bluuebunny/crossref_metadata_2025 huggingface dataset:
High resolution vertical distributions of NO3 and N2O5 through the nocturnal boundary layer
Authors: Brown S. S. , Dubé W. P. , Osthoff H. D. , Wolfe D. E. , Angevine W. M. , Ravishankara A. R.
Published: April 2010

Abstract. The shallow mixing depth and vertical stratification of the lowest levels of the atmosphere at night has implications for the chemistry of nitrogen oxides emitted from the surface. Here we report vertical profiles of NO3, N2O5 and O3 measured from in-situ instruments on a movable carriage on a 300 m tower. The study offers high-resolution (<1 m) vertical distributions of both NO3 and N2O5 and shows that the nocturnal mixing ratios of these compounds vary widely over short vertical distance scales (10 m or less). Furthermore, there are systematic differences in the steady state lifetimes of NO3 and NO5 and in the partitioning among nitrogen oxides between different near-surface layers. These differences imply that NO3 and N2O5 occupy distinct chemical regimes as a function of altitude, potentially serving as sinks for nitrogen oxides and O3 near the surface but as reservoirs of NOx and O3 aloft.
MAX-DOAS detection of glyoxal during ICARTT 2004
Authors: Sinreich R. , Volkamer R. , Filsinger F. , Frieß U. , Kern C. , Platt U. , Sebastián O. , Wagner T.
Published: April 2010

Abstract. The direct detection of glyoxal (CHOCHO), the smallest α-dicarbonyl, in the open atmosphere by active differential optical absorption spectroscopy (DOAS) has recently been demonstrated (Volkamer et al., 2005a) and triggered the very recent successful detection of CHOCHO from space (Kurosu et al., 2005; Wittrock et al., 2006; Beirle et al., 2006). Here we report the first detection of CHOCHO by passive multi axis differential optical absorption spectroscopy (MAX-DOAS). CHOCHO and NO2 slant column measurements were conducted at MIT, Cambridge, USA, and on board the research vessel Ron Brown in the Gulf of Maine as part of the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) 2004 campaign. For a day with nearly clear sky conditions, radiative transfer modeling was employed to derive diurnal CHOCHO mixing ratios for both sites. CHOCHO mixing ratios at MIT varied from 40 to 120 ppt, with peak values observed around noon. Mixing ratios over the Gulf of Maine were found to be up to 3 times larger than at MIT. The CHOCHO-to-NO2ratio at MIT was <0.03, and enhancements of this ratio by up to two orders of magnitude were found over the Gulf of Maine. This paper focuses on the instrumental aspects involved with MAX-DOAS measurements of CHOCHO.
The Chisholm firestorm: observed microstructure, precipitation and lightning activity of a pyro-Cb
Authors: Rosenfeld D. , Fromm M. , Trentmann J. , Luderer G. , Andreae M. O. , Servranckx R.
Published: April 2010

Abstract. A fire storm that occured on 28 May 2001 devastated the town of Chisholm, ~150 km north of Edmonton, Alberta, induced a violent fire-invigorated cumulonimbus cloud. This pyro-cumulonimbus (pyro-Cb) had overshooting tops of 2.5–3 km above the tropopause, and injected massive amounts of smoke into the lower stratosphere. Fortunately, this event occurred under good coverage of radar, rain gauge, lightning and satellite measurements, which allowed in-depth documentation of the event. The combination of heat and smoke created a cloud with extremely small drops, which ascended rapidly in violent updrafts. There appeared to be little freezing up to the homogeneous freezing isotherm level of –38°C. A cloud with such small and short-lived highly supercooled drops is incapable of producing precipitation except for few large graupel and hail, which produced the observed radar echoes and charged the cloud with positive lightning. The small cloud drops froze homogeneously to equally small ice particles, for which there is no mechanism to aggregate into precipitation particles that hence remain in the anvil. The small precipitation efficiency implies that only a small fraction of the smoke is scavenged, so that most of it is exhausted through the anvil to the upper troposphere and lower stratosphere. Comparisons with other cases suggest that a pyro-Cb does not have to be as violent as the Chisholm case to have strongly suppressed precipitation. However, this level of convective vigor is necessary to create the overshooting updraft that injects the smoke into the lower stratosphere.
Retrieval of aerosol complex refractive index from a synergy between lidar, sunphotometer and in situ measurements during LISAIR experiment
Authors: Raut J.-C. , Chazette P.
Published: April 2010

Abstract. Particulate pollutant exchanges between the streets and the Planetary Boundary Layer (PBL), and their daily evolution linked to human activity were studied in the framework of the LIdar pour la Surveillance de l'AIR (LISAIR) experiment. This program lasted from 10 to 30 May 2005. A synergetic approach combining dedicated active (lidar) and passive (sunphotometer) remote sensors as well as ground based in situ instrumentation (nephelometer, aethalometer and particle sizers) was used to investigate urban aerosol optical properties within Paris. Aerosol complex refractive indices were assessed to be 1.56–0.034i at 355 nm and 1.59–0.040i at 532 nm, thus leading to single-scattering albedo values between 0.80 and 0.88. These retrievals are consistent with soot components in the aerosol arising from traffic exhausts indicating that these pollutants have a radiative impact on climate. We also discussed the influence of relative humidity on aerosol properties. A good agreement was found between vertical extinction profile derived from lidar backscattering signal and retrieved from the coupling between radiosounding and ground in situ measurements.
Predicting diurnal variability of fine inorganic aerosols and their gas-phase precursors near downtown Mexico City
Authors: Moya M. , Fountoukis C. , Nenes A. , Matías E. , Grutter M.
Published: April 2010

Abstract. Partitioning of semi-volatile nitrate and ammonium between the gas and particulate phases is studied combining two thermodynamic models that explicitly include crustal elements and simulate both branches (deliquescence, efflorescence) of aerosol behavior and measurements taken near downtown Mexico City during a field campaign conducted in February–March, 2005. Overall, no significant differences between model predictions (within 30% of error) are observed for particulate ammonium (PM2.5, PM1). In cases of moderate to high RH (40–70%), mostly occurring during the 1st and 2nd daily sampling periods (06:00–10:00 h, 10:00–14:00 h, LST), 4 h PM2.5 nitrate measurements are predicted within 30%. When RH drops below 30%, characteristic of the afternoon sampling periods (14:00-18:00 h), the efflorescence branch is most consistent with observed PM nitrate. Residual error analysis of these low RH cases suggest that aerosol nitrate loading or sulfate-to-nitrate molar ratio control phase behavior, hence the partitioning of semi-volatile PM2.5 nitrate in gas and particulate phases. Finally, inclusion of crustal elements in the modeling framework reduces the error in predicted PM2.5 ammonium by 25%. These findings, if generally applicable, can help improve air quality modeling in nitrate deficient environments.
Weekly periodicities of aerosol optical thickness over Central Europe – evidence of an anthropogenic direct aerosol effect
Authors: Bäumer D. , Rinke R. , Vogel B.
Published: April 2010

Abstract. Statistical analyses of data from 14 ground-based sun photometer stations all over Central Europe are presented. All stations are part of the Aerosol Robotic Network (AERONET), and only data of the highest data quality level 2.0 had been applied. The averages by weekday of aerosol optical thickness (AOT) at a wavelength of 440 nm of 12 of the 14 stations show a weekly periodicity with lowest values on Sunday and Monday, but greatest values from Wednesday until Saturday, that is significant at least on a 90% level. The stations in Germany and in Greater Paris show weekly cycles with ranges of about 20% on average. In Northern Italy and Switzerland this range is about 10% on average. The corresponding weekly cycle of anthropogenic gaseous and particulate emissions leads us to the conclusion of the anthropogenic origin of the weekly AOT cycle. Since these AOT patterns are derived from the reduction of the direct sun radiation by the columnar atmospheric aerosol, this result represents strong evidence for an anthropogenic direct aerosol effect on shortwave radiation. Furthermore, this study makes a first contribution to the understanding and explanation of recently observed weekly periodicities in meteorological variables as temperature in Germany.
The relevance of aerosol optical depth to cumulus fraction changes: a five-year climatology at the ACRF SGP site
Authors: Kassianov E. I. , Berg L. K. , Flynn C. , McFarlane S.
Published: April 2010

Abstract. The objective of this study is to investigate, by observational means, the magnitude and sign of the actively discussed relationship between cloud fraction N and aerosol optical depth τa. Collocated and coincident ground-based measurements and Terra/Aqua satellite observations at the Atmospheric Radiation Measurement (ARM) Climate Research Facility (ACRF) Southern Great Plains (SGP) site form the basis of this study. The N–τa relationship occurred in a specific 5-year dataset of fair-weather cumulus (FWC) clouds and mostly non-absorbing aerosols. To reduce possible contamination of the aerosols on the cloud properties estimation (and vice versa), we use independent datasets of τa and N obtained from the Multi-filter Rotating Shadowband Radiometer (MFRSR) measurements and from the ARM Active Remotely Sensed Clouds Locations (ARSCL) value-added product, respectively. Optical depth of the FWC clouds τcld and effective radius of cloud droplets re are obtained from the MODerate resolution Imaging Spectroradiometer (MODIS) data. We found that relationships between cloud properties (N,τcld, re) and aerosol optical depth are time-dependent (morning versus afternoon). Observed time-dependent changes of cloud properties, associated with aerosol loading, control the variability of surface radiative fluxes. In comparison with pristine clouds, the polluted clouds are more transparent in the afternoon due to smaller cloud fraction, smaller optical depth and larger droplets. As a result, the corresponding correlation between the surface radiative flux and τa is positive (warming effect of aerosol). Also we found that relationship between cloud fraction and aerosol optical depth is cloud size dependent. The cloud fraction of large clouds (larger than 1 km) is relatively insensitive to the aerosol amount. In contrast, cloud fraction of small clouds (smaller than 1 km) is strongly positively correlated with τa. This suggests that an ensemble of polluted clouds tends to be composed of smaller clouds than a similar one in a pristine environment. One should be aware of these time- and size-dependent features when qualitatively comparing N–τa relationships obtained from the satellite observations, surface measurements, and model simulations.
MIPAS measurements of upper tropospheric C2H6 and O3 during the Southern hemispheric biomass burning season in 2003
Authors: von Clarmann T. , Glatthor N. , Stiller G. P. , Grabowski U. , Höpfner M. , Kellmann S. , Linden A. , Milz M. , Steck T. , Fischer H. , Funke B. , Koukouli M. E.
Published: April 2010

Abstract. Under cloud free conditions, the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) provides measurements of spectrally resolved limb radiances down to the upper troposphere. These are used to infer global distributions of mixing ratios of atmospheric constituents in the upper troposphere and the stratosphere. From 21 October to 14 November 2003, MIPAS observed enhanced amounts of upper tropospheric C2H6 (up to about 400 pptv, depending on spectroscopic data chosen) and ozone (up to about 80 ppbv). By means of trajectory calculations, the enhancements observed in the Southern hemisphere are, at least partly, attributed to a biomass burning plume, which covers wide parts of the Southern hemisphere, from South America, the Atlantic ocean, Africa, the Indian Ocean to Australia. The chemical composition of the part of the plume-like pollution belt associated with South American rainforest burning appears different from the part associated with Southern African savanna burning. In particular, African savanna fires lead to a larger ozone enhancement than South American rainforest fires.
Humidity observations in the Arctic troposphere over Ny-Ålesund, Svalbard based on 14 years of radiosonde data
Authors: Treffeisen R. , Krejci R. , Ström J. , Engvall A. C. , Herber A. , Thomason L. W.
Published: April 2010

Abstract. Water vapour is an important component in the radiative balance of the polar atmosphere. We present a study covering fourteen-years of data of tropopsheric humidity profiles measured with standard radiosondes at Ny-Ålesund (78°55' N 11°52' E) during the period from 1991 to 2005. It is well known that relative humidity measurements are less reliable at cold temperatures when measured with standard radiosondes. The data were corrected for errors and used to determine key characteristic features of the vertical and temporal RH evolution in the Arctic troposphere over Ny-Ålesund. We present frequency occurrence of ice-supersaturation layers in the troposphere, their vertical span, temperature and statistical distribution. Supersaturation with respect to ice shows a clear seasonal behaviour. In winter (October–February) it occurred in 22% of all cases and less frequently in spring (March–May 13%), and summer (June–September, 10%). The results are finally compared with findings from the SAGE II satellite instrument on subvisible clouds.
Modelling the optical properties of fresh biomass burning aerosol produced in a smoke chamber: results from the EFEU campaign
Authors: Hungershöfer K. , Zeromskiene K. , Iinuma Y. , Helas G. , Trentmann J. , Trautmann T. , Parmar R. S. , Wiedensohler A. , Andreae M. O. , Schmid O.
Published: April 2010

Abstract. A better characterisation of the optical properties of biomass burning aerosol as a function of the burning conditions is required in order to quantify their effects on climate and atmospheric chemistry. Controlled laboratory combustion experiments with different fuel types were carried out at the combustion facility of the Max Planck Institute for Chemistry (Mainz, Germany) as part of the 'Impact of Vegetation Fires on the Composition and Circulation of the Atmosphere' (EFEU) project. Using the measured size distributions as well as mass scattering and absorption efficiencies, Mie calculations provided mean effective refractive indices of 1.60−0.010i and 1.56−0.010i (λ=0.55 μm) for smoke particles emitted from the combustion of savanna grass and an African hardwood (musasa), respectively. The relatively low imaginary parts suggest that the light-absorbing carbon of the investigated fresh biomass burning aerosol is only partly graphitized, resulting in strongly scattering and less absorbing particles. While the observed variability in mass scattering efficiencies was consistent with changes in particle size, the changes in the mass absorption efficiency can only be explained, if the chemical composition of the particles varies with combustion conditions.
Aerosol lidar observations and model calculations of the planetary boundary layer evolution over Greece, during the March 2006 total solar eclipse
Authors: Amiridis V. , Melas D. , Balis D. S. , Papayannis A. , Founda D. , Katragkou E. , Giannakaki E. , Mamouri R. E. , Gerasopoulos E. , Zerefos C.
Published: April 2010

Abstract. An investigation of the Planetary Boundary Layer (PBL) height evolution over Greece, during the solar eclipse of 29 March 2006, is presented. Ground based observations were carried out using lidar detection and ranging devices (Lidars) and ground meteorological instruments, to estimate the height of the Mixing Layer (ML) before, during and after the solar eclipse in Northern and Southern parts of Greece exhibiting different sun obscuration. Data demonstrate that the solar eclipse has induced a decrease of the PBL height, indicating a suppression of turbulence activity similar to that during the sunset hours. The changes in PBL height were associated with a very shallow entrainment zone, indicating a significant weakening of the penetrative convection. Heat transfer was confined to a thinner layer above ground. The thickness of the entrainment zone exhibited its minimum during the maximum of the eclipse, demonstrative of turbulence mechanisms suppression at that time. Model estimations of the PBL evolution were additionally conducted using the Comprehensive Air Quality Model with extensions (CAMx) coupled with the Weather Research and Forecasting model (WRF). Model diagnosed PBL height decrease during the solar eclipse due to vertical transport decay, in agreement with the experimental findings; vertical profiles of atmospheric particles and gaseous species showed an important vertical mixing attenuation.
Methane emissions from boreal and tropical forest ecosystems derived from in-situ measurements
Authors: Sinha V. , Williams J. , Crutzen P. J. , Lelieveld J.
Published: April 2010

Abstract. Methane is a climatologically important greenhouse gas, which plays a key role in regulating water vapour in the stratosphere and hydroxyl radicals in the troposphere. Recent findings that vegetation emits methane have stimulated efforts to ascertain the impact of this source on the global budget. In this work, we present the results of high frequency (ca. 1 min−1) methane measurements conducted in the boreal forests of Finland and the tropical forests of Suriname, in April–May, 2005 and October 2005 respectively. The measurements were performed using a gas chromatograph – flame ionization detector (GC-FID). The average of the median mixing ratios during a typical diel cycle were 1.83 μmol mol−1 and 1.74 μmol mol−1 for the boreal forest ecosystem and tropical forest ecosystem respectively, with remarkable similarity in the time series of both the boreal and tropical diel profiles. Night time methane emission flux of the boreal forest ecosystem, calculated from the increase of methane during the night and measured nocturnal boundary layer heights yields a flux of (3.62±0.87)×1011 molecules cm−2 s−1(or 45.5±11 Tg CH4 yr−1 for global boreal forest area). This is a source contribution of circa 8% of the global methane budget. These results highlight the importance of the boreal and tropical forest ecosystems for the global budget of methane. The results are also discussed in the context of recent work reporting high methane mixing ratios over tropical forests using space borne near infra-red spectroscopy measurements.
Ammonia at Blodgett Forest, Sierra Nevada, USA
Authors:   M. L. Fischer and D. Littlejohn
Published: April 2010

Abstract. Ammonia is a reactive trace gas that is emitted in large quantities by animal agriculture and other sources in California, which subsequently forms aerosol particulate matter, potentially affecting visibility, climate, and human health. We performed initial measurements of NH3 at the Blodgett Forest Research Station (BFRS) during a two week study in June, 2006. The site is used for ongoing air quality research and is a relatively low-background site in the foothills of the Sierra Nevada. Measured NH3 mixing ratios were quite low (<1 to ~2 ppb), contrasting with typical conditions in many parts of the Central Valley. Eddy covariance measurements showed NH3 fluxes that scaled with measured NH3 mixing ratio and calculated aerodynamic deposition velocity, suggesting dry deposition is a significant loss mechanism for atmospheric NH3 at BFRS. A simple model of NH3 transport to the site supports the hypothesis that NH3 is transported from the Valley to BFRS, but deposits on vegetation during the summer. Further work is necessary to determine whether the results obtained in this study can be generalized to other seasons.
Long-term tropospheric formaldehyde concentrations deduced from ground-based fourier transform solar infrared measurements
Authors: Jones N. B. , Riedel K. , Allan W. , Wood S. , Palmer P. I. , Chance K. , Notholt J.
Published: April 2010

Abstract. Long-term total column measurements of formaldehyde (HCHO) covering a 12 year period from 1992 to 2004 are reported from spectra recorded with a high-resolution Fourier Transform Spectrometer (FTS) using the sun as a light source at a Southern Hemisphere site (Lauder, New Zealand). The ambient HCHO concentrations at this rural location are often at background levels (<250 ppt) typical for remote marine environments. Due to these low values of HCHO, which are often at or below the detection limit of standard techniques, a method of analysis has been developed that successfully produces HCHO columns with sufficient sensitivity throughout the whole season. The HCHO column over Lauder was found to have a strong seasonal cycle (±50%), with a mean column of 4.2×1015 molecules cm−2, the maximum occurring in the summer. A simple box model of CH4 oxidation reproduces the seasonal cycle, but significantly underestimates the maximum HCHO ground concentrations deduced from the column observations, particularly in summer. This implies the existence of a significant source of HCHO that cannot be explained by oxidation of CH4 alone. The ground-based FTS column data compares well with collocated HCHO column measurements from the Global Ozone Monitoring Experiment (GOME) satellite instrument (r2=0.65, mean bias=10%, n=48).
Source apportionment of the particulate PAHs at Seoul, Korea: impact of long range transport to a megacity
Authors: Lee J. Y. , Kim Y. P.
Published: April 2010

Abstract. Northeast Asia including China, Korea, and Japan is one of the world's largest fossil fuel consumption regions. Seoul is a megacity in Northeast Asia and its emissions of air pollutants can affect the region and is also affected by the regional emissions. To understand the degree of this relationship, major sources of ambient particulate PAHs at Seoul, Korea were identified and quantified based on the measurement data between August 2002 and December 2003. The chemical mass balance (CMB) model was applied. Seven major emission sources were identified based on the emission data in Seoul and Northeast Asia: Gasoline and diesel vehicles, coal residential, coke oven, coal power plant, biomass burning, natural gas (NG) combustion. The major source of particulate PAHs at Seoul on the whole measurement period was gasoline and diesel vehicles, accounted for 31% of the measured particulate PAHs levels. However, the source contributions showed distinct seasonal variations. High contributions of biomass burning and coal (residential and coke oven) were shown in fall and winter accounted for 63% and 82% of the total PAHs concentration, respectively. Since these sources were not strong in and around Seoul, these might be related to transport from outside of Seoul, from China and/or North Korea. It implies that the air quality in the large urban city such as Seoul can be influenced by the long range transport of air pollutants such as PAHs.
Towards closure between measured and modelled UV under clear skies at four diverse sites
Authors: Badosa J. , McKenzie R. L. , Kotkamp M. , Calbó J. , González J. A. , Johnston P. V. , O'Neill M. , Anderson D. J.
Published: April 2010

Abstract. The purpose of this work is determine the extent of closure between measurements and models of UV irradiances at diverse sites using state of the art instruments, models, and the best available data as inputs to the models. These include information about aerosol optical depth (unfortunately not extending down as far into the UVB region as desirable because such information is not generally available), ozone column amounts, as well as vertical profiles of ozone and temperature. We concentrate on clear-sky irradiances, and report the results in terms of UV Index (UVI). Clear-sky data from one year of measurements at each of four diverse sites (Lauder – New Zealand, Mauna Loa Observatory – Hawaii, Boulder – Colorado, and Melbourne – Australia) have been analysed in detail, also taking account of different measurements of ozone, including satellite-derived values, as well as ground measured values, both from Dobson instruments and as retrieved from the UV spectra under study. Previous studies have generally focussed on data from a single site, and for shorter periods. Consequently, this study is the most comprehensive of its kind to date. At Lauder, which is the cleanest low altitude site, we obtained agreement between measurement and model at 5% level, which is consistent with the best agreement found previously. At Mauna Loa Observatory, similar agreement was achieved, but model calculations need to allow for reflections from cloud that are present below the observatory. At this site, there are occasional problems with using satellite-derived ozone. At Boulder, mean agreements were similar but the dispersion around the mean was slightly larger, corresponding to larger uncertainties in the aerosol inputs to the model. However, at Melbourne, which is the only non-NDACC (Network for the Detection of Atmospheric Composition Change) site, there remain unexplained discrepancies. The measured values are significantly lower than the calculated values. We investigate the extent to which this discrepancy can be explained by incomplete knowledge of aerosol extinctions in the UV at this site. We conclude that further information about aerosol optical depth and single scattering albedo in the UVB region is needed to resolve the issues. At the three NDACC sites, the closure provided by the study gives confidence in both the measurements and our ability to model them. The study revealed a limitation in the use of PTFE diffusers when temperatures are lower than approximately 20°C. It also documents the range of clear sky UVI values expected at these diverse sites.
Dust aerosol radiative effect and influence on urban atmospheric boundary layer
Authors: Zhang L. , Chen M. , Li L.
Published: April 2010

Abstract. An 1.5-level-closure and 3-D non-stationary atmospheric boundary layer (ABL) model and a radiation transfer model with the output of Weather Research and Forecast (WRF) Model and lidar AML-1 are employed to simulate the dust aerosol radiative effect and its influence on ABL in Beijing for the period of 23–26 January 2002 when a dust storm occurred. The simulation shows that daytime dust aerosol radiative effect heats up the ABL at the mean rate of about 0.68 K/h. The horizontal wind speed from ground to 900 m layer is also overall increased, and the value changes about 0.01 m/s at 14:00 LT near the ground. At night, the dust aerosol radiative effect cools the ABL at the mean rate of −0.21 K/h and the wind speed lowers down at about −0.19 m/s at 02:00 LT near the ground.
Short-lived pollutants in the Arctic: their climate impact and possible mitigation strategies
Authors: Quinn P. K. , Bates T. S. , Baum E. , Doubleday N. , Fiore A. M. , Flanner M. , Fridlind A. , Garrett T. J. , Koch D. , Menon S. , Shindell D. , Stohl A. , Warren S. G.
Published: April 2010

Abstract. Several short-lived pollutants known to impact Arctic climate may be contributing to the accelerated rates of warming observed in this region relative to the global annually averaged temperature increase. Here, we present a summary of the short-lived pollutants that impact Arctic climate including methane, tropospheric ozone, and tropospheric aerosols. For each pollutant, we provide a description of the major sources, the mechanism of forcing, seasonally averaged forcing values for the Arctic, and the corresponding surface temperature response. We suggest strategies for reducing the warming based on current knowledge and discuss directions for future research to address remaining uncertainties.
20-year LiDAR observations of stratospheric sudden warming over a mid-latitude site, Observatoire de Haute Provence (OHP; 44° N, 6° E): case study and statistical characteristics
Authors: Charyulu D. V. , Sivakumar V. , Bencherif H. , Kirgis G. , Hauchecorne A. , Keckhut P. , Narayana Rao D.
Published: April 2010

Abstract. The present study delineates the characteristics of Stratospheric Sudden Warming (SSW) events observed over the Observatoire de Haute Provence (OHP: 44° N, 6° E). The study uses 20 years of Rayleigh LiDAR temperature measurements for the period, 1982–2001, which corresponds to 2629 daily temperature profiles. Characteristics of warming events, such as type of warming (major and minor), magnitude of warming, height of occurrence and day period of occurrence are presented with emphasis on wave propagation and isentropic transport conditions. The major and minor warming events are classified with respect to temperature increase and reversal in the zonal wind direction in the polar region using reanalysis data from the National Centre for Environmental Prediction (NCEP). SSWs occur with a mean frequency of 2.15 events per winter season. The percentage of occurrence of major and minor warming events are found to be ~23% and ~77%, respectively. The observed major and minor SSW is associated with a descent of the stratopause layer by −6 to 6 km range. The heights of occurrences of major SSWs are distributed between 38 km and 54 km with magnitudes in the 12.2–35.7 K temperature range, while minor SSW occurrences appear in the 42–54 km range, closer to the usual stratopause layer (~47 km) and with a slightly larger range of temperature magnitude (10.2–32.8 K). The observed major and minor events are examined in connection with Quasi-Biennial Oscillation (QBO) phases.
Method for evaluating trends in greenhouse gases from ground-based remote FTIR measurements over Europe
Authors: Gardiner T. , Forbes A. , Woods P. , deMaziere M. , Vigouroux C. , Mahieu E. , Demoulin P. , Velazco V. , Notholt J. , Blumenstock T. , Hase F. , Kramer I. , Sussman R. , Stremme W. , Mellqvist J. , Strandberg A. , Ellingsen K. , Gauss M.
Published: April 2010

Abstract. This paper describes the statistical analysis of annual trends in long term datasets of greenhouse gas measurements taken over ten or more years. The analysis technique employs a bootstrap resampling method to determine both the long-term and intra-annual variability of the datasets, together with the uncertainties on the trend values. The method has been applied to data from a European network of ground-based solar FTIR instruments to determine the trends in the tropospheric, stratospheric and total columns of ozone, nitrous oxide, carbon monoxide, methane, ethane and HCFC-22. The suitability of the method has been demonstrated through statistical validation of the technique, and comparison with ground-based in-situ measurements and 3-D atmospheric models.
On the diurnal variability of particle properties related to black carbon in Mexico City
Authors: Baumgardner D. , Kok G. L. , Raga G. B.
Published: April 2010

Abstract. The black carbon mass (BCM) of individual, internally mixed aerosol particles was measured with the Single Particle Soot Photometer (SP2) in April of 2003 and 2005. The average BCM, single particle BC mass fraction and BCM equivalent diameter were evaluated with respect to concentrations of carbon monoxide (CO), particle bound polycyclic aromatic hydrocarbons (PPAH) and condensation nuclei (CN). The BCM and CO have matching diurnal trends that are linked to traffic patterns and boundary layer growth. The PPAH reaches a maximum at the same hour as CO and BCM but returns rapidly back to nighttime values within three hours of the peak. The number of particles containing BCM ranges between 10% to 40% of all particles between 200 nm and 700 nm and the BCM is between 4% and 12% of the total mass in this size range. The average BC equivalent mass diameter varies between 300 and 400 nm and reaches its daily minimum value when BCM is a maximum. The BC particles have the thinnest coating of non-light absorbing material during periods of maximum BCM. The scattering and absorption coefficients, Bscat and Babs , derived from the SP2 measurements were compared with direct measurements from a nephelometer and soot photometer. The measured and derived Babs are in close agreement whereas the Bscat comparisons show larger discrepancies in absolute value and daily trends. Even though approximately 40% of the BCM is in particles with diameters smaller than 200 nm, the extinction coefficient is dominated by the BCM in particles larger than this size. The BCM contributes up to 20% of the total extinction in this size range. BCM is emitted at a rate of 1200 metric tons per year in Mexico City, based upon the SP2 measurements and correlations between BCM and CO.
A revised linear ozone photochemistry parameterization for use in transport and general circulation models: multi-annual simulations
Authors: Cariolle D. , Teyssèdre H.
Published: April 2010

Abstract. This article describes the validation of a linear parameterization of the ozone photochemistry for use in upper tropospheric and stratospheric studies. The present work extends a previously developed scheme by improving the 2D model used to derive the coefficients of the parameterization. The chemical reaction rates are updated from a compilation that includes recent laboratory works. Furthermore, the polar ozone destruction due to heterogeneous reactions at the surface of the polar stratospheric clouds is taken into account as a function of the stratospheric temperature and the total chlorine content. Two versions of the parameterization are tested. The first one only requires the resolution of a continuity equation for the time evolution of the ozone mixing ratio, the second one uses one additional equation for a cold tracer. The parameterization has been introduced into the chemical transport model MOCAGE. The model is integrated with wind and temperature fields from the ECMWF operational analyses over the period 2000–2004. Overall, the results show a very good agreement between the modelled ozone distribution and the Total Ozone Mapping Spectrometer (TOMS) satellite data and the "in-situ" vertical soundings. During the course of the integration the model does not show any drift and the biases are generally small. The model also reproduces fairly well the polar ozone variability, with notably the formation of "ozone holes" in the southern hemisphere with amplitudes and seasonal evolutions that follow the dynamics and time evolution of the polar vortex. The introduction of the cold tracer further improves the model simulation by allowing additional ozone destruction inside air masses exported from the high to the mid-latitudes, and by maintaining low ozone contents inside the polar vortex of the southern hemisphere over longer periods in spring time. It is concluded that for the study of climatic scenarios or the assimilation of ozone data, the present parameterization gives an interesting alternative to the introduction of detailed and computationally costly chemical schemes into general circulation models.
Organic composition of carbonaceous aerosols in an aged prescribed fire plume
Authors: Yan B. , Zheng M. , Hu Y. T. , Lee S. , Kim H. K. , Russell A. G.
Published: April 2010

Abstract. Aged smoke from a prescribed fire (dominated by conifers) impacted Atlanta, GA on 28 February 2007 and dramatically increased hourly ambient concentrations of PM2.5 and organic carbon (OC) up to 140 and 72 μg m−3, respectively. It was estimated that over 1 million residents were exposed to the smoky air lasting from the late afternoon to midnight. To better understand the processes impacting the aging of fire plumes, a detailed chemical speciation of carbonaceous aerosols was conducted by gas chromatography/mass spectrometry (GC/MS) analysis. Ambient concentrations of many organic species (levoglucosan, resin acids, retene, n-alkanes, n-alkanoic acids) associated with wood burning emission were significantly elevated on the event day. Levoglucosan increased by a factor of 10, while hopanes, steranes, cholesterol and major polycyclic aromatic hydrocarbons (PAHs) did not show obvious increases. Strong odd over even carbon number predominance was found for n-alkanes versus even over odd predominance for n-alkanoic acids. Alteration of resin acids during transport from burning sites to monitors is suggested by the observations. Our study also suggests that large quantities of biogenic volatile organic compounds (VOCs) and semivolatile organic compounds (SVOCs) were released both as products of combustion and unburned vegetation heated by the fire. Higher leaf temperature can stimulate biogenic VOC and SVOC emissions, which enhanced formation of secondary organic aerosols (SOA) in the atmosphere. This is supported by elevated ambient concentrations of secondary organic tracers (dicarboxylic acids, 2-methyltetrols, pinonic acid and pinic acid). An approximate source profile was built for the aged fire plume to help better understand evolution of wood smoke emission and can be used for source apportionment.
Validation and data characteristics of methane and nitrous oxide profiles observed by MIPAS and processed with Version 4.61 algorithm
Authors: Payan S. , Camy-Peyret C. , Oelhaf H. , Wetzel G. , Maucher G. , Keim C. , Pirre M. , Huret N. , Engel A. , Volk M. C. , Kuellmann H. , Kuttippurath J. , Cortesi U. , Bianchini G. , Mencaraglia F. , Raspollini P. , Redaelli G. , Vigouroux C. , De Mazière M. , Mikuteit S. , Blumenstock T. , Velazco V. , Notholt J. , Mahieu M. , Duchatelet P. , Smale D. , Wood S. , Jones N. , Piccolo C. , Payne V. , Bracher A. , Glatthor N. , Stiller G. , Grunow K. , Jeseck P. , Te Y. , Pfeilsticker K. , Butz A.
Published: April 2010

Abstract. The ENVISAT validation programme for the atmospheric instruments MIPAS, SCIAMACHY and GOMOS is based on a number of balloon-bone, aircraft and ground-based correlative measurements. In particular the activities of validation scientists were coordinated by ESA within the ENVISAT Stratospheric Aircraft and Balloon Campaign of ESABC. As part of a series of similar papers on other species [this issue] and in parallel to the contribution of the individual validation teams, the present paper provides a synthesis of comparisons performed between MIPAS CH4 and N2O profiles produced by the current ESA operational software (Instrument Processing Facility version 4.61 or IPF v4.61) and correlative measurements obtained from balloon and aircraft experiments as well as from satellite sensors or from ground-based instruments. The MIPAS-E CH4 values show a positive bias in the lower stratosphere of about 10%. In case of N2O no systematic deviation with respect to the validation experiments could be identified. The individual used MIPAS data version 4.61 still exhibits some unphysical oscillations in individual CH4 and N2O profiles caused by the processing algorithm (with almost no regularization). Taking these problems into account, the MIPAS CH4 and N2O profiles are behaving as expected from the internal error estimation of IPF v4.61.
Modeling the effect of plume-rise on the transport of carbon monoxide over Africa and its exports with NCAR CAM
Authors: Guan H. , Chatfield R. B. , Freitas S. R. , Bergstrom R. W. , Longo K. M.
Published: April 2010

Abstract. We investigated the effects of fire-induced plume-rise on the predicted export of carbon monoxide (CO) over Africa during SAFARI 2000 using the NCAR Community Atmosphere Model (CAM) with a CO tracer and plume-rise parameterization scheme. The plume-rise parameterization scheme simulates the consequences of strong buoyancy of hot gases emitted from biomass burning, including both dry and cloud-associated (pyrocumulus) lofting. The scheme was first adapted from a regional model. The current implementation of the plume-rise parameterization scheme into the global model provides an opportunity to examine the effect of plume-rise on long-range transport. The CAM simulation with the plume-rise parameterization scheme shows a substantial improvement of the agreements between the modeled and aircraft-measured vertical distribution of CO over southern Africa biomass burning area. The plume-rise mechanism plays a crucial role in lofting biomass burning pollutants to the middle troposphere. In the presence of deep convection we found that the plume-rise mechanism results in a decrease of CO concentration in the upper troposphere. The plume rise depletes the boundary layer, and thus leaves lower concentrations of CO to be lofted by the deep convection process. The effect of the plume-rise on free troposphere CO concentration is more important for the source area (short-distance transport) than for remote areas (long-distance transport). The plume-rise scheme also increases the CO export fluxes from Africa to the Atlantic and Indian Oceans. These results further confirm and extend previous findings in a regional model study. Effective lofting of large concentration of CO by the plume-rise mechanism also has implication for local air quality forecast in areas affected by other fire-related pollutants.
Enhanced tropospheric BrO concentrations over the Antarctic sea ice belt in mid winter observed from MAX-DOAS observations on board the research vessel Polarstern
Authors: Wagner T. , Ibrahim O. , Sinreich R. , Frieß U. , Platt U.
Published: April 2010

Abstract. We present Multi AXis-Differential Optical Absorption Spectroscopy (MAX-DOAS) observations of tropospheric BrO carried out on board the German research vessel Polarstern during the Antarctic winter 2006. Polarstern entered the area of first year sea ice around Antarctica on 24 June 2006 and stayed within this area until 15 August 2006. For the period when the ship cruised inside the first year sea ice belt, enhanced BrO concentrations were almost continuously observed. One interesting exception appeared on 7 July 2006, when the sun elevation angle was < about –2.8° indicating that for low insulation the photolysis of Br2 and/or HOBr is too slow to provide sufficient amounts of Br radicals. Before and after the period inside the first year sea ice belt, typically low BrO concentrations were observed. Our observations indicate that enhanced BrO concentrations around Antarctica exist about one month earlier than observed by satellite instruments. The small BrO concentrations over the open oceans indicate a short atmospheric lifetime of activated bromine without contact to areas of first year sea ice. From detailed radiative transfer simulations we find that MAX-DOAS observations are about one order of magnitude more sensitive to near-surface BrO than satellite observations. In contrast to satellite observations the MAX-DOAS sensitivity hardly decreases for large solar zenith angles and is almost independent from the ground albedo. Thus this technique is very well suited for observations in polar regions close to the solar terminator. Furthermore, combination of both techniques could yield additional information on the vertical distribution of BrO in the lower troposphere.
In-situ observations and modeling of nitric acid-containing particles in a cirrus cloud formation region
Authors: Voigt C. , Kärcher B. , Schlager H. , Schiller C. , Krämer M. , de Reus M. , Vössing H. , Borrmann S. , Mitev V.
Published: April 2010

Abstract. Measurements in nascent ice forming regions are very rare and help understand cirrus cloud formation and the interactions of trace gases with ice crystals. A cirrus cloud has very likely been probed in its formation stage with in-situ and remote sensing instruments onboard the high altitude research aircraft Geophysica M55 in the tropical upper troposphere. Besides microphysical and optical particle properties, water (H2O) and nitric acid (HNO3) have been measured. In slightly ice supersaturated air between 14.2 and 15 km altitude, an unusually low ice water content of 0.026 mg m–3 and small ice crystals with mean radii of 5 μm have been detected. A high HNO3/H2O molar ratio in ice of 5×10–5 has been observed in this region, about an order of magnitude higher compared to previous observations in cirrus at similar temperatures (near 202 K). A model describing the trapping of HNO3 in growing ice particles shows that a high HNO3 content in ice crystals is expected during early growth stages, mainly originating from uptake in aerosol particles prior to freezing. Water vapor deposition on ice crystals and trapping of additional HNO3 reduces the molar ratio to values close to the ratio of HNO3/H2O in the gas phase while the cloud ages.
Ozonolysis of α-pinene: parameterization of secondary organic aerosol mass fraction
Authors: Pathak R. K. , Presto A. A. , Lane T. E. , Stanier C. O. , Donahue N. M. , Pandis S. N.
Published: April 2010

Abstract. Existing parameterizations tend to underpredict the α-pinene aerosol mass fraction (AMF) by a factor of 2–5 at low organic aerosol concentrations (<5 μg m−3). A wide range of smog chamber results obtained at various conditions (low/high NOx, presence/absence of UV radiation, dry/humid conditions, and temperatures ranging from 15–40°C) collected by various research teams during the last decade are used to derive new parameterizations of the SOA formation from α-pinene ozonolysis. Parameterizations are developed by fitting experimental data to a basis set of saturation concentrations (from 10−2 to 104 μg m−3) using an absorptive equilibrium partitioning model. Separate parameterizations for α-pinene SOA mass fractions are developed for: 1) Low NOx, dark, and dry conditions, 2) Low NOx, UV, and dry conditions, 3) Low NOx, dark, and high RH conditions, 4) High NOx, dark, and dry conditions, 5) High NOx, UV, and dry conditions. According to the proposed parameterizations the α-pinene SOA mass fractions in an atmosphere with 5 μg m−3 of organic aerosol range from 0.032 to 0.1 for reacted α-pinene concentrations in the 1 ppt to 5 ppb range.
Investigative modeling of new pathways for secondary organic aerosol formation
Authors: Pun B. K. , Seigneur C.
Published: April 2010

Abstract. Recent advances in secondary organic aerosol (SOA) research are reviewed and the status of current understanding is investigated using a model of SOA formation. Benzene and isoprene are newly identified precursors that are included in this SOA model; these precursors form SOA via secondary products. The model is also extended to include some representation of aqueous partitioning and the formation of high molecular weight products via oligomerization. Experimental data and empirical relationships are used where possible, because a detailed representation of SOA formation is not supported by the current state of information. Sensitivity studies are conducted with the SOA model and SOA predictions are found to be very sensitive to the treatment of the interactions between particulate water and organic compounds. While uncertainties due to model formulation are significant, influential model parameters include the aerosol partitioning ratios for several small products of isoprene and the partitioning constants for unidentified products (currently, the partitioning constants are derived by fitting experimental data). The pH value used as the reference for the activation of oligomerization is also a critical parameter. Recommendations for future work needed to improve SOA models include the elucidation of the water-organic relationship, the extent of phase separation, and laboratory experiments conducted under conditions more relevant to ambient studies (e.g. lower concentrations, higher relative humidity).