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Evaluation of urban surface parameterizations in the WRF model using measurements during the Texas Air Quality Study 2006 field campaign

Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 5. Lee S.-H.; Kim S.-W.; Angevine W.M.; et al. - Copernicus GmbH, 2011

The performance of different urban surface parameterizations in the WRF (Weather Research and Forecasting) in simulating urban boundary layer (UBL) was investigated using extensive measurements during the Texas Air Quality Study 2006 field campaign. The extensive field measurements collected on surface (meteorological, wind profiler, energy balance flux) sites, a research aircraft, and a research vessel characterized 3-dimensional atmospheric boundary layer structures over the Houston-Galveston Bay area, providing a unique opportunity for the evaluation of the physical parameterizations. The m ...

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Evaluation of urban surface parameterizations in the WRF model using measurements during the Texas Air Quality Study 2006 field campaign

  Available online: http://www.atmos-chem-phys.net/11/2127/2011/

S.-H. Lee ; S.-W. Kim ; W.M. Angevine ; L. Bianco ; S.A. McKeen ; C.J. Senff ; M. Trainer ; S.C. Tucker ; R.J. Zamora

in Atmospheric Chemistry and Physics (ACP) > Vol. 11. N° 5 [03/11/2011] . - p.2127-2143

The performance of different urban surface parameterizations in the WRF (Weather Research and Forecasting) in simulating urban boundary layer (UBL) was investigated using extensive measurements during the Texas Air Quality Study 2006 field campaign. The extensive field measurements collected on surface (meteorological, wind profiler, energy balance flux) sites, a research aircraft, and a research vessel characterized 3-dimensional atmospheric boundary layer structures over the Houston-Galveston Bay area, providing a unique opportunity for the evaluation of the physical parameterizations. The model simulations were performed over the Houston metropolitan area for a summertime period (12–17 August) using a bulk urban parameterization in the Noah land surface model (original LSM), a modified LSM, and a single-layer urban canopy model (UCM). The UCM simulation compared quite well with the observations over the Houston urban areas, reducing the systematic model biases in the original LSM simulation by 1–2 °C in near-surface air temperature and by 200–400 m in UBL height, on average. A more realistic turbulent (sensible and latent heat) energy partitioning contributed to the improvements in the UCM simulation. The original LSM significantly overestimated the sensible heat flux (~200 W m−2) over the urban areas, resulting in warmer and higher UBL. The modified LSM slightly reduced warm and high biases in near-surface air temperature (0.5–1 °C) and UBL height (~100 m) as a result of the effects of urban vegetation. The relatively strong thermal contrast between the Houston area and the water bodies (Galveston Bay and the Gulf of Mexico) in the LSM simulations enhanced the sea/bay breezes, but the model performance in predicting local wind fields was similar among the simulations in terms of statistical evaluations. These results suggest that a proper surface representation (e.g. urban vegetation, surface morphology) and explicit parameterizations of urban physical processes are required for accurate urban atmospheric numerical modeling.

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Tags: Environment and landscape ; Measure ; Urban zone ; Air quality ; United States of America Add tag

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Dependence of aerosol-precipitation interactions on humidity in a multiple-cloud system

Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 5. Lee S.S. - Copernicus GmbH, 2011

This study examines the dependence of aerosol-precipitation interactions on environmental humidity in a mesoscale cloud ensemble (MCE) which is composed of convective and stratiform clouds. The author found that increases in aerosol concentration enhance evaporative cooling, which raises not only the intensity of vorticity and entrainment but also that of downdrafts and low-level convergence. The increase in vorticity tends to suppress precipitation. The increase in low-level convergence tends to enhance precipitation by generating more secondary clouds in a muptiple-cloud system simulated her ...

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Dependence of aerosol-precipitation interactions on humidity in a multiple-cloud system

  Available online: http://dx.doi.org/10.5194/acp-11-2179-2011

S.S. Lee

in Atmospheric Chemistry and Physics (ACP) > Vol. 11. N° 5 [03/11/2011] . - p.2179-2196

This study examines the dependence of aerosol-precipitation interactions on environmental humidity in a mesoscale cloud ensemble (MCE) which is composed of convective and stratiform clouds. The author found that increases in aerosol concentration enhance evaporative cooling, which raises not only the intensity of vorticity and entrainment but also that of downdrafts and low-level convergence. The increase in vorticity tends to suppress precipitation. The increase in low-level convergence tends to enhance precipitation by generating more secondary clouds in a muptiple-cloud system simulated here.

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Tags: Aerosols ; Water ; Environment and landscape ; Hydrology ; Cloud ; Stratiform cloud ; Precipitation Add tag

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Corrigendum to "Controls of carbon dioxide concentrations and fluxes above central London" published in Atmos. Chem. Phys., 11, 1913–1928, 2011

Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 5. Helfter C.; Famulari D.; Phillips G.J.; et al. - Copernicus GmbH, 2011

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Corrigendum to "Controls of carbon dioxide concentrations and fluxes above central London" published in Atmos. Chem. Phys., 11, 1913–1928, 2011

  Available online: http://dx.doi.org/10.5194/acp-11-2081-2011

C. Helfter ; D. Famulari ; G.J. Phillips ; J.F. Barlow ; C.R. Wood ; C.S.B. Grimmond ; E. Nemitz

in Atmospheric Chemistry and Physics (ACP) > Vol. 11. N° 5 [03/11/2011] . - p.2081

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Tags: Carbon dioxide (CO2) ; Environment and landscape ; Air pollution ; United Kingdom of Great Britain and Northern Ireland Add tag

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Charge induced stability of water droplets in subsaturated environment

Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 5. Nielsen J.K.; Maus C.; Rzesanke D.; et al. - Copernicus GmbH, 2011

Atmospheric liquid and solid water particles are stabilized if they are coated with either negative or positive electric charge. The surface charge causes an increase of the partial pressure of water vapour close to the surface of each particle, effectively allowing the particles to remain in their condensed phase even if the environmental relative humidity drops below unity. The theory, briefly presented in this paper, predicts a zero parameter relation between surface charge density and water vapour pressure. This relation was tested in a series of Electrodynamic Balance experiments. The mea ...

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Charge induced stability of water droplets in subsaturated environment

  Available online: http://dx.doi.org/10.5194/acp-11-2031-2011

J.K. Nielsen ; C. Maus ; D. Rzesanke ; T. Leisner

in Atmospheric Chemistry and Physics (ACP) > Vol. 11. N° 5 [03/11/2011] . - p.2031-2037

Atmospheric liquid and solid water particles are stabilized if they are coated with either negative or positive electric charge. The surface charge causes an increase of the partial pressure of water vapour close to the surface of each particle, effectively allowing the particles to remain in their condensed phase even if the environmental relative humidity drops below unity. The theory, briefly presented in this paper, predicts a zero parameter relation between surface charge density and water vapour pressure. This relation was tested in a series of Electrodynamic Balance experiments. The measurements were performed by stabilizing charged droplets of pure water near an ice-surface. We observed a divergence in radius as the temperature approached the freezing point from below. We find that the measurements confirm the theory within the experimental uncertainty. In some cases this generally overlooked effect may have impact on cloud processes and on results produced by Electrodynamic Balance experiments.

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Tags: Water ; Environment and landscape ; Air pollution Add tag

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Boundary layer dynamics over London, UK, as observed using Doppler lidar during REPARTEE-II

Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 5. Barlow J.F.; Dunbar T.M.; Nemitz E.G.; et al. - Copernicus GmbH, 2011

Urban boundary layers (UBLs) can be highly complex due to the heterogeneous roughness and heating of the surface, particularly at night. Due to a general lack of observations, it is not clear whether canonical models of boundary layer mixing are appropriate in modelling air quality in urban areas. This paper reports Doppler lidar observations of turbulence profiles in the centre of London, UK, as part of the second REPARTEE campaign in autumn 2007. Lidar-measured standard deviation of vertical velocity averaged over 30 min intervals generally compared well with in situ sonic anemometer measure ...

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Boundary layer dynamics over London, UK, as observed using Doppler lidar during REPARTEE-II

  Available online: http://dx.doi.org/10.5194/acp-11-2111-2011

J.F. Barlow ; T.M. Dunbar ; E.G. Nemitz ; C.R. Wood ; M.W. Gallagher ; F. Davies ; E. O'Connor ; R.M. Harrison

in Atmospheric Chemistry and Physics (ACP) > Vol. 11. N° 5 [03/11/2011] . - p.2111-2125

Urban boundary layers (UBLs) can be highly complex due to the heterogeneous roughness and heating of the surface, particularly at night. Due to a general lack of observations, it is not clear whether canonical models of boundary layer mixing are appropriate in modelling air quality in urban areas. This paper reports Doppler lidar observations of turbulence profiles in the centre of London, UK, as part of the second REPARTEE campaign in autumn 2007. Lidar-measured standard deviation of vertical velocity averaged over 30 min intervals generally compared well with in situ sonic anemometer measurements at 190 m on the BT telecommunications Tower. During calm, nocturnal periods, the lidar underestimated turbulent mixing due mainly to limited sampling rate. Mixing height derived from the turbulence, and aerosol layer height from the backscatter profiles, showed similar diurnal cycles ranging from c. 300 to 800 m, increasing to c. 200 to 850 m under clear skies. The aerosol layer height was sometimes significantly different to the mixing height, particularly at night under clear skies. For convective and neutral cases, the scaled turbulence profiles resembled canonical results; this was less clear for the stable case. Lidar observations clearly showed enhanced mixing beneath stratocumulus clouds reaching down on occasion to approximately half daytime boundary layer depth. On one occasion the nocturnal turbulent structure was consistent with a nocturnal jet, suggesting a stable layer. Given the general agreement between observations and canonical turbulence profiles, mixing timescales were calculated for passive scalars released at street level to reach the BT Tower using existing models of turbulent mixing. It was estimated to take c. 10 min to diffuse up to 190 m, rising to between 20 and 50 min at night, depending on stability. Determination of mixing timescales is important when comparing to physico-chemical processes acting on pollutant species measured simultaneously at both the ground and at the BT Tower during the campaign. From the 3 week autumnal data-set there is evidence for occasional stable layers in central London, effectively decoupling surface emissions from air aloft.

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Tags: Aerosols ; Observations ; Doppler radar ; United Kingdom of Great Britain and Northern Ireland Add tag

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New cloud chamber experiments on the heterogeneous ice nucleation ability of oxalic acid in the immersion mode

Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 5. Wagner R.; Möhler O.; Saathoff H.; et al. - Copernicus GmbH, 2011

The heterogeneous ice nucleation ability of oxalic acid in the immersion mode has been investigated by controlled expansion cooling runs with airborne, ternary solution droplets composed of, (i), sodium chloride, oxalic acid, and water (NaCl/OA/H2O) and, (ii), sulphuric acid, oxalic acid, and water (H2SO4/OA/H2O). Polydisperse aerosol populations with median diameters ranging from 0.5–0.7 μm and varying solute concentrations were prepared. The expansion experiments were conducted in the AIDA aerosol and cloud chamber of the Karlsruhe Institute of Technology at initial temperatures of 244 and 2 ...

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New cloud chamber experiments on the heterogeneous ice nucleation ability of oxalic acid in the immersion mode

  Available online: http://dx.doi.org/10.5194/acp-11-2083-2011

R. Wagner ; O. Möhler ; H. Saathoff ; M. Schnaiter ; T. Leisner

in Atmospheric Chemistry and Physics (ACP) > Vol. 11. N° 5 [03/11/2011] . - p.2083-2110

The heterogeneous ice nucleation ability of oxalic acid in the immersion mode has been investigated by controlled expansion cooling runs with airborne, ternary solution droplets composed of, (i), sodium chloride, oxalic acid, and water (NaCl/OA/H2O) and, (ii), sulphuric acid, oxalic acid, and water (H2SO4/OA/H2O). Polydisperse aerosol populations with median diameters ranging from 0.5–0.7 μm and varying solute concentrations were prepared. The expansion experiments were conducted in the AIDA aerosol and cloud chamber of the Karlsruhe Institute of Technology at initial temperatures of 244 and 235 K. In the ternary NaCl/OA/H2O system, solid inclusions of oxalic acid, presumably nucleated as oxalic acid dihydrate, were formed by temporarily exposing the ternary solution droplets to a relative humidity below the efflorescence point of NaCl. The matrix of the crystallised NaCl particulates triggered the precipitation of the organic crystals which later remained as solid inclusions in the solution droplets when the relative humidity was subsequently raised above the deliquescence point of NaCl. The embedded oxalic acid crystals reduced the critical ice saturation ratio required for the homogeneous freezing of pure NaCl/H2O solution droplets at a temperature of around 231 K from 1.38 to about 1.32. Aqueous solution droplets with OA inclusions larger than about 0.27 μm in diameter efficiently nucleated ice by condensation freezing when they were activated to micron-sized cloud droplets at 241 K, i.e., they froze well above the homogeneous freezing temperature of pure water droplets of about 237 K. Our results on the immersion freezing potential of oxalic acid corroborate the findings from a recent study with emulsified aqueous solutions containing crystalline oxalic acid. In those experiments, the crystallisation of oxalic acid diyhdrate was triggered by a preceding homogeneous freezing cycle with the emulsion samples. The expansion cooling cycles with ternary H2SO4/OA/H2O solution droplets were aimed to analyse whether those findings can be transferred to ice nucleation experiments with airborne oxalic acid containing aerosol particles. Under our experimental conditions, the efficiency by which the surface of homogeneously nucleated ice crystals triggered the precipitation of oxalic acid dihydrate was very low, i.e., less than one out of a hundred ice crystals that were formed by homogeneous freezing in a first expansion cooling cycle left behind an ice-active organic crystal that acted as immersion freezing nucleus in a second expansion cooling cycle.

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Insights into the secondary fraction of the organic aerosol in a Mediterranean urban area: Marseille

Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 5. El Haddad I.; Marchand N.; Temime-Roussel B.; et al. - Copernicus GmbH, 2011

A comprehensive aerosol characterization was conducted at Marseille during summer, including organic (OC) and elemental carbon (EC), major ionic species, radiocarbon (14C), water-soluble OC and HULIS (HUmic LIke Substances), elemental composition and primary and secondary organic markers. This paper is the second paper of a two-part series that uses this dataset to investigate the sources of Organic Aerosol (OA). While the first paper investigates the primary sources (El Haddad et al., 2010), this second paper focuses on the secondary fraction of the organic aerosol.

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Insights into the secondary fraction of the organic aerosol in a Mediterranean urban area: Marseille

  Available online: http://dx.doi.org/10.5194/acp-11-2059-2011

I. El Haddad ; N. Marchand ; B. Temime-Roussel ; H. Wortham ; C. Piot ; J.-L. Besombes ; C. Baduel ; D. Voisin ; A. Armengaud ; J.-L. Jaffrezo

in Atmospheric Chemistry and Physics (ACP) > Vol. 11. N° 5 [03/11/2011] . - p.2059-2079

A comprehensive aerosol characterization was conducted at Marseille during summer, including organic (OC) and elemental carbon (EC), major ionic species, radiocarbon (14C), water-soluble OC and HULIS (HUmic LIke Substances), elemental composition and primary and secondary organic markers. This paper is the second paper of a two-part series that uses this dataset to investigate the sources of Organic Aerosol (OA). While the first paper investigates the primary sources (El Haddad et al., 2010), this second paper focuses on the secondary fraction of the organic aerosol.

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Tags: Aerosols ; Environment and landscape ; Urban zone ; Air pollution ; France Add tag

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Three-year ground based measurements of aerosol optical depth over the Eastern Mediterranean: the urban environment of Athens

Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 5. Gerasopoulos E.; Amiridis V.; Kazadzis S.; et al. - Copernicus GmbH, 2011

Three years (2006–2008) of ground-based observations of the Aerosol Optical Depth (AOD) in the urban environment of Athens, in the Eastern Mediterranean, are analysed in this work. Measurements were acquired with a Multi-Filter Rotating Shadowband Radiometer at five wavelengths. The daily average AOD at 500 nm is 0.23, and the mean Ångström coefficient calculated between 415 and 867 nm is 1.41. The annual variability of AOD has a spring maximum dominated by coarse dust particles from the Sahara (AOD 0.34–0.42), while the diurnal pattern is typical for urban sites, with AOD steadily increasing ...

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Three-year ground based measurements of aerosol optical depth over the Eastern Mediterranean: the urban environment of Athens

  Available online: http://dx.doi.org/10.5194/acp-11-2145-2011

E. Gerasopoulos ; V. Amiridis ; S. Kazadzis ; P. Kokkalis ; K. Eleftheratos ; M.O. Andreae ; T.W. Andreae ; H. El-Askary ; Christos S. Zerefos

in Atmospheric Chemistry and Physics (ACP) > Vol. 11. N° 5 [03/11/2011] . - p.2145-2159

Three years (2006–2008) of ground-based observations of the Aerosol Optical Depth (AOD) in the urban environment of Athens, in the Eastern Mediterranean, are analysed in this work. Measurements were acquired with a Multi-Filter Rotating Shadowband Radiometer at five wavelengths. The daily average AOD at 500 nm is 0.23, and the mean Ångström coefficient calculated between 415 and 867 nm is 1.41. The annual variability of AOD has a spring maximum dominated by coarse dust particles from the Sahara (AOD 0.34–0.42), while the diurnal pattern is typical for urban sites, with AOD steadily increasing throughout the day. The greatest contribution to the annually averaged AOD, accounting for almost 40%, comes from regional and local sources (namely the Istanbul metropolitan area, the extended areas of biomass burning around the north coast of the Black Sea, power plants spread throughout the Balkans and the industrial area in the Po valley, with average daily AOD in the range of 0.25–0.35). An additional important contribution (23%) is dust from Africa, whereas the rest of Europe contributes another 22%. The geographical distribution of the above sources in conjunction with the prevailing synoptic situation and contribution of local sources, lead to mixed types of aerosols over Athens, with highly variable contribution of fine and coarse particles to AOD in the range 10%–90%. This is the first long-term, ground based data set available for Athens, and it has also been used for the validation of satellite derived AOD by MODIS, showing good agreement on an annual basis, but with an overestimation of satellite AODs in the warm period.

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Tags: Aerosols ; Environment and landscape ; Urban zone ; Air pollution ; Greece Add tag

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The 2009–2010 Arctic polar stratospheric cloud season: a CALIPSO perspective

Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 5. Pitts M.C.; Poole L.R.; Dörnbrack A.; et al. - Copernicus GmbH, 2011

Spaceborne lidar measurements from CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) are used to provide a vortex-wide perspective of the 2009–2010 Arctic PSC (polar stratospheric cloud) season to complement more focused measurements from the European Union RECONCILE (reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions) field campaign. The 2009–2010 Arctic winter was unusually cold at stratospheric levels from mid-December 2009 until the end of January 2010, and was one of only ...

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The 2009–2010 Arctic polar stratospheric cloud season: a CALIPSO perspective

  Available online: http://dx.doi.org/10.5194/acp-11-2161-2011

M.C. Pitts ; L.R. Poole ; A. Dörnbrack ; L.W. Thomason

in Atmospheric Chemistry and Physics (ACP) > Vol. 11. N° 5 [03/11/2011] . - p.2161-2177

Spaceborne lidar measurements from CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) are used to provide a vortex-wide perspective of the 2009–2010 Arctic PSC (polar stratospheric cloud) season to complement more focused measurements from the European Union RECONCILE (reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions) field campaign. The 2009–2010 Arctic winter was unusually cold at stratospheric levels from mid-December 2009 until the end of January 2010, and was one of only a few winters from the past fifty-two years with synoptic-scale regions of temperatures below the frost point. More PSCs were observed by CALIPSO during the 2009–2010 Arctic winter than in the previous three Arctic seasons combined. In particular, there were significantly more observations of high number density NAT (nitric acid trihydrate) mixtures (referred to as Mix 2-enh) and ice PSCs. We found that the 2009–2010 season could roughly be divided into four periods with distinctly different PSC optical characteristics. The early season (15–30 December 2009) was characterized by patchy, tenuous PSCs, primarily low number density liquid/NAT mixtures. No ice clouds were observed by CALIPSO during this early phase, suggesting that these early season NAT clouds were formed through a non-ice nucleation mechanism. The second phase of the season (31 December 2009–14 January 2010) was characterized by frequent mountain wave ice clouds that nucleated widespread NAT particles throughout the vortex, including Mix 2-enh. The third phase of the season (15–21 January 2010) was characterized by synoptic-scale temperatures below the frost point which led to a rare outbreak of widespread ice clouds. The fourth phase of the season (22–28 January) was characterized by a major stratospheric warming that distorted the vortex, displacing the cold pool from the vortex center. This final phase was dominated by STS (supercooled ternary solution) PSCs, although NAT particles may have been present in low number densities, but were masked by the more abundant STS droplets at colder temperatures. We also found distinct variations in the relative proportion of PSCs in each composition class with altitude over the course of the 2009–2010 Arctic season. Lower number density liquid/NAT mixtures were most frequently observed in the lower altitude regions of the clouds (below ~18–20 km), which is consistent with CALIPSO observations in the Antarctic. Higher number density liquid/NAT mixtures, especially Mix 2-enh, were most frequently observed at altitudes above 18–20 km, primarily downstream of wave ice clouds. This pattern is consistent with the conceptual model whereby low number density, large NAT particles are precipitated from higher number density NAT clouds (i.e. mother clouds) that are nucleated downstream of mountain wave ice clouds.

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Tags: Aerosols ; Environment and landscape ; Cloud ; Observations ; Air pollution ; Stratosphere ; Arctic Add tag

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Primary sources of PM2.5 organic aerosol in an industrial Mediterranean city, Marseille

Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 5. El Haddad I.; Marchand N.; Wortham H.; et al. - Copernicus GmbH, 2011

Marseille, the most important port of the Mediterranean Sea, represents a challenging case study for source apportionment exercises, combining an active photochemistry and multiple emission sources, including fugitive emissions from industrial sources and shipping. This paper presents a Chemical Mass Balance (CMB) approach based on organic markers and metals to apportion the primary sources of organic aerosol in Marseille, with a special focus on industrial emissions. Overall, the CMB model accounts for the major primary anthropogenic sources including motor vehicles, biomass burning and the a ...

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Primary sources of PM2.5 organic aerosol in an industrial Mediterranean city, Marseille

  Available online: http://dx.doi.org/10.5194/acp-11-2039-2011

I. El Haddad ; N. Marchand ; H. Wortham ; C. Piot ; J.-L. Besombes ; J. Cozic ; C. Chauvel ; A. Armengaud ; D. Robin ; J.-L. Jaffrezo

in Atmospheric Chemistry and Physics (ACP) > Vol. 11. N° 5 [03/11/2011] . - p.2039-2058

Marseille, the most important port of the Mediterranean Sea, represents a challenging case study for source apportionment exercises, combining an active photochemistry and multiple emission sources, including fugitive emissions from industrial sources and shipping. This paper presents a Chemical Mass Balance (CMB) approach based on organic markers and metals to apportion the primary sources of organic aerosol in Marseille, with a special focus on industrial emissions. Overall, the CMB model accounts for the major primary anthropogenic sources including motor vehicles, biomass burning and the aggregate emissions from three industrial processes (heavy fuel oil combustion/shipping, coke production and steel manufacturing) as well as some primary biogenic emissions. This source apportionment exercise is well corroborated by 14C measurements. Primary OC estimated by the CMB accounts on average for 22% of total OC and is dominated by the vehicular emissions that contribute on average for 17% of OC mass concentration (vehicular PM contributes for 17% of PM2.5). Even though industrial emissions contribute only 2.3% of the total OC (7% of PM2.5), they are associated with ultrafine particles (Dp<80 nm) and high concentrations of Polycyclic Aromatic Hydrocarbons (PAH) and heavy metals such as Pb, Ni and V. On one hand, given that industrial emissions governed key primary markers, their omission would lead to substantial uncertainties in the CMB analysis performed in areas heavily impacted by such sources, hindering accurate estimation of non-industrial primary sources and secondary sources. On the other hand, being associated with bursts of submicron particles and carcinogenic and mutagenic components such as PAH, these emissions are most likely related with acute ill-health outcomes and should be regulated despite their small contributions to OC. Another important result is the fact that 78% of OC mass cannot be attributed to the major primary sources and, thus, remains un-apportioned. We have consequently critically investigated the uncertainties underlying our CMB apportionments. While we have provided some evidence for photochemical decay of hopanes, this decay does not appear to significantly alter the CMB estimates of the total primary OC. Sampling artifacts and unaccounted primary sources also appear to marginally influence the amount of un-apportioned OC. Therefore, this significant amount of un-apportioned OC is mostly attributed to secondary organic carbon that appears to be the major component of OC during the whole period of study.

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Tags: Aerosols ; Environment and landscape ; Urban zone ; Air pollution ; France Add tag

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