bluuebunny/crossref_metadata_2025 huggingface dataset:
Aerosol-cloud interactions in the NASA GMI: model development and indirect forcing assessments
Authors: Meskhidze N. , Sotiropoulou R. E. P. , Nenes A. , Kouatchou J. , Das B. , Rodriguez J. M.
Published: April 2010

Abstract. This study uses the NASA Global Modeling Initiative (GMI) 3-D chemical transport model (CTM) for assessments of indirect forcing and its sensitivity to the treatment of aerosol, aerosol-cloud interactions and meteorological fields. Three different meteorological datasets from NASA Data Assimilation Office (DAO), NASA finite volume GCM (FVGCM) and the Goddard Institute for Space Studies version II' (GISS II') GCM were used. GMI is ideal for this study as different model components (such as meteorological fields and chemical mechanisms) can easily be interchanged under the same model framework to capture the first aerosol indirect effect (AIE), and its sensitivity to parameterizations and meteorological fields. Cloud droplet number concentration was calculated by implementing both diagnostic and physically based droplet parameterizations. Derived cloud properties, such as cloud optical thickness and effective radius were compared with the remotely sensed data from Moderate Resolution Imaging Spectroradiometer (MODIS). GMI was able to capture the spatial variability and the land-ocean contrast observed in the satellite record. Depending on the meteorological field and droplet parameterization used, the annual mean first AIE ranged from −0.99 to −1.48 W m−2. It is found that, roughly 80% of the variation is attributed to changes in the meteorology (primarily from variations in liquid water path), while the remaining 20% is attributed to different cloud droplet parameterizations.
Oceanic phytoplankton, atmospheric aerosol and Raman scattering impacts on space-based ultraviolet radiance measurements
Authors: Hu R.-M. , Sokhi R. S.
Published: April 2010

Abstract. Oceanic phytoplankton can affect in-water and atmospheric radiation fields. In this study, we develop case 1 (without noncovarying particles) and case 2 (including noncovarying particles) waters model including Raman scattering in order to examine the chlorophyll impacts on the Total Ozone Mapping Spectrometer (TOMS) Aerosol Index and aerosol single scattering albedo. The waters model is coupled with a radiation transfer model (VLIDORT) for calculating TOMS Aerosol Index and retrieval of aerosol single scattering albedo. The retrieval is constrained by chlorophyll concentration from Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and Moderate Resolution Imaging SpectroRadiometer (MODIS) data, aerosol optical depth from MODIS, and aerosol vertical profiles from a global chemical transport model (GEOS-CHEM). We find the retrieved aerosol single scattering albedo is strongly influenced by chlorophyll concentration, particularly in the regions of subtropical Atlantic Ocean and Indian Ocean. The maximum deviation between the aerosol single scattering albedo retrieved with and withouout considering chlorophyll can reach 10 percent. Thus, it is important to take account of the phytoplankton impacts on atmospheric remote sensing measurements.
Tropospheric aerosol microphysics simulation with assimilated meteorology: model description and intermodel comparison
Authors: Trivitayanurak W. , Adams P. J. , Spracklen D. V. , Carslaw K. S.
Published: April 2010

Abstract. We implement the TwO-Moment Aerosol Sectional (TOMAS) microphysics module into GEOS-CHEM, a CTM driven by assimilated meteorology. TOMAS has 30 size sections covering 0.01–10 μm diameter with conservation equations for both aerosol mass and number. The implementation enables GEOS-CHEM to simulate aerosol microphysics, size distributions, mass and number concentrations. The model system is developed for sulfate and sea-salt aerosols, a year-long simulation has been performed, and results are compared to observations. Additionally model intercomparison was carried out involving global models with sectional microphysics: GISS GCM-II' and GLOMAP. Comparison with marine boundary layer observations of CN and CCN(0.2%) shows that all models perform well with average errors of 30–50%. However, all models underpredict CN by up to 42% between 15° S and 45° S while overpredicting CN up to 52% between 45° N and 60° N, which could be due to the sea-salt emission parameterization and the assumed size distribution of primary sulfate emission, in each case respectively. Model intercomparison at the surface shows that GISS GCM-II' and GLOMAP, each compared against GEOS-CHEM, both predict 40% higher CN and predict 20% and 30% higher CCN(0.2%) on average, respectively. Major discrepancies are due to different emission inventories and transport. Budget comparison shows GEOS-CHEM predicts the lowest global CCN(0.2%) due to microphysical growth being a factor of 2 lower than other models because of lower SO2 availability. These findings stress the need for accurate meteorological inputs and updated emission inventories when evaluating global aerosol microphysics models.
Observationally derived transport diagnostics for the lowermost stratosphere and their application to the GMI chemistry and transport model
Authors: Strahan S. E. , Duncan B. N. , Hoor P.
Published: April 2010

Abstract. Transport from the surface to the lowermost stratosphere can occur on timescales of a few months or less, making it possible for short-lived tropospheric pollutants to influence stratospheric composition and chemistry. Models used to study this influence must demonstrate the credibility of their chemistry and transport in the upper troposphere and lower stratosphere (UT/LS). Data sets from satellite and aircraft instruments measuring CO, O3, N2O, and CO2 in the UT/LS are used to create a suite of diagnostics of the seasonally-varying transport into and within the lowermost stratosphere, and of the coupling between the troposphere and stratosphere in the extratropics. The diagnostics are used to evaluate a version of the Global Modeling Initiative (GMI) Chemistry and Transport Model that uses a combined tropospheric and stratospheric chemical mechanism and meteorological fields from the GEOS-4 general circulation model. The diagnostics derived from N2O and O3 show that the model lowermost stratosphere (LMS) has realistic input from the overlying high latitude stratosphere in all seasons. Diagnostics for the LMS show two distinct layers. The upper layer (~350 K–380 K) has a strong annual cycle in its composition, while the lower layer, just above the tropopause, shows no seasonal variation in the degree of tropospheric coupling or composition. The GMI CTM agrees closely with the observations in both layers and is realistically coupled to the UT in all seasons. This study demonstrates the credibility of the GMI CTM for the study of the impact of tropospheric emissions on the stratosphere.
Global modeling of secondary organic aerosol formation from aromatic hydrocarbons: high- vs low-yield pathways
Authors: Henze D. K. , Seinfeld J. H. , Ng N. L. , Kroll J. H. , Fu T. -M. , Jacob D. J. , Heald C. L.
Published: April 2010

Abstract. Formation of SOA from the aromatic species toluene, xylene, and, for the first time, benzene, is added to a global chemical transport model. A simple mechanism is presented that accounts for competition between low and high-yield pathways of SOA formation, wherein secondary gas-phase products react further with either nitrogen oxide (NO) or hydroperoxy radical (HO2) to yield semi- or non-volatile products, respectively. Aromatic species yield more SOA when they react with OH in regions where the [NO]/[HO2] ratios are lower. The SOA yield thus depends upon the distribution of aromatic emissions, with biomass burning emissions being in areas with lower [NO]/[HO2] ratios, and the reactivity of the aromatic with respect to OH, as a lower initial reactivity allows transport away from industrial source regions, where [NO]/[HO2] ratios are higher, to more remote regions, where this ratio is lower and, hence, the ultimate yield of SOA is higher. As a result, benzene is estimated to be the most important aromatic species with regards to formation of SOA, with a total production nearly equal that of toluene and xylene combined. In total, while only 39% percent of the aromatic species react via the low-NOx pathway, 72% of the aromatic SOA is formed via this mechanism. Predicted SOA concentrations from aromatics in the Eastern United States and Eastern Europe are actually largest during the summer, when the [NO]/[HO2] ratio is lower. Global production of SOA from aromatic sources is estimated at 3.5 Tg/yr, resulting in a global burden of 0.08 Tg, twice as large as previous estimates. The contribution of these largely anthropogenic sources to global SOA is still small relative to biogenic sources, which are estimated to comprise 90% of the global SOA burden, about half of which comes from isoprene. Compared to recent observations, it would appear there are additional pathways beyond those accounted for here for production of anthropogenic SOA. However, owing to differences in spatial distributions of sources and seasons of peak production, there are still regions in which aromatic SOA produced via the mechanisms identified here are predicted to contribute substantially to, and even dominate, the local SOA concentrations, such as outflow regions from North America and South East Asia during the wintertime, though total SOA concentrations there are small (~0.1 μg/m³).
The ozonolysis of primary aliphatic amines in single and multicomponent fine particles
Authors: Zahardis J. , Geddes S. , Petrucci G. A.
Published: April 2010

Abstract. The oxidative processing by ozone of the particulate amines octadecylamine (ODA) and hexadecylamine (HDA) is reported. Ozonolysis of these amines resulted in strong NO2− and NO3− ion signals that increased with ozone exposure as monitored by photoelectron resonance capture ionization aerosol mass spectrometry. These products suggest a mechanism of progressive oxidation of the particulate amines to nitro alkanes. Additionally, a strong ion signal at 125 m/z is assigned to the ion NO3−(HNO3). For ozonized mixed particles containing ODA or HDA + oleic acid (OL), with pO3≥3×10−7 atm, imine, secondary amide, and tertiary amide products were measured. These products most likely arise from reactions of amines with aldehydes (for imines) and stabilized Criegee intermediates (SCI) or secondary ozonides (for amides) from the fatty acid. The routes to amides via SCI and/or secondary ozonides was shown to be more important than comparable amide forming reactions between amines and organic acids, using azelaic acid as a test compound. Finally, direct evidence is provided for the formation of a surface barrier in the ODA + OL reaction system that resulted in the retention of OL at high ozone exposures (up to 10−3 atm for 17 s). This effect was not observed in HDA + OL or single component OL particles, suggesting that it may be a species-specific surfactant effect from an in situ generated amide or imine. Implications to tropospheric chemistry, including particle bound amines as sources of oxidized gas phase nitrogen species (e.g. NO2, NO3), formation of nitrogen enriched HULIS via ozonolysis of amines and source apportionment are discussed.
Global anthropogenic aerosol effects on convective clouds in ECHAM5-HAM
Authors: Lohmann U.
Published: April 2010

Abstract. Aerosols affect the climate system by changing cloud characteristics in many ways. They act as cloud condensation and ice nuclei and may have an influence on the hydrological cycle. Here we investigate aerosol effects on convective clouds by extending the double moment cloud microphysics scheme developed for stratiform clouds to convective clouds in the ECHAM5 general circulation model. This increases the liquid water path in the tropics and reduces the sensitivity of the liquid water path with increasing aerosol optical depth in better agreement with observations and large-eddy simulation studies. In simulations in which greenhouse gases and aerosols emissions are increased since pre-industrial times, accounting for microphysics in convective clouds matches most closely the observed increase in precipitation. The total anthropogenic aerosol effect since pre-industrial time is slightly reduced from −1.6 to −1.9 W m−2 when microphysics are only included in stratiform clouds to −1.5 W m−2 when microphysics are included both in stratiform and convective clouds.
Influence of Giant CCN on warm rain processes in the ECHAM5 GCM
Authors: Posselt R. , Lohmann U.
Published: April 2010

Abstract. Increased Cloud Condensation Nuclei (CCN) load due to anthropogenic activity might lead to non-precipitating clouds because the cloud drops become smaller (for a constant liquid water content) and, therefore, less efficient in rain formation (aerosol indirect effect). Adding giant CCN (GCCN) into such a cloud can initiate precipitation (namely, drizzle) and, therefore, might counteract the aerosol indirect effect. The effect of GCCN on global climate, especially on clouds and precipitation, within a General Circulation Model (GCM) is investigated. GCCN are aerosol particles larger than 5–10 μm in radius that can act as cloud condensation nuclei. One prominent GCCN species is sea salt. Sea salt concentrations depend mainly on wind speed but also on relative humidity, stability and precipitation history. Natural variability is much larger than the simulated one because sea salt emissions within ECHAM5 are a function of wind speed only. Giant sea salt concentrations in ECHAM5 are determined by using the tail of the coarse mode aerosol distribution with cutoff radii of 5 μm or 10 μm. It is assumed that activated GCCN particles directly form rain drops (of 25 μm size). Thereby, the added rain water mass and number stems from the redistribution of the condensed water into cloud and rain water according to the number of activated GCCN. As the formed precipitation is most likely drizzle with rather small drops a prognostic rain scheme is applied to account for the lower fall speeds and, therefore, slower sedimentation of the drizzle drops. The ECHAM5 simulations with incorporated GCCN show that precipitation is affected only locally. Cloud properties like liquid water and cloud drop number show a larger sensitivity to GCCN. On the one hand, the increased rain water mass causes an increase in the accretion rate and, therefore, in the rain production. On the other hand, very high GCCN concentrations can lead to an artificially exaggerated transfer of cloud water to the rain class which then results in a strong decrease of the conversion rate and the rain production. The introduction of the GCCN reduces the anthropogenic increase of liquid water in the atmosphere from pre-industrial to present day because clouds are precipitating faster in the presence of the GCCN. Hence, the accumulation of liquid water in the atmosphere is reduced. According to those changes in the cloud properties, the radiative budget is also changing. The GCCN cause a reduction of the anthropogenic aerosol indirect effect of about 0.1–0.25 W m−2 which corresponds to 5–10% of the total effect. Thus, the GCCN in ECHAM5 partly offset the anthropogenic aerosol indirect effect.
Lightning activity in Brazilian thunderstorms during TROCCINOX: implications for NOx production
Authors: Huntrieser H. , Schumann U. , Schlager H. , Höller H. , Giez A. , Betz H.-D. , Brunner D. , Forster C. ,   O. Pinto Jr., Calheiros R.
Published: April 2010

Abstract. During the TROCCINOX field experiment in January and February 2005, the contribution of lightning-induced nitrogen oxides (LNOx) from tropical and subtropical thunderstorms in Southern Brazil was investigated. Airborne trace gas measurements (NO, NOy, CO and O3) were performed up to 12.5 km with the German research aircraft Falcon. During anvil penetrations in selected tropical and subtropical thunderstorms of 4 and 18 February, NOx mixing ratios were on average enhanced by 0.7–1.2 and 0.2–0.8 nmol mol−1 totally, respectively. The relative contributions of boundary layer NOx (BL-NOx) and LNOx to anvil-NOx were derived from the NOx-CO correlations. On average ~80–90% of the anvil-NOx was attributed to LNOx. A Lightning Location Network (LINET) was set up to monitor the local distribution of cloud-to-ground (CG) and intra-cloud (IC) radiation sources (here called "strokes") and compared with lightning data from the operational Brazilian network RINDAT (Rede Integrada Nacional de Detecção de Descargas Atmosféricas). The horizontal LNOx mass flux out of the anvil was determined from the mean LNOx mixing ratio, the horizontal outflow velocity and the size of the vertical cross-section of the anvil, and related to the number of strokes contributing to LNOx. The values of these parameters were derived from the airborne measurements, from lightning and radar observations, and from a trajectory analysis. The amount of LNOx produced per LINET stroke depending on measured peak current was determined. The results were scaled up with the Lightning Imaging Sensor (LIS) flash rate (44 flashes s−1) to obtain an estimate of the global LNOx production rate. The final results gave ~1 and ~2–3 kg(N) per LIS flash based on measurements in three tropical and one subtropical Brazilian thunderstorms, respectively, suggesting that tropical flashes may be less productive than subtropical ones. The equivalent mean annual global LNOx nitrogen mass production rate was estimated to be 1.6 and 3.1 Tg a−1, respectively. By use of LINET observations in Germany in July 2005, a comparison with the lightning activity in mid-latitude thunderstorms was also performed. In general, the same frequency distribution of stroke peak currents as for tropical thunderstorms over Brazil was found. The different LNOx production rates per stroke in tropical thunderstorms compared with subtropical and mid-latitude thunderstorms seem to be related to the different stroke lengths (inferred from comparison with laboratory data and observed lengths). In comparison, the impact of other lightning parameters as stroke peak current and stroke release height was assessed to be minor. The results from TROCCINOX suggest that the different vertical wind shear may be responsible for the different stroke lengths.
The daytime mixing layer observed by radiosonde, profiler, and lidar during MILAGRO
Authors: Shaw W. J. , Pekour M. S. , Coulter R. L. , Martin T. J. , Walters J. T.
Published: April 2010

Abstract. During the MILAGRO campaign centered in the Mexico City area, Pacific Northwest National Laboratory (PNNL) and Argonne National Laboratory (ANL) operated atmospheric profiling systems at Veracruz and at two locations on the Central Mexican Plateau in the region around Mexico City. These systems included radiosondes, wind profilers, a sodar, and an aerosol backscatter lidar. An additional wind profiler was operated by the University of Alabama in Huntsville (UAH) at the Mexican Petroleum Institue (IMP) near the center of Mexico City. Because of the opportunity afforded by collocation of profilers, radiosondes, and a lidar, and because of the importance of boundary layer depth for aerosol properties, we have carried out a comparison of mixing layer depth as determined independently from these three types of measurement systems during the campaign. We have then used results of this comparison and additional measurements to develop a detailed description of the daily structure and evolution of the boundary layer on the Central Mexican Plateau during MILAGRO. Our analysis indicates that the profilers were more consistently successful in establishing the mixing layer depth during the daytime. The boundary layer growth was similar at the three locations, although the mixing layer tended to be slightly deeper in the afternoon in central Mexico City. The sodar showed that convection began about an hour after sunrise. Maximum daily mixing layer depths always reached 2000 m a.g.l. and frequently extended to 4000 m. The rate and variability of mixing layer growth was essentially the same as that observed during the IMADA-AVER campaign in the same season in 1997. This growth did not seem to be related to whether deep convection was reported on a given day. Wind speeds within the boundary layer exhibited a daily low-altitude maximum in the late afternoon with lighter winds aloft, consistent with previous reports of diurnal regional circulations. Norte events, which produced high winds at Veracruz, did not appreciably modulate the winds on the plateau. Finally, despite the typically dry conditions at the surface, radiosonde profiles showed that relative humidity often exceeded 50% in the early morning and in the upper part of the boundary layer. This suggests that aerosol particles would have experienced hygroscopic growth within the boundary layer on many days.
Nitrogen Oxide biogenic emissions from soils: impact on NOx and ozone formation in West Africa during AMMA (African Monsoon Multidisciplinary Analysis)
Authors: Delon C. , Reeves C. E. , Stewart D. J. , Serça D. , Dupont R. , Mari C. , Chaboureau J.-P. , Tulet P.
Published: April 2010

Abstract. Nitrogen Oxide biogenic emissions from soils are driven by soil and environmental parameters. The relationship between these parameters and NO fluxes is highly non linear. A new algorithm, based on a neural network calculation, is used to reproduce the NO biogenic emissions in West Africa during the AMMA campaign, in August 2006. It has been coupled in the surface scheme of a coupled chemistry dynamics model to estimate the impact of the NO emissions on NOx and O3 formation in the lower troposphere. Four different simulations on the same domain and at the same period are compared: CTRL run (without soil NO emissions), YL95 run (with NO emissions inventory, at low time and space resolution), SOILNOx run (with NO emissions from neural network) and ALLNOx run (with NO from neural network). The influence of NOx from lightning is assessed, and is limited to the upper troposphere. Compared to parameterisations generally used at the global and regional scales, the neural network parameterisation can give higher NOx (up to +380 ppt) and ozone (up to +7ppb), closer to the ones measured in aircrafts during the AMMA field campaign. The NO emission from soils calculated with neural network responds to changes in soil moisture giving enhanced emissions over the wetted soil, as observed by aircraft measurements after the passing of a convective system, well reproduced by the model. Consecutive enhancement of NOx and ozone is limited to the lowest layers of the atmosphere in modelling, whereas measurements show higher levels above 500 m. This equation allows an immediate response of fluxes to environmental parameters, on the contrary to fixed emission inventories. The annual cycle of emissions from this algorithm will be simulated in a future work
Characterizing mega-city pollution with TES O3 and CO measurements
Authors: Shim C. , Li Q. , Luo M. , Kulawik S. , Worden H. , Worden J. , Eldering A. , Diskin G. , Sachse G. , Weinheimer A. , Knapp D. , Montzca D. , Campos T.
Published: April 2010

Abstract. Concurrent tropospheric O3 and CO vertical profiles from the Tropospheric Emission Spectrometer (TES) during the MILAGRO/INTEX-B aircraft campaigns over the Mexico City Metropolitan Area (MCMA) allow us to characterize mega-city pollution. Outflow from the MCMA occurred predominantly at 600–800 hPa, evident in O3, CO, and NOx enhancements in the in situ observations. We examined O3, CO, and their correlation at 600–800 hPa from TES retrievals, aircraft measurements, and GEOS-Chem model results over the aircraft coverage (within a radius of ~700 km around MCMA). The enhancements in O3 and CO seen in the in situ measurements are not apparent in TES data, due to the lack of TES coverage during several strong pollution events. However, TES O3 and CO data are consistent with the aircraft observations on a daily mean basis (50–60 ppbv and 100–130 ppbv for O3 and CO respectively). The O3-CO correlation coefficients and enhancement ratios (ΔO3/ΔCO) derived from TES data are in good agreements with those derived from the aircraft observations and GEOS-Chem model results (r : 0.5–0.9; ΔO3/ΔCO: 0.3–0.4), reflecting significant springtime photochemical production over MCMA and the surrounding region.
Turbulence dissipation rate derivation for meandering occurrences in a stable planetary boundary layer
Authors: Degrazia G. A. , Goulart A. , Carvalho J. C. , Szinvelski C. R. P. , Buligon L. , Timm A. U.
Published: April 2010

Abstract. A new formulation for the turbulence dissipation rate ε occurring in meandering conditions has been presented. The derivation consists of a MacLaurin series expansion of a lateral dispersion parameter that represents cases in which turbulence and oscillatory movements associated to the meandering events coexist. The new formulation presents the identical physical premises contained in the classical and largely used one, but the new formulation derived from meandering situations is expressed in terms of the loop parameter m that controls the absolute value of the negative lobe in the meandering autocorrelation function. Therefore, the m magnitude regulates the turbulence dissipation rate. This dissipation rate decreases for cases in which turbulence and low frequency horizontal wind oscillations coexist and increases for a fully developed turbulence. Furthermore, a statistical comparison to observed concentration data shows that the alternative relation for the turbulent dissipation rate occurring in situations of meandering enhanced dispersion is suitable for applications in Lagrangian Stochastic dispersion models.
A model intercomparison analysing the link between ozone and geopotential height anomalies in January
Authors: Braesicke P. , Brühl C. , Dameris M. , Deckert R. , Eyring V. , Giorgetta M. A. , Mancini E. , Manzini E. , Pitari G. , Pyle J. A. , Steil B.
Published: April 2010

Abstract. A statistical framework to evaluate the performance of chemistry-climate models with respect to the interaction between meteorology and ozone during northern hemisphere mid-winter, in particularly January, is used. Different statistical diagnostics from four chemistry-climate models (E39C, ME4C, UMUCAM, ULAQ) are compared with the ERA-40 re-analysis. First, we analyse vertical coherence in geopotential height anomalies as described by linear correlations between two different pressure levels (30 and 200 hPa) of the atmosphere. In addition, linear correlations between (partial) column ozone and geopotential height anomalies at 200 hPa are discussed to motivate a simple picture of the meteorological impacts on ozone on interannual timescales. Secondly, we discuss characteristic spatial structures in geopotential height and (partial) column ozone anomalies as given by their first two empirical orthogonal functions. Finally, we describe the covariance patterns between reconstructed anomalies of geopotential height and (partial) column ozone. In general we find good agreement between the models with higher horizontal resolution (E39C, ME4C, UMUCAM) and ERA-40. Some diagnostics seem to be capable of picking up model similarities (either that the models use the same dynamical core (E39C, ME4C), or that they have a high upper boundary (ME4C, UMUCAM)). The methodology allows to identify the leading modes of variability contributing to the overall ozone-geopotential height correlations and points to interesting differences between the chemistry-climate models and ERA-40. Those discrepancies have to be taken into account when providing confidence intervals for climate change integrations.
Evaluation of model-simulated source contributions to tropospheric ozone with aircraft observations in the factor-projected space
Authors: Shim C. , Wang Y. , Yoshida Y.
Published: April 2010

Abstract. Trace gas measurements of TOPSE and TRACE-P experiments and corresponding global GEOS-CHEM model simulations are analyzed with the Positive Matrix Factorization (PMF) method for model evaluation purposes. Specially, we evaluate the model simulated contributions to O3 variability from stratospheric transport, intercontinental transport, and production from urban/industry and biomass burning/biogenic sources. We select a suite of relatively long-lived tracers, including 7 chemicals (O3, NOy, PAN, CO, C3H8, CH3Cl, and 7Be) and 1 dynamic tracer (potential temperature). The largest discrepancy is found in the stratospheric contribution to 7Be. The model underestimates this contribution by a factor of 2–3, corresponding well to a reduction of 7Be source by the same magnitude in the default setup of the standard GEOS-CHEM model. In contrast, we find that the simulated O3 contributions from stratospheric transport are in reasonable agreement with those derived from the measurements. However, the springtime increasing trend over North America derived from the measurements are largely underestimated in the model, indicating that the magnitude of simulated stratospheric O3 source is reasonable but the temporal distribution needs improvement. The simulated O3 contributions from long-range transport and production from urban/industry and biomass burning/biogenic emissions are also in reasonable agreement with those derived from the measurements, although significant discrepancies are found for some regions.
Physical and optical aerosol properties at the Dutch North Sea coast
Authors: Kusmierczyk-Michulec J. , de Leeuw G. , Moerman M. M.
Published: April 2010

Abstract. Sun photometer measurements at the AERONET station at the North Sea coast in The Hague (The Netherlands) provide a climatology of optical and physical aerosol properties for the area. Results are presented from the period January 2002 to July 2003. For the analysis and interpretation these data are coupled to chemical aerosol data from a nearby station of the Dutch National Air Quality Network. This network provides PM10 and black carbon concentrations. Meteorological conditions and air mass trajectories are also used. Due to the location close to the coast, the results are strongly dependent on wind direction, i.e.~air mass trajectory. In general the aerosol optical properties are governed by industrial aerosol emitted form various industrial, agricultural and urban areas surrounding the site in almost all directions over land. For maritime air masses industrial aerosols are transported from over the North Sea, whereas very clean air is transported from the NW in clean polar air masses from the North Atlantic. In the winter the effect of the production of sea salt aerosol at high wind speeds is visible in the optical and physical aerosol data. In these cases fine and coarse mode radii are similar to those reported in the literature for marine aerosol. Relations are derived between the Ångström coefficients with both the fine/coarse mode fraction and the ratio of black carbon and PM10.
New particle formation in the front range of the Colorado Rocky Mountains
Authors: Boy M. , Karl T. , Turnipseed A. , Mauldin R. L. , Kosciuch E. , Greenberg J. , Rathbone J. , Smith J. , Held A. , Barsanti K. , Wehner B. , Bauer S. , Wiedensohler A. , Bonn B. , Kulmala M. , Guenther A.
Published: April 2010

Abstract. New particle formation is of interest because of its influence on the properties of aerosol population, and due to the possible contribution of newly formed particles to cloud condensation nuclei. Currently no conclusive evidence exists as to the mechanism or mechanisms of nucleation and subsequent particle growth. However, nucleation rates exhibit a clear dependence on ambient sulphuric acid concentrations and particle growth is often attributed to the condensation of organic vapours. A detailed study of new particle formation in the Front Range of the Colorado Rocky Mountains is presented here. Gas and particle measurement data for 32 days was analyzed to identify event days, possible event days, and non-event days. A detailed analysis of nucleation and growth is provided for four days on which new particle formation was clearly observed. Evidence for the role of sesquiterpenes in new particle formation is presented.
Technical Note: Intercomparison of formaldehyde measurements at the atmosphere simulation chamber SAPHIR
Authors: Wisthaler A. , Apel E.C. , Bossmeyer J. , Hansel A. , Junkermann W. , Koppmann R. , Meier R. , Müller K. , Solomon S. J. , Steinbrecher R. , Tillmann R. , Brauers T.
Published: April 2010

Abstract. The atmosphere simulation chamber SAPHIR at the Research Centre Jülich was used to test the suitability of state-of-the-art analytical instruments for the measurement of gas-phase formaldehyde (HCHO) in air. Five analyzers based on four different sensing principles were deployed: a differential optical absorption spectrometer (DOAS), cartridges for 2,4-dinitro-phenyl-hydrazine (DNPH) derivatization followed by off-line high pressure liquid chromatography (HPLC) analysis, two different types of commercially available wet chemical sensors based on Hantzsch fluorimetry, and a proton-transfer-reaction mass spectrometer (PTR-MS). A new optimized mode of operation was used for the PTR-MS instrument which significantly enhanced its performance for on-line HCHO detection at low absolute humidities. The instruments were challenged with typical ambient levels of HCHO ranging from zero to several ppb. Synthetic air of high purity and particulate-filtered ambient air were used as sample matrices in the atmosphere simulation chamber onto which HCHO was spiked under varying levels of humidity and ozone. Measurements were compared to mixing ratios calculated from the chamber volume and the known amount of HCHO injected into the chamber; measurements were also compared between the different instruments. The formal and blind intercomparison exercise was conducted under the control of an independent referee. A number of analytical problems associated with the experimental set-up and with individual instruments were identified, the overall agreement between the methods was good.
Cloud condensation nuclei activity at Jeju Island, Korea in spring 2005
Authors: Kuwata M. , Kondo Y. , Miyazaki Y. , Komazaki Y. , Kim J. H. , Yum S. S. , Tanimoto H. , Matsueda H.
Published: April 2010

Abstract. We measured the number concentrations of cloud condensation nuclei (CCN) and the size distributions of CCN/CN (CN: condensation nuclei) ratios at supersaturations (SSs) of 0.097, 0.27, 0.58, and 0.97% at Jeju-Island, Korea during March-April 2005. Measurements of aerosol inorganic ions, water-soluble organic carbon (WSOC), organic carbon (OC), and elemental carbon (EC) in PM2.5 were simultaneously made. The CCN/CN ratios increased with increasing particle diameter, and the diameter at CCN/CN=0.5 was defined as D50. D50 represents the activation dry diameter of atmospheric particles. The average D50 at SS=0.097% and 0.97% was 136 nm and 31 nm, respectively. The temporal variation of D50 at SS=0.097% was correlated with the mass fraction of water-soluble components (inorganic ions + WSOC), indicating that the temporal variation of CCN activity was mainly controlled by changes in the water-soluble components fraction. The critical dry diameter (Dcrit), which is the threshold dry diameter for CCN activation, was calculated from the observed aerosol chemical compositions by Köhler theory for comparison with D50. The D50 at SS=0.097% was correlated (r2=0.48) with calculated Dcrit, although Dcrit were larger than D50 by 20–29% on average. The systematic difference between D50 and Dcrit could be caused by the size dependence of the aerosol chemical compositions or surface tension lowering caused by the mixing of water-soluble organic compounds. This difference corresponds to a 27±14% uncertainty in the CCN number concentration estimated from the observed particle number size distribution.
Discriminating raining from non-raining clouds at mid-latitudes using Meteosat Second Generation daytime data
Authors: Thies B. , Nauss T. , Bendix J.
Published: April 2010

Abstract. A new method for the delineation of precipitation during daytime using multispectral satellite data is proposed. The approach is not only applicable to the detection of mainly convective precipitation by means of the commonly used relation between infrared cloud top temperature and rainfall probability but enables also the detection of stratiform precipitation (e.g. in connection with mid-latitude frontal systems). The presented scheme is based on the conceptual model that precipitating clouds are characterized by a combination of particles large enough to fall, an adequate vertical extension (both represented by the cloud water path (cwp)), and the existence of ice particles in the upper part of the cloud. The technique considers the VIS0.6 and the NIR1.6 channel to gain information about the cloud water path. Additionally, the channel differences ΔT8.7-10.8 and ΔT10.8-12.1 are considered to supply information about the cloud phase. Rain area delineation is realized by using a minimum threshold of the rainfall confidence. To obtain a statistical transfer function between the rainfall confidence and the channel differences, the value combination of the four variables is compared to ground based radar data. The retrieval is validated against independent radar data not used for deriving the transfer function and shows an encouraging performance as well as clear improvements compared to existing optical retrieval techniques using only IR thresholds for cloud top temperature.
Characteristics of particle size distributions in the tropical tropopause based on optical particle counter and lidar measurements
Authors: Iwasaki S. , Maruyama K. , Hayashi M. , Ogino S. Y. , Ishimoto H. , Tachibana Y. , Shimizu A. , Matsui I. , Sugimoto N. , Yamashita K. , Saga K. , Iwamoto K. , Kamiakito Y. , Chabangborn A. , Thana B. , Hashizume M. , Koike T. , Oki T.
Published: April 2010

Abstract. An optical particle counter (OPC) is used in conjunction with lidar measurements to examine the characteristics of the particle size distribution in cirrus cloud at the tropical tropopause (TT) over Thailand. Of 11 OPC launches, cirrus cloud was detected at 10–15 km high on 7 occasions, cirrus was detected at the TT in 6 cases, and simultaneous OPC and lidar measurements were made on two occasions. Comparison of lidar and OPC measurements reveal that the cloud height of cirrus in the TT varies by several hundred meters over distances of tens kilometers; hence the height is not horizontally uniform. The mode radii of particles constituting the clouds are estimated by lidar and OPC measurements to be less than approximately 10 μm. The regression lines of the particle size distribution with and without cirrus cloud exhibit similar features at equivalent radii of <0.7 μm. Enhancement in the integrated number concentration at radii greater than 0.7 μm indicates that liquid particles tend to be frozen at a radius of 0.7 μm, with cirrus clouds above 10 km exhibiting similar features. In addition, common features of cirrus clouds at the TT include a local maximum in the particle size distribution at 2.0 μm and a peak between 0.5 μm and 1.7 μm in the ratio of the standard deviation of count values to that of the Poisson distribution of the averaged count values. Each feature implies that all ice particles in the clouds may be nucleated by the same mechanism and particles in this size range are actively frozen at the TT. These parameters are thus good indicators for checking the results of cirrus cloud models in the TT.
Advection patterns and aerosol optical and microphysical properties by AERONET over south-east Italy in the central Mediterranean
Authors: Santese M. , De Tomasi F. , Perrone M. R.
Published: April 2010

Abstract. Aerosol products by AERONET sun-sky radiometer measurements combined with air-mass backtrajectories were analyzed to identify source regions and pathways of air masses carrying aerosols to south-east Italy, and to determine the dependence of aerosol mean optical properties on advection patterns. Aerosol optical depth (AOD), fine mode fraction (η), single scattering albedo (SSA), asymmetry factor (g), and lidar ratio (Lr) at 440 nm were used to characterize aerosol properties. The analysis of 5-day-backtrajectories ending in Lecce on south-east Italy and referring to 240 measurement days of the 2003–2004 years revealed that 32% of the measurement days were characterized by air masses coming from Sector A, which includes all continental European sources with the exception of Spain. 3% of the measurement days were characterized by air masses coming from both the Sector B, which includes the Southern Mediterranean Sea and the Africa continent, and the Sector C, which includes the Western Mediterranean, the Iberian Peninsula, and the Atlantic Ocean. 62% of the measurement days were characterized by mixed advection patterns (Sector M). We found that AOD, SSA and g average values were not significantly dependent on air mass source Sector. In contrast, η and Lr average values were quite affected by the air mass source Sector. AOD, η, SSA, g, and Lr average values, which were equal to 0.29±0.15, 0.93±0.03, 0.93±0.03, 0.67±0.03, and 72±20 sr, respectively indicated that the Sector A aerosol could be considered representative of "continental average aerosol", mostly made of water soluble and a small amount of soot and insoluble components. Polluted-desert dust particles characterized by AOD=0.29±0.05, η=0.72±0.05, SSA=0.94±0.03, g=0.69±0.02, Lr=56±13 sr, were advected over south-east Italy from Sector B. Sector C was instead responsible for the advection of maritime-polluted particles, which were characterized by AOD=0.3±0.2, η=0.8±0.1, SSA=0.94±0.03, g=0.67±0.03, Lr=60±20 sr. Hence, we found that the aerosol load over south-east Italy was dominated by moderately-absorbing, fine-mode particles even if it was also affected by the minor contribution of desert and maritime type aerosol. The application of an aerosol mask to the Sector M data points supported last comment
Biogenic emissions of NOx from recently wetted soils over West Africa observed during the AMMA 2006 campaign
Authors: Stewart D. J. , Taylor C. M. , Reeves C. E. , McQuaid J. B.
Published: April 2010

Abstract. Chemical and meteorological parameters measured on board the Facility for Airborne Atmospheric Measurements (FAAM) BAe 146 Atmospheric Research Aircraft during the African Monsoon Multidisciplinary Analysis (AMMA) campaign are presented to show the impact of NOx emissions from recently wetted soils in West Africa. NOx emissions from soils have been previously observed in many geographical areas with different types of soil/vegetation cover during small scale studies and have been inferred at large scales from satellite measurements of NOx. This study is the first dedicated to showing the emissions of NOx at an intermediate scale between local surface sites and continental satellite measurements. The measurements reveal pronounced mesoscale variations in NOx concentrations closely linked to spatial patterns of antecedent rainfall. Fluxes required to maintain the NOx concentrations observed by the BAe-146 in a number of cases studies and for a range of assumed OH concentrations (0 to 1×107 molecules cm–3) are calculated to be in the range 4.7 to 37.3 ng N m−2 s−1. These values are comparable to the range of fluxes from 2 to 83 ng N m−2 s−1 reported from small scale field studies in a variety of tropical and sub-tropical locations reported in the review of Davidson and Kingerlee (1997). The fluxes calculated in the present study have been scaled up to cover the area of the Sahel bounded by 10 to 20 N and 10 E to 20 W giving an estimated emission of up to 0.05 TgN from this area for July and August 2006. The observed chemical data also suggest that the NOx emitted from soils is taking part in ozone formation as ozone concentrations exhibit similar fine scale structure to the NOx, with enhancements over the wet soils. Such variability can not be explained on the basis of transport from other areas.
Intercomparison of UV-visible measurements of ozone and NO2 during the Canadian Arctic ACE validation campaigns: 2004–2006
Authors: Fraser A. , Goutail F. , Strong K. , Bernath P. F. , Boone C. , Daffer W. H. , Drummond J. R. , Dufour D. G. , Kerzenmacher T. E. , Manney G. L. , McElroy C. T. , Midwinter C. , McLinden C. A. , Nichitiu F. , Nowlan C. R. , Walker J. , Walker K. A. , Wu H. , Zou J.
Published: April 2010

Abstract. The first three Canadian Arctic ACE validation campaigns were held during polar sunrise at Eureka, Nunavut, Canada (80° N, 86° W) from 2004 to 2006 in support of validation of the ACE (Atmospheric Chemistry Experiment) satellite mission. Three or four zenith-sky viewing UV-visible spectrometers have taken part in each of the three campaigns. The differential slant column densities and vertical column densities from these instruments have been compared following the methods of the UV-visible Working Group of the NDACC (Network for Detection of Atmospheric Composition Change). The instruments are found to partially agree within the required accuracies for both species, although both the vertical and slant column densities are more scattered than required. This might be expected given the spatial and temporal variability of the Arctic stratosphere in spring. The vertical column densities are also compared to integrated total columns from ozonesondes and integrated partial columns from the ACE-FTS (ACE-Fourier Transform Spectrometer) and ACE-MAESTRO (ACE-Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) instruments on board ACE. For both species, the columns from the ground-based instruments and the ozonesondes are found to generally agree within their combined error bars. The ACE-FTS ozone partial columns and the ground-based total columns agree within 4.5%, averaged over the three campaigns. The ACE-MAESTRO ozone partial columns are generally smaller than those of the ground-based instruments, by an average of 9.9%, and are smaller than the ACE-FTS columns by an average of 14.4%. The ACE-FTS NO2 partial columns are an average of 13.4% smaller than the total columns from the ground-based instruments, as expected. The ACE-MAESTRO NO2 partial columns are larger than the total columns of the ground-based instruments by an average of 2.5% and larger than the partial columns of the ACE-FTS by an average of 15.5%.
Evaluated kinetic and photochemical data for atmospheric chemistry: Volume IV – gas phase reactions of organic halogen species
Authors: Atkinson R. , Baulch D. L. , Cox R. A. , Crowley J. N. , Hampson R. F. , Hynes R. G. , Jenkin M. E. , Rossi M. J. , Troe J. , Wallington T. J.
Published: April 2010

Abstract. This article, the fourth in the series, presents kinetic and photochemical data sheets evaluated by the IUPAC Subcommittee on Gas Kinetic Data Evaluation for Atmospheric Chemistry. It covers the gas phase and photochemical reactions of organic halogen species, which were last published in 1997, and were updated on the IUPAC website in 2006. The article consists of a summary sheet, containing the recommended kinetic parameters for the evaluated reactions, and four appendices containing the data sheets, which provide information upon which the recommendations are made.