We show evidence that, to zero order, the formation of the convective asymmetry is driven by the balanced dynamical response of the TC vortex to the vertical shear forcing. Thus a close link is provided between the thermodynamic impact in the near-core boundary layer and the balanced dynamics governing the TC vortex evolution.
Diagnostics of the Tropical Tropopause Layer from in-situ observations and CCM data
Authors: Palazzi E. , Fierli F. , Cairo F. , Cagnazzo C. , Di Donfrancesco G. , Manzini E. , Ravegnani F. , Schiller C. , D'Amato F. , Volk C. M.
Published: April 2010

Abstract. A suite of diagnostics is applied to in-situ aircraft measurements and one Chemistry-Climate Model (CCM) data to characterize the vertical structure of the Tropical Tropopause Layer (TTL). The diagnostics are based on the vertical tracers profiles, relative vertical tracers gradients, and tracer-tracer relationships in the tropical Upper Troposphere/Lower Stratosphere (UT/LS), using tropopause coordinates. Observations come from the four tropical campaigns performed from 1998 to 2006 with the research aircraft Geophysica and have been directly compared to the output of the ECHAM5/MESSy CCM. The model vertical resolution in the TTL allows for appropriate comparison with high-resolution aircraft observations and the diagnostics used highlight common TTL features between the model and the observational data. The analysis of the vertical profiles of water vapour, ozone, and nitrous oxide, in both the observations and the model, shows that concentration mixing ratios exhibit a strong gradient change across the tropical tropopause, due to the role of this latter as a transport barrier and that transition between the tropospheric and stratospheric regimes occurs within a finite layer. The use of relative vertical ozone gradients, in addition to the vertical profiles, helps to highlight the region where this transition occurs and allows to give an estimate of its thickness. The analysis of the CO-O3 and H2O-O3 scatter plots and of the Probability Distribution Function (PDF) of the H2O-O3 pair completes this picture as it allows to better distinguish tropospheric and stratospheric regimes that can be identified, first, by their differing chemical composition. The joint analysis and comparison of observed and modelled data allows us to evaluate the capability of the model in reproducing the observed vertical structure of the TTL and its variability, and also to assess whether observations from particular regions on a monthly timescale can be representative of the fine scale mean structure of the Tropical Tropopause Layer.
Evaluation of tropospheric ozone columns derived from assimilated GOME ozone profile observations
Authors: de Laat A. T. J. , van der A R. J. , van Weele M.
Published: April 2010

Abstract. Tropospheric O3 column estimates are produced and evaluated from spaceborne O3 observations by the subtraction of assimilated O3 profile observations from total column observations, the so-called Tropospheric O3 ReAnalysis or TORA method. Here we apply the TORA method to six years (1996–2001) of ERS-2 GOME/TOMS total O3 and ERS-2 GOME O3 profile observations using the TM5 global chemistry-transport model with a linearized O3 photochemistry parameterization scheme. Free running TM5 simulations show good agreement with O3 sonde observations in the upper-tropospheric and lower stratospheric (UTLS). Assimilation of GOME O3 profile observations improves the comparisons in the tropical UTLS region but slightly degrades the model-to-sonde comparisons in the extra-tropical UTLS for both short day-do-day variability as well as for monthly means. We suggest that this degradation is related to the large ground pixel size of the GOME O3 measurements (960×100 km) in combination with retrieval and calibration errors. The assimilation of GOME O3 profile observations does counter the gradual multiyear mid-latitude stratospheric O3 accumulation caused by the overstrong stratospheric meridional circulation in TM5. The evaluation of daily and monthly tropospheric O3 columns obtained from total column observations and using the TORA methodology shows realistic residuals within the tropics but unrealistically large deviations outside of the tropics, although average biases remain small for the monthly means. The findings of this paper suggest that improvements can be expected by using O3 observations from present-day instruments like MetOp/GOME-2 and EOS-AURA/OMI.
Northern winter stratospheric temperature and ozone responses to ENSO inferred from an ensemble of Chemistry Climate Models
Authors: Cagnazzo C. , Manzini E. , Calvo N. , Douglass A. , Akiyoshi H. , Bekki S. , Chipperfield M. , Dameris M. , Deushi M. , Fischer A. , Garny H. , Gettelman A. , Giorgetta M. A. , Plummer D. , Rozanov E. , Shepherd T. G. , Shibata K. , Stenke A. , Struthers H. , Tian W.
Published: April 2010

Abstract. The connection between the El Niño Southern Oscillation (ENSO) and the northern polar stratosphere has been established from observations and atmospheric modeling. Here a systematic inter-comparison of the sensitivity of the modeled stratosphere to ENSO in Chemistry Climate Models (CCMs) is reported. This work uses results from a number of the CCMs included in the 2006 ozone assessment. In the lower stratosphere, the mean of all model simulations reports a warming of the polar vortex during strong ENSO events in February–March, consistent with but smaller than the estimate from satellite observations and ERA40 reanalysis. This anomalous warming is associated with an anomalous dynamical increase of total ozone north of 70° N that is accompanied by coherent total ozone decrease in the Tropics, in agreement with that deduced from the NIWA total ozone database, implying an increased residual circulation in the mean of all model simulations, during ENSO. The spread in the model responses is partly due to the large internal stratospheric variability but it is shown that it crucially depends on the representation of the tropospheric ENSO teleconnection in the models.
Comparative study of the effect of water on the heterogeneous reactions of carbonyl sulfide on the surface of α-Al2O3 and MgO
Authors: Liu Y. , Ma Q. , He H.
Published: April 2010

Abstract. The heterogeneous reaction on mineral dust was considered as a new sink of OCS in the troposphere. Here we compared the heterogeneous reactions of carbonyl sulfide (OCS) on the surface of α-Al2O3 and MgO and the effect of water on the reactions at 300 K using Knudsen cell – mass spectrometry, diffuse reflectance infrared Fourier transform spectroscopy, and temperature programmed reactions. H2S and CO2 were found to be hydrolysis products of OCS on both α-Al2O3 and MgO at ambient temperature. At low water vapor pressure, when water vapor pressure in the Knudsen cell reactor increased from 2.3×10−6 to 6.8×10−6 Torr, the initial true uptake coefficient of OCS on α-Al2O3 decreased from 4.70×10−7 to 3.59×10−7; while it increased from 5.19×10−7 to 6.48×10−7 on MgO under the same conditions. At high relative humidity, the observed uptake coefficients of OCS on α-Al2O3 and MgO decreased from 4.63×10−6 to 1.00×10−6 and from 9.72×10−5 to 7.68×10−5, respectively, when RH increased from 0.07 to 0.67 which corresponding to 1.7–15.9 Torr of water vapor pressure. In the RH region of 0.17–0.67, the average observed uptake coefficient of OCS on α-Al2O3 and MgO was equal to 8.34±2.19×10−7 and 8.19±0.48×10−5, respectively. The restrictive effect of water on the heterogeneous reaction of OCS on the surface of α-Al2O3 and MgO was found to be related to competitive adsorption between water and OCS molecules; while the promotive effect of water on the heterogeneous reaction of OCS on the surface of MgO at low coverage was ascribed to the formation of surface hydroxyl groups. When the environmental RH was greater than the RH of the monolayer, which occurred readily at the typical relative humidity of the troposphere, liquid membrane formed on the mineral dusts, especially, the basic liquid membrane formed on the basic component of mineral dusts may be the primary contributor to the heterogeneous hydrolysis of OCS in the troposphere.
Use of a mobile laboratory to evaluate changes in on-road air pollutants during the Beijing 2008 Summer Olympics
Authors: Wang M. , Zhu T. , Zheng J. , Zhang R. Y. , Zhang S. Q. , Xie X. X. , Han Y. Q. , Li Y.
Published: April 2010

Abstract. China implemented systematic air pollution control measures during the 2008 Beijing Summer Olympics and Paralympics to improve air quality. This study used an innovative mobile laboratory to conduct in situ monitoring of on-road air pollutants along Beijing's 4th Ring Road on 31 selected days before, during, and after the Olympics air pollution control period. A suite of instruments with response times of less than 30 s was used to measure temporal and spatial variations in traffic-related air pollutants, including NOx, CO, PM1.0 surface area (SPM1), black carbon (BC), and benzene, toluene, ethylbenzene, and m-, p-, and o-xylene (BTEX). During the Olympics (8–23 August 2008), on-road air pollutant concentrations decreased significantly by up to 54% for CO, 41% for NOx, 70% for SO2, 66% for BTEX, 12% for BC, and 18% for SPM1 compared to the pre-control period (before 20 July). Concentrations increased again after the control period ended (after 20 September), with average increases of 33% for CO, 42% for NOx, 60% for SO2, 40% for BTEX, 26% for BC, and 37% for SPM1. Variations in pollutants concentrations were correlated with changes in traffic speed and the number and types of vehicles on the road. Throughout the measurement periods, the concentrations of NOx, CO, and BTEX varied markedly with the numbers of light- and medium-duty vehicles (LDVs and MDVs, respectively) on the road. Only after 8 August was a noticeable relationship between BC and SPM1 and the number of heavy-duty vehicles (HDVs) found. Additionally, BC and SPM1 showed a strong correlation with SO2 before the Olympics, indicating possible industrial sources from local emissions as well as regional transport activities in the Beijing area. Such factors were identified in measurements conducted on 6 August in an area southwest of Beijing. The ratio of benzene to toluene, a good indicator of traffic emissions, shifted suddenly from about 0.26 before the Olympics to approximately 0.48 after the Olympics began. This finding suggests that regulations on traffic volume and restrictions on the use of painting solvents were effective after the Olympics began. This study demonstrated the effectiveness of air pollution control measures and identified local and regional pollution sources within and surrounding the city of Beijing. The findings will be invaluable for emission inventory evaluations and model verifications.
Technical Note: In-situ quantification of aerosol sources and sinks over regional geographical scales
Authors: Buzorius G.
Published: April 2010

Abstract. In order to obtain the source/sink functions for atmospheric particulates located on the planetary surface or elevated in the atmosphere; direct aerosol emission measurements are required. For this purpose, the performance of an airborne aerosol flux measurement system with an improved 3-km spatial resolution is evaluated in this study. Eddy covariance method was used in flux calculations. A footprint for airborne flux sampling with the increased resolution becomes comparable in area to the footprint for tower sampling (with the footprint length being 2 to 10 km). The improvement in spatial resolution allows quantification of emission rates from individual sources located several kilometers apart. Locally measured aerosol flux provides useful information about aerosol sources and sinks located below or aloft of measurement altitude. The advantage is a moving platform that allows scanning of aerosol emissions or depositions over practically unlimited geographic scales. The technique delivers effective emission rates of atmospheric particulates from specific sources such as highway segments, city blocks, and remote and industrial areas. The improved spatial resolution airborne flux measurements were conducted in ambient conditions with low (<500 m) mixed boundary layer heights. Measurement results are reported from clean and partly polluted marine environments, and heavily polluted continental environments. The upward and downward fluxes from the clean marine environment were smaller than 0.5×106 particles m−2 s−1 in absolute value. The effective emissions measured from a ship plume ranged from 2×108 to 3×108 m−2 s−1, and effective fluxes measured crossing cities plumes with populations of 10 000 to 12 000 inhabitants were in the range of 2×108 to 3×108 m−2 s−1. Correlations between heat and aerosol fluxes are evaluated.