Rapid ventilation of the Mexico City basin and regional fate of the urban plume

International audienceUrban areas can be large emitters of air pollutants leading to negative health effects and environmental degradation. The rate of venting of these airsheds determines the pollutant loading for given emission levels, and also determines the regional impacts of the urban plume. Mexico City has approximately 20 million people living in a high altitude basin with air pollutant concentrations above the health limits most days of the year. A mesoscale meteorological model (MM5) and a particle trajectory model (FLEXPART) are used to simulate air flow within the Mexico City basin and the fate of the urban plume during the MCMA-2003 field campaign. The simulated trajectories are validated against pilot balloon and radiosonde trajectories. The residence time of air within the basin and the impacted areas are identified by episode type. Three specific cases are analysed to identify the meteorological processes involved. For most days, residence times in the basin are less than 12 h with little carry-over from day to day and little recirculation of air back into the basin. Very efficient vertical mixing leads to a vertically diluted plume which, in April, is transported predominantly towards the Gulf of Mexico. Regional accumulation was found to take place for some days however, with urban emissions sometimes staying over Mexico for more than 6 days. Knowledge of the residence times, recirculation patterns and venting mechanisms will be useful in guiding policies for improving the air quality of the MCMA

Measurement of ambient aerosols in northern Mexico City by single particle mass spectrometry

International audienceContinuous ambient measurements with aerosol time-of-flight mass spectrometry (ATOFMS) were carried out in an industrial/residential section in the northern part of Mexico City as part of the Mexico City Metropolitan Area ? 2006 campaign (MCMA-2006) between 7?27 March, 2006. Biomass and organic carbon (OC) particle types were found to dominate the accumulation mode both day and night. The concentrations of both organic carbon and biomass particles were roughly equal early in the morning, but biomass became the largest contributor to the accumulation mode mass from the late morning until early evening. The diurnal pattern can be attributed to aging and/or a change in meteorology. Fresh elemental carbon (EC) particles were observed during rush hour. The majority of the EC particles were mixed with nitrate, sulfate, organic carbon and potassium. Submicron particles from industrial sources in the northeast were composed of an internal mixture of Pb, Zn, EC and Cl and peaked early in the morning. A unique nitrogen-containing organic (NOC) particle type was observed, and is hypothesized to be from industrial emissions based on the temporal profile and back trajectory analysis. This study provides unique insights into the real-time changes in single particle mixing state as a function of size and time for aerosols in Mexico City. These new findings indicate that biomass burning and industrial operations make significant contributions to particles in Mexico City. These sources have received relatively little attention in previous intensive field campaigns

Broadband X-ray spectrum of the newly discovered broad line radio galaxy IGR J21247+5058

In this paper we present radio and high energy observations of the INTEGRAL source IGR J21247+5058, a broad line emitting galaxy obscured by the Galactic plane. Archival VLA radio data indicate that IGR J21247+5058 can be classified as an FRII Broad Line Radio Galaxy. The spectrum between 610 MHz and 15 GHz is typical of synchrotron self-absorbed radiation with a peak at 8 GHz and a low energy turnover; the core fraction is 0.1 suggestive of a moderate Doppler boosting of the base of the jet. The high energy broad-band spectrum was obtained by combining XMM-Newton and Swift/XRT observation with INTEGRAL/IBIS data. The 0.4-100 keV spectrum is well described by a power law, with slope $\Gamma$=1.5, characterised by complex absorption due to two layers of material partially covering the source and a high energy cut-off around 70-80 keV. Features such as a narrow iron line and a Compton reflection component, if present, are weak, suggesting that reprocessing of the power law photons in the accretion disk plays a negligible role in the source.Comment: 7 pages, 7 figures, 3 tables, accepted for pubblication on MNRA

Measurement of ambient aerosols in northern Mexico City by single particle mass spectrometry

Continuous ambient measurements with aerosol time-of-flight mass spectrometry (ATOFMS) were made in an industrial/residential section in the northern part of Mexico City as part of the Mexico City Metropolitan Area-2006 campaign (MCMA-2006). Results are presented for the period of 15–27 March 2006. The submicron size mode contained both fresh and aged biomass burning, aged organic carbon (OC) mixed with nitrate and sulfate, elemental carbon (EC), nitrogen-organic carbon, industrial metal, and inorganic NaK inorganic particles. Overall, biomass burning and aged OC particle types comprised 40% and 31%, respectively, of the submicron mode. In contrast, the supermicron mode was dominated by inorganic NaK particle types (42%) which represented a mixture of dry lake bed dust and industrial NaK emissions mixed with soot. Additionally, aluminosilicate dust, transition metals, OC, and biomass burning contributed to the supermicron particles. Early morning periods (2–6 a.m.) showed high fractions of inorganic particles from industrial sources in the northeast, composed of internal mixtures of Pb, Zn, EC and Cl, representing up to 73% of the particles in the 0.2–3μm size range. A unique nitrogen-containing organic carbon (NOC) particle type, peaking in the early morning hours, was hypothesized to be amines from local industrial emissions based on the time series profile and back trajectory analysis. A strong dependence on wind speed and direction was observed in the single particle types that were present during different times of the day. The early morning (3:30–10 a.m.) showed the greatest contributions from industrial emissions. During mid to late mornings (7–11 a.m.), weak northerly winds were observed along with the most highly aged particles. Stronger winds from the south picked up in the late morning (after 11 a.m.), resulting in a decrease in the concentrations of the major aged particle types and an increase in the number fraction of fresh biomass particles. The highest wind speeds were correlated with the highest number fraction of fresh biomass particles (up to 76% of the submicron number fraction) when winds were coming directly from fires that were located south and southeast of the city based on MODIS fire count data. This study provides a unique clock of hourly changes in single particle mixing state and sources as a function of meteorology in Mexico City. These new findings indicate that biomass burning and industrial emissions can make significant contributions to primary particle loadings in Mexico City that are strongly coupled with local meteorology

Impact of primary formaldehyde on air pollution in the Mexico City Metropolitan Area

Formaldehyde (HCHO) is a radical source that plays an important role in urban atmospheric chemistry and ozone formation. The Mexico City Metropolitan Area (MCMA) is characterized by high anthropogenic emissions of HCHO (primary HCHO), which together with photochemical production of HCHO from hydrocarbon oxidation (secondary HCHO), lead to high ambient HCHO levels. The CAMx chemical transport model was employed to evaluate the impact of primary HCHO on its ambient concentration, on the ROx radical budget, and on ozone (O3) formation in the MCMA. Important radical sources, including HCHO, HONO, and O3-olefin reactions, were constrained by measurements from routine observations of the local ambient air monitoring network and the MCMA-2003 field campaign. Primary HCHO was found not only to contribute significantly to the ambient HCHO concentration, but also to enhance the radical budget and O3 production in the urban atmosphere of the MCMA. Overall in the urban area, total daytime radical production is enhanced by up to 10% and peak O3 concentration by up to 8%; moreover primary HCHO tends to make O3 both production rates and ambient concentration peak half an hour earlier. While primary HCHO contributes predominantly to the ambient HCHO concentration between nighttime and morning rush hours, significant influence on the radical budget and O3 production starts early in the morning, peaks at mid-morning and is sustained until early afternoon.Mexican Metropolitan Commission of EnvironmentNational Science Foundation (U.S.) (ATM-0528227

Swift-XRT observation of 34 new INTEGRAL/IBIS AGNs: discovery of Compton thick and other peculiar sources

For a significant number of the sources detected at high energies (>10 keV) by the INTEGRAL/IBIS and Swift/BAT instruments there is either a lack information about them in the 2-10 keV range or they are totally unidentified. Herein, we report on a sample of 34 IBIS AGN or AGN candidate objects for which there is X-ray data in the Swift/XRT archive. Thanks to these X-ray follow up observations, the identification of the gamma ray emitters has been possible and the spectral shape in terms of photon index and absorption has been evaluated for the first time for the majority of our sample sources. The sample, enlarged to include 4 more AGN already discussed in the literature, has been used to provide photon index and column density distribution. We obtain a mean value of 1.88 with a dispersion of 0.12, i.e. typical of an AGN sample. Sixteen objects (47%) have column densities in excess of 10^{22} cm^{-2} and, as expected, a large fraction of the absorbed sources are within the Sey 2 sample. We have provided a new diagnostic tool (NH versus F(2-10)keV/F(20-100)keV softness ratio) to isolate peculiar objects; we find at least one absorbed Sey 1 galaxy, 3 Compton thick AGN candidates; and one secure example of a "true" type 2 AGN. Within the sample of 10 still unidentified objects, 3 are almost certainly AGN of type 2; 3 to 4 have spectral slopes typical of AGN; and two are located high on the galactic plane and are strong enough radio emitters so that can be considered good AGN candidates.Comment: 15 pages, 5 figures, ApJ accepte

Specifying and Analysing SOC Applications with COWS

COWS is a recently defined process calculus for specifying and combining service-oriented applications, while modelling their dynamic behaviour. Since its introduction, a number of methods and tools have been devised to analyse COWS specifications, like e.g. a type system to check confidentiality properties, a logic and a model checker to express and check functional properties of services. In this paper, by means of a case study in the area of automotive systems, we demonstrate that COWS, with some mild linguistic additions, can model all the phases of the life cycle of service-oriented applications, such as publication, discovery, negotiation, orchestration, deployment, reconfiguration and execution. We also provide a flavour of the properties that can be analysed by using the tools mentioned above

Characterizing ozone production in the Mexico City Metropolitan Area: a case study using a chemical transport model

International audienceAn episodic simulation is conducted to characterize ozone (O3) photochemical production and investigate its sensitivity to emission changes of ozone precursors in the Mexico City Metropolitan Area (MCMA) using the Comprehensive Air Quality Model with extensions (CAMx). High Ox (O3+NO2) photochemical production rates of 10?80 ppb/h are predicted due to the high reactivity of volatile organic compounds (VOCs) in which alkanes, alkenes, and aromatics exert comparable contributions. The predicted ozone production efficiency is between 4?10 O3 molecules per NOx molecule oxidized, and increases with VOC-to-NO2 reactivity ratio. Process apportionment analyses indicate significant outflow of pollutants such as O3 and peroxyacetyl nitrate (PAN) from the urban area to the surrounding regional environment. PAN is not in chemical-thermal equilibrium during the photochemically active periods. Sensitivity studies of O3 production suggest that O3 formation in the MCMA urban region with less chemical aging (NOz/NOy3 production and its sensitivities to precursors suggest that midday O3 formation during this episode is VOC sensitive in the urban region on the basis of the current emissions inventory. More episodic studies are needed to construct a comprehensive and representative picture of the O3 production characteristics and its response to emission controls