bluuebunny/crossref_metadata_2025 huggingface dataset:
Process-based modelling of biogenic monoterpene emissions: sensitivity to temperature and light
Authors: Schurgers G. , Arneth A. , Holzinger R. , Goldstein A.
Published: April 2010

Abstract. Monoterpenes, primarily emitted by terrestrial vegetation, can influence atmospheric ozone chemistry, and can form precursors for secondary organic aerosol. The short-term emissions of monoterpenes have been well studied and understood, but their long-term variability, which is particularly important for atmospheric chemistry, has not. This understanding is crucial for the understanding of future changes. In this study, two algorithms of terrestrial biogenic monoterpene emissions, the first one based on the short-term volatilization of monoterpenes, as commonly used for temperature-dependent emissions, and the second one based on long-term production of monoterpenes (linked to photosynthesis) combined with emissions from storage, were compared and evaluated with measurements from a Ponderosa pine plantation (Blodgett Forest, California). The measurements were used to parameterize the long-term storage of monoterpenes, which takes place in specific storage organs and which determines the temporal distribution of the emissions over the year. The difference in assumptions between the first (emission-based) method and the second (production-based) method, which causes a difference in upscaling from instantaneous to daily emissions, requires roughly a doubling of emission capacities to bridge the gap to production capacities. The sensitivities to changes in temperature and light were tested for the new methods, the temperature sensitivity was slightly higher than that of the short-term temperature dependent algorithm. Applied on a global scale, the first algorithm resulted in annual total emissions of 29.6 Tg C a−1, the second algorithm resulted in 31.8 Tg C a−1 when applying the correction factor 2 between emission capacities and production capacities. However, the exact magnitude of such a correction is spatially varying and hard to determine as a global average.
Validation of northern latitude tropospheric emission spectrometer stare ozone profiles with ARC-IONS sondes during ARCTAS
Authors: Boxe C. S. , Worden J. R. , Bowman K. W. , Kulawik S. S. , Neu J. L. , Ford W. C. , Osterman G. B. , Herman R. L. , Eldering A. , Tarasick D. W. , Thompson A. M. , Doughty D. C. , Hoffmann M. R. , Oltmans S. J.
Published: April 2010

Abstract. We compare Tropospheric Emission Spectrometre (TES) versions 3 and 4, V003 and V004, respectively, nadir-stare ozone profiles with ozonesonde profiles from the Arctic Intensive Ozonesonde Network Study (ARCIONS, http://http://croc.gsfc.nasa.gov/arcions/) during the Arctic Research on the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) field mission. The ozonesonde data are from launches timed to match the Aura's overpass, where 11 coincidences spanned 44° N to 71° N from April to July 2008. Using the TES "stare" observation mode, 32 observations are taken over each coincident ozonesonde launch. By effectively sampling the same air mass 32 times, comparisons are made between the empirically-calculated random errors to the expected random errors from measurement noise, temperature and interfering species, such as water. This study represents the first validation of high latitude (>60°) TES ozone. We find that the calculated errors are consistent with the actual errors with a similar vertical distribution that varies between 5% and 20% for V003 and V004 TES data. In general, TES ozone profiles are positively biased (by less than 15%) from the surface to the upper troposphere (~1000 to 100 hPa) and negatively biased (by less than 20%) from the upper troposphere to the lower stratosphere (100 to 30 hPa) when compared to the ozonesonde data. Lastly, for V003 and V004 TES data between 44° N and 71° N there is a small variability in the mean biases (from −14 to +15%), mean theoretical errors (from 6 to 13%), and mean random errors (from 9 to 19%).
Aerosol-cloud interaction determined by both in situ and satellite data over a northern high-latitude site
Authors: Lihavainen H. , Kerminen V.-M. , Remer L. A.
Published: April 2010

Abstract. The first aerosol indirect effect over a clean, northern high-latitude site was investigated by determining the aerosol cloud interaction (ACI) using three different approaches; ground-based in situ measurements, combined ground-based in situ measurements and satellite retrievals and using only satellite retrievals. The obtained values of ACI were highest for in situ ground-based data, clearly lower for combined ground-based and satellite data, and lowest for data relying solely on satellite retrievals. One of the key findings of this study was the high sensitivity of ACI to the definition of the aerosol burden. We showed that at least a part of the variability in ACI can be explained by how different investigators have related different cloud properties to "aerosol burden".
Elemental analysis of chamber organic aerosol using an aerodyne high-resolution aerosol mass spectrometer
Authors: Chhabra P. S. , Flagan R. C. , Seinfeld J. H.
Published: April 2010

Abstract. The elemental composition of laboratory chamber secondary organic aerosol (SOA) from glyoxal uptake, α-pinene ozonolysis, isoprene photooxidation, single-ring aromatic photooxidation, and naphthalene photooxidation is evaluated using Aerodyne high-resolution time-of-flight mass spectrometer data. SOA O/C ratios ranged from 1.13 for glyoxal to 0.30–0.43 for α-pinene ozonolysis. The elemental composition of α-pinene and naphthalene SOA was also confirmed by offline mass spectrometry. The fraction of organic signal at m/z 44 is generally a good measure of SOA oxygenation for all systems except for glyoxal uptake, in which m/z 44 substantially underpredicts O/C. Although chamber SOA has generally been considered less oxygenated than ambient SOA, single-ring aromatic- and naphthalene-derived SOA can reach O/C ratios upward of 0.7, well within the range of OOA, though still not as high as some ambient measurements. The spectra of aromatic- and isoprene-high-NOx SOA resemble that of OOA, but the spectrum of glyoxal uptake does not resemble that of any PMF component.
Aerosol spectral absorption in the Mexico City area: results from airborne measurements during MILAGRO/INTEX B
Authors: Bergstrom R. W. , Schmidt K. S. , Coddington O. , Pilewskie P. , Guan H. , Livingston J. M. , Redemann J. , Russell P. B.
Published: April 2010

Abstract. This paper presents estimates of the spectral solar absorption due to atmospheric aerosols during the 2006 MILAGRO/INTEX-B (Megacity Initiative-Local And Global Research Observations/Phase B of the Intercontinental Chemical Transport Experiment) field campaign. The aerosol absorption was derived from measurements of the spectral solar radiation and the spectral aerosol optical depth made on the J31 aircraft flying over the Gulf of Mexico and over Mexico City. We present the spectral single scattering albedo (SSA) and aerosol absorption optical depth (AAOD) for two flights over the Gulf of Mexico and three flights over Mexico City for wavelengths from 350 to approximately 1650 nm. The spectral aerosol optical properties of each case are different and illustrate the variability of the aerosol optical properties in the Mexico City area. The results can be described in terms of three different wavelength region: The 350–500 nm region where the aerosol absorption often falls off sharply presumably due to organic carbonaceous particles and windblown dust; the 500–1000 nm region where the decrease with wavelength is slower presumably due to black carbon; and the near infrared spectral region (1000 nm to 1650 nm) where it is difficult to obtain reliable results since the aerosol absorption is relatively small and the gas absorption dominates. However, there is an indication of a small and somewhat wavelength independent absorption in the region beyond 1000 nm. For one of the flights over the Gulf of Mexico near the coastline it appears that a cloud/fog formation and evaporation led to an increase of absorption possibly due to a water shell remaining on the particles after the cloud/fog had dissipated. For two of the Mexico City cases, the single scattering albedo is roughly constant between 350–500 nm consistent with other Mexico City results. In three of the cases a single absorption Angstrom exponent (AAE) fits the aerosol absorption optical depth over the entire wavelength range of 350 to 1650 nm relatively well (r2>0.86).
Distribution of gaseous and particulate organic composition during dark α-pinene ozonolysis
Authors: Camredon M. , Hamilton J. F. , Alam M. S. , Wyche K. P. , Carr T. , White I. R. , Monks P. S. , Rickard A. R. , Bloss W. J.
Published: April 2010

Abstract. Secondary organic aerosol (SOA) affects atmospheric composition, air quality and radiative transfer. However major difficulties are encountered in the development of reliable models for SOA formation. Constraints on processes involved in SOA formation can be obtained by interpreting the speciation and evolution of organics in the gaseous and condensed phase simultaneously. In this study we investigate SOA formation from dark α-pinene ozonolysis with particular emphasis upon the mass distribution of gaseous and particulate organic species. A detailed model for SOA formation is compared with the results from experiments performed in the EUropean PHOtoREactor (EUPHORE) simulation chamber, including on-line gas-phase composition obtained from Chemical-Ionization-Reaction Time-Of-Flight Mass-Spectrometry measurements, and off-line analysis of SOA samples performed by Electrospray Ionisation Ion Trap Mass Spectrometry. The temporal profile of SOA mass concentration is relatively well reproduced by the model. Sensitivity analysis highlights the importance of the choice of vapour pressure estimation method. Comparisons of the simulated gaseous- and condensed-phase mass distributions with those observed show a generally good agreement. The simulated speciation has been used to (i) propose a chemical structure for the principal gaseous semi-volatile organic compounds and condensed monomer organic species and (ii) explore the possible contribution of a range of accretion reactions occurring in the condensed phase. We find that oligomer formation through esterification reactions gives the best agreement between the observed and simulated mass spectra.
Inferring ozone production in an urban atmosphere using measurements of peroxynitric acid
Authors: Spencer K. M. , McCabe D. C. , Crounse J. D. , Olson J. R. , Crawford J. H. , Weinheimer A. J. , Knapp D. J. , Montzka D. D. , Cantrell C. A. , Anderson R. S. , Mauldin R. L. , Wennberg P. O.
Published: April 2010

Abstract. Observations of peroxynitric acid (HO2NO2) obtained simultaneously with those of NO and NO2 provide a sensitive measure of the ozone photochemical production rate. We illustrate this technique for constraining the ozone production rate with observations obtained from the NCAR C-130 aircraft platform during the Megacity Initiative: Local and Global Research Observations (MILAGRO) intensive in Mexico during the spring of 2006. Sensitive and selective measurements of HO2NO2 were made in situ using chemical ionization mass spectrometry (CIMS). Observations were compared to modeled HO2NO2 concentrations obtained from the NASA Langley highly-constrained photochemical time-dependent box model. The median observed-to-calculated ratio of HO2NO2 is 1.18. At NOx levels greater than 15 ppbv, the photochemical box model underpredicts observations with an observed-to-calculated ratio of HO2NO2 of 1.57. As a result, we find that at high NOx, the ozone production rate calculated using measured HO2NO2 is faster than predicted using accepted photochemistry. Inclusion of an additional HOx source from the reaction of excited state NO2 with H2O or reduction in the rate constant of the reaction of OH with NO2 improves the agreement.
A new physically-based quantification of isoprene and primary organic aerosol emissions from the world's oceans
Authors: Gantt B. , Meskhidze N. , Kamykowski D.
Published: April 2010

Abstract. The global marine sources of organic carbon (OC) are estimated here using a physically-based parameterization for the emission of marine isoprene and primary organic matter. The model developed in this study allowed us, for the first time, to explore the relative contributions of sub- and super-micron organic matter and phytoplankton-produced secondary organic aerosol (SOA) to the total OC fraction of marine aerosol. New laboratory measurements of isoprene production by some of the main phytoplankton species under a range of environmental conditions was scaled up, with the help of satellite products, to infer the total annual mean ocean isoprene emissions of 0.92 Tg C yr−1. The sensitivity studies using different schemes for the euphotic zone depth and ocean phytoplankton speciation produced the upper and the lower range of marine-isoprene emissions of 0.31 to 1.09 Tg C yr−1, respectively. Empirical relationships between fluxes of water soluble (WSOM) and water insoluble (WIOM) organic matter (OM) and chlorophyll-a concentration was used to estimate the total primary sources of oceanic sub- and super-micron OC of 1.26 and 19.01 Tg C yr−1, respectively. Using a fixed 3% mass yield for the conversion of isoprene to SOA, our model simulations show minor (less than 0.2%) contribution of ocean produced isoprene to the total marine source of OC. However, our model calculations also indicate that over the tropical waters, marine isoprene-derived SOA could contribute over 40% of the total monthly-averaged sub-micron OC fraction of marine aerosol. The estimated contribution of ocean-isoprene SOA to hourly averaged sub-micron marine OC fluxes is even higher, reaching nearly 100% over the vast regions of the oceans during the midday hours. As it is widely believed that cloud condensation nuclei (CCN) is typically dominated by sub-micron sized particles, our findings suggest that marine sources of SOA could play a critical role in modulating properties of shallow marine clouds and influencing the climate.
Photochemical production of aerosols from real plant emissions
Authors: Mentel Th. F. , Wildt J. , Kiendler-Scharr A. , Kleist E. , Tillmann R. , Dal Maso M. , Fisseha R. , Hohaus Th. , Spahn H. , Uerlings R. , Wegener R. , Griffiths P. T. , Dinar E. , Rudich Y. , Wahner A.
Published: April 2010

Abstract. By emission of volatile organic compounds (VOC) which on oxidation form secondary organic aerosols (SOA) the vegetation is coupled to atmosphere and climate. New particle formation from tree emissions was investigated in a new setup: a plant chamber coupled to a reaction chamber for oxidizing the plant emissions and for forming SOA. The boreal tree species birch, pine, and spruce were studied and α-pinene was used as reference compound. Under the experimental conditions OH radicals were essential for inducing new particle formation, although O3 (≤80 ppb) was always present and a part of the monoterpenes and the sesquiterpenes reacted already with ozone before OH was generated. Formation rates of 3 nm particles were linearly related to the carbon mixing ratios of the VOC, as were the maximum observed volume and the condensational growth rates. The threshold of new particle formation was lower for the tree emissions than for α-pinene. It was lowest for birch with the largest fraction of oxygenated VOC (OVOC) suggesting that OVOC may play a pivotal role in new particle formation. Incremental mass yields were ≈5% for pine, spruce and α-pinene, and ≈10% for birch. α-Pinene was a good model compound to describe the yield and the growth of SOA particles from coniferous emissions. The mass fractional yields agreed well with observations for boreal forests. Despite our somewhat enhanced VOC and OH concentrations our results may thus be up-scaled to eco-system level. Using the mass fractional yields observed for the tree emissions and weighting them with the abundance of the respective trees in boreal forests we calculate SOA mass concentrations which agree within 6% with field observations. For a future VOC increase of 50% we predict a particle mass increase due to SOA of 19% assuming today's mass contribution of pre-existing aerosol.
Contributions from DMS and ship emissions to CCN observed over the summertime North Pacific
Authors: Phinney L. , Leaitch W. R. , Lohmann U. , Shantz N. C. , Worsnop D. R.
Published: April 2010

Abstract. Measurements of cloud condensation nuclei (CCN) made over the remote North Pacific Ocean in July 2002 are analysed with concurrent measurements of aerosol number, mass and composition. Overall the CCN are controlled by the sulphate, including one case of particle nucleation and growth resulting from dimethyl sulphide oxidation that enhanced CCN concentrations. Hourly CCN concentrations are correlated with concentrations of sulphate plus methanesulphonic acid (MSA) over the entire study period (r2=0.43 and 0.52 for supersaturations of 0.34 and 0.19%, respectively), and are not well correlated with other organics (r2<0.2). One case study reveals elevated mass and number concentrations of ultrafine and fine organic particles due to regional ship emissions, during which organic mass concentrations (see Fig. 2). In Fig. 7c, the 80–90 nm particle concentrations are correlated with CCN values (r2=0.39 and 0.46 for supersaturations of 0.19 and 0.34%, respectively). The evolution of the time series and mass distributions of organics, sulphate and MSA over this timeframe indicate that the regional distribution of small, diffuse ship-sourced organic particles act as condensation sites for sulphur species, resulting in a subsequent increase in number concentrations of CCN. Direct emissions of organic particles may exert a strong control on marine CCN concentrations once diffused into the marine atmosphere by acting as condensation sites for biogenic and anthropogenic sulphur species.
Cloud-type dependencies of MODIS and AMSR-E liquid water path differences
Authors: de la Torre Juárez M. , Kahn B. H. , Fetzer E. J.
Published: April 2010

Abstract. Comparisons of cloud liquid water path (LWP) retrievals are presented from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Advanced Microwave Scanning Radiometer (AMSR-E) located aboard the Aqua spacecraft. LWP differences as a function of cloud top height, cloud fraction, cloud top temperature, LWP, cloud effective radius and cloud optical thickness are quantified in most geophysical conditions. The assumption of vertically homogeneous distributions of cloud water content in the MODIS LWP retrieval yields a slightly poorer agreement than the assumption of stratified cloud liquid water. Furthermore, for a fixed cloud top pressure, the cloud top temperature can lead to sign changes in the LWP difference. In general, AMSR-E LWP is larger than MODIS for small cloud fractions, low values of LWP, and warmer cloud top temperatures. On the other hand, clouds with optical thicknesses above 20 lead to larger MODIS LWP. Using cloud optical thickness as a proxy for cloud type, deep convective clouds and stratus are shown to have the poorest agreement between AMSR-E and MODIS LWP. Particularly large differences are also found at latitudes poleward of 50°. The results of this work help characterize the scene- and cloud-dependent performance of microwave and visible/near infrared retrievals of LWP.
Deep-convective vertical transport: what is mass flux?
Authors: Yano J.-I.
Published: April 2010

Abstract. Conceptual basis for the convective mass flux that is used in parameterizations is reviewed from a historical perspective. The main idea of the convective mass flux formulation does not purely reside in dividing the grid-box averaged vertical velocity into several mass flux components such as convective updrafts, downdrafts, and environmental subsidence. The main point rather resides on assuming different vertical profiles for transported quantities for different components. From this point of view, the best way to turn off the convective transport of chemical species is to set the vertical profile of chemical species within convective components (both updrafts and downdrafts) equal to that of the environment. This procedure turns out to be equivalent of simply turning off a standard convective chemical transport package.
Evaluation of new secondary organic aerosol models for a case study in Mexico City
Authors: Dzepina K. , Volkamer R. M. , Madronich S. , Tulet P. , Ulbrich I. M. , Zhang Q. , Cappa C. D. , Ziemann P. J. , Jimenez J. L.
Published: April 2010

Abstract. Recent field studies have found large discrepancies in the measured vs. modeled SOA mass loadings in both urban and regional polluted atmospheres. The reasons for these large differences are unclear. Here we revisit a case study of SOA formation in Mexico City described by Volkamer et al. (2006), during a photochemically active period when the impact of regional biomass burning is minor or negligible, and show that the observed increase in OA/ΔCO is consistent with results from several groups during MILAGRO 2006. Then we use the case study to evaluate three new SOA models: 1) the update of aromatic SOA yields from recent chamber experiments (Ng et al., 2007); 2) the formation of SOA from glyoxal (Volkamer et al., 2007a); and 3) the formation of SOA from primary semivolatile and intermediate volatility species (P-S/IVOC) (Robinson et al., 2007). We also evaluate the effect of reduced partitioning of SOA into POA (Song et al., 2007). Traditional SOA precursors (mainly aromatics) by themselves still fail to produce enough SOA to match the observations by a factor of 7. The new low-NOx aromatic pathways with very high SOA yields make a very small contribution in this high-NOx urban environment as the RO2.+NO reaction dominates the fate of the RO2. radicals. Glyoxal contributes several μg m−3 to SOA formation, with similar timing as the measurements. P-S/IVOC are estimated from equilibrium with emitted POA, and introduce a large amount of gas-phase oxidizable carbon that was not in models before. With the formulation in Robinson et al. (2007) these species have a high SOA yield, and this mechanism can close the gap in SOA mass between measurements and models in our case study. However the volatility of SOA produced in the model is too high and the O/C ratio is lower than observations. Glyoxal SOA helps to bring the O/C ratio of predicted and observed SOA into better agreement. The sensitivities of the model to some key uncertain parameters are evaluated.
Impact of prescribed SSTs on climatologies and long-term trends in CCM simulations
Authors: Garny H. , Dameris M. , Stenke A.
Published: April 2010

Abstract. Chemistry-Climate Model (CCM) simulations are commonly used to project the past and future development of the dynamics and chemistry of the stratosphere, and in particular the ozone layer. So far, CCMs are usually not interactively coupled to an ocean model, so that sea surface temperatures (SSTs) and sea ice coverage are prescribed in the simulations. While for future integrations SSTs have to be taken from precalculated climate model projections, for CCM experiments resembling the past either modelled or observed SSTs can be used. This study addresses the question to which extent atmospheric climatologies and long-term trends for the recent past simulated in the CCM E39C-A differ when choosing either observed or modelled SSTs. Furthermore, the processes of how the SST signal is communicated to the atmosphere, and in particular to the stratosphere are examined. Two simulations that differ only with respect to the prescribed SSTs and that span years 1960 to 1999 are used. Significant differences in temperature and ozone climatologies between the model simulations are found, but long-term trends over 40 years in annual mean temperature and ozone differ only in the troposphere, where temperatures are directly influenced by the local SST trends. However, differences in trends are found on shorter time scales and the results suggest that these differences in trends are induced by associated SST trends. The SST trends lead to modifications in planetary wave activity and therefore a modulation of the Brewer-Dobson Circulation (BDC). This results in time series of tropical upwelling, as a measure of the strength of the BDC, differing strongly between the simulations. A reverse from negative to positive trends is found in the simulation using observed SSTs while trends are positive throughout the simulation when using modelled SSTs.
Global emissions of non-methane hydrocarbons deduced from SCIAMACHY formaldehyde columns through 2003–2006
Authors: Stavrakou T. , Müller J.-F. , De Smedt I. , Van Roozendael M. , van der Werf G. R. , Giglio L. , Guenther A.
Published: April 2010

Abstract. Formaldehyde columns retrieved from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography/Chemistry (SCIAMACHY) instrument onboard ENVISAT satellite through 2003 to 2006 are used as top-down constraints to derive updated global biogenic and biomass burning flux estimates for the non-methane volatile organic compounds (NMVOCs) precursors of formaldehyde. Our interest is centered over regions experiencing strong emissions, and hence exhibiting a high signal-to-noise ratio and lower measurement uncertainties. The formaldehyde dataset used in this study has been recently made available to the community and complements the long record of formaldehyde measurements from the Global Ozone Monitoring Experiment (GOME). We use the IMAGESv2 global chemistry-transport model driven by the Global Fire Emissions Database (GFED) version 1 or 2 for biomass burning, and from the newly developed MEGAN-ECMWF isoprene emission database. The adjoint of the model is implemented in a grid-based framework within which emission fluxes are derived at the model resolution, together with a differentiation of the sources in a grid cell. Two inversion studies are conducted using either the GFEDv1 or GFEDv2 as prior for the pyrogenic fluxes. Although on the global scale the inferred emissions from the two categories exhibit only weak deviations from the corresponding prior estimates, the regional updates often present large departures from their prior values. The posterior isoprene emissions over North America, amounting to about 34 Tg C/yr, are estimated to be on average by 25% lower than the prior over 2003–2006, whereas a strong increase (55%) is deduced over the south African continent, the optimized emission being estimated at 57 Tg C/yr. Over Indonesia the biogenic emissions appear to be overestimated by 20–30%, whereas over Indochina and the Amazon basin during the wet season the prior inventory captures both the seasonality and the magnitude of the observed columns. Although neither biomass burning inventory seems to be consistent with the data over all regions, pyrogenic estimates inferred from the two inversions are reasonably similar, despite their prior deviations. A number of sensitivity experiments are conducted in order to assess the impact of uncertainties related to the inversion setup and the chemical mechanism. Whereas changes in the background error covariance matrix have only a limited impact on the posterior fluxes, the use of an alternative isoprene mechanism characterized by lower HCHO yields (the GEOS-Chem mechanism) increases the posterior isoprene source estimate by 11% over Northern America, and by up to 40% in tropical regions.
Detection of pollution transport events southeast of Mexico City using ground-based visible spectroscopy measurements of nitrogen dioxide
Authors: Melamed M. L. , Basaldud R. , Steinbrecher R. , Emeis S. , Ruíz-Suárez L. G. , Grutter M.
Published: April 2010

Abstract. This work presents ground based differential optical absorption spectroscopy (DOAS) measurements of nitrogen dioxide (NO2) during the MILAGRO field campaign in March 2006 at the Tenango del Aire research site located to the southeast of Mexico City. The DOAS NO2 column density measurements are used in conjunction with ceilometer, meteorological and surface nitrogen oxides (NOx) and total reactive nitrogen (NOy) measurements to show a more comprehensive view of air pollution results when a research site has both surface and remote sensing instruments. An in depth analysis of 13 March 2006 demonstrates how DOAS NO2, surface NO2 and ceilometer data can be used to determine the extent of mixing of the pollution layer. In addition, we show the effectiveness of how DOAS measurements can be used to observe pollution sources that may reside above the mixing layer, such as the presence of lightning produced NO2 as seen on 28 March 2006.
Influence of line mixing on the retrievals of atmospheric CO2 from spectra in the 1.6 and 2.1 μm regions
Authors: Hartmann J.-M. , Tran H. , Toon G. C.
Published: April 2010

Abstract. We present the first study of the influence of line mixing among CO2 lines on the remote sensing retrieval of atmospheric carbon dioxide. This is done in the bands near 1.6 and 2.1 μm which have been retained by the Orbiting Carbon Observatory (OCO) and Greenhouse Gases Observatory Satellite (GOSAT) instruments. A purely theoretical analysis is first made, based on simulations of atmospheric spectra. It shows that line mixing cannot be neglected since disregarding this process induces significant errors in the calculated absorption coefficients, leading to systematic structures in the spectral fit residuals and airmass-dependent biases in the retrieved CO2 amounts. These theoretical predictions are then confirmed by using atmospheric solar-absorption spectra measured by a ground-based Fourier transform spectrometer. Indeed, it is first shown that including line mixing in the forward model used for the inversion leads to a very significant reduction of the residuals in the 2.1 μm region. Secondly, the inclusion of line mixing reduces the dependence of the retrieved CO2 on the airmass and greatly improves the consistency between values obtained independently from spectra in the 1.6 and 2.1 μm bands. These results open very promising prospects for various ground-based and space-borne experiments monitoring the carbon dioxide atmospheric amounts.
Closure on the single scattering albedo in the WRF-Chem framework using data from the MILAGRO campaign
Authors: Barnard J. C. , Fast J. D. , Paredes-Miranda G. , Arnott W. P.
Published: April 2010

Abstract. Data from the MILAGRO field campaign, which took place in the Mexico City Metropolitan Area (MCMA) during March 2006, is used to perform a closure experiment between aerosol chemical properties and aerosol optical properties. Measured aerosol chemical properties, obtained from the MILAGRO T1 site, are fed to two different "chemical to optical properties" modules. One module uses a sectional approach and is identical to that used in the WRF-Chem model, while the other is based on a modal approach. This modal code is employed as an independent check on the WRF-Chem module. Both modules compute aerosol optical properties and, in particular, the single-scattering albedo, ϖ0, as a function of time. The single-scattering albedos are compared to independent measurements obtained from a photoacoustic spectrometer (PAS). Because chemical measurements of the aerosol coarse mode were not available, and the inlet of the PAS could not ingest aerosols larger than about 2 to 3 μm, we focus here on the fine-mode ϖ0. At 870 nm, the wavelength of the PAS measurements, the agreement between the computed (modal and WRF-Chem) and observed fine-mode ϖ0, averaged over the course of the campaign, is reasonably good. The observed ϖ0 value is 0.77, while for both modules, the calculated value was 0.75 resulting in a difference of 0.02 between observations and both computational approaches. This difference is less than the uncertainty of the observed ϖ0 values (6%, or 0.05), and therefore "closure" is achieved, at least for mean values. After adjusting some properties of black carbon absorption and mass concentration within plausible uncertainty limits, the two modules simulate well the diurnal variation of ϖ0, and the absorption coefficient, Babs, but are less successful in calculating the variation of the scattering coefficient, Bscat. This difficulty is probably caused by the presence of larger particles during the day when windblown dust is ubiquitous; this dust likely increases the proportion of large particles introduced into the PAS. The dust also contributes to a very large aerosol mass loading in the coarse mode, and neglect of the coarse mode may cause significant errors, estimated to be as large as 0.07, in the calculation and measurement of ambient ϖ0. Finally, the observed ϖ0 is compared to the ϖ0 computed by the full WRF-Chem model, which includes prognostic aerosol chemistry. Unlike the results discussed above, a comparison between observed and simulated ϖ0 values reveals major differences. This large discrepancy is probably due, in part, to poor characterization of emissions near the T1 site, particularly black carbon emissions.
Effects of boundary layer particle formation on cloud droplet number and changes in cloud albedo from 1850 to 2000
Authors: Merikanto J. , Spracklen D. V. , Pringle K. J. , Carslaw K. S.
Published: April 2010

Abstract. We use a global aerosol microphysics model to estimate the effect of boundary layer particle formation on cloud droplet number concentration (CDNC) on global and regional scales. The calculations are carried out for years 1850 and 2000 using historical emissions inventories for primary particles and aerosol precursor gases. Predicted CDNC in 2000 are in good agreement with in-situ observations when particle formation is included. We find that particle formation increases global annual mean CDNC by approximately the same amount in both years (16.0% in 1850 and 13.5% in 2000). Thus, global mean changes in cloud albedo are similar with and without particle formation. However, there are substantial regional effects of up to 50% enhancement or suppression of the 1850–2000 albedo change. Over most modern-day polluted Northern Hemisphere regions particle formation suppresses the 1850–2000 increase in CDNC and cloud albedo. Over the Arctic the albedo change is suppressed by 23% in the annual mean and by 43% in summer when particle formation is taken into account. The albedo change of the persistent stratocumulus cloud deck west of Chile is enhanced by 49%.
Modelling the impacts of ammonia emissions reductions on North American air quality
Authors: Makar P. A. , Moran M. D. , Zheng Q. , Cousineau S. , Sassi M. , Duhamel A. , Besner M. , Davignon D. , Crevier L.-P. , Bouchet V. S.
Published: April 2010

Abstract. A unified regional air-quality modelling system (AURAMS) was used to investigate the effects of reductions in ammonia emissions on regional air quality, with a focus on particulate-matter formation. Three simulations of one-year duration were performed for a North American domain: (1) a base-case simulation using 2002 Canadian and US national emissions inventories augmented by a more detailed Canadian emissions inventory for agricultural ammonia; (2) a 30% North-American-wide reduction in agricultural ammonia emissions; and (3) a 50% reduction in Canadian beef-cattle ammonia emissions. The simulations show that a 30% continent-wide reduction in agricultural ammonia emissions lead to reductions in median hourly ±2.5 mass of <1 μg m−3 on an annual basis. The atmospheric response to these emission reductions displays marked seasonal variations, and on even shorter time scales the impacts of the emissions reductions are highly episodic: 95-percentile hourly ±2.5 mass decreases can be up to a factor of six larger than the median values. A key finding of the modelling work is the linkage between gas and aqueous chemistry and transport; reductions in ammonia emissions affect gaseous ammonia concentrations close to the emissions site, but substantial impacts on particulate matter and atmospheric deposition often occur at considerable distances downwind, with particle nitrate being the main vector of ammonia/um transport. Ammonia emissions reductions therefore have trans-boundary and possibly trans-oceanic consequences downwind. Calculations of critical-load exceedances for sensitive ecosystems in Canada suggest that ammonia emission reductions will have a minimal impact on current ecosystem acidification within Canada, but may have a substantial impact on future ecosystem acidification. The 50% Canadian beef-cattle ammonia emissions reduction scenario was used to examine model sensitivity to uncertainties in the new Canadian agricultural ammonia emissions inventory, and the simulation results suggest that further work is needed to improve the emissions inventory for this particular sector.
SCIAMACHY CO over the oceans: 2003–2007 interannual variability
Authors: Gloudemans A. M. S. , de Laat A. T. J. , Schrijver H. , Aben I. , Meirink J. F. , van der Werf G. R.
Published: April 2010

Abstract. We present a new method to obtain accurate SCIAMACHY CO columns over clouded ocean scenes. Based on an improved version of the Iterative Maximum Likelihood Method (IMLM) retrieval algorithm, we now have retrieved five years of data over both land and clouded ocean scenes between 2003 and 2007. The ocean-cloud method uses the CH4 columns retrieved simultaneously with the CO columns to determine the cloud top height. The CH4 cloud top height is in good agreement with the FRESCO+ cloud top height determined from UV-VIS oxygen-A band measurements, providing confidence that the CH4 cloud top height is a good diagnostic of the cloud top height over (partially) clouded ocean scenes. The CO measurements over clouded ocean scenes have been compared with collocated modeled CO columns over the same clouds and agree well. Using clouded ocean scenes quadruples the number of useful CO measurements compared to land-only measurements. The five-year CO data set over land and clouded ocean scenes presented here is based on an improved version of the IMLM algorithm which includes a more accurate determination of the random instrument-noise error for CO. This leads to a smaller spread in the differences between single CO measurements and the corresponding model values. The new version, IMLM version 7.4, also uses updated spectroscopic parameters for H2O and CH4 but this has only a minor impact on the retrieved CO columns. The five-year data set shows significant interannual variability over land and over clouded ocean scenes. Three examples are highlighted: the Asian outflow of pollution over the northern Pacific, the biomass-burning outflow over the Indian Ocean originating from Indonesia, and biomass burning in Brazil. In general there is good agreement between observed and modeled seasonal cycles and interannual variability.
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. Yu. , 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.
In-cloud processes of methacrolein under simulated conditions – Part 3: Hygroscopic and volatility properties of the formed Secondary Organic Aerosol
Authors: Michaud V. , El Haddad I. , Liu Y. , Sellegri K. , Laj P. , Villani P. , Picard D. , Marchand N. , Monod A.
Published: April 2010

Abstract. The hygroscopic and volatility properties of SOA produced from the nebulization of solutions after aqueous phase photooxidation of methacrolein was experimentally studied in laboratory, using a Volatility-Hygroscopicity Tandem DMA (VHTDMA). The obtained SOA were 80% 100°C-volatile after 5 h of reaction and only 20% 100°C-volatile after 22 h of reaction. The Hygroscopic Growth Factor (HGF) of the SOA produced from the nebulization of solutions after aqueous-phase photooxidation of methacrolein is 1.34–1.43, which is significantly higher than the HGF of SOA formed by gas-phase phtooxidation of terpenes, usually found nearly hydrophobic. These hygroscopic properties were confirmed for SOA formed by the nebulization of the same solutions where NaCl was added. The hygroscopic properties of the cloud droplet residuals decrease with the reaction time, in parallel with the formation of more refractory compounds. This decrease was mainly attributed to the 250°C-refractive fraction (presumably representative of the highest molecular weigh compounds), evolved from moderately hygroscopic (HGF of 1.52) to less hygroscopic (HGF of 1.36). Oligomerization is suggested as a process responsible for the decrease of both volatility and hygroscopicity with time. The NaCl seeded experiments enabled us to show that 19±4 mg L−1 of SOA was produced after 9.5 h of reaction and 41±9 mg L−1 after 22 h of in-cloud reaction. Because more and more SOA is formed as the reaction time increases, our results show that the reaction products formed during the aqueous-phase OH-oxidation of methacrolein may play a major role in the properties of residual particles upon droplet's evaporation. Therefore, the specific physical properties of SOA produced during cloud processes should be taken into account for a global estimation of SOA and their atmospheric impacts.
An operational system for the assimilation of satellite information on wild-land fires for the needs of air quality modelling and forecasting
Authors: Sofiev M. , Vankevich R. , Lanne M. , Prank M. , Petukhov V. , Ermakova T. , Kukkonen J.
Published: April 2010

Abstract. This paper investigates a potential of two remotely sensed wild-land fire characteristics: 4-μm Brightness Temperature Anomaly (TA) and Fire Radiative Power (FRP) for the needs of operational chemical transport modelling and the short-term forecasting of the atmospheric composition and air quality. Two treatments of the TA and FRP data are presented and a methodology for evaluating the emission fluxes is described. The method does not contain a complicated analysis of vegetation state, fuel load, burning efficiency and related factors, which are comparatively uncertain but inevitably involved in approaches based on burnt-area scars or similar products. The core of the current methodology is based on the empirical emission factors that have been derived from the analysis of several fire episodes in Europe (28 April–5 May 2006, 15–25 August 2006, August 2008 etc.). These episodes were characterised by: (i) well-identified FRP and TA values, and (ii) available independent observations of aerosol concentrations and optical thickness for the regions where fire smoke was dominant in comparison with contributions of other pollution sources. The emission factors were determined separately for the forested and grassland areas; in case of mixed-type land use an intermediate scaling was assumed. Despite significant difference between the TA and FRP products, an accurate non-linear fitting between the approaches was found. The agreement was comparatively weak only for small fires where the accuracy of both products is low. The re-analysis and forecasting applications of the Fire Assimilation System (FAS) showed that both TA and FRP products are suitable for evaluation of the emission fluxes from the wild-land fires. The concentrations of aerosols predicted by the regional dispersion modelling system SILAM appear within a factor of 2–3 from observations. The main areas of improvement include further refining the emission factors over the globe, explicit determination and appropriate treatment of the type of fires, evaluation of the injection height of the plumes and predicting the fire temporal evolution.
Characterization of organic ambient aerosol during MIRAGE 2006 on three platforms
Authors: Gilardoni S. , Shang L. , Takahama S. , Russell L. M. , Allan J. D. , Steinbrecher R. , Jimenez J. L. , Decarlo P. F. , Dunlea E. J. , Baumgardner D.
Published: April 2010

Abstract. Submicron atmospheric aerosol particles were collected during the Megacity Initiative: Local and Global Research Observation (MILAGRO) in March 2006 at three platforms located in the Mexico City urban area (at the Mexico City Atmospheric Monitoring System building – SIMAT), at about 60 km south-west of the metropolitan area (Altzomoni in the Cortes Pass), and on board the NSF/NCAR aircraft C130. Organic functional group and elemental composition were measured by FTIR and XRF. The average organic mass (OM) concentration, calculated as the sum of organic functional group concentrations, was 9.9 μg m−3 at SIMAT, 6.6 μg m−3 at Altzomoni, and 5.7 μg m−3 on the C130. Aliphatic saturated C-C-H and carboxylic acid COOH groups dominated OM (more than 60%) at the ground sites. On the C130, a non-acid carbonyl C=O, and amine NH2 groups were observed in concentrations above detection limit only outside the Mexico City basin. From the elemental composition of SIMAT samples, we estimated the upper bound of average contribution of biomass burning to the organic carbon (OC) as 33–39%. The average OM/OC ratio was 1.8 at SIMAT, 2.0 at Altzomoni, and 1.6–1.8 on the C130. On the aircraft, higher OM/OC ratios were measured outside of the Mexico City basin, north of the urban area, along the city outflow direction. The average carboxylic acid plus non-acid carbonyl to aliphatic saturated ratio was higher at Altzomoni relative to SIMAT, reflecting a larger average contribution of carbonyl functional groups (largely in carboxylic acids) at the mountain site.
Comparison of analytical methods for HULIS measurements in atmospheric particles
Authors: Baduel C. , Voisin D. , Jaffrezo J. L.
Published: April 2010

Abstract. Humic-Like Substances (HULIS) are a major contributor to the organic carbon in atmospheric aerosol. It would be necessary to standardise an analytical method that could be easily and routinely used for HULIS measurements. We present one of the first comparisons of two of the main methods in use to extract HULIS, using i) a weak anion exchanger (DEAE) and ii) the combination of two separation steps, one according to polarity (on C18) and the second according to acidity (with a strong anion exchanger SAX). The quantification is performed with a DOC analyzer, complemented by an investigation of the chemical structure of the extracted fractions by UV-Visible spectroscopy. The analytical performances of each method are determined and compared for humic substances standards. These methods are further applied to determine the water extractable HULIS (HULISWS) and the 0.1M NaOH alkaline extractable HULIS (HULIST) in atmospheric aerosol collected in an Alpine Valley during winter time. This comparison shows that the simpler DEAE isolation procedure leads to higher recoveries and better reproducibility and should therefore be recommended.