bluuebunny/crossref_metadata_2025 huggingface dataset:
Dust storms come to central and southwestern China, too: implications from a major dust event in Chongqing
Authors: Zhao Q. , He K. , Rahn K. A. , Ma Y. , Jia Y. , Yang F. , Duan F. , Lei Y. , Chen G. , Cheng Y. , Liu H. , Wang S.
Published: April 2010

Abstract. Dust storms from major Asian sources are usually carried by northwesterly or westerly winds over northern and southeastern China to the Pacific Ocean. These pathways leave central and southwestern China nearly free of incursions. But a strong dust event on 5–6 May 2005 was captured in a 15-month series of weekly filter samples of PM2.5 at three sites in Chongqing. It illustrated that desert dust can be transported to this region, and sometimes strongly. Annual PM2.5 and dust were similar at the three sites, but higher than in simultaneous samples in Beijing. High correlations of dust concentration were found between the cites during spring, indicating that Asian dust affects a broader swath of China than is often realized. During the event, the concentrations of mineral dust were high at all sites (20–30 μg m−3; 15%–20% of PM2.5 in Chongqing, and 15 μg m−3; 20%–30% of PM2.5 in Beijing), and were part of a broader spring maximum. The proportions of crustal elements and pollution-derived components such as Pb, SO42−, and organic carbon indicated that the sources for this dust differed from Beijing. The dust was considerably enriched in Ca and Mg, characteristic of western deserts, whereas Beijing's dust had the lower Ca and Mg of eastern deserts. This observation agrees with synoptic patterns and back-trajectories. Driven by a cold air outbreak from the northwest, dust from the western Gobi Desert was transported at lower altitudes (<2 km above ground level), while dust from the Takla Makan Desert was transported to Chongqing at higher altitudes. Desert dust can also be important to wide areas of China during the cold season, since almost all the weekly dust peaks in the two cities coincided with extensive dust emissions in source regions. These findings collectively suggest that the amount of Asian-dust in China has been underestimated both spatially and temporally, and that transported alkaline dust can even be mitigating the effects of acidic deposition in southern China.
Hygroscopicity and chemical composition of Antarctic sub-micrometre aerosol particles and observations of new particle formation
Authors: Asmi E. , Frey A. , Virkkula A. , Ehn M. , Manninen H. E. , Timonen H. , Tolonen-Kivimäki O. , Aurela M. , Hillamo R. , Kulmala M.
Published: April 2010

Abstract. The Antarctic near-coastal sub-micrometre aerosol particle features in summer were characterised based on measured data on aerosol hygroscopicity, size distributions, volatility and chemical ion and organic carbon mass concentrations. Hysplit model was used to calculate the history of the air masses to predict the particle origin. Additional measurements of meteorological parameters were utilised. The hygroscopic properties of particles mostly resembled those of marine aerosols. The measurements took place at 130 km from the Southern Ocean, which was the most significant factor affecting the particle properties. This is explained by the lack of additional sources on the continent of Antarctica. The Southern Ocean was thus a likely source of the particles and nucleating and condensing vapours. The particles were very hygroscopic (HGF 1.75 at 90 nm) and very volatile. Most of the sub-100 nm particle volume volatilised below 100 °C. Based on chemical data, particle hygroscopic and volatile properties were explained by a large fraction of non-neutralised sulphuric acid together with organic material. The hygroscopic growth factors assessed from chemical data were similar to measured. Hygroscopicity was higher in dry continental air masses compared with the moist marine air masses. This was explained by the aging of the marine organic species and lower methanesulphonic acid volume fraction together with the changes in the inorganic aerosol chemistry as the aerosol had travelled long time over the continental Antarctica. Special focus was directed in detailed examination of the observed new particle formation events. Indications of the preference of negative over positive ions in nucleation could be detected. However, in a detailed case study, the neutral particles dominated the particle formation process. Freshly nucleated particles had the smallest hygroscopic growth factors, which increased subsequent to particle aging.
Can a global model chemical mechanism reproduce NO, NO2, and O3 measurements above a tropical rainforest?
Authors: Pike R. C. , Lee J. D. , Young P. J. , Moller S. , Carver G. D. , Yang X. , Misztal P. , Langford B. , Stewart D. , Reeves C. E. , Hewitt C. N. , Pyle J. A.
Published: April 2010

Abstract. A cross-platform field campaign, OP3, was conducted in the state of Sabah in Malaysian Borneo between April and July of 2008. Among the suite of observations recorded, the campaign included measurements of NOx and O3–crucial outputs of any model chemistry mechanism. We describe the measurements of these species made from both the ground site and aircraft. We examine the output from the global model p-TOMCAT at two resolutions for this location during the April campaign period. The models exhibit reasonable ability in capturing the NOx diurnal cycle, but ozone is overestimated. We use a box model containing the same chemical mechanism to explore the weaknesses in the global model and the ability of the simplified global model chemical mechanism to capture the chemistry at the rainforest site. We achieve a good fit to the data for all three species (NO, NO2, and O3), though the model is much more sensitive to changes in the treatment of physical processes than to changes in the chemical mechanism. Indeed, without some parameterization of the nighttime boundary layer-free troposphere mixing, a time dependent box model will not reproduce the observations. The final simulation uses this mixing parameterization for NO and NO2 but not O3, as determined by the vertical structure of each species, and matches the measurements well.
Variable CCN formation potential of regional sulfur emissions
Authors: Manktelow P. T. , Carslaw K. S. , Mann G. W. , Spracklen D. V.
Published: April 2010

Abstract. Aerosols are short lived so their geographical distribution and impact on climate depends on where they are emitted. Previous model studies have shown that the mass of sulfate aerosol produced per unit sulfur emission (the sulfate burden potential) and the associated direct radiative forcing vary regionally because of differences in meteorology and photochemistry. Using a global model of aerosol microphysics, we show that the total number of aerosol particles produced per unit sulfur emission (the aerosol number potential) has a different regional variation to that of sulfate mass. The aerosol number potential of N. American and Asian emissions is calculated to be a factor of 3 to 4 times greater than that of European emissions, even though Europe has a higher sulfate burden potential. Pollution from North America and Asia tends to reach higher altitudes than European pollution so forms more new particles through nucleation. These regional differences in particle production mean that sulfur emissions from N. America and E. Asia produce cloud condensation nuclei up to 70% more efficiently than Europe. Taking account of the higher sulfate burden potential of Europe in these simulations shows that E. Asian sulfate produces CCN twice as effectively as European sulfate. The impact of regional sulfur emissions on particle concentrations is also much more widely spread than the impact on sulfate mass, due to efficient particle production in the free troposphere during long range transport. These results imply that regional sulfur emissions will have different climate forcing potentials through changes in cloud drop number.
The relationship between aerosol and cloud drop number concentrations in a global aerosol microphysics model
Authors: Pringle K. J. , Carslaw K. S. , Spracklen D. V. , Mann G. M. , Chipperfield M. P.
Published: April 2010

Abstract. Empirical relationships that link cloud droplet number (CDN) to aerosol number or mass are commonly used to calculate global fields of CDN for climate forcing assessments. In this work we use a sectional global model of sulfate and sea-salt aerosol coupled to a mechanistic aerosol activation scheme to explore the limitations of this approach. We find that a given aerosol number concentration produces a wide range of CDN concentrations due to variations in the shape of the aerosol size distribution. On a global scale, the dependence of CDN on the size distribution results in regional biases in predicted CDN (for a given aerosol number). Empirical relationships between aerosol number and CDN are often derived from regional data but applied to the entire globe. In an analogous process, we derive regional "correlation-relations" between aerosol number and CDN and apply these regional relations to calculations of CDN on the global scale. The global mean percentage error in CDN caused by using regionally derived CDN-aerosol relations is 20 to 26%, which is about half the global mean percentage change in CDN caused by doubling the updraft velocity. However, the error is as much as 25–75% in the Southern Ocean, the Arctic and regions of persistent stratocumulus when an aerosol-CDN correlation relation from the North Atlantic is used. These regions produce much higher CDN concentrations (for a given aerosol number) than predicted by the globally uniform empirical relations. CDN-aerosol number relations from different regions also show very different sensitivity to changing aerosol. The magnitude of the rate of change of CDN with particle number, a measure of the aerosol efficacy, varies by a factor 4. CDN in cloud processed regions of persistent stratocumulus is particularly sensitive to changing aerosol number. It is therefore likely that the indirect effect will be underestimated in these important regions.
Interannual variability in hindcasts of atmospheric chemistry: the role of meteorology
Authors: Hess P. , Mahowald N.
Published: April 2010

Abstract. Two 40-year meteorological datasets are used to drive the Model of Ozone and Related Tracers chemical transport model, version 2 (MOZART2) in hindcast simulations. One dataset is from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis, the second dataset uses meteorology from the Community Atmosphere Model (CAM3) forced with observed interannually varying sea surface temperatures. All emissions, except those from lightning are annually constant. Analysis of these simulations is from 1979–1999, due to meteorological discontinuities in the NCEP reanalysis during the 1970s. The meteorology using CAM3 captures observed trends in temperature, water vapor, precipitation and cloudiness; the simulation using NCEP meteorology does not. This paper examines the regional and global interannual variability of various chemical and meteorological fields: CO, OH, O3 and HNO3, the surface photolysis rate of NO2 (as a proxy for overhead cloudiness), lightning NO emissions, water vapor, planetary boundary layer height, and temperature. The variability due to changes in emissions is not considered in this analysis. In both the NCEP and CAM3 simulations the relative variability of CO, OH, O3 and HNO3 are qualitatively similar, with variability maxima both in the tropics and the high latitudes. Locally, relative variability generally ranges between 3 and 10%; globally the tropospheric variability generally ranges from half to one percent, but can be higher. For most fields the leading Empirical Orthogonal Function explains approximately 10% of the variability and correlates significantly with El Niño. In both simulations the first principal component of a multiple tracer, globally averaged analysis shows a strong coupling between surface temperature, measures of the hydrological cycle, CO and OH, but is not correlated with El Niño. In both simulations we examine the global response of the selected variables to changes in global surface temperature, and compare with a climate simulation over the 21st century.
The heterogeneous reaction of hydroxyl radicals with sub-micron squalane particles: a model system for understanding the oxidative aging of ambient aerosols
Authors: Smith J. D. , Kroll J. H. , Cappa C. D. , Che D. L. , Liu C. L. , Ahmed M. , Leone S R. , Worsnop D. R. , Wilson K. R.
Published: April 2010

Abstract. The heterogeneous reaction of OH radicals with sub-micron squalane particles, in the presence of O2, is used as a model system to explore the fundamental chemical mechanisms that control the oxidative aging of organic aerosols in the atmosphere. Detailed kinetic measurements combined with elemental mass spectrometric analysis reveal that the reaction proceeds sequentially by adding an average of one oxygenated functional group per reactive loss of squalane. The reactive uptake coefficient of OH with squalane particles is determined to be 0.3±0.07 at an average OH concentration of ~1×1010 molecules·cm−3. Based on a comparison between the measured particle mass and model predictions it appears that significant volatilization of a reduced organic particle would be extremely slow in the real atmosphere. However, as the aerosols become more oxygenated, volatilization becomes a significant loss channel for organic material in the particle phase. Together these results provide a chemical framework in which to understand how heterogeneous chemistry transforms the physiochemical properties of particle phase organic matter in the troposphere.
Trans-Pacific dust transport: integrated analysis of NASA/CALIPSO and a global aerosol transport model
Authors: Eguchi K. , Uno I. , Yumimoto K. , Takemura T. , Shimizu A. , Sugimoto N. , Liu Z.
Published: April 2010

Abstract. Detailed 3-D structures of Trans-Pacific Asian dust transport occurring during 5–15 May 2007 were investigated using the NASA/CALIOP vertical-resolved measurements and a three-dimensional aerosol model (SPRINTARS). Both CALIOP and SPRINTARS dust extinctions showed a good agreement along the way of the transport from the dust source regions across North Pacific into North America. A vertically two-layered dust distribution was observed over the northeastern Pacific and North America. The lower dust layer originated from a dust storm generated in the Gobi Desert on 5 May. It was transported at an altitude of around 4 km MSL and has mixed with Asian anthropogenic air pollutants during the course of transport. The upper dust layer mainly originated from a dust storm that occurred in the Taklimakan Desert 2–3 days after the Gobi dust storm generation. The upper dust cloud was transported in higher altitudes above the major clouds layer during the Trans-Pacific transport. It therefore has remained unmixed with the Asian air pollutants and almost unaffected by wet removal. The decay of its concentration level was small (only one-half after its long-distance transport crossing the Pacific). Our dust budget analysis revealed that the Asian dust flux passing through the longitude plane of 140° E was 2.1 Tg, and one third of that arrived North America. The cases analyzed in this study revealed that, while the Gobi Desert is an important source that can contribute to the long-range dust transport, the Taklimakan Desert appears to be another important source that can contribute to the dust transport occurring particularly at high altitudes.
Exposure-plant response of ambient ozone over the tropical Indian region
Authors: Roy S. , Beig G. , Ghude S.
Published: April 2010

Abstract. A high resolution regional chemistry-transport model has been used to study the distribution of exposure-plant response index (AOT40, Accumulated exposure Over a Threshold of 40 ppb, expressed as ppb h) over the Indian geographical region for the year 2003 as case study. The directives on ozone pollution in ambient air provided by United Nations Economic Commission for Europe (UNECE) and World Health Organization (WHO) for vegetation protection (AOT40) have been used to assess the air quality. A substantial temporal and spatial variation in AOT40 values has been observed across the Indian region. Large areas of India show ozone values above the AOT40 threshold limit (3000 ppb h for 3 months). Simulated AOT40 values are found to be substantially higher throughout the year over the most fertile Indo-Gangetic plains than the other regions of India, which can have an adverse effect on plants and vegetation in this region. The observed monthly AOT40 values reported from an Indian station, agree reasonably well with model simulated results. We find that the simulated AOT40 target values for protection of vegetation is exceeded even in individual months, especially during November and April. Necessary and effective emission reduction strategies are therefore required to be developed in order to curb the surface level ozone pollution to protect the vegetation from further damage in India whose economy is highly dependent on agricultural sector and may influence the global balance.
Oxygenated organic functional groups and their sources in single and submicron organic particles in MILAGRO 2006 campaign
Authors: Liu S. , Takahama S. , Russell L. M. , Gilardoni S. , Baumgardner D.
Published: April 2010

Abstract. Fourier Transform Infrared (FTIR) and X-ray Fluorescence (XRF) were used to measure organic functional groups and elements of submicron particles collected during MILAGRO in March 2006 on three platforms: the Mexico City urban area (SIMAT), the high altitude site at 4010 m (Altzomoni), and the NCAR C130 aircraft. Scanning transmission X-ray Microscopy (STXM) and Near-Edge X-ray Absorption Fine Structure (NEXAFS) were applied to single particle organic functional group abundance analysis of particles simultaneously collected at SIMAT and C130. Correlations of elemental concentrations showed different groups of source related elements at SIMAT, Altzomoni, and C130, suggesting different processes affecting the air masses sampled at the three platforms. Cluster analysis resulted in seven distinct Clusters of FTIR spectra, with the last three clusters consisting of spectra collected almost exclusively on the C130 platform, reflecting the variety of sources contributing to C130 samples. Positive Matrix Factorization (PMF) of NEXAFS-STXM spectra identified three main factors representing soot, secondary, and biomass burning type spectra. PMF of FTIR spectra resulted in three fossil fuel combustion type factors, one biomass burning factor, and one mixed or processed factor. The fossil fuel combustion type factors were found to have the largest contributions to OM, while the processed factor has the largest O/C among all factors. Alkane, carboxylic acid, and amine functional groups were mainly associated with combustion related sources, while alcohol groups were likely from atmospheric processing of mixed sources. While the processed factor has the highest O/C, half of the OM and O/C measured could be attributed directly to fossil fuel combustion sources. Both PMF of NEXAFS-STXM spectra and PMF of FTIR spectra indicate that the combustion type factors are more affected by fluctuations in local sources, while the processed factors are more consistent during the sampling period.
Impacts of aerosol indirect effect on past and future changes in tropospheric composition
Authors: Unger N. , Menon S. , Shindell D. T. , Koch D. M.
Published: April 2010

Abstract. The development of effective emissions control policies that are beneficial to both climate and air quality requires a detailed understanding of all the feedbacks in the atmospheric composition and climate system. We perform sensitivity studies with a global atmospheric composition-climate model to assess the impact of aerosols on tropospheric chemistry through their modification on clouds, the aerosol indirect effect (AIE). The model includes coupling between both tropospheric gas-phase and aerosol chemistry and aerosols and liquid-phase clouds. We investigate past impacts from preindustrial (PI) to present day (PD) and future impacts from PD to 2050 (for the moderate IPCC A1B scenario) that embrace a wide spectrum of precursor emission changes and consequential aerosol-cloud interactions. The AIE is estimated to be −2.0 W m−2 for PD–PI and −0.6 W m−2 for 2050–PD, at the high end of current estimates. Inclusion of aerosol-cloud interactions substantially impacts changes in global mean methane lifetime across both time periods, enhancing the past and future increases by 10% and 30%, respectively. In regions where pollution emissions increase, inclusion of aerosol-cloud effects leads to 20% enhancements in in-cloud sulfate production and ~10% enhancements in sulfate wet deposition that is displaced away from the immediate source regions. The enhanced in-cloud sulfate formation leads to larger increases in surface sulfate across polluted regions (~10–30%). Nitric acid wet deposition is dampened by 15–20% across the industrialized regions due to AIE allowing additional re-release of reactive nitrogen that contributes to 1–2 ppbv increases in surface ozone in outflow regions. Our model findings indicate that aerosol-cloud interactions must be considered in studies of methane trends and projections of future changes to particulate matter air quality.
Dynamical modes associated with the Antarctic ozone hole
Authors: Weare B. C.
Published: April 2010

Abstract. Generalized Maximum Covariance Analysis (GMCA) has been developed and applied to diagnosing the dynamical modes associated with variations in the Antarctic spring ozone hole. GMCA is used to identify the most important patterns of co-variability between interannual ozone mixing ratio variations in the Antarctic region and temperature, zonal, meridional and vertical velocities between 100 and 10 hPa in the same region. The most important two pairs of GMCA time coefficients show large year-to-year variations and trends, which are connected with the growth of the Antarctic Ozone Hole and the increase of ozone depleting substances. The associated spatial patterns of ozone variations may be characterized as being quasi-symmetric and asymmetric about the pole. These patterns of ozone variations are associated with comparable patterns of variations of temperature and winds through most of the vertical domain. The year 2000 is shown to be dominated by the asymmetric mode, whereas the adjacent year 2001 is dominated by the quasi-symmetric mode. A case study, focusing on the asymmetric differences between these two years, shows the magnitude of the ozone mixing ratio, temperature and zonal wind differences to be in the range of 2 e-6, 10°C and 10 m/s, respectively. Budget calculations show that transport processes contribute substantially to the ozone and temperature changes in the middle stratosphere over the Antarctic continent. However, both radiative and chemical processes also play important roles in the changes.
How important is the vertical structure for the representation of aerosol impacts on the diurnal cycle of marine stratocumulus?
Authors: Sandu I. , Brenguier J.-L. , Thouron O. , Stevens B.
Published: April 2010

Abstract. Large Eddy Simulations (LES) are performed to examine the impact of hygroscopic aerosols on the diurnal cycle of marine stratocumulus clouds, under varying meteorological forcing conditions. When the cloud condensation nuclei concentration increase is sufficient to inhibit drizzle formation in the cloud layer, the precipitating and the non-precipitating cloud layers exhibit contrasting evolutions, with noticeable differences in liquid water path. Aerosol induced modifications of the droplet sedimentation and drizzle precipitation result in noticeable changes of the entrainment velocity at cloud top, but also in significant changes of the vertical stratification in the boundary layer. This set of simulations is then used to evaluate whether a model which does not explicitly represent the effects of the interactions occurring within the boundary layer on its vertical stratification (i.e. such as a mixed layer model) is capable of reproducing at least the sign, if not the amplitude, of these aerosol impacts on the liquid water path. It is shown that the deviations from the mixed layer idealized state are crucial ingredients of the aerosol impacts so that a mixed layer model is unable to even replicate the sign of the liquid water path changes.
Wave fluxes of equatorial Kelvin waves and QBO zonal wind forcing derived from SABER and ECMWF temperature space-time spectra
Authors: Ern M. , Preusse P.
Published: April 2010

Abstract. The quasi-biennial oscillation (QBO) of the zonal mean zonal wind is one of the most important processes in the dynamics of the middle atmosphere in the tropics. Influences of the QBO can even be found at mid and high latitudes. It is widely accepted that the phase descent of alternating tropical easterlies and westerlies is driven by atmospheric waves of both global scale (equatorial wave modes like Kelvin, equatorial Rossby, Rossby-gravity, or inertia-gravity waves), as well as mesoscale gravity waves. However, the relative distribution of the different types of waves to the forcing of the QBO winds is highly uncertain. This is the case because until recently there were no high resolution long-term global measurements in the stratosphere. In our study we estimate Kelvin wave momentum flux and the contribution of zonal wind forcing by Kelvin waves based on space-time spectra determined from both Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature measurements as well as temperatures from European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses. Peak values of total Kelvin wave zonal wind forcing found are about 0.2 m/s/day. There is good agreement between SABER and ECMWF results. Global distributions are shown and the results are compared to the total wave forcing required to balance the background atmosphere. Sometimes Kelvin wave forcing is sufficient to explain almost the whole total wave forcing required for the momentum balance during the transition from QBO easterly to westerly winds. This is especially the case during the later parts of the periods of westerly wind shear at the equator between 20 and 35 km altitude. During other phases of the westerly wind shear periods, however, the contribution of Kelvin waves can be comparably low and the missing wave forcing, which is often attributed to mesoscale gravity waves or intermediate scale waves, can be the by far dominant contribution of the QBO forcing.
A~model study of the January 2006 low total ozone episode over Western Europe and comparison with ozone sonde data
Authors: Mangold A. , Grooß J.-U. , De Backer H. , Kirner O. , Ruhnke R. , Müller R.
Published: April 2010

Abstract. Total column and stratospheric ozone levels at mid-latitudes often reveal strong fluctuations on time scales of days caused by dynamic processes. In some cases the total ozone column is distinctly reduced below climatological values. Here, a very low total ozone episode around 19 January 2006 over Western Europe is investigated when the observed total ozone column over Uccle (BE), measured by a Brewer spectrophotometer, reached a daily minimum of 200 DU, the lowest recorded value at this station. In order to investigate the mechanisms leading to the ozone minimum, the present study used data from (i) six ozone sounding stations in Western and Middle Europe, (ii) ECMWF meteorological fields, (iii) a simulation of the CLaMS model for January 2006, (iv) a multi-year run of the chemistry transport model KASIMA, and (v) a six-year run of the climate chemistry model ECHAM5/MESSy1. The ozone decrease at different heights was quantified and it was determined to what extent different transport mechanisms, and instantaneous, in-situ chemical ozone depletion contributed to the event. All three models reproduced well the evolution and formation of the event. The ozone column decrease between Θ=300 and 750 K was strongest at Uccle (BE) and De Bilt (NL) with 108 and 103 DU, respectively, and somewhat lower at Hohenpeissenberg (DE), Payerne (CH), Prague (CZ) and Lerwick (UK) with 85, 84, 83 and 74 DU, respectively. Our analysis demonstrated that mainly the displacement of the ozone depleted polar vortex contributed to the ozone column decrease (between 55 and 82%), compared to the advection of ozone-poor low-latitude air in the UTLS region, connected with divergence of air out of the column caused by uplift of isentropes in the lower stratosphere. This dominance was significant only at Lerwick, De Bilt and Uccle. Severe low total ozone episodes seem to occur preferentially when the two mentioned transport mechanisms occur at the same time. Instantaneous, in-situ chemical ozone depletion accounted for only 2±1% of the overall total ozone decrease at the sounding stations.
Source-receptor relationships for airborne measurements of CO2, CO and O3 above Siberia: a cluster-based approach
Authors: Paris J.-D. , Stohl A. , Ciais P. , Nédélec P. , Belan B. D. , Arshinov M. Y. , Ramonet M.
Published: April 2010

Abstract. We analysed three intensive campaigns above Siberia resulting in a total of ~70 h of continuous CO2, CO and O3 measurements. The flight route consists of consecutive ascents and descents between Novosibirsk (55° N, 82° E) and Yakutsk (62° N, 129° E). Our data analysis uses clustering of footprints obtained with the Lagrangian particle dispersion model FLEXPART. The model-based technique was found to be able to separate efficiently tracers' concentrations. High CO and O3 concentrations (median values 121 ppb and 54.5 pb respectively) were found in clusters associated with fires in Kazakhstan in September 2006. High correlation (as high as R2=0.68) and robust linear relationships with regression slope between −0.10 and 0.24 ppb ppb−1 were found in individual plumes. Summer (August 2007, September 2006) uptake of CO2 was found to be largely (~50% of variance) explained by exposure to boreal and sub-arctic ecosystems, most likely by photosynthesis. This results in an average 5 to 10 ppm gradient in the August 2007 campaign. European emissions seem to contribute to high O3 concentrations above Siberia in altitude were it is also near stratospheric inputs. Large-scale deposition processes reduce O3 in the boreal and sub-arctic BL, resulting in a ~20 ppb gradient. This first attempt of Lagrangian footprint clustering is very promising and could also be advantageously applied to the interpretation of ground based measurements including calculation of tracers' sources and sinks.
Adjoint inverse modeling of a CO emission inventory at the city scale: Santiago de Chile's case
Authors: Saide P. , Osses A. , Gallardo L. , Osses M.
Published: April 2010

Abstract. Emission inventories (EIs) are key-tools for air quality management. However, EIs are expensive, and they have uncertainties. A way to improve the accuracy of EIs is data assimilation. Multiple inverse methods have been used at various scales. However, typically, when applying these methods at the city scale, one encounters, in addition to problems related to the precision of the first guess, or the reliability and representativeness of the observations, or the shortcomings of the dispersion model, the problem of co-location of sources and observation sites. The latter problem results in spurious corrections to the a priori EI. Here we present a methodology to improve an EI of carbon monoxide over a city. We use a 3-D variational approach, in which a cost function that includes balanced terms addressing observation and emission errors is minimized to obtain an ameliorated EI. In addition to positivity, the method addresses the co-location of sources and observations by means of a factor that multiplies the emission error covariance matrix. The factor is chosen so that the reliability of the initial inventory is increased at the observation sites, reducing the local influence of the observations, avoiding spurious corrections to the EI and increasing the temporal and spatial extent of the corrections. The method is applied to Santiago de Chile. We find that the a posteriori inventory shows a decrease in total emissions of 8% with respect to the a priori inventory. Nevertheless, locally over 100% changes are found in the eastern area of Santiago during the morning hours.
Evaluation of mobile emissions contributions to Mexico City's emissions inventory using on-road and cross-road emission measurements and ambient data
Authors: Zavala M. , Herndon S. C. , Wood E. C. , Onasch T. B. , Knighton W. B. , Kolb C. E. , Molina L. T.
Published: April 2010

Abstract. Mobile emissions represent a significant fraction of the total anthropogenic emissions burden in the Mexico City Metropolitan Area (MCMA) and, therefore, it is crucial to use top-down techniques informed by on-road exhaust measurements to evaluate and improve traditional bottom-up official emissions inventory (EI) for the city. We present the measurements of on-road fleet-average emission factors obtained using the Aerodyne mobile laboratory in the MCMA in March 2006 as part of the MILAGRO/MCMA-2006 field campaign. A comparison of our on-road emission measurements with those obtained in 2003 using essentially the same measurement techniques and analysis methods indicates that, in the three year span, NO emission factors remain within the measured variability ranges whereas emission factors of aldehydes and aromatics species were reduced for all sampled driving conditions. We use a top-down fuel-based approach to evaluate the mobile emissions from the gasoline fleet estimated in the bottom-up official 2006 MCMA mobile sources. Within the range of measurement uncertainties, we found probable slight overpredictions of mean EI estimates on the order of 20–28% for CO and 14–20% for NO. However, we identify a probable EI underprediction of VOC mobile emissions between 1.4 and 1.9; although estimated benzene and toluene mobile emissions in the inventory seem to be well within the uncertainties of the corresponding emissions estimates. Aldehydes mobile emissions in the inventory, however, seem to be under predicted by factors of 3 for HCHO and 2 for CH3CHO. Our on-road measurement based estimate of annual emissions of organic mass from PM1 particles suggests a severe underprediction (larger than a factor of 4) of PM2.5 mobile emissions in the inventory. Analyses of ambient CO, NOx and CO/NOx concentration trends in the MCMA indicate that the early morning ambient CO/NOx ratio has decreased at a rate of about 1.9 ppm/ppm/year over the last two decades and that the decrease has been driven by reductions in CO levels rather than by NOx concentration changes, suggesting that the relative contribution of diesel vehicles to overall NOx levels has increased over time in the city. Despite the impressive increases in the size of the vehicle fleet between 2000 and 2006, the early morning ambient concentrations of CO and NOx have not increased accordingly, probably due to the reported low removal rates of older vehicles, which do not have emissions control technologies, and partially due to the much lower emissions from newer gasoline vehicles. This indicates that an emission-based air quality control strategy targeting large reductions of emissions from mobile sources should be directed towards a significant increase of the removal rate of older, highly-polluting, vehicles.
Particulate absorption of solar radiation: anthropogenic aerosols vs. dust
Authors: Wang C. , Jeong G.-R. , Mahowald N.
Published: April 2010

Abstract. Particulate solar absorption is a critical factor in determining the value and even sign of the direct radiative forcing of aerosols. The heating to the atmosphere and cooling to the Earth's surface caused by this absorption are hypothesized to have significant climate impacts. We find that anthropogenic aerosols play an important role around the globe in total particulate absorption of solar radiation. The global-average anthropogenic fraction in total aerosol absorbing optical depth exceeds 65% in all seasons. Combining the potentially highest dust absorption with the lowest anthropogenic absorption within our model range, this fraction would still exceed 47% in most seasons except for boreal spring (36%) when dust abundance reaches its peak. Nevertheless, dust aerosol is still a critical absorbing constituent over places including North Africa, the entire tropical Atlantic, and during boreal spring in most part of Eurasian continent. The equality in absorbing solar radiation of dust and anthropogenic aerosols appears to be particularly important over Indian subcontinent and nearby regions as well as North Africa.
Study of successive contrasting monsoons (2001–2002) in terms of aerosol variability over a tropical station Pune, India
Authors: Bhawar R. L. , Devara P. C. S.
Published: April 2010

Abstract. The present study confirms that aerosols play a major role in cloud formation and affect significantly the precipitation over a regional scale. The study here shows that there is a high variability of aerosol index during a bad monsoon year 2002 indicating an extension of cycle to more than 100 days from a normal 50 day cycle of absorbing and non- absorbing aerosols over a tropical urban station Pune. Pre-monsoon 2002 shows a high loading of coarse mode aerosols (absorbing aerosols) which indicates vertical and horizontal temperature variations in turn affecting the seasonal rainfall at a regional scale. Cloud formation highly depends on aerosol concentration, where surface meteorological features are essential to initiate the process. The surface temperatures were high during the pre-monsoon of 2002 as compared to 2001. The effect of wind speed though, complicated to understand, reveal low values in 2002 with high aerosol optical depth and vice versa in 2001.
Ozone budget in the West African lower troposphere during the AMMA (African Monsoon Multidisciplinary Analysis) campaign
Authors: Saunois M. , Reeves C. E. , Mari C. , Murphy J. G. , Stewart D. J. , Mills G. P. , Oram D. E. , Purvis R. M.
Published: April 2010

Abstract. A bi-dimensional latitudinal-vertical meterological model coupled with O3-NOx-VOC chemistry is used to reproduce the distribution of ozone and precursors in the boundary layer over West Africa during the African Monsoon Multidisciplinary Analysis (AMMA) campaign as observed on board the Facility for Airborne Atmospheric Measurements (FAAM) BAe 146 Atmospheric Research Aircraft. The model reproduces the increase of ozone mixing ratios in the boundary layer observed between the forested region south of 13° N and the Sahelian area northward. Sensitivity and budget analysis reveals that the intertropical convergence zone is a moderate source of O3 rich-air in the boundary layer due to convective downdrafts. Dry deposition drives the ozone minimum over the vegetated area. The combination of high NOx emissions from soil north of 13° N and northward advection by the monsoon flux of VOC-enriched air masses contributes to the ozone maximum simulated at higher latitudes. Simulated OH exhibit a well marked latitudinal gradient with minimum concentrations over the vegetated region where the reactions with biogenic compounds predominate. The model underestimates the observed OH mixing ratios, however this model discrepancy has slight effect on ozone budget and does not alter the conclusions.
Kinetics and mechanisms of heterogeneous reaction of NO2 on CaCO3 surfaces under dry and wet conditions
Authors: Li H. J. , Zhu T. , Zhao D. F. , Zhang Z. F. , Chen Z. M.
Published: April 2010

Abstract. Calcium nitrate (Ca(NO3)2) was observed in mineral dust and could change the hygroscopic and optical properties of mineral dust significantly due to its strong water solubility. The reaction of calcium carbonate (CaCO3) with nitric acid (HNO3) is believed the main reason for the observed Ca(NO3)2 in the mineral dust. In the atmosphere, the concentration of nitrogen dioxide (NO2) is orders of magnitude higher than that of HNO3; however, little is known about the reaction of NO2 with CaCO3. In this study, the heterogeneous reaction of NO2 on the surface of CaCO3 particles was investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) combined with X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) under wet and dry conditions. Nitrate formation was observed in both conditions, and nitrite was observed under wet conditions, indicating the reaction of NO2 on the CaCO3 surface produced nitrate and probably nitrous acid (HONO). Relative humidity (RH) influenced both the initial uptake coefficient and the reaction mechanism. With RH<52%, surface –OH was formed through dissociation of the surface adsorbed water via oxygen vacancy, thus determining the reaction order. With RH>52%, a monolayer of water formed on the surface of the CaCO3 particles, which reacted with NO2 as a first order reaction, forming HNO3 and HONO. The initial uptake coefficient γ0 was determined to be (1.66±0.38)×10−7 under dry conditions and up to (0.84±0.44)×10−6 under wet conditions. Considering that NO2 concentrations in the atmosphere are orders of magnitude higher than those of HNO3, the reaction of NO2 on CaCO3 particle should have similar importance as that of HNO3 in the atmosphere and could also be an important source of HONO in the atmosphere.
Sources and transport of Δ14C on CO2 within the Mexico City Basin and vicinity
Authors: Vay S. A. , Tyler S. C. , Choi Y. , Blake D. R. , Blake N. J. , Sachse G. W. , Diskin G. S. , Singh H. B.
Published: April 2010

Abstract. Radiocarbon samples taken over Mexico City and the surrounding region during the MILAGRO field campaign in March 2006 exhibited an unexpected distribution: (1) relatively few samples (23%) were below the North American free tropospheric background value (57‰) despite the fossil fuel emissions from one of the world's most highly polluted environments; and (2) frequent enrichment well above the background value was observed. Correlate source tracer species and air transport characteristics were examined to elucidate influences on the radiocarbon distribution. Our analysis suggests that a combination of radiocarbon sources biased the "regional radiocarbon background" above the North American value thereby decreasing the apparent fossil fuel signature. These sources included the release of bomb or "hot" radiocarbon sequestered in plant carbon pools via the ubiquitous biomass burning in the region as well as the direct release of radiocarbon as CO2. Plausible large local perturbations include the burning of hazardous waste in cement kilns; medical waste incineration; and emissions from the Laguna Verde Nuclear Power Plant. These observations provide insight into the use of Δ14CO2 to constrain fossil fuel emissions in the megacity environment, indicating that underestimation of the fossil fuel contribution to the CO2 flux is likely wherever biomass burning coexists with urban emissions. Our findings increase the complexity required to quantify fossil fuel-derived CO2 in source-rich environments characteristic of megacities, and have implications for the use of Δ14CO2 observations in evaluating bottoms-up emission inventories and their reliability as a tool for validating national emission claims of CO2 within the framework of the Kyoto Protocol.
Tracking the emission and transport of pollution from wildfires using the IASI CO retrievals: analysis of the summer 2007 Greek fires
Authors: Turquety S. , Hurtmans D. , Hadji-Lazaro J. , Coheur P.-F. , Clerbaux C. , Josset D. , Tsamalis C.
Published: April 2010

Abstract. In this paper, we analyze the performance of the Infrared Atmospheric Sounding Interferometer (IASI), launched in October 2006 on board METOP-A, for the monitoring of carbon monoxide (CO) during extreme fire events, focusing on the record-breaking fires which devastated thousands of square kilometers of forest in Greece during the last week (23–30) of August 2007. After an assessment of the quality of the profiles retrieved using the Fast Optimal Retrievals on Layers for IASI (FORLI) algorithm, the information provided on fire emissions and subsequent pollution outflow is discussed. Large CO plumes were observed above the Mediterranean Basin and North Africa, with total CO columns exceeding 30×1018 molecules/cm2 and absolute volume mixing ratio up to 22 ppmv. The average root-mean-square (RMS) difference between simulated and observed spectra is close to the estimated radiometric noise level, slightly increasing (by ~14%) in the fresh fire plumes. CO profiles are retrieved with a vertical resolution of about 8 km, with ~1.7 pieces of independent information on the vertical in the region considered and a maximum sensitivity in the free troposphere (~4–5 km). Using the integrated total amount, the increase in CO burden due to these fires is estimated to 0.321 Tg, ~40% of the total annual anthropogenic emissions in Greece. These CO enhancements are in good agreement with the aerosol optical depth (AOD) retrieved from the MODIS measurements, highlighting a rapid transport of trace gases and aerosols across the Mediterranean Basin (less than one day). While the coarse vertical resolution will not allow the location of the exact plume height, the large CO enhancements observed in the lower troposphere are consistent with the maximum aerosol backscatter coefficient at ~2 km detected by the CALIPSO lidar in space (CALIOP). This indicates that the general level of transport can be derived (lower, middle or upper troposphere) but that it needs to be accompanied by a systematic confrontation with sensitivity profiles and boundary layer height.
Clarification on the generation of absolute and potential vorticity in mesoscale convective vortices
Authors: Conzemius R. J. , Montgomery M. T.
Published: April 2010

Abstract. The purpose of this paper is to clarify what we think are several outstanding issues concerning the predominant mechanism of vorticity generation in mesoscale convective vortices (MCVs). Using idealized mesoscale numerical simulations of MCV development, we examine here the vertical vorticity budgets in order to quantify the contributions of flux convergence of absolute vorticity versus tilting in the generation of MCV vorticity. In addition, we examine the corresponding diabatic heating profiles. By partitioning the diabatic heating between convective and stratiform regions, we elucidate the respective roles of convective and stratiform precipitation in the generation of potential vorticity (PV). The analyses indicate that the horizontal flux convergence of vertical vorticity is the dominant mechanism for the spin-up and intensification of mid-level absolute vorticity. Indeed, diabatic heating and circulation budgets demonstrate that the vertical gradient of diabatic heating is supportive of low- to mid-level PV generation. During the early stages of MCV development, convective precipitation plays the dominant role in the PV generation; later on, the stratiform precipitation expands and becomes a larger contributor, particularly in low-CAPE background environments.
Technical note: Functional sliced inverse regression to infer temperature, water vapour and ozone from IASI data
Authors: Amato U. , Antoniadis A. , De Feis I. , Masiello G. , Matricardi M. , Serio C.
Published: April 2010

Abstract. A retrieval algorithm that uses a statistical strategy based on dimension reduction is proposed. The methodology and details of the implementation of the new algorithm are presented and discussed. The algorithm has been applied to high resolution spectra measured by the Infrared Atmospheric Sounding Interferometer instrument to retrieve atmospheric profiles of temperature, water vapour and ozone. The performance of the inversion strategy has been assessed by comparing the retrieved profiles to the ones obtained by co-locating in space and time profiles from the European Centre for Medium-Range Weather Forecasts analysis.