bluuebunny/crossref_metadata_2025 huggingface dataset:
Positive sampling artifact of carbonaceous aerosols and its influence on the thermal-optical split of OC/EC
Authors: Cheng Y. , He K. B. , Duan F. K. , Zheng M. , Ma Y. L. , Tan J. H.
Published: April 2010

Abstract. Accurate measurement of carbonaceous aerosols is challenging, due to the sampling artifact and the problems of the split of OC/EC. Two approaches have been used to account for the positive artifact: backup quartz approach in which a backup quartz filter is placed either behind a front quartz filter (QBQ) or in a parallel port behind a Teflon filter (QBT), and organic denuder approach in which an organic denuder is placed upstream of the quartz filter. Both approaches were evaluated in Beijing, China, from January to February 2009. 10% of the OC captured by the bare quartz filter was from the positive artifact. The origin of backup OC was quantitatively evaluated by the denuder-based method. All of the QBQ OC was from gaseous organics passing through the front filter, but the QBQ had not reached equilibrium with gas phase due to the relative small sampling volume resulting in an undercorrection of the positive artifact by 3.7%. QBT OC was from both gaseous organics passing through the front filter (82%) and the evaporated organic carbon (18%), thus overcorrecting the positive artifact by 6.3%. Even the positive artifact-contributed QBT OC was found to overestimate the positive artifact, perhaps due to the difference in the adsorption properties of the loaded filter and the filter without particle loading. Re-partitioning of PC and EC was performed by the multiple linear regression approach. The attenuation coefficient of PC was twofold higher than that of EC, indicating PC was darker than EC, resulting in the underestimation of native EC by TOT-split-EC. It was also found that PC formed on the bare quartz filter (45.56 m2/g) was darker than that formed on the denuded filter (38.64 m2/g), indicating that the underestimation for the bare quartz filter was more significant.
Evolution of Asian aerosols during transpacific transport in INTEX-B
Authors: Dunlea E. J. , DeCarlo P. F. , Aiken A. C. , Kimmel J. R. , Peltier R. E. , Weber R. J. , Tomlinson J. , Collins D. R. , Shinozuka Y. , McNaughton C. S. , Howell S. G. , Clarke A. D. , Emmons L. K. , Apel E. C. , Pfister G. G. , van Donkelaar A. , Martin R. V. , Millet D. B. , Heald C. L. , Jimenez J. L.
Published: April 2010

Abstract. Measurements of aerosol composition were made with an Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) on board the NSF/NCAR C-130 aircraft as part of the Intercontinental Chemical Transport Experiment Phase B (INTEX-B) field campaign over the Eastern Pacific Ocean. The HR-ToF-AMS measurements of non-refractory submicron aerosol mass are shown to compare well with other aerosol instrumentation in the INTEX-B field study. Two case studies are described for pollution layers transported across the Pacific from the Asian continent, intercepted 3–4 days and 7–10 days downwind of Asia, respectively. Aerosol chemistry is shown to be a robust tracer for air masses originating in Asia, specifically the presence of sulfate dominated aerosol is a distinguishing feature of Asian pollution layers that have been transported to the Eastern Pacific. We examine the time scales of processing for sulfate and organic aerosol in the atmosphere and show that our observations confirm a conceptual model for transpacific transport from Asia proposed by Brock et al. (2004). Our observations of both sulfate and organic aerosol in aged Asian pollution layers are consistent with fast formation near the Asian continent, followed by washout during lofting and subsequent transformation during transport across the Pacific. Our observations are the first atmospheric measurements to indicate that although secondary organic aerosol (SOA) formation from pollution happens on the timescale of one day, the oxidation of organic aerosol continues at longer timescales in the atmosphere. Comparisons with chemical transport models of data from the entire campaign reveal an under-prediction of organic aerosol mass in the MOZART model, but much smaller discrepancies with the GEOS-Chem model than found in previous studies over the Western Pacific. No evidence is found to support a previous hypothesis for significant secondary organic aerosol formation in the free troposphere.
Intercomparison of Aerosol Optical Depth from Brewer Ozone spectrophotometers and CIMEL sunphotometers measurements
Authors: Cheymol A. , Gonzalez Sotelino L. , Lam K. S. , Kim J. , Fioletov V. , Siani A. M. , De Backer H.
Published: April 2010

Abstract. The Langley plot method applied on the Brewer Ozone measurements can provide accurate Aerosol Optical Depth (AOD) in the UV-B. We present seven intercomparisons between AOD retrieved from Brewer Ozone measurements at 320 nm and AOD measured by CIMEL sunphotometer at 340 nm or 440 nm (shifted to 320 nm in using the Angström's law), which are stored in the international AERONET database. Only the intercomparisons between co-located instruments can be used to validate the Langley Plot Method applied to the Brewer measurements: in this case, all the correlation coefficients are above 0.82. If the instruments are not at the same site, the correlation between the AOD retrieved by both instruments is much lower. In applying the Angström's law the intercomparison is improved compared to previous study.
Detailed heterogeneous chemistry in an urban plume box model: reversible co-adsorption of O3, NO2, and H2O on soot coated with benzo[a]pyrene
Authors: Springmann M. , Knopf D. A. , Riemer N.
Published: April 2010

Abstract. This study assesses in detail the effects of heterogeneous chemistry on the particle surface and gas-phase composition by modeling the reversible co-adsorption of O3, NO2, and H2O on soot coated with benzo[a]pyrene (BaP) for an urban plume scenario over a period of five days. By coupling the Pöschl-Rudich-Ammann (PRA) kinetic framework for aerosols (Pöschl et al., 2007) to a box model version of the gas phase mechanism RADM2, we are able to track individual concentrations of gas-phase and surface species over the course of several days. The flux-based PRA formulation takes into account changes in the uptake kinetics due to changes in the chemical gas-phase and particle surface compositions. This dynamic uptake coefficient approach is employed for the first time in a broader atmospheric context of an urban plume scenario. Our model scenarios include one to three adsorbents and three to five coupled surface reactions. The results show a variation of the O3 and NO2 uptake coefficients of more than five orders of magnitude over the course of the simulation time and a decrease in the uptake coefficients in the various scenarios by more than three orders of magnitude within the first six hours. Thereafter, periodic peaks of the uptake coefficients follow the diurnal cycle of gas-phase O3-NOx reactions. Physisorption of water vapor reduces the half-life of the coating substance BaP by up to a factor of seven by permanently occupying ~75% of the soot surface. Soot emissions modeled by replenishing reactive surface sites lead to maximum gas-phase O3 depletions of 41 ppbv and 7.8 ppbv for an hourly and six-hourly replenishment cycle, respectively. This conceptual study highlights the interdependence of co-adsorbing species and their non-linear gas-phase feedback. It yields further insight into the atmospheric importance of the chemical oxidation of particles and emphasizes the necessity to implement detailed heterogeneous kinetics in future modeling studies.
Reactive nitrogen in atmospheric emission inventories
Authors: Reis S. , Pinder R. W. , Zhang M. , Lijie G. , Sutton M. A.
Published: April 2010

Abstract. Excess reactive Nitrogen (Nr) has become one of the most pressing environmental problems leading to air pollution, acidification and eutrophication of ecosystems, biodiversity impacts, leaching of nitrates into groundwater and global warming. This paper investigates how current inventories cover emissions of Nr to the atmosphere in Europe, the United States of America, and China. The focus is on anthropogenic sources, assessing the state-of-the-art of quantifying emissions of Ammonia (NH3), Nitrogen Oxides (NOx) and Nitrous Oxide (N2O), the different purposes for which inventories are compiled, and to which extent current inventories meet the needs of atmospheric dispersion modelling. The paper concludes with a discussion of uncertainties involved and a brief outlook on emerging trends in the three regions investigated is conducted. Key issues are substantial differences in the overall magnitude, but as well in the relative sectoral contribution of emissions in the inventories that have been assessed. While these can be explained by the use of different methodologies and underlying data (e.g. emission factors or activity rates), they may lead to quite different results when using the emission datasets to model ambient air quality or the deposition with atmospheric dispersion models. Hence, differences and uncertainties in emission inventories are not merely of academic interest, but can have direct policy implications when the development of policy actions is based on these model results. The level of uncertainty of emission estimates varies greatly between substances, regions and emission source sectors. This has implications for the direction of future research needs and indicates how existing gaps between modelled and measured concentration or deposition rates could be most efficiently addressed. The observed current trends in emissions display decreasing NOx emissions and only slight reductions for NH3 in both Europe and the US. However, in China projections indicate a steep increase of both.
Loading-dependent elemental composition of α-pinene SOA particles
Authors: Shilling J. E. , Chen Q. , King S. M. , Rosenoern T. , Kroll J. H. , Worsnop D. R. , DeCarlo P. F. , Aiken A. C. , Sueper D. , Jimenez J. L. , Martin S. T.
Published: April 2010

Abstract. The chemical composition of secondary organic aerosol (SOA) particles, formed by the dark ozonolysis of α-pinene, was characterized by a high-resolution time-of-flight aerosol mass spectrometer. The experiments were conducted using a continuous-flow chamber, allowing the particle mass loading and chemical composition to be maintained for several days. The organic portion of the particle mass loading was varied from 0.5 to >140 μg/m3 by adjusting the concentration of reacted α-pinene from 0.9 to 91.1 ppbv. The mass spectra of the organic material changed with loading. For loadings below 5 μg/m3 the unit-mass-resolution m/z 44 (CO2+) signal intensity exceeded that of m/z 43 (predominantly C2H3O+), suggesting more oxygenated organic material at lower loadings. The composition varied more for lower loadings (0.5 to 15 μg/m3) compared to higher loadings (15 to >140 μg/m3). The high-resolution mass spectra showed that from >140 to 0.5 μg/m3 the mass percentage of fragments containing carbon and oxygen (CxHyOz+) monotonically increased from 48% to 54%. Correspondingly, the mass percentage of fragments representing CxHy+ decreased from 52% to 46%, and the atomic oxygen-to-carbon ratio increased from 0.29 to 0.45. The atomic ratios were accurately parameterized by a four-product basis set of decadal volatility (viz. 0.1, 1.0, 10, 100 μg/m3) employing products having empirical formulas of C1H1.32O0.48, C1H1.36O0.39, C1H1.57O0.24, and C1H1.76O0.14. These findings suggest considerable caution is warranted in the extrapolation of laboratory results that were obtained under conditions of relatively high loading (i.e., >15 μg/m3) to modeling applications relevant to the atmosphere, for which loadings of 0.1 to 20 μg/m3 are typical. For the lowest loadings, the particle mass spectra resembled observations reported in the literature for some atmospheric particles.
Composition of the TTL over Darwin: local mixing or long-range transport?
Authors: Heyes W. J. , Vaughan G. , Allen G. , Volz-Thomas A. , Pätz H.-W. , Busen R.
Published: April 2010

Abstract. We present ozone and carbon monoxide measurements taken in Darwin, Australia, during the wet season of 2005/2006, to examine whether the composition of the Tropical Tropopause Layer (TTL) reflects that of the local boundary layer or is influenced more by advection from distant sources. We find that the latter predominates in the upper TTL, and is also the major influence in the lower TTL, except during an active monsoon phase. The day-to-day variability of ozone in the TTL is far greater than that in the lower troposphere, and correlates closely with air mass origin deduced from trajectory calculations based on standard ECMWF wind analyses. Although clear evidence of recent local uplift was found in carbon monoxide tracer measurements recorded inside convective anvils, no such signal was found out-of-cloud in the background TTL, where the measured variability correlated well with air mass origin deduced from back-trajectories. This study suggests that the composition of the TTL is ultimately determined by vertical mixing in certain "hot spot" regions of the tropics, with advection from these regions dominating the composition elsewhere.
Orographic cirrus in a future climate
Authors: Joos H. , Spichtinger P. , Lohmann U.
Published: April 2010

Abstract. A cloud resolving model (CRM) is used to investigate the formation of orographic cirrus clouds in the current and future climate. The formation of cirrus clouds depends on a variety of dynamical and thermodynamical processes, which act on different scales. First, the capability of the CRM in realistically simulating orographic cirrus clouds has been tested by comparing the simulated results to aircraft measurements of an orographic cirrus cloud. The influence of a warmer climate on the microphysical and optical properties of cirrus clouds has been investigated by initializing the CRM with vertical profiles of horizontal wind, potential temperature and equivalent potential temperature, respectively. The vertical profiles are extracted from IPCC A1B simulations for the current climate and for the period 2090–2099 for two regions representative for North and South America. The influence of additional moisture in a future climate on the propagation of gravity waves and the formation of orographic cirrus could be estimated. In a future climate, the increase in moisture dampens the vertical propagation of gravity waves and the occurring vertical velocities in the moist simulations. Together with higher temperatures fewer ice crystals nucleate homogeneously. Assuming that the relative humidity does not change in a warmer climate the specific humidity in the model is increased. This increase in specific humidity in a warmer climate results in a higher ice water content. The net effect of a reduced ice crystal number concentration and a higher ice water content is an increased optical depth. However, in some moist simulations dynamical changes contribute to changes in the ice water content, ice crystal number concentration and optical depth. For the corresponding dry simulations dynamical changes are more pronounced leading to a decreased optical depth in a future climate in some cases.
Simultaneous measurements of OClO, NO2 and O3 in the Arctic polar vortex by the GOMOS instrument
Authors: Tétard C. , Fussen D. , Bingen C. , Capouillez N. , Dekemper E. , Loodts N. , Mateshvili N. , Vanhellemont F. , Kyrölä E. , Tamminen J. , Sofieva V. , Hauchecorne A. , Dalaudier F. , Bertaux J.-L. , Fanton d'Andon O. , Barrot G. , Guirlet M. , Fehr T. , Saavedra L.
Published: April 2010

Abstract. We present the first nighttime measurements of OClO from a limb-viewing satellite instrument in the Arctic polar vortex. The relationship between OClO, NO2 and O3 slant column densities in the Arctic polar vortex are analyzed from the GOMOS measurements. The retrieval process is based on a differential optical absorption spectroscopy (DOAS) method applied on the weighted median GOMOS transmittances. A study of the longitudinal distributions of OClO, NO2 and O3 above 65° north in January 2008 is presented. It shows a strong halogen activation in the lower stratosphere and a strong denoxification in the entire stratosphere inside the Arctic polar vortex. Time series of temperatures and OClO, NO2 and O3 slant column densities for the winters 2002/2003 to 2007/2008 are also presented. They highlight the correlation between temperature, OClO and NO2. The GOMOS instrument appears to be a very suitable instrument for the monitoring of OClO, NO2 and O3 in the stratosphere during nighttime.
Global distributions of nitric acid from IASI/MetOP measurements
Authors: Wespes C. , Hurtmans D. , Clerbaux C. , Santee M. L. , Martin R. V. , Coheur P. F.
Published: April 2010

Abstract. This paper presents the first global distributions of HNO3 total columns acquired by the Infrared Atmospheric Sounding Interferometer (IASI) instrument, launched onboard the MetOp platform in October 2006. IASI is an infrared nadir-looking Fourier transform spectrometer providing atmospheric radiance spectra at 0.5 cm−1 spectral resolution, from which temperature and infrared absorbing gas concentration profiles are retrieved with global Earth coverage twice a day. A first analysis of the IASI measurements in terms of information content demonstrates the possibility of retrieving a total column for HNO3 at all latitudes with a maximal sensitivity in the middle stratosphere. The retrievals are performed from IASI spectra in the atmospheric window using a fast radiative transfer model and inversion software (FORLI) relying on the Optimal Estimation Method. The operational processing of HNO3 total columns is achieved since March 2008. We show that FORLI-HNO3 performs well at all latitudes (RMS of the spectral residuals around 2.3×10−6 W/m2 sr m−1) and provides HNO3 total columns with on average statistical errors of about 12%, reaching the threshold value of 32% at the equatorial belt. The global distributions of the retrieved total columns for one year (from March 2008 to February 2009) are presented and discussed with emphasis given to seasonal and interhemispheric variations. Local seasonal variations at 6 specific locations are also described and discussed in comparison with MLS volume mixing ratios at 46.5 hPa. The seasonal cycle observed in Polar regions is highlighted, with maxima observed in fall-winter and minima during spring-summer. The denitrification inside the Antarctic polar vortex during winter is clearly revealed with unprecedented horizontal resolution: HNO3 columns decreasing down to about 1×1016 molecules cm−2 are observed, which is consistent with the lower values of temperature observed between 50 and 15 hPa (~20–25 km) and the resulting formation and sedimentation of polar stratospheric clouds. During the same period, the collar region of high quantities of HNO3 at the vortex edge is also observed around 65–60° S latitude. Preliminary correlations between IASI derived HNO3 and O3 columns inside the polar vortex are presented and discussed.
Relating CCN activity, volatility, and droplet growth kinetics of β-caryophyllene secondary organic aerosol
Authors: Asa-Awuku A. , Engelhart G. J. , Lee B. H. , Pandis S. N. , Nenes A.
Published: April 2010

Abstract. This study investigates the droplet formation characteristics of secondary organic aerosol (SOA) formed during the ozonolysis of sesquiterpene β-caryophyllene (with and without hydroxyl radicals present). Emphasis is placed on understanding the role of semi-volatile material on Cloud Condensation Nucleus (CCN) activity and droplet growth kinetics. Aging of β-caryophyllene SOA significantly affects all CCN-relevant properties measured throughout the experiments. Using a thermodenuder and two CCN instruments, we find that CCN activity is a strong function of temperature (activation diameter at ~0.6% supersaturation: 100±10 nm at 20°C and 130±10 nm at 35°C), suggesting that the hygroscopic fraction of the SOA is volatile. The water-soluble organic carbon (WSOC) is extracted from the SOA and characterized with Köhler Theory Analysis (KTA); the results suggest that the WSOC is composed of low molecular weight (<200 g mol−1) slightly surface-active material that constitute 5–15% of the SOA mass. These properties are similar to the water-soluble fraction of monoterpene SOA, suggesting that predictive understanding of SOA CCN activity requires knowledge of the WSOC fraction but not its exact speciation. Droplet growth kinetics of the CCN are found to be strongly anticorrelated with WSOC fraction, suggesting that the insoluble material in the SOA forms a kinetic barrier that delays droplet growth. Overall, volatilization effects can increase activation diameters by 30%, and depress droplet growth rate by a factor of two; these results may have important implications for the droplet formation characteristics of SOA, and the atmospheric relevance of CCN measurements carried out at temperatures different from ambient.
Now you see it, now you don't: Impact of temporary closures of a coal-fired power plant on air quality in the Columbia River Gorge National Scenic Area
Authors: Jaffe D. A. , Reidmiller D. R.
Published: April 2010

Abstract. The goal of this study is to identify major point sources that contribute to elevated particulate matter in the Columbia River Gorge, USA and to quantify their contribution. To answer this question we analyzed 14 years of aerosol data spanning 1993–2006 from the IMPROVE site at Wishram, Washington (45.66° N, 121.00° W; 178 m a.s.l.) in the Columbia River Gorge (CRG) National Scenic Area of the Pacific Northwest of the USA. Two types of analyses were conducted. First, we examined the transport for days with the highest fine mass (PM2.5) concentrations using HYSPLIT backtrajectories. We found that the highest PM2.5 concentrations occurred during autumn and were associated with easterly flow, down the CRG. Such flow transports emissions from a large coal power plant in Boardman, Oregon and a large agricultural facility into the CRG. This transport was found on 20 out of the 50 worst PM2.5 days and resulted in an average daily concentration of 20.1 μg/m3, compared with an average of 18.8 μg/m3 for the 50 highest days and 5.9 μg/m3 for all days. These airmasses contain not only high PM2.5 concentrations, but also elevated levels of aerosol NO3−. In the second analysis, we examined PM2.5 concentrations in the CRG during periods when the Boardman power plant was shut down due to repairs and compared these values with concentrations when the facility was operating at near full capacity. We also examined this relationship on the days when backtrajectories suggested the greatest influence from the power plant on air quality in the CRG. From this analysis, we found significantly higher PM2.5 concentrations when the power plant was operating at or near full capacity. We use these data to calculate that the contribution to PM2.5 mass in the CRG from the Boardman power plant was 0.90 μg/m3 averaged over the entire year, 3.94 μg/m3 if only the month of November is considered and 7.40 μg/m3 if only November days when the airflow is "down-gorge" (from east to west). This represents 14, 46 and 56% of the PM2.5 mass in the CRG for the full year, November only and November days with "down-gorge" transport, respectively.
In situ aerosol optics in Reno, NV, USA during and after the summer 2008 California wildfires and the influence of absorbing and non-absorbing organic coatings on spectral light absorption
Authors: Gyawali M. , Arnott W. P. , Lewis K. , Moosmüller H.
Published: April 2010

Abstract. Hundreds of wildfires in Northern California were sparked by lightning during the summer of 2008, resulting in downwind smoke for the months of June and July. Comparisons are reported for aerosol optics measurements in Reno, Nevada made during the very smoky month of July and the relatively clean month of August. Photoacoustic instruments equipped with integrating nephelometers were used to measure aerosol light scattering and absorption coefficients at wavelengths of 405 nm and 870 nm, revealing a strong variation of aerosol light absorption with wavelength. Insight on fuels burned is gleaned from comparison of Ångström exponents of absorption (AEA) versus single scattering albedo (SSA) of the ambient measurements with laboratory biomass smoke measurements for many fuels. Measurements during the month of August, which were largely unaffected by fire smoke, exhibit surprisingly low AEA for aerosol light absorption when the SSA is highest, again likely as a consequence of the underappreciated wavelength dependence of aerosol light absorption by particles coated with non-absorbing organic and inorganic matter. Coated sphere calculations were used to show that AEA as large as 1.6 are possible for wood smoke even with non-absorbing organic coatings on black carbon cores, suggesting care be exercised when diagnosing AEA.
The representation of dust transport and missing urban sources as major issues for the simulation of PM episodes in a Mediterranean area
Authors: Flaounas E. , Coll I. , Armengaud A. , Schmechtig C.
Published: April 2010

Abstract. Due to its adverse effects on human health, atmospheric particulate matter (PM) constitutes a growing challenge for air quality management. It is also a complex subject of study. The understanding of its atmospheric evolution is indeed made difficult by the wide number of sources and the numerous processes that govern its evolution in the troposphere. As a consequence, the representation of particulate matter in chemistry-transport models needs to be permanently evaluated and enhanced in order to refine our comprehension of PM pollution events and to propose consistent environmental policies. The study presented here focuses on two successive summer particulate pollution episodes that occurred on the French Mediterranean coast. We identify and analyze the constitutive elements of the first and more massive episode and we discuss their representation within a eulerian model. The results show that the model fails in reproducing the variability and the amplitude of dust import from western Africa, and that it constitutes a strong bias in PM daily forecasts. We then focus on the lack of diurnal variability in the model, which is attributed to missing urban sources in standard emission inventories, and notably the resuspension of particles by urban road traffic. Through a sensitivity study based on PM and NOx measurements, we assess the sensitivity of PM to local emissions and the need to reconsider road traffic PM sources. In parallel, by coupling the CHIMERE-DUST model outputs to our simulation, we show that the representation of transcontinental dust transport allows a much better representation of atmospheric particles in southern France, and that it is needed in the frame of air quality management for the quantification of the anthropogenic part of particulate matter pollution.
On the diagnosis of climate sensitivity using observations of fluctuations
Authors: Kirk-Davidoff D. B.
Published: April 2010

Abstract. It has been shown that lag-covariance based statistical measures, suggested by the Fluctuation Dissipation Theorem (FDT), may allow estimation of climate sensitivity in a climate model. Recently Schwartz (2007) has used measures of the decay of autocorrelation in a global surface temperature time series to estimate the real world climate sensitivity. Here we use a simple climate model, and analysis of archived coupled climate model output from the IPCC AR4 runs, for which the climate sensitivity is known, to test the utility of this approach. Our analysis of these archived model output data show that estimates of climate sensitivity derived from century-long time scales typically grossly underestimate the models' true climate sensitivity. We analyze the behavior of the simple model with adjustable heat capacity in two surface layers, subject to various stochastic forcings and for various climate sensitivities, modulated by albedo and water vapor feedbacks. We use our simple climate model to demonstrate: 1. that a much longer time series would be required to accurately diagnose the earth's climate sensitivity than is presently available 2. that for shorter time series there is a systematic bias towards underpredicting climate sensitivity, 3. that the addition of a second heat reservoir weakly coupled to the first greatly reduces the decorrelation timescale of short temperature time series produced by the model, aggravating the tendency to underestimate climate sensitivity, and 4. that because of this it is possible to have a selection of models in which the climate sensitivity is inversely related to the decorrelation time scale, as is true for the IPCC models.
Retrieval of water vapor profile in the mesosphere from satellite ozone and hydroxyl measurements by the basic dynamic model of mesospheric photochemical system
Authors: Kulikov M. Y. , Feigin A. M. , Sonnemann G. R.
Published: April 2010

Abstract. We propose an indirect method for retrieving a number of significant minor gas constituents of the atmosphere. The technique is based on the use of so-called basic dynamic models of atmospheric photochemical systems simplified mathematically correctly in a special manner. It is applied to a mesospheric system describing day evolution of key minor gas constituents at these heights. We take as initial data experimental data of the CRISTA-MAHRSI satellite campaign of August 1997 during which ozone and hydroxyl (O3 and OH) concentrations were measured simultaneously. It is demonstrated that the use of the basic dynamic model allows retrieval of vertical distribution (within the 53–85 km range of heights) of water vapor concentration that is one of the control parameters of the mesospheric photochemistry.
Use of a mobile laboratory to evaluate changes in on-road air pollutants during the Beijing 2008 Summer Olympics
Authors: Wang M. , Zhu T. , Zheng J. , Zhang R. Y. , Zhang S. Q. , Xie X. X. , Han Y. Q. , Li Y.
Published: April 2010

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

Abstract. We provide an atmospheric aerosol characterization for North Africa, Northeastern Atlantic, Mediterranean and Middle East based on the analysis of quality-assured direct-sun observations of 39 stations of the AErosol RObotic NETwork (AERONET) which include at least an annual cycle within the 1994–2007 period. We extensively test and apply the recently introduced graphical method of Gobbi and co-authors to track and discriminate different aerosol types and quantify the contribution of mineral dust. The method relies on the combined analysis of the Ångström exponent (α) and its spectral curvature δα. Plotting data in these coordinates allows to infer aerosol fine mode radius (Rf) and fractional contribution (η) to total Aerosol Optical Depth (AOD) and separate AOD growth due to fine-mode aerosol humidification and/or coagulation from AOD growth due to the increase in coarse particles or cloud contamination. Our results confirm the robustness of this graphical method. Large mineral dust is found to be the most important constituent in Northern Africa and Middle East. Under specific meteorological conditions, its transport to Southern Europe is observed from spring to autumn and decreasing with latitude. We observe "pure Saharan dust" conditions to show AOD>0.7 (ranging up to 5), α<0.3 and δα<0 corresponding to η<40% and (Rf)~0.13 μm. Small pollution particles are abundant in sites close to urban and industrial areas of Continental and Eastern Europe and Middle East, as well as, important contributions of biomass burning are observed in the sub-Sahel region in winter. These small aerosols are associated to AOD<1, α>1.5 and δα~−0.2 corresponding to η>70% and Rf~0.13 μm. Here, dust mixed with fine pollution aerosols shifts the observations to the region α<0.75, in which the fine mode contribution is less than 40%.
Carbon monoxide distributions from the IASI/METOP mission: evaluation with other space-borne remote sensors
Authors: George M. , Clerbaux C. , Hurtmans D. , Turquety S. , Coheur P.-F. , Pommier M. , Hadji-Lazaro J. , Edwards D. P. , Worden H. , Luo M. , Rinsland C. , McMillan W.
Published: April 2010

Abstract. The Infrared Atmospheric Sounding Interferometer (IASI) onboard the MetOp satellite measures carbon monoxide (CO) on a global scale, twice a day. CO total columns and vertical profiles are retrieved in near real time from the nadir radiance spectra measured by the instrument in the thermal infrared (TIR) spectral range. This paper describes the measurement vertical sensitivity and provides a first assessment of the capabilities of IASI to measure CO distributions. On the global scale, 0.8 to 2.4 independent pieces of information are available for the retrieval. At mid latitudes, the information ranges between 1.5 and 2, which enables the lower and upper troposphere to be distinguished, especially when thermal contrast is significant. Global distributions of column CO are evaluated with correlative observations available from other nadir looking TIR missions currently in operation: the Measurements of Pollution in the Troposphere (MOPITT) onboard TERRA, the Atmospheric Infrared Sounder (AIRS) onboard AQUA and the Tropospheric Emission Spectrometer (TES) onboard AURA. The IASI CO columns are compared with MOPITT, AIRS and TES CO columns, adjusted with the a priori, for three different months: August 2008, November 2008 and February 2009. On average, total column discrepancies of about 7% are found between IASI and the three other sounders in the Northern Hemisphere and in the equatorial region. However when strong CO concentrations are present, such as during fire events, these discrepancies can climb as high as 17%. Instrument specifications of IASI versus other missions are also discussed.
VOC measurements within a boreal forest during spring 2005: on the occurrence of elevated monoterpene concentrations during night time intense particle concentration events
Authors: Eerdekens G. , Yassaa N. , Sinha V. , Aalto P. P. , Aufmhoff H. , Arnold F. , Fiedler V. , Kulmala M. , Williams J.
Published: April 2010

Abstract. In this study we present measurements of selected trace gases and aerosols made in a boreal forest during the BACCI-QUEST IV intensive field campaign in Hyytiälä, Finland in April 2005. Springtime diel and vertical variations of VOCs are discussed in connection with the variations in other trace gases and with the prevailing meteorological conditions. A daytime and a nighttime event have been analysed in detail. The nighttime particle event occurred synchronously with huge increases in monoterpenes, while the second event type involved nucleation and was anti-correlated with sulphuric acid. Here we discuss the possible origins of these two distinct forms of aerosol production at the Hyytiälä site using the measurement data, air mass back trajectories and the optical stereoisomery of monoterpenes. Optical stereoisomery is used in source identification to distinguish between unnatural and natural monoterpene emissions.
Toward a general parameterization of N2O5 reactivity on aqueous particles: the competing effects of particle liquid water, nitrate and chloride
Authors: Bertram T. H. , Thornton J. A.
Published: April 2010

Abstract. The heterogeneous reaction of N2O5 on mixed organic-inorganic aerosol particles was investigated using an entrained aerosol flow tube coupled to a custom-built chemical ionization mass spectrometer. Laboratory results on aqueous particles confirm a strong dependence of the reactive uptake coefficient (γ) on particle liquid water, for particle water concentrations below 15 M, and the molar ratio of particle water to nitrate. Measurements of γ (N2O5) on mixed chloride-nitrate particles indicate that the presence of trace chloride can negate the suppression of γ(N2O5) at high nitrate loadings with implications for polluted coastal regions. These results are used to construct a new parameterization for γ (N2O5), that when coupled to an aerosol thermodynamics model, can be used within regional and/or global chemical transport models.
Origin of aerosol particles in the mid-latitude and subtropical upper troposphere and lowermost stratosphere from cluster analysis of CARIBIC data
Authors: Köppe M. , Hermann M. , Brenninkmeijer C. A. M. , Heintzenberg J. , Schlager H. , Schuck T. , Slemr F. , Sprung D. , van Velthoven P. F. J. , Wiedensohler A. , Zahn A. , Ziereis H.
Published: April 2010

Abstract. The origin of aerosol particles in the upper troposphere and lowermost stratosphere over the Eurasian continent was investigated by applying cluster analysis methods to in situ measured data. Number concentrations of submicrometer aerosol particles and trace gas mixing ratios derived by the CARIBIC (Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container) measurement system on flights between Germany and South-East Asia were used for this analysis. Four cluster analysis methods were applied to a test data set and their capability of separating the data points into scientifically reasonable clusters was assessed. The best method was applied to seasonal data subsets for summer and winter resulting in five cluster or air mass types: stratosphere, tropopause, free troposphere, high clouds, and boundary layer influenced. Other source clusters, like aircraft emissions could not be resolved in the present data set with the used methods. While the cluster separation works satisfactory well for the summer data, in winter interpretation is more difficult, which is attributed to either different vertical transport pathways or different chemical lifetimes in both seasons. The geographical distribution of the clusters together with histograms for nucleation and Aitken mode particles within each cluster are presented. Aitken mode particle number concentrations show a clear vertical gradient with the lowest values in the lowermost stratosphere (750–2820 particles/cm3 STP, minimum of the two 25% – and maximum of the two 75%-percentiles of both seasons) and the highest values for the boundary-layer-influenced air (4290–22 760 particles/cm3 STP). Nucleation mode particles are also highest in the boundary-layer-influenced air (1260–29 500 particles/cm3 STP), but are lowest in the free troposphere (0–450 particles/cm3 STP). The given submicrometer particle number concentrations represent the first large-scale seasonal data sets for the upper troposphere and lowermost stratosphere over the Eurasian continent.
The effect of nonlinearity in CO2 heating rates on the attribution of stratospheric ozone and temperature changes
Authors: Jonsson A. I. , Fomichev V. I. , Shepherd T. G.
Published: April 2010

Abstract. An analysis of the attribution of past and future changes in stratospheric ozone and temperature to anthropogenic forcings is presented. The analysis is an extension of the study of Shepherd and Jonsson (2008) who analyzed chemistry-climate simulations from the Canadian Middle Atmosphere Model (CMAM) and attributed both past and future changes to changes in the external forcings, i.e. the abundances of ozone-depleting substances (ODS) and well-mixed greenhouse gases. The current study is based on a new CMAM dataset and includes two important changes. First, we account for the nonlinear radiative response to changes in CO2. It is shown that over centennial time scales the radiative response in the upper stratosphere to CO2 changes is significantly nonlinear and that failure to account for this effect leads to a significant error in the attribution. To our knowledge this nonlinearity has not been considered before in attribution analysis, including multiple linear regression studies. For the regression analysis presented here the nonlinearity was taken into account by using CO2 heating rate, rather than CO2 abundance, as the explanatory variable. This approach yields considerable corrections to the results of the previous study and can be recommended to other researchers. Second, an error in the way the CO2 forcing changes are implemented in the CMAM was corrected, which significantly affects the results for the recent past. As the radiation scheme, based on Fomichev et al. (1998), is used in several other models we provide some description of the problem and how it was fixed.
Extreme Saharan dust event over the southern Iberian Peninsula in september 2007: active and passive remote sensing from surface and satellite
Authors: Guerrero-Rascado J. L. , Olmo F. J. , Avilés-Rodríguez I. , Navas-Guzmán F. , Pérez-Ramírez D. , Lyamani H. , Alados Arboledas L.
Published: April 2010

Abstract. This study investigates aerosol optical properties during the extreme Saharan dust event detected from 3 to 7 September 2007 over Granada, southern Iberian Peninsula, with both active and passive remote sensing instrumentation from surface and satellite. The intensity of the event was visualized on the aerosol optical depth series obtained by the sun-photometer Cimel CE 318-4 operated at Granada in the framework of AERONET from August 2004 until December 2008 (level 2 data). A combination of large aerosol optical depth (0.86–1.50) at 500 nm, and reduced Angström exponent (0.1–0.25) in the range 440–870 nm, was detected on 6 September during daytime. This Saharan dust event also affected other Iberian Peninsula stations included in AERONET (El Arenosillo and Évora stations), and it was monitored by MODIS instrument on board Aqua satellite. Vertically resolved measurements were performed by a ground-based Raman Lidar and by CALIPSO satellite. During the most intense stage, on 6 September, maximum aerosol backscatter values were a factor of 8 higher than other maxima during this Saharan dust event. Values up to 1.5×10−2 km−1 sr−1 at 355 and 532 nm were detected in the layer with the greatest aerosol load between 3–4 km a.s.l., although aerosol particles were also detected up to 5.5 km a.s.l. In this stage of the event, dust particles at these altitudes showed a backscatter-related Angström exponent between –0.44 and 0.53 for the two spectral intervals considered. The results from different measurements (active/passive and ground-based/satellite) reveal the importance of performing multi-instrumental measurements to properly characterize the contribution of different aerosol types from different sources during extreme events. The atmospheric stabilization effect of the aerosol particles has been characterized by computing the solar heating rates using SBDART code.
Direct estimates of emissions from the megacity of Lagos
Authors: Hopkins J. R. , Evans M. J. , Lee J. D. , Lewis A. C. , H Marsham J. , McQuaid J. B. , Parker D. J. , Stewart D. J. , Reeves C. E. , Purvis R. M.
Published: April 2010

Abstract. We report here top-down emissions estimates for an African megacity. A boundary layer circumnavigation of Lagos, Nigeria was completed using the FAAM BAe146 aircraft as part of the AMMA project. These observations together with an inferred boundary layer height allow the flux of pollutants to be calculated. Extrapolation gives annual emissions for CO, NOx, and VOCs of 1.44 Tg yr−1, 0.03 Tg yr−1 and 0.37 Tg yr−1 respectively with uncertainties of +250/−60%. These inferred emissions are consistent with bottom-up estimates for other developing megacities and are attributed to the evaporation of fuels, mobile combustion and natural gas emissions.
A consistent molecular hydrogen isotope chemistry scheme based on an independent bond approximation
Authors: Pieterse G. , Krol M. C. , Röckmann T.
Published: April 2010

Abstract. The isotopic composition of molecular hydrogen (H2) produced by photochemical oxidation of methane (CH4) and Volatile Organic Compounds (VOCs) is a key quantity in the global isotope budget of (H2). The many individual reaction steps involved complicate its investigation. Here we present a simplified structure-activity approach to assign isotope effects to the individual elementary reaction steps in the oxidation sequence of CH4 and some other VOCs. The approach builds on and extends the work by Gerst and Quay (2001) and Feilberg et al. (2007b). The description is generalized and allows the application, in principle, also to other compounds. The idea is that the C-H and C-D bonds – seen as reactive sites – have similar relative reaction probabilities in isotopically substituted, but otherwise identical molecules. The limitations of this approach are discussed for the reaction CH4+Cl. The same approach is applied to VOCs, which are important precursors of H2 that need to be included into models. Unfortunately, quantitative information on VOC isotope effects and source isotope signatures is very limited and the isotope scheme at this time is limited to a strongly parameterized statistical approach, which neglects kinetic isotope effects. Using these concepts we implement a full hydrogen isotope scheme in a chemical box model and carry out a sensitivity study to identify those reaction steps and conditions that are most critical for the isotope composition of the final H2 product. The reaction scheme is directly applicable in global chemistry models, which can thus include the isotope pathway of H2 produced from CH4 and VOCs in a consistent way.