bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationships between size-fractionated indoor and outdoor trace elements at four retirement communities in Southern California
Authors: Polidori A. , Cheung K. L. , Arhami M. , Delfino R. J. , Schauer J. J. , Sioutas C.
Published: April 2010

Abstract. Indoor and outdoor water soluble trace elements (TEs) were analyzed on quasi-ultrafine (UF), accumulation, and coarse PM filter samples collected at four retirement communities, three located in the San Gabriel Valley and one in Riverside, CA. Our analysis indicates that a complex mix of vehicular, industrial, and soil-related emissions was responsible for the elemental concentrations measured at the three San Gabriel sites, while regional transport, soil re-suspension and, to a lower degree, local traffic contributed to TE levels observed in Riverside. In the quasi-UF mode, the magnitude of indoor/outdoor concentration ratios (I/O) for elements of anthropogenic origin was highly variable, reflecting the spatial heterogeneity of combustion sources in the study area. Indoor/outdoor ratios in accumulation mode PM were closer to 1, and more homogeneous across sites, indicating that elements associated with this size fraction penetrate indoors with high efficiencies. The lowest overall I/O ratios were obtained for elements found in coarse particles, consistent with the fact that only a small portion of coarse outdoor PM infiltrates indoors. The potential of S and other TEs to serve as tracers of indoor-penetrated particles of outdoor origin was also examined. Our results suggest that using the I/O ratio of S (I/OS) as a surrogate of the infiltration factor for PM2.5 [Finf(PM2.5)] might lead to an overestimation of the indoor PM2.5 originating outdoors. This is in contrast with what was reported in previous studies conducted in the Eastern US, where S has been consistently used as a reliable tracer of outdoor PM2.5 infiltrating indoors. Our differences may be due to the fact that in the Los Angeles basin (and in general in the Western US) PM2.5 includes a number of semi-volatile labile species, such as ammonium nitrate and several organic compounds, which volatilize either entirely or to a substantial degree upon building entry.
Observational study of aerosol hygroscopic growth factors over rural area near Beijing mega-city
Authors: Pan X. L. , Yan P. , Tang J. , Ma J. Z. , Wang Z. F. , Gbaguidi A.
Published: April 2010

Abstract. We investigated aerosol hygroscopic growth property and its influence on scattering coefficient using M9003 nephelometers in coupling with a relative humidity controlled inlet system at a rural site near Beijing mega-city (Jingjintang) from 24th April to15th May 2006. Inlet relative humidity was controlled in an increasing range of 40%–90% while the aerosol hygroscopic growth factor, f(RH=80%), varied in a range of 1.07–2.35 during the measurement. Estimated periodic mean values of aerosol hygroscopic growth factors are 1.27–1.34, 1.17–1.23, 1.55–1.59 and 2.33–2.48 for clean, dust, urban pollution and mixed pollution periods respectively. An examination of chemical composition of daily filter samples highlighted that aerosol hygroscopicity was generally enhanced with the increasing ratio of ammonium sulfate (AS) to organic matter (OMC). Furthermore, strong hygroscopic organic aerosols were observed on 11th (f(RH=80%)=2.23) and 15th (f(RH=80%)=2.21) of May with organic carbon proportions of PM2.1 reaching 42.3% and 43.0% respectively. Back-trajectory analysis indicated that solar radiation and vertical convective movement along the air mass pathway might strongly influence the hygroscopic properties of organic matter.
Changing sources and environmental factors reduce the rates of decline of organochlorine pesticides in the Arctic Atmosphere
Authors: Becker S. , Halsall C. J. , Tych W. , Kallenborn R. , Schlabach M. , Manø S.
Published: April 2010

Abstract. An extensive database of organochlorine (OC) pesticide concentrations measured at the Norwegian Arctic Monitoring Station was analysed to assess longer-term trends in the Arctic atmosphere. Dynamic Harmonic Regression (DHR) is employed to investigate the seasonal and cyclical behaviour of chlordanes, DDTs and hexachlorobenzene (HCB), and to isolate underlying inter-annual trends. Although a simple comparison of annual mean concentrations (1994–2005) suggest a decline for all of the OCs investigated, the longer-term trends identified by DHR only show a significant decline for p,p'-DDT. Indeed, HCB shows an increase from 2003–2005. This is thought to be due to changes in source types and the presence of impurities in current use pesticides, together with retreating sea ice affecting air-water exchange. Changes in source types were revealed by using isomeric ratios for the chlordanes and DDTs. Declining trends in ratios of trans-chlordane/cis-chlordane (TC/CC) indicate a shift from primary sources, to more ''weathered'' secondary sources, whereas an increasing trend in o,p'-DDT/p,p'-DDT ratios indicate a shift from use of technical DDT to dicofol. Continued monitoring of these OC pesticides is required to fully understand the influence of a changing climate on the behaviour and environmental cycling of these chemicals in the Arctic as well as possible impacts from ''new'' sources.
A product study of the isoprene+NO3 reaction
Authors: Perring A. E. , Wisthaler A. , Graus M. , Wooldridge P. J. , Lockwood A. L. , Mielke L. H. , Shepson P. B. , Hansel A. , Cohen R. C.
Published: April 2010

Abstract. Oxidation of isoprene through reaction with NO3 is a significant sink for isoprene that persists after dark. The products of the reaction are multifunctional nitrates. These nitrates constitute a significant NOx sink in the nocturnal boundary layer and they likely play an important role in formation of secondary organic aerosol. Products of the isoprene+NO3 reaction will, in many locations, be abundant enough to affect nighttime radical chemistry and to persist into daytime where they may represent a source of NOx. Product formation in the isoprene+NO3 reaction was studied in a smog chamber at Purdue University. Isoprene nitrates and other hydrocarbon products were observed using Proton Transfer Reaction-Mass Spectrometry (PTR-MS) and reactive nitrogen products were observed using Thermal Dissociation–Laser Induced Fluorescence (TD-LIF). The organic nitrate yield is found to be 62±6% and the combined yield of MACR+MVK is found to be ~10%. Additional hydrocarbon products, thought to be primarily C4 and C5 carbonyl compounds, were observed by the PTR-MS at various m/z ratios and their yields quantified. These other oxidation products are used as additional constraints on the reaction mechanism.
Modelling multi-phase halogen chemistry in the remote marine boundary layer: investigation of the influence of aerosol size resolution on predicted gas- and condensed-phase chemistry
Authors: Lowe D. , Topping D. , McFiggans G.
Published: April 2010

Abstract. A coupled box model of photochemistry and aerosol microphysics which explicitly accounts for size-dependent chemical properties of the condensed-phase has been developed to simulate the multi-phase chemistry of chlorine, bromine and iodine in the marine boundary layer (MBL). The model contains separate seasalt and non-seasalt modes, each of which may be composed of 1–16 size-sections. By comparison of gaseous and aerosol compositions predicted using different size-resolutions with both fixed and size-dependent aerosol turnover rates, it was found that, for halogen-activation processes, the physical property initialisation of the aerosol-mode has a significant influence on gas-phase chemistry. Failure to adequately represent the appropriate physical properties can lead to substantial errors in gas-phase chemistry. The size-resolution of condensed-phase composition has a less significant influence on gas-phase chemistry.
Primary and secondary organic carbon downwind of Mexico City
Authors: Yu X.-Y. , Cary R. A. , Laulainen N. S.
Published: April 2010

Abstract. In order to study particulate matter transport and transformation in the Megacity environment, fine particulate carbons were measured simultaneously at two supersites, suburban T1 and rural T2, downwind of Mexico City during the MILAGRO field campaign in March 2006. Organic carbon (OC), element carbon (EC), and total carbon (TC=OC+EC) were determined in near real-time using a Sunset semi-continuous OC/EC field analyzer. The semi-empirical EC tracer method was used to derive primary organic carbon (POC) and secondary organic carbon (SOC). Diurnal variations of primary and secondary carbons were observed at T1 and T2, which resulted from boundary layer inversion and impacted by local traffic patterns. The majority of organic carbon particles at T1 and T2 were secondary. The SOC% (SOC%=SOC/TC×100%) at T1 ranged from 1.2–100% with an average of 80.7±14.4%. The SOC% at T2 ranged from 12.8–100% with an average of 80.1±14.0%. The average EC to PM2.5 percentage (ECPM%=EC/PM2.5×100%) and OCPM% were 6.0% and 20.0% over the whole sampling time at T1. The POC to PM percentage (POCPM%) and SOCPM% were 3.7% and 16.3%, respectively at the same site. The maximum ECPM% was 21.2%, and the maximum OCPM% was 57.2% at T1. The maximum POCPM% was 12.9%, and the maximum SOCPM% was 49.7% at the suburban site. Comparison of SOC and POC at T1 and T2 showed similar characteristics under favorable meteorological conditions, which indicated that transport between the two supersites took place. Strong correlations between EC and carbon monoxide (CO) and odd nitrogen species (NO and NOx) were observed at T1. This indicated that EC had nearby sources, such as local traffic emissions. The EC/CO ratio derived by linear regression analysis, when parameters in μg C/m3 and μg/m3, respectively, was 0.0045 at T1. Correlations were also seen between OC and SOC vs. the sum of oxidants, such as O3 and NO2, suggesting the secondary nature of carbons observed at T1.
Reassessment of causes of ozone column variability following the eruption of Mount Pinatubo using a nudged CCM
Authors: Telford P. , Braesicke P. , Morgenstern O. , Pyle J.
Published: April 2010

Abstract. The eruption of Mount Pinatubo produced the largest loading of stratospheric sulphate aerosol in the twentieth century. This heated the tropical lower stratosphere, affecting stratospheric circulation, and provided enhanced surface area for heterogeneous chemistry. These factors combined to produce record low values of extra-polar total ozone column. Though well studied, there remains some uncertainty about the attribution of this low ozone, with contributions from both chemical and dynamical effects. We take a complementary approach to previous studies, nudging the temperature and horizontal winds in the new UKCA CCM to reproduce the atmospheric response and assess the impact on global total ozone. We then combine model runs and observations to attribute the variability to chemical and dynamical effects. To estimate the effects of increased heterogeneous chemistry we compare runs with volcanically enhanced and background surface aerosol density, noting that this causes depletion of global ozone peaking at about 7 DU in early 1993, in good agreement with observations. We subtract this effect from the observed variability and attribute the remaining variability to dynamical effects. We see that the remaining variability is dominated by the QBO. In addition to global averages we examine tropical and mid-latitude ozone, diagnosing contributions from El Niño in the tropics and some dynamically driven low ozone in northern mid-latitudes, which we see as possible evidence of changes in the QBO. We conclude that, on a global scale, the record lows of extra-polar ozone are produced by the increased heterogeneous chemistry, although there is evidence for dynamics having producing low ozone in certain regions, such as northern mid-latitudes.
The climatic effects of the direct injection of water vapour into the stratosphere by large volcanic eruptions
Authors: Joshi M. M. , Jones G. S.
Published: April 2010

Abstract. We describe a novel mechanism that can significantly lower the amplitude of the climatic response to certain large volcanic eruptions. The proximity of oceans to some volcanoes can cause significant entrainment of water into coignimbrite clouds during the eruption. If sufficiently large amounts of this entrained water vapour enter the stratosphere, a climatically significant amount of water vapour can be left over in the lower stratosphere after the eruption, even after sulphate aerosol formation. This excess stratospheric humidity warms the climate, and acts to balance the climatic cooling induced by the volcanic aerosol, especially because the humidity anomaly lasts for a period that is longer that the residence time of aerosol in the stratosphere. In particular, Northern Hemisphere cooling is reduced in magnitude. We discuss this mechanism in the context of the discrepancy between the observed and modelled cooling following the Krakatau eruption in 1883.
Data assimilation of CALIPSO aerosol observations
Authors: Sekiyama T. T. , Tanaka T. Y. , Shimizu A. , Miyoshi T.
Published: April 2010

Abstract. We have developed an advanced data assimilation system for a global aerosol model with a four-dimensional ensemble Kalman filter in which the Level 1B data from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) were successfully assimilated for the first time, to the best of the authors' knowledge. A one-month data assimilation cycle experiment for dust, sulfate, and sea-salt aerosols was performed in May 2007. The results were validated via two independent observations: 1) the ground-based lidar network in East Asia, managed by the National Institute for Environmental Studies of Japan, and 2) weather reports of aeolian dust events in Japan. Detailed four-dimensional structures of aerosol outflows from source regions over oceans and continents for various particle types and sizes were well reproduced. The intensity of dust emission at each grid point was also globally corrected. These results are valuable for the comprehensive analysis of aerosol behavior as well as aerosol forecasting.
Distribution and sources of bioaccumulative air pollutants at Mezquital Valley, Mexico, as reflected by the atmospheric plant Tillandsia recurvata L.
Authors: Zambrano García A. , Medina Coyotzin C. , Rojas Amaro A. , López Veneroni D. , Chang Martínez L. , Sosa Iglesias G.
Published: April 2010

Abstract. Mezquital Valley (MV), a Mexican wastewater-based agricultural and industrial region, is a ''hot spot'' of regulated air pollutants emissions, but the concurrent unregulated ones, like hazardous metals and polycyclic aromatic hydrocarbons (PAH), remain undocumented. A biomonitoring survey with the epiphytic Tillandsia recurvata was conducted there to detect spatial patterns and potential sources of 20 airborne elements and 15 PAH. The natural δ13C and δ15N ratios of this plant helped in source identification. The regional mean concentrations of most elements was two (Cr) to over 40 times (Ni, Pb, V) higher than reported for Tillandsia in other countries. Eleven elements, pyrene and chrysene had 18–214% higher mean concentration at the industrial south than at the agricultural north of MV. The total quantified PAH (mean, 572 ng g−1; range, 142.6–2568) were composed by medium (65%, phenanthrene to chrysene), low (28%, naphthalene to fluorene) and high molecular weight compounds (7%, Benzo(b)fluoranthene to indeno(1,2,3-cd)pyrene). The δ13C (mean, −14.6‰; range, −5.7 to −13.7‰) was lower (<−15‰) near the major petroleum combustion sources. The δ15N (mean, −3.0‰; range, −9.9 to 3.3‰) varied from positive at agriculture/industrial areas to negative at rural sites. Factor analysis provided a five-factor solution for 74% of the data variance: (1) crustal rocks, 39.5% (Al, Ba, Cu, Fe, Sr, Ti); (2) soils, 11.3%, contrasting contributions from natural (Mg, Mn, Zn) and saline agriculture soils (Na); (3) cement production and fossil fuel combustion, 9.8% (Ca, Ni, V, chrysene, pyrene); (4) probable agricultural biomass burning, 8.1% (K and benzo(g,h,i)perylene), and (5) agriculture with wastewater, 5.2% (δ15N and P). These results indicated high deposition of bioaccumulative air pollutants at MV, especially at the industrial area. Since T. recurvata reflected the regional differences in exposition, it is recommended as a biomonitor for comparisons within and among countries where it is distributed: southern USA to Argentina.
Regional CO pollution in China simulated by the high-resolution nested-grid GEOS-Chem model
Authors: Chen D. , Wang Y. , McElroy M. B. , He K. , Yantosca R. M. , Le Sager P.
Published: April 2010

Abstract. An updated version of the nested-grid GEOS-Chem model is developed allowing for higher horizontal (0.5°×0.667°) and vertical resolution as compared to global models. CO transport over a heavily polluted region, the Beijing-Tianjin-Hebei (BTH) city cluster in China, and the pattern of outflow from East China in summertime are investigated. Comparison of the nested-grid with global models indicates that the fine-resolution nested-grid model is capable of resolving individual cities with high associated emission intensities. The nested-grid model indicates the presence of a high CO column density over the Sichuan Basin in summer, attributable to the low-level stationary vortex associated with the Basin's topographical features. The nested-grid model provides good agreement also with measurements from a suburban monitoring site in Beijing during summer 2005. Tagged CO simulation results suggest that regional emissions make significant contributions to elevated CO levels over Beijing on polluted days and that the southeastward moving cyclones bringing northwest winds to Beijing are the key meteorological mechanisms responsible for dispersion of pollution over Beijing in summer. Overall CO fluxes to the NW Pacific from Asia are found to decrease by a factor of 3–4 from spring to summer. Much of the seasonal change is driven by decreasing fluxes from India and Southeast Asia in summer, while fluxes from East China are only 30% lower in summer than in spring. Compared to spring, summertime outflow from Chinese source regions is strongest at higher latitudes (north of 35° N). The deeper convection in summer transporting CO to higher altitudes where export is more efficient is largely responsible for enhanced export in summer.
Regional modelling of tracer transport by tropical convection – Part 2: Sensitivity to model resolutions
Authors: Arteta J. , Marécal V. , Rivière E. D.
Published: April 2010

Abstract. The general objective of this series of two papers is to evaluate long duration limited-area simulations with idealised tracers as a tool to assess the tracer transport in chemistry-transport models (CTMs). In this second paper we analyse the results of three simulations using different horizontal and vertical resolutions against meteorological observations and their impact on idealized tracer transport. The reference simulation (REF) uses a 60 km horizontal resolution and 300 m vertically in the upper troposphere/lower stratosphere (UTLS). A 20 km horizontal resolution simulation (HR) is run as well as a simulation (CVR) with 850 m vertical resolution in the UTLS. The simulations are run for one month during the SCOUT-O3 field campaign. The Falcon and Geophysica aircraft data and the TRMM rainrate estimates have been used to evaluate the simulations. They show that the HR configuration gives generally a better agreement with the measurements than the REF simulation, the CVR simulation giving generally the worst results. The vertical distribution of the tropospheric tracers for the simulations has a similar shape with a 15 km altitude maximum of 0.4 ppbv for REF, 1.2 for HR and 0.04 for CVR. This is related to the dynamics produced by the three simulations that leads to larger values of the upward velocities on average for HR and lower for CVR compared to REF. The HR provides more frequent overshoots over the cold point dynamical barrier than REF and CVR. For the stratospheric tracers the differences between the three simulations are small. The diurnal cycle of the fluxes of all tracers in the TTL (Tropical Tropopause Layer) exhibits a maximum linked to the maximum of convective activity that is particularly well marked in the HR simulation. The largest integrated fluxes are found for tropospheric tracers in HR.
Process based inventory of isoprenoid emissions from European forests: model comparisons, current knowledge and uncertainties
Authors: Keenan T. , Niinemets Ü. , Sabate S. , Gracia C. , Peñuelas J.
Published: April 2010

Abstract. Large uncertainties exist in our knowledge of regional emissions of non-methane biogenic volatile organic compounds (BVOC). We address these uncertainties through a two-pronged approach by compiling a state of the art database of the emissions potentials for 80 European forest species, and by a model assessment and inter-comparison, both at the local and regional scale, under present and projected future climatic conditions. We coupled three contrasting isoprenoid models with the ecophysiological forest model GOTILWA+ to explore the interactive effects of climate, vegetation distribution, and productivity, on leaf and ecosystem isoprenoid emissions, and to consider model behaviour in present climate and under projected future climate change conditions. Hourly, daily and annual isoprene emissions as simulated by the models were evaluated against flux measurements. The validation highlighted a general model capacity to capture gross fluxes but inefficiencies in capturing short term variability. A regional inventory of isoprenoid emissions for European forests was created using each of the three modelling approaches. The models agreed on an average European emissions budget of 1.03 TgC a−1 for isoprene and 0.97 TgC a−1 for monoterpenes for the period 1960–1990, which was dominated by a few species with largest aerial coverage. Species contribution to total emissions depended both on species emission potential and geographical distribution. For projected future climate conditions, however, emissions budgets proved highly model dependent, illustrating the current uncertainty associated with isoprenoid emissions responses to potential future conditions. These results suggest that current model estimates of isoprenoid emissions concur well, but future estimates are highly uncertain. We conclude that development of reliable models is highly urgent, but for the time being, future BVOC emission scenario estimates should consider results from an ensemble of available emission models.
Day-time concentrations of biogenic volatile organic compounds in a boreal forest canopy and their relation to environmental and biological factors
Authors: Lappalainen H. K. , Sevanto S. , Bäck J. , Ruuskanen T. M. , Kolari P. , Taipale R. , Rinne J. , Kulmala M. , Hari P.
Published: April 2010

Abstract. Atmospheric concentrations of methanol, acetaldehyde, acetone, isoprene and monoterpenes were measured using a PTR-MS (proton transfer reaction mass spectrometry) in a boreal forest site in Hyytiälä, Finland (61°51 N, 24°17 E). The concentration measurements were made in the upper canopy of a Scots pine forest during 6 June 2006 – 31 August 2007. Meteorological variables such as temperature and photosynthetically active radiation were measured simultaneously. We also detected biologically sensitive turnover points such as the onsets of photosynthetic activity, onset of growing season, budburst and stem growthduring during the annual cycle and compared them to changes in BVOC (biogenic volatile organic compound) concentrations. A typical seasonal pattern of winter minimum and summer maximum was found for all studied compounds except acetaldehyde. Spring time methanol and acetone concentrations increased together with photosynthetic capacity. The day-time daily median BVOC concentrations correlated best with air temperature. The inter correlations between compounds and the analysis of meteorological conditions indicated that the measured concentrations presented well the local source. During an exceptional summer drought period the concentrations were neither connected with photosynthesis nor transpiration, but they were regulated by some other, yet unknown factors.
Exploring atmospheric boundary layer characteristics in a severe SO2 episode in the north-eastern Adriatic
Authors: Prtenjak M. T. , Jeričević A. , Nitis T. , Klaić Z. B.
Published: April 2010

Abstract. Stable atmospheric conditions are often connected with the occurrence of high pollutant episodes especially in urban or industrial areas. In this work we investigate a severe pollution SO2 episode observed on 3–5 February 2002 in a coastal industrial town of Rijeka, Croatia. The episode occurred under anticyclonic high pressure conditions during which a fog, low wind speeds and very high daily associated mean SO2 concentration of 353.5 μg m−3 were observed. First, the EMEP model was used to evaluate the long-range transport and its contribution to the local SO2 concentrations. The comparison between the EMEP modelled regional SO2 concentrations and measured ones in Rijeka showed that the episode was caused predominately by local sources. Furthermore, using three-dimensional, higher-order turbulence closure mesoscale models (WRF and MEMO), the wind regimes and thermo-dynamical structure of the lower troposphere above the greater Rijeka area were examined in detail. The obtained results suggest several factors responsible for elevated SO2 concentrations. The polluted air is transported towards Rijeka from nearby industrial areas where major pollution sources are located. This transport is associated with strong, ground-based temperature inversion and with a corresponding very low, mixing layer (below 140 m). Light winds or almost calm conditions in Rijeka town were another causative factor of the episode. Also, a vertical circulation cell formed between the mainland and a nearby island, causing the air subsidence and stability increase in the lowermost layer south of Rijeka.
In-cloud processes of methacrolein under simulated conditions – Part 1: Aqueous phase photooxidation
Authors: Liu Y. , El Haddad I. , Scarfogliero M. , Nieto-Gligorovski L. , Temime-Roussel B. , Quivet E. , Marchand N. , Picquet-Varrault B. , Monod A.
Published: April 2010

Abstract. The photooxidation of methacrolein was studied in the aqueous phase under simulated cloud droplet conditions. The obtained rate constant of OH-oxidation of methacrolein at 6°C in unbuffered solutions was 5.8 (±0.9)×109 M−1 s−1. This kinetic study showed that the oxidation proceeds mainly by OH-addition on the C=C bond. This was confirmed by the mechanism established on the study of the reaction products (at 25°C in unbuffered solutions) where methylglyoxal, formaldehyde, hydroxyacetone and acetic acid/acetate were the main reaction products. An upper limit for the total carbon yield was estimated to range from 53 to 85%, indicating that some reaction products remain unidentified. A possible source of this mismatch is the formation of higher molecular weight compounds as primary reaction products which are presented in El Haddad et al. (2009) and Michaud et al. (2009).
In-cloud processes of methacrolein~under simulated conditions – Part 2: Formation of Secondary Organic Aerosol
Authors: El Haddad I. , Liu Y. , Nieto-Gligorovski L. , Michaud V. , Temime-Roussel B. , Quivet E. , Marchand N. , Sellegri K. , Monod A.
Published: April 2010

Abstract. The fate of methacrolein in cloud evapo-condensation cycles was experimentally investigated. To this end, aqueous-phase reactions of methacrolein with OH radicals were performed (as described in Liu et al., 2009), and the obtained solutions were then nebulized and dried into a mixing chamber. The ESI-MS and ESI-MS/MS analyses of the aqueous phase composition denoted the formation of high molecular weight multifunctional products containing hydroxyl, carbonyl and carboxylic acid moieties. The time profiles of these products suggest that their formation can imply radical pathways. These high molecular weight organic products are certainly responsible for the formation of SOA observed during the nebulization experiments. The size, number and mass concentration of these particles increased significantly with the reaction time: after 22 h of reaction, the aerosol mass concentration was about three orders of magnitude higher than the initial aerosol quantity. The evaluated SOA yield ranged from 2 to 12%. This provides, for the first time to our knowledge, strong experimental evidence that cloud processes can act as important contributors to secondary organic aerosol formation in the troposphere. The hygroscopic properties of these secondary organic aerosols are analysed in Michaud et al. (2009).
Recent trends in atmospheric methyl bromide: analysis of post-Montreal Protocol variability
Authors: Yvon-Lewis S. A. , Saltzman E. S.
Published: April 2010

Abstract. The atmospheric methyl bromide (CH3Br) burden has declined in recent years, in response to the phaseout of agricultural and structural fumigation consumption under the amendments to the Montreal Protocol. The timing and magnitude of this decrease represents an opportunity to examine our current understanding of the CH3Br budget, the phaseout schedule, and recent estimates of interannual variability in biomass burning and global OH. In this study, simulations obtained from a time-dependent global model of atmospheric CH3Br emissions and uptake are compared to observations from the NOAA flask network. The model includes an updated global methyl bromide source inventory that includes biofuel combustion emissions estimated at 6.1±3 Gg yr−1 globally. The phaseout of CH3Br production for agricultural uses began in 1998, concurrent with the pulse in biomass burning associated with the 1998 El Niño. The combined effects of three factors (biomass burning, global OH, and anthropogenic phaseout) appear to explain most of the observed atmospheric methyl bromide trend over the 1997–2005 period. The global budget remains imbalanced, with a large missing source. These results suggest that more than 80% of the missing source does not exhibit significant interannual variability during the phaseout period and, therefore, does not result from underestimating agricultural CH3Br emissions.
Evolution, current capabilities, and future advances in satellite ultra-spectral IR sounding
Authors: Smith W. L. , Revercomb H. , Bingham G. , Larar A. , Huang H. , Zhou D. , Li J. , Liu X. , Kireev S.
Published: April 2010

Abstract. Infrared ultra-spectral spectrometers have brought in a new era of satellite remote atmospheric sounding capability. During the 1970's, after the implementation of the first satellite sounding instruments, it became evident that much higher vertical resolution sounding information was needed to be able to forecast life and property threatening localized severe weather. The demonstration of the ultra-spectral radiance measurement technology required to achieve higher vertical resolution began in 1985, with the aircraft flights of the High-resolution Interferometer Sounder (HIS) instrument. The development of satellite instruments designed to have a HIS-like measurement capability was initiated in the late 1980's. Today, after more than a decade of development time, the Atmospheric Infrared Sounder (AIRS) and the Infrared Atmospheric Sounding Interferometer (IASI) are now operating successfully from the Aqua and MetOp polar orbiting satellites, respectively. The successful development and ground demonstration of the Geostationary Imaging Fourier Transform Spectrometer (GIFTS), during this decade, is now paving the way toward future implementation of the ultra-spectral sounding capability on the international system of geostationary environmental satellites.
Spatio-temporal observations of tertiary ozone maximum
Authors: Sofieva V. F. , Kyrölä E. , Verronen P. T. , Seppälä A. , Tamminen J. , Marsh D. R. , Smith A. K. , Bertaux J.-L. , Hauchecorne A. , Dalaudier F. , Fussen D. , Vanhellemont F. , Fanton d'Andon O. , Barrot G. , Guirlet M. , Fehr T. , Saavedra L.
Published: April 2010

Abstract. We present spatio-temporal distributions of tertiary ozone maximum (TOM), based on GOMOS (Global Ozone Monitoring by Occultation of Stars) ozone measurements in 2002–2006. The tertiary ozone maximum is typically observed in the high-latitude winter mesosphere at altitude ~72 km. Although the explanation for this phenomenon has been found recently – low concentrations of odd-hydrogen cause the subsequent decrease in odd-oxygen losses – models have had significant deviations from existing observations until recently. Good coverage of polar night regions by GOMOS data has allowed for the first time obtaining spatial and temporal observational distributions of night-time ozone mixing ratio in the mesosphere. The distributions obtained from GOMOS data have specific features, which are variable from year to year. In particular, due to a long lifetime of ozone in polar night conditions, the downward transport of polar air by the meridional circulation is clearly observed in the tertiary ozone maximum time series. Although the maximum tertiary ozone mixing ratio is achieved close to the polar night terminator (as predicted by the theory), TOM can be observed also at very high latitudes, not only in the beginning and at the end, but also in the middle of winter. We have compared the observational spatio-temporal distributions of tertiary ozone maximum with that obtained using WACCM (Whole Atmosphere Community Climate Model) and found that the specific features are reproduced satisfactorily by the model. Since ozone in the mesosphere is very sensitive to HOx concentrations, energetic particle precipitation can significantly modify the shape of the ozone profiles. In particular, GOMOS observations have shown that the tertiary ozone maximum was temporarily destroyed during the January 2005 and December 2006 solar proton events as a result of the HOx enhancement from the increased ionization.
Regional differences in organic composition of submicron and single particles during INTEX-B 2006
Authors: Day D. A. , Takahama S. , Gilardoni S. G. , Russell L. M.
Published: April 2010

Abstract. Organic functional group and elemental concentrations were measured with Fourier transform infrared (FTIR) spectroscopy and X-ray fluorescence (XRF) from an aircraft platform as part of the Intercontinental Chemical Transport Experiment – Phase B (INTEX-B) conducted over the Eastern Pacific and Western North America. Single particle spectra were obtained using scanning transmission X-ray microscopy-near edge X-ray absorption fine structure spectrometry (STXM-NEXAFS). Organic mass (OM) concentrations ranged from 1 to 7 μg m−3 and averaged 2.4–4.1 μg m−3. Alkane functional groups were the largest fraction of OM, averaging 1.9–2.1 μg m−3 or 50–76% of OM. Alcohol functional groups comprised the second largest fraction of OM (0.35–0.39 μg m−3, 9–14%). Organic and elemental concentrations are compared within and among geographical air mass regions: "Pacific" free troposphere, "Continental" free troposphere, "Seattle" metropolitan region, and the California "Central Valley". OM concentrations were highest and most variable in the Central Valley (3.5±2 μg m−3). Alcohol functional group concentrations were highest in the Continental and Central Valley and lowest in the Pacific and Seattle air masses. Oxygen-to-carbon ratios were relatively constant in the Central Valley but variable for the Continental air masses. Most elemental concentrations did not show large variations among or within air mass categories. Overall, the OM concentrations showed greater variability within air mass categories as compared to averages among them, suggesting sampled air mass regions included a variety of sources, processing, and losses of organic aerosol. Single particle spectra obtained by STXM-NEXAFS were classified into metaclasses associated with different sources and atmospheric processing. Particles with spectra indicative of secondary organic aerosol production and combustion sources were found at several locations and a range of altitudes. At lower altitudes, particles with spectra resembling soil dust and biomass burning fingerprints were commonly observed. Single particle spectra provided evidence that condensation and surface-limited oxidation contributed to particle growth.
Ambient new particle formation parameter indicates potential rise in future events
Authors: Bonn B. , Boy M. , Kulmala M. , Groth A. , Trawny K. , Borchert S. , Jacobi S.
Published: April 2010

Abstract. Atmospheric new particle formation is a general phenomenon observed over coniferous forests. So far nucleation is described as a function of gaseous sulfuric acid concentration only, which is unable to explain the observed seasonality of nucleation events at different measurement sites. Here we introduce a new nucleation parameter including ozone and water vapor concentrations as well as UV-B radiation as a proxy for OH radical formation. Applying this new parameter to field studies conducted at Finnish and German measurement sites it is found capable to predict the occurrence of nucleation events and their seasonal and annual variation indicating a significant role of organics. Extrapolation to possible future conditions of ozone, water vapor and organic concentrations leads to a significant potential increase in nucleation event number.
A new insight on tropospheric methane in the Tropics – first year from IASI hyperspectral infrared observations
Authors: Crevoisier C. , Nobileau D. , Fiore A. M. , Armante R. , Chédin A. , Scott N. A.
Published: April 2010

Abstract. Simultaneous observations from the Infrared Atmospheric Sounding Interferometer (IASI) and from the Advanced Microwave Sounding Unit (AMSU), launched together onboard the European MetOp platform in October 2006, are used to retrieve a mid-to-upper tropospheric content of methane (CH4) in clear-sky conditions, in the Tropics, over sea, for the first 16 months of operation of MetOp (July 2007–October 2008). With its very high spectral resolution, IASI provides nine channels in the 7.7 μm band highly sensitive to CH4 with reduced sensitivities to other atmospheric variables. These channels, sensitive to both CH4 and temperature, are used in conjunction with AMSU channels, only sensitive to temperature, to decorrelate both signals through a non-linear inference scheme based on neural networks. A key point of this approach is that no use is made of prior information in terms of methane seasonality, trend, or geographical patterns. The accuracy of the retrieval is estimated to be about 16 ppbv (~0.9%). Features of the retrieved methane space-time distribution include: (1) a strong seasonal cycle of 30 ppbv in the Northern Tropics with a maximum in January–March and a minimum in July–September, and a flat seasonal cycle in the Southern Tropics, in agreement with in-situ measurements; (2) a latitudinal decrease of 30 ppbv from 20° N to 20° S, in boreal spring and summer, lower than what is observed at the surface but in excellent agreement with tropospheric aircraft measurements; (3) geographical patterns in good agreement with simulations from the atmospheric transport and chemistry model MOZART-2, but with a higher variability and a higher concentration in boreal winter; (4) signatures of CH4 emissions transported to the middle troposphere such as a large plume of elevated tropospheric methane south of the Asian continent, which might be due to Asian emissions from rice paddies uplifted by deep convection during the monsoon period and then transported towards Indonesia. In addition to bringing a greatly improved view of methane distribution, these results from IASI should provide a means to observe and understand atmospheric transport pathways of methane from the surface to the upper troposphere.
Hygroscopic growth of urban aerosol particles in Beijing (China) during wintertime: a comparison of three experimental methods
Authors: Meier J. , Wehner B. , Massling A. , Birmili W. , Nowak A. , Gnauk T. , Brüggemann E. , Herrmann H. , Min H. , Wiedensohler A.
Published: April 2010

Abstract. This paper presents hygroscopicity measurements of aerosol particles in the urban atmosphere of Beijing carried out in January 2005. Therefore, three different methods were used: 1) Combining Humidifying Differential Mobility Particle Sizer (H-DMPS) and Twin Differential Mobility Particle Sizer (TDMPS) measurements; 2) Hygroscopicity Tandem Differential Mobility Analyzer (H-TDMA) technique; 3) Calculating hygroscopic growth factors on the basis of a solubility model quantified by Micro Orifice Uniform Deposit Impactor (MOUDI) samples. Particle number size distributions from H-DMPS and TDMPS were evaluated to derive size-resolved descriptive hygroscopic growth factors (DHGF) of 30–400 nm particles at relative humidities (RH) of 55%, 77% and 90%. The atmospheric particles in Beijing were rather hydrophobic, with a maximum growth factor in the accumulation mode around 1.40 (±0.03) at 90% RH. The descriptive hygroscopic growth factors decreased significantly towards the lower measurement limit (1.04 (±0.15) at Dp=30 nm). A good agreement was found between the DHGFs and the H-TDMA-derived hygroscopic growth factors in the accumulation mode (100–400 nm), the DHGFs underestimated the values from the H-TDMA in the Aitken mode (<100 nm) by up to 0.1 at 90% RH. The calculation of hygroscopic growth factors based on the measured chemical composition showed that different modes of combining the inorganic ions caused a variation in growth factor of 0.1 at 90% RH. The solubility model was able to reproduce the size-dependent trend in the growth factor found by the other methods. In two cases of ion-dominated aerosol, the composition-derived growth factors tended to agree (±0.05) or underestimate (up to 0.1) the values measured by the other two methods. In the case of the organic-dominated aerosol, the reverse was true, with an overestimation of up to 0.2. The results shed light on the real experimental and methodological uncertainties that are still connected with the determination of hygroscopic growth factors.
Effect of regional precursor emission controls on long-range ozone transport – Part 1: short-term changes in ozone air quality
Authors: West J. J. , Naik V. , Horowitz L. W. , Fiore A. M.
Published: April 2010

Abstract. Observations and models demonstrate that ozone and its precursors can be transported between continents and across oceans. We model the influences of 10% reductions in anthropogenic nitrogen oxide (NOx) emissions from each of nine world regions on surface ozone air quality in that region and all other regions. In doing so, we quantify the relative importance of long-range transport between all source-receptor pairs, for direct short-term ozone changes. We find that for population-weighted concentrations during the three-month "ozone-season", the strongest inter-regional influences are from Europe to the Former Soviet Union, East Asia to Southeast Asia, and Europe to Africa. The largest influences per unit of NOx reduced, however, are seen for source regions in the tropics and Southern Hemisphere, which we attribute mainly to greater sensitivity to changes in NOx in the lower troposphere, and secondarily to increased vertical convection to the free troposphere in tropical regions, allowing pollutants to be transported further. Results show, for example, that NOx reductions in North America are ~20% as effective per unit NOx in reducing ozone in Europe during summer, as NOx reductions from Europe itself. Reducing anthropogenic emissions of non-methane volatile organic compounds (NMVOCs) and carbon monoxide (CO) by 10% in selected regions, can have as large an impact on long-range ozone transport as NOx reductions, depending on the source region. We find that for many source-receptor pairs, the season of greatest long-range influence does not coincide with the season when ozone is highest in the receptor region. Reducing NOx emissions in most source regions causes a larger decrease in export of ozone from the source region than in ozone production outside of the source region.
Effect of regional precursor emission controls on long-range ozone transport – Part 2: steady-state changes in ozone air quality and impacts on human mortality
Authors: West J. J. , Naik V. , Horowitz L. W. , Fiore A. M.
Published: April 2010

Abstract. Large-scale changes in ozone precursor emissions affect ozone directly in the short term, and also affect methane, which in turn causes long-term changes in ozone that affect surface ozone air quality. Here we assess the effects of changes in ozone precursor emissions on the long-term change in surface ozone via methane, as a function of the emission region, by modeling 10% reductions in anthropogenic nitrogen oxide (NOx) emissions from each of nine world regions. Reductions in NOx emissions from all world regions increase methane and long-term surface ozone. While this long-term increase is small compared to the intra-regional short-term ozone decrease, it is comparable to or larger than the short-term inter-continental ozone decrease for some source-receptor pairs. The increase in methane and long-term surface ozone per ton of NOx reduced is greatest in tropical and Southern Hemisphere regions, exceeding that from temperate Northern Hemisphere regions by roughly a factor of ten. We also assess changes in premature ozone-related human mortality associated with regional precursor reductions and long-range transport, showing that for 10% regional NOx reductions, the strongest inter-regional influence is for emissions from Europe affecting mortalities in Africa. Reductions of NOx in North America, Europe, the Former Soviet Union, and Australia are shown to reduce more mortalities outside of the source regions than within. Among world regions, NOx reductions in India cause the greatest number of avoided mortalities per ton, mainly in India itself. Finally, by increasing global methane, NOx reductions in one hemisphere tend to cause long-term increases in ozone concentration and mortalities in the opposite hemisphere. Reducing emissions of methane, and to a lesser extent carbon monoxide and non-methane volatile organic compounds, alongside NOx reductions would avoid this disbenefit.