bluuebunny/crossref_metadata_2025 huggingface dataset:
Midlatitude stratosphere – troposphere exchange as diagnosed by MLS O3 and MOPITT CO assimilated fields
Authors: El Amraoui L. , Attié J.-L. , Semane N. , Claeyman M. , Peuch V.-H. , Warner J. , Ricaud P. , Cammas J.-P. , Piacentini A. , Cariolle D. , Massart S. , Bencherif H.
Published: April 2010

Abstract. This paper presents a complete characterization of a very deep stratospheric intrusion which occurred over the British Isles on 15 August 2007. The signature of this event is diagnosed using ozonesonde measurements over Lerwick, UK (60.14° N, 1.19° W) and is also well characterized using meteorological analyses from the global operational weather prediction model of Météo-France, ARPEGE. Modelled as well as assimilated fields of both ozone (O3) and carbon monoxide (CO) have been used in order to better document this event. The paper also presents a demonstration of the capability of O3 and CO assimilated fields to better describe a stratosphere-troposphere exchange (STE) event in comparison with the free run modelled O3 and CO fields. O3 and CO from Aura/MLS and Terra/MOPITT instruments, respectively, are assimilated into the three-dimensional chemical transport model MOCAGE of Météo-France using a variational 3-D-FGAT (First Guess at Appropriate Time) method within the MOCAGE-PALM assimilation system. The usefulness of assimilated MOPITT CO data in a STE study is demonstrated in this novel result. The study shows that the use of the model MOCAGE gives consistent 3-D fields capable of describing the synoptic evolution of the event. However, modelled O3 and CO vertical distributions do not provide a quantitative evaluation of the intrusion. Although the assimilation of MLS data improves the distribution of O3 above the tropopause compared to the free model run, it is not sufficient to reproduce the stratospheric intrusion event well. Conversely, assimilated MOPITT CO allows a better description of the stratospheric intrusion event. Indeed, the horizontal distribution of the CO assimilated field is consistent with meteorological analyses. Moreover, the vertical distribution of the CO assimilated field is in accordance with the potential vorticity distribution and reveals a deeper intrusion from the lower stratosphere downward to the mid-troposphere compared to the O3 assimilated field. This study clearly demonstrates the capability of the assimilation of MOPITT CO to improve the CO distribution in the upper troposphere and lower stratosphere region. In addition, the behaviour of CO assimilated field is consistent with the synoptic evolution of the meteorological conditions. Therefore, the results of this study open the perspectives for using MOPITT CO in the STE studies.
Turbulence associated with mountain waves over Northern Scandinavia – a case study using the ESRAD VHF radar and the WRF mesoscale model
Authors: Kirkwood S. , Mihalikova M. , Rao T. N. , Satheesan K.
Published: April 2010

Abstract. We use measurements by the 52 MHz wind-profiling radar ESRAD, situated near Kiruna in Arctic Sweden, and simulations using the Advanced Research and Weather Forecasting model, WRF, to study vertical winds and turbulence in the troposphere in mountain-wave conditions on 23 , 24 and 25 January 2003. We find that WRF can accurately match the vertical wind signatures at the radar site when the spatial resolution for the simulations is 1 km. The horizontal and vertical wavelengths of the dominating mountain-waves are ∼10–20 km and the amplitudes in vertical wind 1–2 m/s. Turbulence below 5500 m height, is seen by ESRAD about 40% of the time. This is a much higher rate than WRF predictions for conditions of Richardson number (Ri) >1 but similar to WRF predictions of Ri>2. WRF predicts that air crossing the 100 km wide model domain centred on ESRAD has a ∼10% chance of encountering convective instabilities (Ri>0.) somewhere along the path. The cause of low Ri is a combination of wind-shear at synoptic upper-level fronts and perturbations in static stability due to the mountain-waves. Comparison with radiosondes suggests that WRF underestimates wind-shear and the occurrence of thin layers with very low static stability, so that vertical mixing by turbulence associated with mountain waves may be significantly more than suggested by the model.
Spatial variation of modelled and measured NO, NO2 and O3 concentrations in the polluted urban landscape – relation to meteorology during the Göte-2005 campaign
Authors: Klingberg J. , Tang L. , Chen D. , Pihl Karlsson G. , Bäck E. , Pleijel H.
Published: April 2010

Abstract. Knowledge about temporal and spatial variations of the O3 and NOx relationship in the urban environment are necessary to assess the exceedance of air quality standards for NO2. Both reliable measurements and validated high-resolution air quality models are important to assess the effect of traffic emission on air quality. In this study, measurements of NO, NO2 and O3 concentrations were performed in Gothenburg, Sweden, during the Göte-2005 campaign in February 2005. The aim was to evaluate the variation of pollutant concentrations in the urban landscape in relation to urban air quality monitoring stations and wind speed. A brief description of the meteorological conditions and the air pollution situation during the Göte-2005 campaign was also given. Furthermore, the Air Pollution Model (TAPM) was used to simulate the NOx-regime close to an urban traffic route and the simulations were compared to the measurements. Important conclusions were that the pollutant concentrations varied substantially in the urban landscape and the permanent monitoring stations were not fully representative for the most polluted environments. As expected, wind speed strongly influenced measured pollutant concentrations and gradients. Higher wind speeds dilute NO2 due to stronger dispersion; while at the same time vertical transport of O3 is enhanced, which produces NO2 through oxidation of NO. The oxidation effect was predominant at the more polluted sites, while the dilution effect was more important at the less polluted sites. TAPM reproduced the temporal variability in pollutant concentrations satisfactorily, but was not able to resolve the situation at the most polluted site, due to the local scale site-specific conditions.
Depositional ice nucleation on solid ammonium sulfate and glutaric acid particles
Authors: Baustian K. J. , Wise M. E. , Tolbert M. A.
Published: April 2010

Abstract. Heterogeneous ice nucleation on solid ammonium sulfate and solid amorphous glutaric acid particles was studied using optical microscopy and Raman spectroscopy. Optical microscopy was used to detect selective nucleation events as water vapor was slowly introduced into an environmental sample cell. Particles that nucleated ice were dried via sublimation and examined in detail using Raman spectroscopy. Depositional ice nucleation occurred preferentially on just a few ammonium sulfate and glutaric acid particles in each sample. For freezing temperatures between 214 K and 235 K average ice saturation ratios of S=1.10±0.07 for solid ammonium sulfate and S=1.39±0.16 for solid amorphous glutaric acid particles were determined. Experiments with externally mixed particles further show that ammonium sulfate is a more potent ice nucleus that glutaric acid. Our results suggest that heterogeneous nucleation on ammonium sulfate may be an important pathway for atmospheric ice nucleation and cirrus cloud formation when solid aerosol particles are available for ice formation. This pathway for ice formation may be particularly significant near the tropopause region where sulfates are abundant and other species known to be good ice nuclei are depleted.
Comparison of a global-climate model to a cloud-system resolving model for the long-term response of thin stratocumulus clouds to preindustrial and present-day aerosol conditions
Authors: Lee S. S. , Penner J. E.
Published: April 2010

Abstract. The response of a case of thin, warm marine-boundary-layer (MBL) clouds to preindustrial (PI) and present-day (PD) conditions is simulated by a cloud-system resolving model (CSRM). Here, both the aerosol conditions and environmental conditions match those of a general circulation model (GCM). The environmental conditions are characterized by the initial condition and the large-scale forcings of humidity and temperature, as well as the surface fluxes. The response of the CSRM is compared to that simulated by GCM. The percentage increase of liquid-water path (LWP) due to a change from the PI to PD conditions is ~3 times larger in the CSRM than that in the GCM due to the formation of cumulus clouds. The formation of cumulus clouds is controlled by a larger increase in the surface latent-heat (LH) flux in the PD environment than in the PI environment rather than by the change in aerosols. However, the aerosol increase from the PI to PD level determines the LWP response in the stratocumulus clouds, while the impacts of changes in environmental conditions are negligible for stratocumulus clouds. The conversion of cloud liquid to rain through autoconversion and accretion plays a negligible role in the CSRM in the response to aerosols, whereas it plays a role that is as important as condensation in the GCM. Supplementary simulations show that increasing aerosols increase the sensitivity of the cloud responses to the PI and PD environmental conditions and that aerosol effects on clouds depend on the cloud type; the liquid water path (LWP) of warm cumulus clouds is more sensitive to aerosols than the LWP of stratocumulus clouds.
The organic fraction of bubble-generated, accumulation mode Sea Spray Aerosol (SSA)
Authors: Modini R. L. , Harris B. , Ristovski Z. D.
Published: April 2010

Abstract. Recent studies have detected a dominant accumulation mode (~100 nm) in the Sea Spray Aerosol (SSA) number distribution. There is evidence to suggest that particles in this mode are composed primarily of organics. To investigate this hypothesis we conducted experiments on NaCl, artificial SSA and natural SSA particles with a Volatility-Hygroscopicity-Tandem-Differential-Mobility-Analyser (VH-TDMA). NaCl particles were atomiser generated and a bubble generator was constructed to produce artificial and natural SSA particles. Natural seawater samples for use in the bubble generator were collected from biologically active, terrestrially-affected coastal water in Moreton Bay, Australia. Differences in the VH-TDMA-measured volatility curves of artificial and natural SSA particles were used to investigate and quantify the organic fraction of natural SSA particles. Hygroscopic Growth Factor (HGF) data, also obtained by the VH-TDMA, were used to confirm the conclusions drawn from the volatility data. Both datasets indicated that the organic fraction of our natural SSA particles evaporated in the VH-TDMA over the temperature range 170–200°C. The organic volume fraction for 71–77 nm natural SSA particles was 8±6%. Organic volume fraction did not vary significantly with varying water residence time (40 s0 to 24 h) in the bubble generator or SSA particle diameter in the range 38–173 nm. At room temperature we measured shape- and Kelvin-corrected HGF at 90% RH of 2.46±0.02 for NaCl, 2.35±0.02 for artifical SSA and 2.26±0.02 for natural SSA particles. Overall, these results suggest that the natural accumulation mode SSA particles produced in these experiments contained only a minor organic fraction, which had little effect on hygroscopic growth. Our measurement of 8±6% is an order of magnitude below two previous measurements of the organic fraction in SSA particles of comparable sizes. Further studies with a variety of different seawaters are required to better quantify how much organic material is present in accumulation mode SSA.
Statistical properties of aerosol-cloud-precipitation interactions in South America
Authors: Jones T. A. , Christopher S. A.
Published: April 2010

Abstract. Given the complex interaction between aerosol, cloud, atmospheric properties, it is difficult to extract their individual effects to observed rainfall amount. This research uses principle component analysis (PCA) that combines Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol and cloud products, NCEP Reanalysis atmospheric products, and rainrate estimates from the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) to assess the specific combinations of these inputs that most affect warm rain processes. Data collected during September 2006 over the South America, which includes the Amazon basin, are used as aerosols, clouds, and precipitation are all present in this region at this time. The goal of this research is to combine these observations into a smaller number of variables through PCA with each having a unique physical interpretation. In particular, we are concerned with PC variables whose weightings include aerosol optical thickness (AOT), as these may be an indicator of aerosol indirect effects. If they are indeed occurring, then PC values that include AOT should change as a function of rainrate. To emphasize the advantage of PCA, changes in aerosol, cloud, and atmospheric observations are compared to rainrate. Comparing no-rain, rain, and heavy rain (>5 mm h−1) samples, cloud thicknesses, humidity, and upward motion are all larger for the rain and heavy rain samples. However, no statistically significant difference in AOT exists, indicating that atmospheric conditions are more important to rainfall than aerosol concentrations as expected. If aerosols are affecting warm process clouds, it would be expected that stratiform precipitation would decrease as a function increasing aerosol concentration through either Twomey and/or semi-direct effects. PCA extracts the latter signal in a variable labeled PC2, which explains 15% of the total variance and is second in importance the variable (PC1) containing the broad atmospheric conditions. PC2 contains weightings showing that AOT is inversely proportional to low-level humidity and cloud optical thickness. Increasing AOT is also positively correlated with increasing low-level instability due to aerosol absorption. The nature of these weightings is strongly suggestive that PC2 is an indicator of the semi-direct effect with larger values associated with lower rainfall rates. PC weightings consistent with the Twomey effect (an anti-correlation between AOT and cloud droplet effective radius) are only present in PC13, which explains less than 1% of the total variance. Also, it does not vary significantly with rainrate. Thus, if the Twomey effect is occurring, it is highly non-linear and/or being overshadowed by other processes. Using the raw variables alone, these determinations could not be made; thus, we are able to show the advantage of using advanced statistical techniques such as PCA for analysis of aerosols impacts on precipitation in South America.
Water-soluble atmospheric HULIS in urban environments
Authors: Baduel C. , Voisin D. , Jaffrezo J.-L.
Published: April 2010

Abstract. Major contributors to the organic aerosol include water-soluble macromolecular compounds (e.g. HULISWS). The nature and sources of HULISWSare still largely unknown. This work is based on a monitoring in six different French cities performed during summer and winter seasons. HULISWS analysis was performed with a selective method of extraction complemented by carbon quantification. UV spectroscopy was also applied for their chemical characterisation. Strong differences in the optical properties and therefore in the chemical structure (i.e. the aromaticity) between HULISWS from samples of summer- and wintertime are found. These differences highlight different processes responsible for emissions and formation of HULISWS according to the season. Specific absorbance can also be considered as a rapid and useful indicator of the origin of HULISWS in urban environment.
Hydrogen cyanide in the upper troposphere: GEM-AQ simulation and comparison with ACE-FTS observations
Authors: Lupu A. , Kaminski J. W. , Neary L. , McConnell J. C. , Toyota K. , Rinsland C. P. , Bernath P. F. , Walker K. A. , Boone C. D. , Nagahama Y. , Suzuki K.
Published: April 2010

Abstract. We investigate the spatial and temporal distribution of hydrogen cyanide (HCN) in the upper troposphere through numerical simulations and comparison with observations from a space-based instrument. To perform the simulations, we used the Global Environmental Multiscale Air Quality model (GEM-AQ), which is based on the three-dimensional global multiscale model developed by the Meteorological Service of Canada for operational weather forecasting. The model was run for the period 2004–2006 on a 1.5°×1.5° global grid with 28 hybrid vertical levels from the surface up to 10 hPa. Objective analysis data from the Canadian Meteorological Centre were used to update the meteorological fields every 24 h. Fire emission fluxes of gas species were generated by using year-specific inventories of carbon emissions with 8-day temporal resolution from the Global Fire Emission Database (GFED) version 2. The model output is compared with HCN profiles measured by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) instrument onboard the Canadian SCISAT-1 satellite. High values of up to a few ppbv are observed in the tropics in the Southern Hemisphere; the enhancement in HCN volume mixing ratios in the upper troposphere is most prominent in October. Low upper-tropospheric mixing ratios of less than 100 pptv are mostly recorded at middle and high latitudes in the Southern Hemisphere in May–July. Mixing ratios in Northern Hemisphere peak in the boreal summer. The amplitude of the seasonal variation is less pronounced than in the Southern Hemisphere. Our model results show that in the upper troposphere GEM-AQ performs well globally for all seasons, except at Northern high and middle latitudes in summer, where the model has a large negative bias, and in the tropics in winter and spring, where it exhibits large positive bias. This may reflect inaccurate emissions or possible inaccuracies in the emission profile. The model is able to explain most of the observed variability in the upper troposphere HCN field, including the interannual variations in the observed mixing ratio. The estimated average global emission equals 1.3 Tg N yr−1. The average atmospheric burden is 0.53 Tg N, and the corresponding lifetime is 4.9 months.
Molecular characterization of urban organic aerosol in tropical India: contributions of biomass/biofuel burning, plastic burning, and fossil fuel combustion
Authors: Fu P. Q. , Kawamura K. , Pavuluri C. M. , Swaminathan T.
Published: April 2010

Abstract. Organic molecular composition of PM10 samples, collected at Chennai in tropical India, was studied using capillary gas chromatography/mass spectrometry. Twelve organic compound classes were detected in the aerosols, including aliphatic lipids, sugar compounds, lignin products, terpenoid biomarkers, sterols, aromatic acids, phthalates, hopanes, and polycyclic aromatic hydrocarbons (PAHs). At daytime, phthalates was found to be the most abundant compound class; while at nighttime, fatty acids was the dominant one. Concentrations of total quantified organics were higher in summer (611–3268 ng m−3, average 1586 ng m−3) than in winter (362–2381 ng m−3, 1136 ng m−3), accounting for 11.5±1.93% and 9.35±1.77% of organic carbon mass in summer and winter, respectively. Di-(2-ethylhexyl) phthalate, C16 fatty acid, and levoglucosan were identified as the most abundant single compounds. The nighttime maxima of most organics in the aerosols indicate a land/sea breeze effect in tropical India, although some other factors such as local emissions and long-range transport may also influence the composition of organic aerosols. The abundances of anhydrosugars (e.g., levoglucosan), lignin and resin products, hopanes and PAHs in the Chennai aerosols suggest that biomass burning and fossil fuel combustion are significant sources of organic aerosols in tropical India. Interestingly, terephthalic acid was maximized at nighttime, which is different from those of phthalic and isophthalic acids. A positive correlation was found between the concentration of 1,3,5-triphenylbenzene (a tracer for plastic burning) and terephthalic acid, suggesting that field burning of municipal solid wastes including plastics is a significant source of terephthalic acid. This study demonstrates that, in addition to biomass burning and fossil fuel combustion, the open-burning of plastics also contributes to the organic aerosols in South Asia.
Physicochemical properties and origin of organic groups detected in boreal forest using an aerosol mass spectrometer
Authors: Raatikainen T. , Vaattovaara P. , Tiitta P. , Miettinen P. , Rautiainen J. , Ehn M. , Kulmala M. , Laaksonen A. , Worsnop D. R.
Published: April 2010

Abstract. An Aerodyne quadrupole aerosol mass spectrometer (Q-AMS) was deployed in Hyytiälä, a forested rural measurement site in southern Finland, during a 2-week measurement campaign in spring 2005. Q-AMS measures mass concentrations of non-refractory species including sulphate, nitrate, ammonium and organics from submicron particles. A positive matrix factorization method was used in identifying two oxygenated organic aerosol (OOA) groups from the measured total organic mass. The properties of these groups were estimated from their diurnal concentration cycles and correlations with additional data such as air mass history, particle number size distributions, hygroscopic and ethanol growth factors and particle volatility. It was found that the aged and highly oxidized background organic aerosol (OOA1) species have a wide range of hygroscopic growth factors and volatilization temperatures, but on the average OOA1 is the less volatile and hygroscopic organic group. It seems that hygroscopic properties and volatilities of the OOA1 species are correlated so that the less volatile species have higher hygroscopic growth factors. The other less oxidized organic aerosol group (OOA2) is more volatile and non-hygroscopic. Trajectory analysis showed that OOA1 and the inorganic species are mainly long-range transported anthropogenic pollutions. On the other hand, OOA2 species and its precursor gases have short atmospheric life times, so they are from local sources. Current results are in good agreement with previous studies, but additional data especially from other seasons is required to verify the generality of the conclusions.
Pollution plumes observed during CARIBIC flights in the upper troposphere between South China and the Philippines
Authors: Lai S. C. , Baker A. K. , Schuck T. J. , van Velthoven P. , Oram D. E. , Zahn A. , Hermann M. , Weigelt A. , Slemr F. , Brenninkmeijer C. A. M.
Published: April 2010

Abstract. A strong pollution episode in the upper troposphere between South China and the Philippines was observed during CARIBIC flights in April 2007. Five pollution plumes were intersected and enhancements in aerosol and trace gas concentrations including CO, CO2, CH4, non-methane hydrocarbons (NMHCs) and halocarbons were observed along the flight tracks during four sequential flights. The importance of the contribution of biomass burning was investigated using chemical tracers, emission factor analysis, back-trajectory analysis and satellite images. The Indochinese peninsula was identified as the probable source region of biomass/biofuel burning. However, enhancements in the urban/industrial tracer C2Cl4 in the plumes also indicate a substantial contribution from anthropogenic emissions. An estimation of the anthropogenic component of CO shows that biomass/biofuel burning contributed 44–63% to the intersected plumes.
Analysis of snow bidirectional reflectance from ARCTAS spring-2008 campaign
Authors: Lyapustin A. , Gatebe C. K. , Kahn R. , Brandt R. , Redemann J. , Russell P. , King M. D. , Pedersen C. A. , Gerland S. , Poudyal R. , Marshak A. , Wang Y. , Schaaf C. , Hall D. , Kokhanovsky A.
Published: April 2010

Abstract. The spring 2008 Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) experiment was one of the major intensive field campaigns of the International Polar Year, aimed at detailed characterization of atmospheric physical and chemical processes in the Arctic region. Part of this campaign was a unique snow bidirectional reflectance experiment on the NASA P-3B aircraft conducted on 7 and 15 April by the Cloud Absorption Radiometer (CAR) jointly with airborne Ames Airborne Tracking Sunphotometer (AATS) and ground-based Aerosol Robotic Network (AERONET) sunphotometers. The CAR data were atmospherically corrected to derive snow bidirectional reflectance at high 1° angular resolution in view zenith and azimuthal angles along with surface albedo. The derived albedo was generally in good agreement with ground albedo measurements collected on 15 April. The CAR snow bidirectional reflectance factor (BRF) was used to study the accuracy of analytical Ross-Thick Li-Sparse (RTLS), Modified Rahman-Pinty-Verstraete (MRPV) and Asymptotic Analytical Radiative Transfer (AART) BRF models. Except for the glint region (azimuthal angles φ<40°), the best fit MRPV and RTLS models fit snow BRF to within ±0.05. The plane-parallel radiative transfer (PPRT) solution was also analyzed with the models of spheres, spheroids, randomly oriented fractal crystals, and with a synthetic phase function. The latter merged the model of spheroids for the forward scattering angles with the fractal model in the backscattering direction. The PPRT solution with synthetic phase function provided the best fit to measured BRF in the full range of angles. Regardless of the snow grain shape, the PPRT model significantly over-/underestimated snow BRF in the glint/backscattering regions, respectively, which agrees with other studies. To improve agreement with the experiment, we introduced a model of macroscopic snow surface roughness by averaging the PPRT solution over the slope distribution function and by adding a simple model of shadows. With macroscopic roughness described by two parameters, the AART model achieved an accuracy of about ±0.05 with a possible bias of ±0.03 in the spectral range 0.4–2.2 μm. This high accuracy holds at view zenith angles below 55–60° covering the practically important range for remote sensing applications, and includes both glint and backscattering directions.
An evaluation of the SAGE III Version 4 aerosol extinction coefficient and water vapor data products
Authors: Thomason L. W. , Moore J. R. , Pitts M. C. , Zawodny J. M. , Chiou E.-W.
Published: April 2010

Abstract. Herein, we provide an assessment of the data quality of Stratospheric Aerosol and Gas Experiment (SAGE III) Version 4 aerosol extinction coefficient and water vapor data products. The evaluation is based on comparisons with data from four instruments: SAGE II, the Polar Ozone and Aerosol Measurement (POAM III), the Halogen Occultation Experiment (HALOE), and the Microwave Limb Sounder (MLS). Since only about half of the SAGE III channels have a direct comparison with measurements by other instruments, we have employed some empirical techniques to evaluate measurements at some wavelengths. We find that the aerosol extinction coefficient measurements at 449, 520, 755, 869, and 1021 nm are reliable with accuracies and precisions on the order of 10% in the primary aerosol range of 15 to 25 km. We also believe this to be true of the aerosol measurements at 1545 nm though we cannot exclude some positive bias below 15 km. We recommend use of the 385 nm measurements above 16 km where the accuracy is on par with other aerosol channels. The 601 nm measurement is much noisier (~20%) than other channels and we suggest caution in the use of these data. We believe that the 676 nm data are clearly defective particularly above 20 km (accuracy as poor as 50%) and the precision is also low (~30%). We suggest excluding this channel under most circumstances. The SAGE III Version 4 water vapor data product appears to be high quality and is recommended for science applications in the stratosphere below 45 km. In this altitude range, the mean differences with all four corroborative data sets are no bigger than 15% and often less than 10% with exceptional agreement with POAM III and MLS. Above 45 km, it seems likely that SAGE III water vapor values are increasingly too large and should be used cautiously or avoided. We believe that SAGE III meets its preflight goal of 15% accuracy and 10% precision between 15 and 45 km. We do not currently recommend limiting the SAGE III water vapor data utility in the stratosphere by aerosol loading.
Seasonality of Peroxyacetyl nitrate (PAN) in the upper troposphere and lower stratosphere using the MIPAS-E instrument
Authors: Moore D. P. , Remedios J. J.
Published: April 2010

Abstract. The Michelson Interferometer for Passive Atmospheric Sounding onboard ENVISAT (MIPAS-E) offers the opportunity to detect and spectrally resolve many atmospheric minor constituents affecting atmospheric chemistry. In this paper, we retrieve global, seasonal PAN volume mixing ratio (vmr) data from MIPAS-E measurements made in January, March, August and October 2003 and present results from this scheme between approximately 300 and 150 hPa. The total error on a single PAN retrieval is better than 20% outside the tropics and better than 50% in the tropics where uncertainties in water vapor dominate the total error budget. We observe clear differences in the seasonal cycle of PAN in our data, linked closely to biomass burning regions and growing seasons. Highest Northern Hemisphere mid-latitude PAN vmrs were observed in August (300–600 pptv on average) compared with the January and October data (less than 250 pptv on average). In the March 2003 data we observe highest PAN vmrs in the tropics with evidence of vmrs between 600 and 1000 pptv over Eastern Asia and over the Central Pacific at 333 hPa. The vertical distribution of PAN as a function of latitude (i.e. the zonal mean) highlights the strong inter-annual variability of PAN in the upper troposphere and lower stratosphere (UTLS), most pronounced poleward of 40° N (up to 400 pptv over the year). The variability of PAN in the tropical UTLS is also significant and we derive a variability of up to 250 pptv in the averages between January and October 2003. These results represent the first seasonal observations of PAN in the UTLS.
Widening the gap between measurement and modelling of secondary organic aerosol properties?
Authors: Good N. , Topping D. O. , Duplissy J. , Gysel M. , Meyer N. K. , Metzger A. , Turner S. F. , Baltensperger U. , Ristovski Z. , Weingartner E. , Coe H. , McFiggans G.
Published: April 2010

Abstract. The link between measured sub-saturated hygroscopicity and cloud activation potential of secondary organic aerosol particles produced by the chamber photo-oxidation of α-pinene in the presence or absence of ammonium sulphate seed aerosol was investigated using two models of varying complexity. A simple single hygroscopicity parameter model and a more complex model (incorporating surface effects) were used to assess the detail required to predict the cloud condensation nucleus (CCN) activity from the sub-saturated water uptake. Sub-saturated water uptake measured by three hygroscopicity tandem differential mobility analyser (HTDMA) instruments was used to determine the water activity for use in the models. The predicted CCN activity was compared to the measured CCN activation potential using a continuous flow CCN counter. Reconciliation using the more complex model formulation with measured cloud activation required widely different assumed surface tension behavior of the growing droplet; this was entirely determined by the instrument used as the source of water activity data. This unreliable derivation of the water activity as a function of solute concentration from sub-saturated hygroscopicity data indicates a limitation in the use of such data in predicting cloud condensation nucleus behavior of particles with a significant organic fraction. Similarly, the ability of the simpler single parameter model to predict cloud activation behaviour was dependent on the instrument used to measure sub-saturated hygroscopicity and the relative humidity used to provide the model input. However, agreement was observed for inorganic salt solution particles, which were measured by all instruments in agreement with theory. The difference in HTDMA data from proven instruments means that it cannot be stated with certainty the detail required to predict the CCN activity from sub-saturated hygroscopicity. In order to narrow the gap between measurements of hygroscopic growth and CCN activity the processes involved must be understood. It is impossible to say from the results presented here whether: i) Surface tension suppression occurs ii) Bulk to surface partitioning is important iii) The water activity coefficient changes significantly as a function of the solute concentration.
Particle characterization at the Cape Verde atmospheric observatory during the 2007 RHaMBLe intensive
Authors: Müller K. , Lehmann S. , van Pinxteren D. , Gnauk T. , Niedermeier N. , Wiedensohler A. , Herrmann H.
Published: April 2010

Abstract. The chemical characterization of filter high volume (HV) and Berner impactor (BI) samples PM during RHaMBLe 2007 shows that the Cape Verde aerosol particles are mainly composed of sea salt, mineral dust and associated water. The influence from the African continent on the aerosol constitution was generally small but air masses which came from south-western Europe crossing the Canary Islands transported dust to the sampling site together with other loadings. The mean mass concentration was determined for PM10 as 17 μg/m3 from the impactor samples and as 24.2 μg/m3 from HV filter samples. Non sea salt (nss) components of PM were found in the submicron fractions including nitrate in the coarse mode fraction. Bromide was found in all samples with much depleted concentrations in the range 1–8 ng/m3 compared to fresh sea salt aerosol indicating intense atmospheric halogen chemistry. A chloride deficit of 31% and 38% for the coarse mode particles (3.5–10 μm; 1.2–3.5 μm), of 67% (0.42–1.2 μm) and 83% (0.14–0.42 μm) for the submicron fractions was determined. During 14 May with high mineral dust loads also the maximum of OC (1.71 μg/m3) and EC (1.25 μg/m3) was measured. The minimum of TC (0.25 μg/m3) was detected during the period 25 to 27 May when pure marine air masses arrived. The concentrations of carbonaceous material decrease with increasing particles size from 60% for the ultra fine particles to 2.5% in coarse mode PM. Total iron (dust vs. non-dust: 0.53 vs. 0.06 μg m−3), calcium (0.22 vs. 0.03 μg m−3) and potassium (0.33 vs. 0.02 μg m−3) were found as good indicators for dust periods because of their heavily increased concentration in the 1.2 to 3.5 μm fraction as compared to their concentration during the non-dust periods. For the organic constituents, oxalate (78–151 ng/m3) and methanesulfonic acid (MSA, 25–100 ng/m3) are the major compounds identified. A good correlation between nss-sulphate and MSA was found for the majority of days indicating active DMS chemistry and low anthropogenic influences.
Bimodal variation in mercury wet deposition to the coastal zone of the southern Baltic
Authors: Siudek P. , Falkowska L. , Urba A.
Published: April 2010

Abstract. In the following periods: November 2005–June 2006 and October 2007–January 2009, concentrations and deposition rates of total mercury (THg) and Hg(II) were measured in precipitation over the urbanized and industrialized area of the southern Baltic – the city of Gdynia. Rains over the coastal zone had different concentrations of total mercury, they ranged from 8.6 to 118.0 ng L−1, out of which about 32% were labile, inorganic forms, easily reducible in a SnCl2 solution. Over the southern Baltic two maxima of concentrations were observed: first, in the heating season and second, in the non-heating season. Elevated concentrations of mercury in precipitations during heating seasons were the result of the activity of local emission sources (intensive combustion of fossil fuels in domestic furnaces and individual power and heat generating plants). During the warm season, precipitation over the southern Baltic could clean the air from Hg reemitted from sea and land surfaces. Precipitations, which purified marine and continental air masses were responsible for the comparable input of mercury to the coastal zone. The wet deposition value in 2008 was estimated to be 28.9 μg m−2. In the coastal zone of the southern Baltic, acid precipitations with the elevated Hg concentrations are very frequent.
The municipal solid waste landfill as a source of ozone-depleting substances in the United States and United Kingdom
Authors: Hodson E. L. , Martin D. , Prinn R. G.
Published: April 2010

Abstract. This study provides observation-based national estimates of CFC-11, CFC-12, CFC-113, and 1,1,1-trichloroethane emissions for the United States (US) and United Kingdom (UK) from municipal solid waste (MSW) landfills. The scarcity of national estimates has lead to the assumption that a significant fraction of the lingering ozone-depleting substance (ODS) emissions, which have been detected in industrialized countries, could be emitted from landfills. Spatial coverage was achieved through sampling at seven landfills in Massachusetts and through data provided by nine UK landfills. Linear least square regressions of recovered ODS vs. CH4 were used in combination with national estimates of landfill CH4 emissions to estimate 2006 national US and UK ODS landfill emissions. The ODS landfill emission estimates were then compared to recent estimates of total US and UK ODS emissions. US ODS landfill emissions were 0.4%–0.9% (0.006–0.09 Gg/year) of total US emissions. UK ODS landfill emission estimates were 1% (0.008 Gg/year) and 6% (0.03 Gg/year) of total UK CFC-11 and CFC-12 emissions, respectively. This indicates that landfills are only a minor source of lingering ODS emissions in the US, but may be more significant for CFC-12 emissions in the UK. The implications are that the majority of current ODS emissions in industrialized countries are likely coming from equipment still in use.
Eta-CMAQ air quality forecasts for O3 and related species using three different photochemical mechanisms (CB4, CB05, SAPRC-99): comparisons with measurements during the 2004 ICARTT study
Authors: Yu S. , Mathur R. , Sarwar G. , Kang D. , Tong D. , Pouliot G. , Pleim J.
Published: April 2010

Abstract. A critical module of air quality models is the photochemical mechanism. In this study, the impact of three photochemical mechanisms (CB4, CB05, SAPRC-99) on the Eta-Community Multiscale Air Quality (CMAQ) model's forecast performance for O3, and its related precursors has been assessed over the eastern United States with the observations obtained by aircraft (NOAA P-3 and NASA DC-8) flights, ship and two surface networks (AIRNow and AIRMAP) during the 2004 International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) study. The results at the AIRNow surface sites show that for the observed O3≥75 ppb, CB05 has the best performance with the normalized mean bias (NMB) of 3.9%, followed by CB4 (NMB=−5.7%) and SAPRC-99 (NMB=10.6%), whereas CB4 has the best performance with the least overestimation for the observed O3<75 ppb. On the basis of comparisons with aircraft P-3 measurements, there were consistent overestimations of O3, NOz, PAN and NOy and consistent underestimations of CO, HNO3, NO2, NO, SO2 and terpenes for all three mechanisms although the NMB values for each species and mechanisms were different. The results of aircraft DC-8 show that CB05 predicts the H2O2 mixing ratios most closely to the observations (NMB=10.8%), whereas CB4 and SAPRC-99 overestimated (NMB=74.7%) and underestimated (NMB=−25.5%) H2O2 significantly, respectively. For different air mass flows over the Gulf of Maine on the basis of the ship data, the three mechanisms have relatively better performance for O3, isoprene and SO2 for the clean marine or continental flows but relatively better performance for CO, NO2 and NO for southwest/west offshore flows. The results of the O3-NOz slope over the ocean indicate that SAPRC-99 has the highest upper limits of the ozone production efficiency (εN) (5.8), followed by CB05 (4.5) and CB4 (4.0) although they are much lower than that inferred from the observation (11.8), being consistent with the fact that on average, SAPRC-99 produces the highest O3, followed by CB05 and CB4, across all O3 mixing ratio ranges.
Study on the impact of sudden stratosphere warming in the upper mesosphere-lower thermosphere regions using satellite and HF radar measurements
Authors: Mbatha N. , Sivakumar V. , Malinga S. B. , Bencherif H. , Pillay S. R.
Published: April 2010

Abstract. The occurrence of sudden stratospheric warming (SSW) excites disturbances in the mesosphere-lower thermospheric (MLT) wind and temperature. Here, we have examined the high frequency (HF) radar wind data from the South African National Antarctic Expedition, SANAE (72° S, 3° W), a radar which is part of the Super Dual Auroral Radar Network (SuperDARN). Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on board the Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics (TIMED) satellite temperature data and National Centre for Environmental Prediction (NCEP) temperature and wind data were use to investigate the dynamical effects of the unprecedented September 2002 SSW in the Antarctica stratosphere and MLT. The mean zonal wind (from SANAE HF radar) at the MLT shows reversal in approximately 7 days before the reversal at 10 hPa (from NCEP). This indicates that there was a downwards propagation of circulation disturbance. Westerly zonal winds dominate the winter MLT, but during the 2002 winter there were many periods of westward winds observed compared to other years. The dynamic spectrums of both meridional and zonal winds show presence of planetary waves (of ~14-day period) before the occurrence of the SSW. The SABER vertical temperature profiles indicated the cooling of the MLT region before the SSW event.
Latitudinal gradient and interannual variation of PM10 concentration over eighty-six Chinese cities
Authors: Qu W. J. , Arimoto R. , Zhang X. Y. , Wang Y. Q. , Sheng L. F. , Fu G.
Published: April 2010

Abstract. The spatial distribution of the aerosols over 86 major Chinese cities was constructed from 137 845 daily averaged PM10 (particles with diameter ≤10 μm) concentrations calculated from air pollution index (API) records spanning from summer 2000 to winter 2006. This dataset was based on days when PM10 was categorized as the principal pollutant, accounting for 91.6% of the total recorded days. The 83 cities in mid-eastern China (longitude 100° E to 130° E) were separated into three latitudinal zones with the Qinlin Mountain – the Huaihe River and the Yunnan-Guizhou Plateau – the Jiangnan Hill – the Wuyi Mountain as the boundaries. The spatial distribution of PM10 was complicated; the high-value spots in northern China (concentration ranged from 127.1 to 192.1 μg m−3) included Urumchi, Lanzhou-Xining, Weinan-Xi'an, Taiyuan-Datong-Yangquan-Changzhi, Pingdingshan-Kaifeng, Beijing-Tianjin-Shijiazhuang, Jinan, and Shenyang-Anshan-Fushun; in the middle zone, the high PM10 spots (concentration within 119.1–146.6 μg m−3) were Chongqing-Chengdu-Luzhou, Changsha-Wuhan, and Nanjing-Hangzhou; while in the southern zone, four cities (Qujing, Guiyang, Guangzhou and Shaoguan) showed higher PM10 concentration (>80 μg m−3). An overall latitudinal gradient was distinct; the median PM10 concentrations decreased from 108 μg m−3 for the 38 northern cities to 95 μg m−3 and 55 μg m−3 for the middle (26 cities) and southern (19 cities) zones, respectively. Linear regression between PM10 concentration and latitude of the cities also confirmed this gradient. PM10 concentration and the APIs exhibited similar seasonality with wintertime maxima and summertime minima, and the second highest values in spring. PM10 level showed a decreasing trend (−23.2 μg m−3) for the northern cities during 2000 to 2006. For the other two zones, the PM10 levels fluctuated, but showed unobvious change (−1.7 μg m−3) for the middle zone and increased slightly (+6.2 μg m−3) for the southern zone during the course.
The impact of MM5 and WRF meteorology over complex terrain on CHIMERE model calculations
Authors: de Meij A. , Gzella A. , Thunis P. , Cuvelier C. , Bessagnet B. , Vinuesa J. F. , Menut L.
Published: April 2010

Abstract. The objective of this study is to evaluate the impact of meteorological input data on calculated gas and aerosol concentrations. We use two different meteorological models (MM5 and WRF) together with the chemistry transport model CHIMERE. We focus on the Po valley area (Italy) for January and June 2005. Firstly we evaluate the meteorological parameters with observations. The analysis shows that the performance of both models is similar, however some small differences are still noticeable. Secondly, we analyze the impact of using MM5 and WRF on calculated PM10 and O3 concentrations. In general CHIMERE/MM5 and CHIMERE/WRF underestimate the PM10 concentrations for January. The difference in PM10 concentrations for January between CHIMERE/MM5 and CHIMERE/WRF is around a factor 1.6 (PM10 higher for CHIMERE/MM5). This difference and the larger underestimation in PM10 concentrations by CHIMERE/WRF are related to the differences in heat fluxes and the resulting PBL heights calculated by WRF. In general the PBL height by WRF meteorology is a factor 2.8 higher at noon in January than calculated by MM5. This study showed that the difference in microphysics scheme has an impact on the profile of cloud liquid water (CLW) calculated by the meteorological driver and therefore on the production of SO4 aerosol. A sensitivity analysis shows that changing the Noah Land Surface Model (LSM) for the 5-layer soil temperature model, the calculated monthly mean PM10 concentrations increase by 30%, due to the change in the heat fluxes and the resulting PBL heights. For June, PM10 calculated concentrations by CHIMERE/MM5 and CHIMERE/WRF are similar and agree with the observations. Calculated O3 values for June are in general overestimated by a factor 1.3 by CHIMERE/MM5 and CHIMRE/WRF. The reason for this is that daytime NO2 concentrations are a higher than the observations and nighttime NO concentrations (titration effect) are underestimated.
Ozone response to emission changes: a modeling study during the MCMA-2006/MILAGRO campaign
Authors: Song J. , Lei W. , Bei N. , Zavala M. , de Foy B. , Volkamer R. , Cardenas B. , Zheng J. , Zhang R. , Molina L. T.
Published: April 2010

Abstract. The sensitivity of ozone production to precursor emissions was investigated under five different meteorological conditions in the Mexico City Metropolitan Area (MCMA) during the MCMA-2006/MILAGRO field campaign using the gridded photochemical model CAMx driven by observation-nudged WRF meteorology. Precursor emissions were constrained by the comprehensive data from the field campaign and the routine ambient air quality monitoring network. Simulated plume mixing and transport were examined by comparing with measurements from the G-1 aircraft during the campaign. The observed concentrations of ozone precursors and ozone were well reproduced by the model. The effects of reducing precursor emissions on urban ozone production were performed for three representative emission control strategies. A 50% reduction in VOC emissions led to 7 to 22 ppb decrease in daily maximum ozone concentrations, while a 50% reduction in NOx emissions leads to 4 to 21 ppb increase, and 50% reductions in both NOx and VOC emission decrease the daily maximum ozone concentrations up to 10 ppb. These results along with a chemical indicator analysis using the chemical production ratios of H2O2 to HNO3 demonstrate that the MCMA urban core region is VOC-limited for all meteorological episodes, which is consistent with the results from MCMA-2003 field campaign; however the degree of the VOC-sensitivity is higher in the MCMA-2006 due to lower VOC/NOx emission ratio and VOC reactivity. Ozone formation in the surrounding mountain/rural area is mostly NOx-limited, but can be VOC-limited, and the range of the NOx-limited or VOC-limited areas depends on meteorology.