bluuebunny/crossref_metadata_2025 huggingface dataset:
The time evolution of aerosol composition over the Mexico City plateau
Authors: Kleinman L. I. , Springston S. R. , Daum P. H. , Lee Y.-N. , Nunnermacker L. J. , Senum G. I. , Wang J. , Weinstein-Lloyd J. , Alexander M. L. , Hubbe J. , Ortega J. , Canagaratna M. R. , Jayne J.
Published: April 2010

Abstract. The time evolution of aerosol concentration and chemical composition in a megacity urban plume was determined based on 8 flights of the DOE G-1 aircraft in and downwind of Mexico City during the March 2006 MILAGRO field campaign. A series of selection criteria are imposed to eliminate data points with non-urban emission influences. Biomass burning has urban and non-urban sources that are distinguished on the basis of CH3CN and CO. In order to account for dilution in the urban plume, aerosol concentrations are normalized to CO which is taken as an inert tracer of urban emission, proportional to the emissions of aerosol precursors. Time evolution is determined with respect to photochemical age defined as –Log10 (NOx/NOy). The geographic distribution of photochemical age and CO is examined, confirming the picture that Mexico City is a source region and that pollutants become more dilute and aged as they are advected towards T1 and T2, surface sites that are located at the fringe of the City and 35 km to the NE, respectively. Organic aerosol (OA) per ppm CO is found to increase 7 fold over the range of photochemical ages studied, corresponding to a change in NOx/NOy from nearly 100% to 10%. In the older samples the nitrate/CO ratio has leveled off suggesting that evaporation and formation of aerosol nitrate are in balance. In contrast, OA/CO increases with age in older samples, indicating that OA is still being formed. The amount of carbon equivalent to the deduced change in OA/CO with age is 56 ppbC per ppm CO. At an aerosol yield of 5% and 8% for low and high yield aromatic compounds, it is estimated from surface hydrocarbon observations that only ~9% of the OA formation can be accounted for. A comparison of OA/CO in Mexico City and the eastern U.S. gives no evidence that aerosol yields are higher in a more polluted environment.
GEM-AQ, an on-line global multiscale chemical weather system: model description and evaluation of gas phase chemistry processes
Authors: Kaminski J. W. , Neary L. , Struzewska J. , McConnell J. C. , Lupu A. , Jarosz J. , Toyota K. , Gong S. L. , Côté J. , Liu X. , Chance K. , Richter A.
Published: April 2010

Abstract. Tropospheric chemistry and air quality processes were implemented on-line in the Global Environmental Multiscale model. The integrated model, GEM-AQ, has been developed as a platform to investigate chemical weather at scales from global to urban. The model was exercised for five years (2001–2005) to evaluate its ability to simulate seasonal variations and regional distributions of trace gases such as ozone, nitrogen dioxide and carbon monoxide on the global scale. The model results presented are compared with observations from satellites, aircraft measurement campaigns and balloon sondes.
Applications of Lagrangian dispersion modeling to the analysis of changes in the specific absorption of elemental carbon
Authors: Doran J. C. , Fast J. D. , Barnard J. C. , Laskin A. , Desyaterik Y. , Gilles M. K. , Hopkins R. J.
Published: April 2010

Abstract. We use a Lagrangian dispersion model driven by a mesoscale model with four-dimensional data assimilation to simulate the dispersion of elemental carbon (EC) over a region encompassing Mexico City and its surroundings, the study domain for the 2006 MAX-MEX experiment, which was a component of the MILAGRO campaign. The results are used to identify periods when biomass burning was likely to have had a significant impact on the concentrations of elemental carbon at two sites, T1 and T2, downwind of the city, and when emissions from the Mexico City Metropolitan Area (MCMA) were likely to have been more important. They are also used to estimate the median ages of EC affecting the specific absorption of light, αABS, at 870 nm as well as to identify periods when the urban plume from the MCMA was likely to have been advected over T1 and T2. Median EC ages at T1 and T2 are substantially larger during the day than at night. Values of αABS at T1, the nearer of the two sites to Mexico City, were smaller at night and increased rapidly after mid-morning, peaking in the mid-afternoon. The behavior is attributed to the coating of aerosols with substances such as sulfate or organic carbon during daylight hours, but such coating appears to be limited or absent at night. Evidence for this is provided by scanning electron microscopy images of aerosols collected at the sampling sites. During daylight hours the values of αABS did not increase with aerosol age for median ages in the range of 1–4 h. There is some evidence for absorption increasing as aerosols were advected from T1 to T2 but the statistical significance of that result is not strong.
NO2 climatology in the northern subtropical region: diurnal, seasonal and interannual variability
Authors: Gil M. , Yela M. , Gunn L. N. , Richter A. , Alonso I. , Chipperfield M. P. , Cuevas E. , Iglesias J. , Navarro M. , Puentedura O. , Rodríguez S.
Published: April 2010

Abstract. Daily NO2 vertical column density (VCD) has been routinely measured by zenith sky spectroscopy at the subtropical station of Izaña (28° N, 16° W) since 1993 in the framework of the Network for the Detection of Atmospheric Composition Change (NDACC). Based on 14 years of data the first low latitudes NO2 VCD climatology has been established and the main characteristics from short scales of one day to inter-annual variability are presented. Instrumental descriptions and different source of errors are described in detail. The observed diurnal cycle follows that expected by gas-phase NOx chemistry, as can be shown by the good agreement with a vertically integrated chemical box model, and is modulated by solar radiation. The seasonal evolution departs from the phase of the hours of daylight, showing the signature of upper stratospheric temperature changes. From the data record no significant long-term trends in NO2 VCD can be inferred. Comparison of the ground-based data sets with nadir looking satellite spectrometers shows excellent agreement for SCIAMACHY with differences between both datasets of 1.1%. GOME displays unrealistic features with largest discrepancies during summer. The ground-based data are compared with long-term output of the SLIMCAT 3-D chemical transport model (CTM). The basic model, forced by ECMWF (ERA-40) analyses, captures the observed NO2 annual cycle but significantly underestimates the spring/summer maximum. In a model run which uses assimilation of satellite CH4 profiles to constrain the model long-lived tracers the agreement is significantly improved. This improvement in modelled column NO2 is due to better modelled NOy profiles and points to transport errors in the ECMWF ERA-40 reanalyses.
CO measurements from the ACE-FTS satellite instrument: data analysis and validation using ground-based, airborne and spaceborne observations
Authors: Clerbaux C. , George M. , Turquety S. , Walker K. A. , Barret B. , Bernath P. , Boone C. , Borsdorff T. , Cammas J. P. , Catoire V. , Coffey M. , Coheur P.-F. , Deeter M. , De Mazière M. , Drummond J. , Duchatelet P. , Dupuy E. , de Zafra R. , Eddounia F. , Edwards D. P. , Emmons L. , Funke B. , Gille J. , Griffith D. W. T. , Hannigan J. , Hase F. , Höpfner M. , Jones N. , Kagawa A. , Kasai Y. , Kramer I. , Le Flochmoën E. , Livesey N. J. , López-Puertas M. , Luo M. , Mahieu E. , Murtagh D. , Nédélec Ph. , Pazmino A. , Pumphrey H. , Ricaud P. , Rinsland C. P. , Robert C. , Schneider M. , Senten C. , Stiller G. , Strandberg A. , Strong K. , Sussmann R. , Thouret V. , Urban J. , Wiacek A.
Published: April 2010

Abstract. The Atmospheric Chemistry Experiment (ACE) mission was launched in August 2003 to sound the atmosphere by solar occultation. Carbon monoxide (CO), a good tracer of pollution plumes and atmospheric dynamics, is one of the key species provided by the primary instrument, the ACE-Fourier Transform Spectrometer (ACE-FTS). This instrument performs measurements in both the CO 1-0 and 2-0 ro-vibrational bands, from which vertically resolved CO concentration profiles are retrieved, from the mid-troposphere to the thermosphere. This paper presents an updated description of the ACE-FTS version 2.2 CO data product, along with a comprehensive validation of these profiles using available observations (February 2004 to December 2006). We have compared the CO partial columns with ground-based measurements using Fourier transform infrared spectroscopy and millimeter wave radiometry, and the volume mixing ratio profiles with airborne (both high-altitude balloon flight and airplane) observations. CO satellite observations provided by nadir-looking instruments (MOPITT and TES) as well as limb-viewing remote sensors (MIPAS, SMR and MLS) were also compared with the ACE-FTS CO products. We show that the ACE-FTS measurements provide CO profiles with small retrieval errors (better than 5% from the upper troposphere to 40 km, and better than 10% above). These observations agree well with the correlative measurements, considering the rather loose coincidence criteria in some cases. Based on the validation exercise we assess the following uncertainties to the ACE-FTS measurement data: better than 15% in the upper troposphere (8–12 km), than 30% in the lower stratosphere (12–30 km), and than 25% from 30 to 100 km.
Particulate polycyclic aromatic hydrocarbon spatial variability and aging in Mexico City
Authors: Thornhill D. A. , Herndon S. C. , Onasch T. B. , Wood E. C. , Zavala M. , Molina L. T. , Gaffney J. S. , Marley N. A. , Marr L. C.
Published: April 2010

Abstract. As part of the Megacities Initiative: Local and Global Research Observations (MILAGRO) study in the Mexico City Metropolitan Area in March 2006, we measured particulate polycyclic aromatic hydrocarbons (PAHs) and other gaseous species and particulate properties at six locations throughout the city. The measurements were intended to support the following objectives: to describe spatial and temporal patterns in PAH concentrations, to gain insight into sources and transformations of PAHs, and to quantify the relationships between PAHs and other pollutants. Total particulate PAHs at the Instituto Mexicano del Petróleo (T0 supersite) located near downtown averaged 50 ng m−3, and aerosol active surface area averaged 80 mm2 m−3. PAHs were also measured on board the Aerodyne Mobile Laboratory, which visited six sites encompassing a mixture of different land uses and a range of ages of air parcels transported from the city core. Weak intersite correlations suggest that local sources are important and variable and that exposure to PAHs cannot be represented by a single regional-scale value. The relationships between PAHs and other pollutants suggest that a variety of sources and ages of particles are present. Among carbon monoxide, nitrogen oxides (NOx), and carbon dioxide, particulate PAHs are most strongly correlated with NOx. Mexico City's PAH-to-black carbon mass ratio of 0.01 is similar to that found on a freeway loop in the Los Angeles area and approximately 8–30 times higher than that found in other cities. Ratios also indicate that primary combustion particles are rapidly coated by secondary aerosol in Mexico City. If so, the lifetime of PAHs may be prolonged if the coating protects them against photodegradation or heterogeneous reactions.
Long-term observation of mass-independent oxygen isotope anomaly in stratospheric CO2
Authors: Kawagucci S. , Tsunogai U. , Kudo S. , Nakagawa F. , Honda H. , Aoki S. , Nakazawa T. , Tsutsumi M. , Gamo T.
Published: April 2010

Abstract. Anomalous oxygen isotopic compositions of stratospheric CO2 were first reported in 1989, although their detailed behavior in the middle atmosphere is still open question. We collected 60 stratospheric air samples over Sanriku, Japan from 1991 to 2004 and Kiruna, Sweden in 1997. Using these accumulated air samples, we performed long-term observations of triple oxygen isotope compositions of stratospheric CO2. It is the first simultaneous observation in the stratosphere of both relations between Δ17OCO2 and [N2O], and δ18OCO2 and δ17OCO2, accurately. Observations confirmed simultaneous linear correlations between δ18OCO2, Δ17OCO2, and [N2O] within [N2O]>50 ppbv: the correlations faded away along with decreasing [N2O] from 50 ppbv. For dividing observation results by [N2O]=50 ppbv, the divided datasets show that 1) both Δ17OCO2 and δ18OCO2 are conservative parameters within the N2O-rich division, 2) the slope of least squares regression on δ18O–δ17O plot for the N2O-rich division is significantly steeper than that of the N2O-depleted one, and 3) the N2O-depleted division shows a discrepancy with recent model calculations, suggesting unconsidered isotope fractionation processes on complicated oxygen interactions in the CO2-O3-O2 system in the upper stratosphere and mesosphere.
Numerical modeling of Asian dust emission and transport with adjoint inversion using LIDAR network observations
Authors: Yumimoto K. , Uno I. , Sugimoto N. , Shimizu A. , Liu Z. , Winker D. M.
Published: April 2010

Abstract. A four-dimensional variational (4D-Var) data assimilation system for a regional dust model (RAMS/CFORS-4DVAR; RC4) is applied to a heavy dust event which occurred between 20 March and 4 April 2007 over eastern Asia. The vertical profiles of the dust extinction coefficients derived from NIES LIDAR observation network are directly assimilated. We conduct two experiments to evaluate impacts of selections of observation sites: Experiment A uses five Japanese observation sites located only downwind of dust source regions; the other Experiment B uses these sites together with two other sites near source regions (China and Korea). Validations using various observation data (e.g., PM10 concentration, MODIS AOT, OMI Aerosol Index, and the dust extinction coefficient derived by space-based LIDAR NASA/CALIPSO) are demonstrated. The modeled dust extinction coefficients are improved considerably through the assimilation. Assimilation results of Experiment A are consistent with those of Experiment B, indicating that observations of Experiment A can capture the dust event correctly and include sufficient information for dust emission inversion. Time series of dust AOT calculated by modeled and LIDAR dust extinction coefficients show good agreement. At Seoul, Matsue, and Toyama, assimilation reduces the root mean square errors of dust AOT by 31–32%. Vertical profiles of the dust layer observed by CALIPSO are also compared with assimilation results. The dense dust layer was trapped between θ=280–300 K and elevated higher toward the north; the model reproduces those characteristics well. The modeled dust AOT along the orbit paths agrees well with the CALIPSO dust AOT, OMI AI, and the coarse mode AOT retrieved from MODIS; especially the modeled dust AOT and the MODIS coarse mode AOT are consistent quantitatively. Assimilation results increase dust emissions over the Gobi Desert and Mongolia considerably; especially between 29 and 30 March, emission flux is increased by about 2–3 times. The heavy dust event is caused by the heavy dust uplift flux over the Gobi Desert and Mongolia during those days. We obtain the total optimized dust emissions of 57.9 Tg (Experiment A; 57.8% larger than before assimilation) and 56.3 Tg (Experiment B; 53.4% larger).
Transport and dispersion of atmospheric sulphur dioxide from an industrial coastal area during a sea-breeze event
Authors: Talbot C. , Leroy C. , Augustin P. , Willart V. , Delbarre H. , Fourmentin M. , Khomenko G.
Published: April 2010

Abstract. Experimental and modelling results of the dynamics of a sea-breeze event and its effects on the three-dimensional (3-D) redistribution of the gaseous SO2 are presented within the framework of a particularly flat and industrialized coastal area of the North Sea. The measurements were carried out at ground level with the stations of the local air quality monitoring agency and with two optical remote sensing instruments. The remote sensing setup consisted of a lidar and a sodar whose measurements allowed us to determine the layers of the lower troposphere during a sea-breeze event up to 1400 m height. The experimental results and measurements of industrial SO2 in the atmosphere are compared to the numerical simulations of the 3-D atmospheric non-hydrostatic chemistry model Meso-NH-C. The transport and the dispersion of gaseous SO2 are studied above the neighbouring industrial and urban areas. We show how the evolution and the redistribution of the SO2 concentrations at ground level are related to the structure and the dynamics of the sea breeze. The gaseous SO2 is brought back inland as soon as the sea breeze commences, mixed inner the thermal internal boundary layer and transported inland by the gravity current up to the sea-breeze front, where gases and particles are uplifted. The elevation of the polluted air masses by the sea-breeze system favours the nucleation of the emitted compounds due to the increase of the relative humidity in the uplifted layer. We show how the dynamical conditions during and after the sea breeze lead to storage of SO2 near and above the emitting industrial coastal areas, and favour the formation of acidic aerosol particles.
Accounting for the effect of horizontal gradients in limb measurements of scattered sunlight
Authors: Puķīte J. , Kühl S. , Deutschmann T. , Platt U. , Wagner T.
Published: April 2010

Abstract. Limb measurements provided by the SCanning Imaging Absorption spectrometer for Atmospheric CHartographY (SCIAMACHY) on the ENVISAT satellite allow retrieving stratospheric profiles of various trace gases on a global scale, among them BrO for the first time. For limb observations in the UV/VIS spectral region the instrument measures scattered light with a complex distribution of light paths: the light is measured at different elevation angles and can be scattered or absorbed in the atmosphere or reflected by the ground. By means of spectroscopy and radiative transfer modelling the measurements can be inverted to retrieve the vertical distribution of stratospheric trace gases. A full spherical 3-D Monte Carlo radiative transfer model "Tracy-II" is applied in this study. The Monte Carlo method benefits from conceptual simplicity and allows realizing the concept of full spherical geometry of the atmosphere and also its 3-D properties, which is important for a realistic description of the limb geometry. Furthermore it allows accounting for horizontal gradients in the distribution of trace gases. In this study the effect ofhorizontal inhomogeneous distributions of trace gases on the retrieval of profiles from limb measurements of scattered UV/VIS light is investigated. We introduce a method to correct for this effect by combining consecutive limb scanning sequences and utilizing the overlap in their measurement sensitivity regions. It is found that if horizontal inhomogenity is not properly accounted for, typical errors of 20% for NO2 and up to 50% for OClO around the altitude of the profile peak can arise for measurements close to the Arctic polar vortex boundary in boreal winter.
Tropical thin cirrus and relative humidity observed by the Atmospheric Infrared Sounder
Authors: Kahn B. H. , Liang C. K. , Eldering A. , Gettelman A. , Yue Q. , Liou K. N.
Published: April 2010

Abstract. Global observations of cloud and humidity distributions in the upper troposphere within all geophysical conditions are critically important in order to monitor the present climate and to provide necessary data for validation of climate models to project future climate change. Towards this end, tropical oceanic distributions of thin cirrus optical depth (τ), effective diameter (De), and relative humidity with respect to ice (RHi) within cirrus (RHic) are simultaneously derived from the Atmospheric Infrared Sounder (AIRS). Corresponding increases in De and cloud temperature are shown for cirrus with τ>0.25 that demonstrate quantitative consistency to other surface-based, in situ and satellite retrievals of cirrus. However, inferred cirrus properties are shown to be less certain for increasingly tenuous cirrus. In-cloud supersaturation is observed for 8–12% of thin cirrus and is several factors higher than all-sky conditions; even higher frequencies are shown for the coldest and thinnest cirrus. Spatial and temporal variations in RHic correspond to cloud frequency while regional variability in RHic is observed to be most prominent over the N. Indian Ocean basin. The largest cloud/clear sky RHi anomalies tend to occur in dry regions associated with vertical descent in the sub-tropics, while the smallest occur in moist ascending regions in the tropics. The characteristics of RHic frequency distributions depend on τ and a peak frequency is located between 60–80% that illustrates RHic is on average biased dry. The geometrical thickness of cirrus is typically less than the vertical resolution of AIRS temperature and specific humidity profiles and thus leads to the observed dry bias, shown with coincident cloud vertical structure obtained from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). The joint distributions of thin cirrus microphysics and humidity derived from AIRS provide unique and important regional and global-scale insights on upper tropospheric processes not available from surface, in situ, and other contemporary satellite observing platforms.
Technical Note: Intercomparison of ILAS-II version 2 and 1.4 trace species with MIPAS-B measurements
Authors: Wetzel G. , Sugita T. , Nakajima H. , Tanaka T. , Yokota T. , Friedl-Vallon F. , Kleinert A. , Maucher G. , Oelhaf H.
Published: April 2010

Abstract. The Improved Limb Atmospheric Spectrometer (ILAS)-II sensor aboard the Japanese ADEOS-II satellite was launched into its sun-synchronous orbit on 14 December 2002 and performed solar occultation measurements of trace species, aerosols, temperature, and pressure in the polar stratosphere until 25 October 2003. Vertical trace gas profiles obtained with the balloon version of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS-B) provide one of the sparse data sets for validating ILAS-II version 2 and 1.4 data. The MIPAS-B limb emission spectra were collected on 20 March 2003 over Kiruna (Sweden, 68° N) at virtually the same location that has been sounded by ILAS-II about 5.5 h prior to the sampling of MIPAS-B. The intercomparison of the new ILAS-II version 2 (Northern Hemispheric sunrise) data to MIPAS-B vertical trace gas profiles shows a good to excellent agreement within the combined error limits for the species O3, N2O, CH4, H2O (above 21 km), HNO3, ClONO2, and CFC-11 (CCl3F) in the compared altitude range between 16 and 31 km such that these data appear to be very useful for scientific analysis. With regard to the previous version 1.4 ILAS-II data, significant improvements in the consistency with MIPAS-B are obvious especially for the species CH4 and H2O, but also for O3, HNO3, ClONO2, NO2, and N2O5. However, comparing gases like NO2, N2O5, and CFC-12 (CCl2F2) exhibits only poor agreement with MIPAS-B such that these species cannot be assumed to be validated at the present time.
Technical Note: Coupling of chemical processes with the Modular Earth Submodel System (MESSy) submodel TRACER
Authors: Jöckel P. , Kerkweg A. , Buchholz J. , Tost H. , Sander R. , Pozzer A.
Published: April 2010

Abstract. The implementation of processes related to chemistry into Earth System Models and their coupling within such systems requires the consistent description of the chemical species involved. We provide a tool (written in Fortran95) to structure and manage information about constituents, herein after referred to as tracers, namely the Modular Earth Submodel System (MESSy) generic (i.e., infrastructure) submodel TRACER. With TRACER it is possible to define a multitude of tracer sets, depending on the spatio-temporal representation (i.e., the grid structure) of the model. The required information about a specific chemical species is split into the static meta-information about the characteristics of the species, and its (generally in time and space variable) abundance in the corresponding representation. TRACER moreover includes two submodels. One is TRACER_FAMILY, an implementation of the tracer family concept. It distinguishes between two types: type-1 families are usually applied to handle strongly related tracers (e.g., fast equilibrating species) for a specific process (e.g., advection). In contrast to this, type-2 families are applied for tagging techniques, in which specific species are artificially decomposed and associated with additional information, in order to conserve the linear relationship between the family and its members. The second submodel is TRACER_PDEF, which corrects and budgets numerical negative overshoots that arise in many process implementations due to the numerical limitations (limited precision, rounding errors). The submodel therefore guarantees the positive definiteness of the tracers and stabilises the integration scheme. As a by-product, it further provides a global tracer mass diagnostic. Last but not least, we present the submodel PTRAC for the definition of prognostic tracers via a Fortran95 namelist. TRACER with its submodels and PTRAC can readily be applied to a variety of models without further requirements. The code and a documentation is included in the electronic supplement.
Emission rate and chemical state estimation by 4-dimensional variational inversion
Authors: Elbern H. , Strunk A. , Schmidt H. , Talagrand O.
Published: April 2010

Abstract. This study aims to assess the potential and limits of an advanced inversion method to estimate pollutant precursor sources mainly from observations. Ozone, sulphur dioxide, and partly nitrogen oxides observations are taken to infer source strength estimates. As methodology, the four–dimensional variational data assimilation technique has been generalised and employed to include emission rate optimisation, in addition to chemical state estimates as usual objective of data assimilation. To this end, the optimisation space of the variational assimilation system has been complemented by emission rate correction factors of 19 emitted species at each emitting grid point, involving the University of Cologne mesoscale EURAD model. For validation, predictive skills were assessed for an August 1997 ozone episode, comparing forecast performances of pure initial value optimisation, pure emission rate optimisation, and joint emission rate/initial value optimisation. Validation procedures rest on both measurements withheld from data assimilation and prediction skill evaluation of forecasts after the inversion procedures. Results show that excellent improvements can be claimed for sulphur dioxide forecasts, after emission rate optimisation. Significant improvements can be claimed for ozone forecasts after initial value and joint emission rate/initial value optimisation of precursor constituents. The additional benefits applying joint emission rate/initial value optimisation are moderate, and very useful in typical cases, where upwind emission rate optimisation is essential. In consequence of the coarse horizontal model grid resolution of 54 km, applied in this study, comparisons indicate that the inversion improvements can rest on assimilating ozone observations only, as the inclusion of NOx observations does not provide additional forecast skill. Emission estimates were found to be largely independent from initial guesses from emission inventories, demonstrating the potential of the 4D-var method to infer emission rate improvements. The study also points to the need for improved horizontal model resolution to more efficient use of NOx observations.
Rapid convective outflow from the U.S. to the upper troposphere over the North Atlantic during the NASA INTEX-NA airborne campaign: flight 13 case study
Authors: Kim S. Y. , Talbot R. , Mao H. , Blake D. , Vay S. , Fuelberg H.
Published: April 2010

Abstract. A case study of convective outflow from the United States (U.S.) was examined using airborne measurements from NASA DC-8 flight 13 during the Intercontinental Chemical Transport Experiment – North America (INTEX-NA). Mixing ratios of methane (CH4) and carbon monoxide (CO) at 8–11 km altitude over the North Atlantic were elevated to 1843 ppbv and 134 ppbv respectively, while those of carbon dioxide (CO2) and carbonyl sulfide (COS) were reduced to 372.4 ppmv and 411 pptv respectively. In this region, urban and industrial influence was evidenced by elevated mixing ratios and good linear relationships between urban and industrial tracers compared to North Atlantic background air. Moreover, low mixing ratios and a good correlation between COS and CO2 showed a fingerprint of terrestrial uptake and minimal dilution during rapid transport over a 1–2 day time period. Analysis of synoptic conditions, backward trajectories, and photochemical aging estimates based on C3H8/C2H6 strongly suggested that elevated anthropogenic tracers in the upper troposphere of the flight region were the result of fast transport via convective uplifting of boundary layer air over the southeastern U.S. This mechanism is supported by the similar slopes values of linear correlations between long-lived (months) anthropogenic tracers (e.g., C2Cl4 and CHCl3) from the flight region and the planetary boundary layer in the southeastern U.S. In addition, the aircraft measurements suggest that outflow from the U.S. augmented the entire tropospheric column at mid-latitudes over the North Atlantic. Overall, the flight 13 data demonstrate a pervasive impact of U.S. anthropogenic emissions on the troposphere over the North Atlantic.
Investigating the sources and atmospheric processing of fine particles from Asia and the Northwestern United States measured during INTEX B
Authors: Peltier R. E. , Hecobian A. H. , Weber R. J. , Stohl A. , Atlas E. L. , Riemer D. D. , Blake D. R. , Apel E. , Campos T. , Karl T.
Published: April 2010

Abstract. During the National Aeronautics and Space Administration (NASA) Intercontinental Chemical Transport Experiment, Phase B (INTEX-B), in the spring of 2006, airborne measurements were made in the United States Pacific Northwest of the major inorganic ions and the water-soluble organic carbon (WSOC) of submicron (PM1.0) aerosol. An atmospheric trajectory (Hysplit) and a Lagrangian particle dispersion model (Flexpart) quantifying source contributions for carbon monoxide (CO) was used to segregate air masses into those of primarily Asian influence (>75% Asian CO) or North American influence (>75% North American CO). Of the measured compounds, fine particle mass mostly consisted of water-soluble organic carbon and sulfate, with highest median WSOC and sulfate concentrations in North American air masses. The fraction of WSOC to sulfate was significantly lower than one at altitudes above 3 km, opposite to what has been observed closer to Asia and in the northeastern United States, where organic components were at higher concentrations than sulfate in the free troposphere. The observations could be explained by loss of sulfate and organic aerosol due to precipitation scavenging, with reformation of mainly sulfate during advection from Asia to North America. WSOC sources were investigated by multivariate linear regression analyses of WSOC and volatile organic compounds (VOCs). In Asian air masses, of the WSOC variability that could be explained (49%), most were related to fossil fuel combustion VOCs, compared to North American air masses, where 75% of the WSOC variability was explained through a nearly equal combination of fossil fuel combustion and biogenic VOCs. Distinct WSOC plumes encountered during the experiment were also studied. A plume observed near the California Central Valley at 0.6 km altitude was related to both fossil fuel combustion and biogenic VOCs. Another Central Valley plume observed over Nevada at 3 to 5 km, in a region of cloud detrainment, was mostly related to biogenic VOCs.
Retrieval of global water vapour columns from GOME-2 and first applications in polar regions
Authors: Noël S. , Mieruch S. , Bovensmann H. , Burrows J. P.
Published: April 2010

Abstract. Global total water vapour columns have been derived from measurements of the Global Ozone Monitoring Experiment 2 (GOME-2) on MetOp. For this purpose, the Air Mass Corrected Differential Optical Absorption Spectroscopy (AMC-DOAS) method has been adapted, which has already been applied successfully to GOME (on ERS-2) and SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY, on ENVISAT) data. Comparisons between the derived GOME-2 and SCIAMACHY water vapour columns show a good overall agreement. This gives confidence that the time series of water vapour columns from GOME-type instruments which started in 1995 can be continued by the MetOp instrumentation until at least 2020. The enhanced temporal and spatial resolution of GOME-2 enables the analysis of short-term variations particularly in the polar regions. This is especially important since atmospheric data sources in the polar regions are generally sparse. As an exemplary application, daily water vapour concentrations over the polar research station Ny Ålesund (78°55'19" N/11°56'33" E) are investigated. At this latitude GOME-2 gives about six data points during daylight hours at varying local times. The results of this study show that it is possible to derive information about the diurnal variability of water vapour in polar regions from GOME-2 measurements.
Aqueous-phase ozonolysis of methacrolein and methyl vinyl ketone: a potentially important source of atmospheric aqueous oxidants
Authors: Chen Z. M. , Wang H. L. , Zhu L. H. , Wang C. X. , Jie C. Y. , Hua W.
Published: April 2010

Abstract. Recent studies indicate that isoprene could contribute a considerable amount of aerosol through aqueous-phase acid-catalyzed oxidation with hydrogen peroxide (H2O2), although the source of H2O2 is unclear. The present study revealed a potentially important route to the formation of aqueous oxidants, including H2O2, from the aqueous-phase ozonolysis of methacrolein (MAC) and methyl vinyl ketone (MVK). Laboratory simulation was used to perform the atmospheric aqueous-phase ozonolysis at different pHs and temperatures. Unexpectedly high molar yields of the products, including hydroxylmethyl hydroperoxide (HMHP), formaldehyde (HCHO) and methylglyoxyl (MG), of both of these reaction systems have been seen. Moreover, these yields are almost independent of pH and temperature and are as follows: (i) for MAC–O3, 70.3±6.3% HMHP, 32.3±5.8% HCHO and 98.6±5.4% MG; and (ii) for MVK–O3, 68.9±9.7% HMHP, 13.3±5.8% HCHO and 75.4±7.9% MG. A yield of 24.2±3.6% pyruvic acid has been detected for MVK–O3. HMHP is unstable in the aqueous phase and can transform into H2O2 and HCHO with a yield of 100%. We suggest that the aqueous-phase ozonolysis of MAC and MVK can contribute a considerable amount of oxidants in a direct and indirect mode to the aqueous phase and that these compounds might be the main source of aqueous-phase oxidants. The formation of oxidants in the aqueous-phase ozonolysis of MAC and MVK effectively confirms the formation of aerosols from the aqueous-phase acid-catalyzed reaction of H2O2 with isoprene, even if there are no other sources of oxidants.
SALSA – a Sectional Aerosol module for Large Scale Applications
Authors: Kokkola H. , Korhonen H. , Lehtinen K. E. J. , Makkonen R. , Asmi A. , Järvenoja S. , Anttila T. , Partanen A.-I. , Kulmala M. , Järvinen H. , Laaksonen A. , Kerminen V.-M.
Published: April 2010

Abstract. The sectional aerosol module SALSA is introduced. The model has been designed to be implemented in large scale climate models, which require both accuracy and computational efficiency. We have used multiple methods to reduce the computational burden of different aerosol processes to optimize the model performance without losing physical features relevant to problematics of climate importance. The optimizations include limiting the chemical compounds and physical processes available in different size sections of aerosol particles; division of the size distribution into size sections using size sections of variable width depending on the sensitivity of microphysical processing to the particles sizes; the total amount of size sections to describe the size distribution is kept to the minimum; furthermore, only the relevant microphysical processes affecting each size section are calculated. The ability of the module to describe different microphysical processes was evaluated against explicit microphysical models and several microphysical models used in air quality models. The results from the current module show good consistency when compared to more explicit models. Also, the module was used to simulate a new particle formation event typical in highly polluted conditions with comparable results to a more explicit model setup.
Representativeness and climatology of carbon monoxide and ozone at the global GAW station Mt. Kenya in equatorial Africa
Authors: Henne S. , Klausen J. , Junkermann W. , Kariuki J. M. , Aseyo J. O. , Buchmann B.
Published: April 2010

Abstract. The tropics strongly influence the global atmospheric chemistry budget. However, continuous in-situ observations of trace gases are rare especially in equatorial Africa. The WMO Global Atmosphere Watch programme aimed to close this gap with the installation of the Mt. Kenya baseline station. Here, the first continuous measurements of carbon monoxide (CO) and ozone O3 at this site are presented. The representativeness of the site was investigated by means of statistical data analysis, air mass trajectory clustering, interpretation of biomass burning variability and evaluation of O3-CO relationships. Despite its location in equatorial Africa the site was rarely directly influenced by biomass burning emissions, making it suitable for background observations. Located at 3678 m above sea level the night-time (21:00–04:00 UTC) measurements were in general representative of the free troposphere, while day-time measurements were influenced by atmospheric boundary layer air. Six representative flow regimes towards Mt. Kenya were determined: eastern Africa (21% of the time), Arabian Peninsula and Pakistan (16%), northern Africa free tropospheric (6%), northern Indian Ocean and India (17%), south-eastern Africa (18%) and southern India Ocean (21%). The seasonal alternation of these flow regimes was determined by the monsoon circulation and caused a distinct semi-annual cycle of CO with maxima during February and August and with minima in April and less pronounced in November. O3 showed a weaker annual cycle with a minimum in November and a broad summer maximum. Inter-annual variations were explained with variations in southern African biomass burning and in transport patterns. The measurements at MKN were representative of air masses with little photochemical activity as indicated by weak O3-CO correlations, underlining the baseline character of the site. Future extensions of the measurement programme will provide better understanding of the atmospheric chemistry of this globally important region.
Total Observed Organic Carbon (TOOC): A synthesis of North American observations
Authors: Heald C. L. , Goldstein A. H. , Allan J. D. , Aiken A. C. , Apel E. , Atlas E. L. , Baker A. K. , Bates T. S. , Beyersdorf A. J. , Blake D. R. , Campos T. , Coe H. , Crounse J. D. , DeCarlo P. F. , de Gouw J. A. , Dunlea E. J. , Flocke F. M. , Fried A. , Goldan P. , Griffin R. J. , Herndon S. C. , Holloway J. S. , Holzinger R. , Jimenez J. L. , Junkermann W. , Kuster W. C. , Lewis A. C. , Meinardi S. , Millet D. B. , Onasch T. , Polidori A. , Quinn P. K. , Riemer D. D. , Roberts J. M. , Salcedo D. , Sive B. , Swanson A. L. , Talbot R. , Warneke C. , Weber R. J. , Weibring P. , Wennberg P. O. , Wittig A. E. , Zhang R. , Zheng J. , Zheng W.
Published: April 2010

Abstract. Measurements of organic carbon compounds in both the gas and particle phases measured upwind, over and downwind of North America are synthesized to examine the total observed organic carbon (TOOC) over this region. These include measurements made aboard the NOAA WP-3 and BAe-146 aircraft, the NOAA research vessel Ronald H. Brown, and at the Thompson Farm and Chebogue Point surface sites during the summer 2004 ICARTT campaign. Both winter and summer 2002 measurements during the Pittsburgh Air Quality Study are also included. Lastly, the spring 2002 observations at Trinidad Head, CA, surface measurements made in March 2006 in Mexico City and coincidentally aboard the C-130 aircraft during the MILAGRO campaign and later during the IMPEX campaign off the northwestern United States are incorporated. Concentrations of TOOC in these datasets span more than two orders of magnitude. The daytime mean TOOC ranges from 4.0 to 456 μgC m−3 from the cleanest site (Trinidad Head) to the most polluted (Mexico City). Organic aerosol makes up 3–17% of this mean TOOC, with highest fractions reported over the northeastern United States, where organic aerosol can comprise up to 50% of TOOC. Carbon monoxide concentrations explain 46 to 86% of the variability in TOOC, with highest TOOC/CO slopes in regions with fresh anthropogenic influence, where we also expect the highest degree of mass closure for TOOC. Correlation with isoprene, formaldehyde, methyl vinyl ketene and methacrolein also indicates that biogenic activity contributes substantially to the variability of TOOC, yet these tracers of biogenic oxidation sources do not explain the variability in organic aerosol observed over North America. We highlight the critical need to develop measurement techniques to routinely detect total gas phase VOCs, and to deploy comprehensive suites of TOOC instruments in diverse environments to quantify the ambient evolution of organic carbon from source to sink.
Particle mass yield in secondary organic aerosol formed by the dark ozonolysis of α-pinene
Authors: Shilling J. E. , Chen Q. , King S. M. , Rosenoern T. , Kroll J. H. , Worsnop D. R. , McKinney K. A. , Martin S. T.
Published: April 2010

Abstract. The yield of particle mass in secondary organic aerosol (SOA) formed by dark ozonolysis was measured for 0.3–22.8 ppbv of reacted α-pinene. Most experiments were conducted using a continuous-flow chamber, allowing nearly constant SOA concentration and chemical composition for several days. For comparison, some experiments were also conducted in batch mode. Reaction conditions were 25°C, 40% RH, dry (NH)4SO4 seed particles, and excess 1-butanol. The organic particle loading was independently measured by an aerosol mass spectrometer and a scanning mobility particle sizer, and the two measurements agreed well. The observations showed that SOA formation occurred for even the lowest reacted α-pinene concentration of 0.3 ppbv. The particle mass yield was 0.09 at 0.15 μg m−3, increasing to 0.27 at 40 μg m−3. Compared to results reported in the literature, the yields were 80 to 100% larger for loadings above 2 μg m−3. At lower loadings, the yields had an offset of approximately +0.07 from those reported in the literature. To as low as 0.15 μg m−3, the yield curve had no inflection point toward null yield, implying the formation of one or several products having vapor pressures below this value. These observations of increased yields, especially for low loadings, are potentially important for accurate prediction by chemical transport models of organic particle concentrations in the ambient atmosphere.
Technical Note: Analytical formulae for the critical supersaturations and droplet diameters of CCN containing insoluble material
Authors: Kokkola H. , Vesterinen M. , Anttila T. , Laaksonen A. , Lehtinen K. E. J.
Published: April 2010

Abstract. In this paper, we consider the cloud drop activation of aerosol particles consisting of water soluble material and an insoluble core. Based on the Köhler theory, we derive analytical equations for the critical diameters and supersaturations of such particles. We demonstrate the use of the equations by comparing the critical supersaturations of particles composed of ammonium sulfate and insoluble substances with those of model organic particles with varying molecular sizes.
Morphology of the tropopause layer and lower stratosphere above a tropical cyclone: A case study on cyclone Davina (1999)
Authors: Cairo F. , Buontempo C. , MacKenzie A. R. , Schiller C. , Volk C. M. , Adriani A. , Mitev V. , Matthey R. , Di Donfrancesco G. , Oulanovsky A. , Ravegnani F. , Yushkov V. , Snels M. , Cagnazzo C. , Stefanutti L.
Published: April 2010

Abstract. During the APE-THESEO mission in the Indian Ocean the Myasishchev Design Bureau stratospheric research aircraft M55 Geophysica performed a flight over and within the inner core region of tropical cyclone Davina. Measurements of total water, water vapour, temperature, aerosol backscattering, ozone and tracers were made and are discussed here in comparison with the averages of those quantities acquired during the campaign time frame. Temperature anomalies in the tropical tropopause layer (TTL), warmer than average in the lower part and colder than average in the upper TTL were observed. Ozone was strongly reduced compared to its average value, and thick cirrus decks were present up to the cold point, sometimes topped by a layer of very dry air. Evidence for meridional transport of trace gases in the stratosphere above the cyclone and the perturbed water distribution in the TTL is illustrated and discussed.
Comparison of the inversion algorithms applied to the ozone vertical profile retrieval from SCIAMACHY limb measurements
Authors: Rozanov A. , Eichmann K.-U. , von Savigny C. , Bovensmann H. , Burrows J. P. , von Bargen A. , Doicu A. , Hilgers S. , Godin-Beekmann S. , Leblanc T. , McDermid I. S.
Published: April 2010

Abstract. This paper is devoted to an intercomparison of ozone vertical profiles retrieved from the measurements of scattered solar radiation performed by the SCIAMACHY instrument in the limb viewing geometry. Three different inversion algorithms including the prototype of the operational Level 1 to 2 processor to be operated by the European Space Agency are considered. The intercomparison was performed for 5 selected orbits of SCIAMACHY showing a good overall agreement of the results in the middle stratosphere, whereas considerable discrepancies were identified in the lower stratosphere and upper troposphere altitude region. Additionally, comparisons with ground-based lidar measurements are shown for selected profiles demonstrating an overall correctness of the retrievals.
Middle atmosphere water vapour and dynamical features in aircraft measurements and ECMWF analyses
Authors: Feist D. G. , Geer A. J. , Müller S. , Kämpfer N.
Published: April 2010

Abstract. The European Centre for Medium-Range Weather Forecasts (ECMWF) provides global analyses of atmospheric humidity from the ground to the lower mesosphere. Unlike in the troposphere, in the stratopshere no humidity observations are assimilated. Humidity analyses here are essentially the results of a free-running model constrained by the ECMWF's well-analysed wind fields. So far only the broad-scale features of the resulting stratospheric water vapour distribution have been validated. This study provides the first in-depth comparison of stratospheric humidity from ECMWF with observations from an airborne microwave radiometer that has measured the distribution of stratospheric water vapour over an altitude range of roughly 15–60 km on several flight campaigns since 1998. The aircraft measurements provide a horizontal resolution that cannot be achieved by current satellite instruments. This study examines dynamical features in the moisture fields such as filamentation and the vortex edge, finding that features in the ERA-40 humidity analyses often do correspond to real atmospheric events that are seen in the aircraft measurements. However, the comparisons also show that in general the ECMWF model produces an unrealistically moist mesosphere. As a result it cannot replicate the descent of relatively dry mesospheric air into the polar vortex in winter and spring.