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Long range transport of air pollution service: Part 1: Trajectories

Long range transport of air pollution service: Part 1: Trajectories Bart Dils, M. De Mazière, J. van Geffen, M. Van Roozendael. Introduction. Air pollution is not only a local problem: highlights Stohl et al. 2003

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Long range transport of air pollution service: Part 1: Trajectories

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  1. Long range transport of air pollution service: Part 1: Trajectories Bart Dils, M. De Mazière, J. van Geffen, M. Van Roozendael

  2. Introduction • Air pollution is not only a local problem: highlights • Stohl et al. 2003 • During favourable conditions intercontinental transport can occur on a very small timescale (~1 day!) • This allows transport of short-lived species such as NO2 • Li et al. (JGR 2002) using GEOS-CHEM model • O3: average 5 ppbv, up to 20 ppbv during transport events. • In 1997 20% of O3 EU threshold violations (55 ppbv, 8-hour average) would not occur without transport! • 86% = direct O3 transport, 14% due to precursors (NOx and PAN)

  3. Introduction:monitoring • Transport can occur over small timescales • High temporal resolution • NO2 lifetime is short => concentration are low • sharp detection limit • High signal to noise ratio • Transport simulations can fill in the gaps & add value to the observations • FLEXPART developed by Andreas Stohl

  4. Trajectories: FLEXPART • FLEXPART is a Lagrangian particle dispersion model which computes the trajectories of a large number of infinitesimally small air parcels to describe the transport and diffusion of tracers in the atmosphere • relatively fast computation times • FLEXPART simulates transport, turbulence, dry and wet deposition, and radioactive (or other) decay • Freely available on: http://zardoz.nilu.no/~andreas/flextra+flexpart.html

  5. FLEXPART:: Input • Windfield data from ECMWF • 1°x1°, 3hourly • NOx emission data from EDGAR 3.2 FT2000 • Yearly mean 1°x1°, 500 highest emission grids within 110°E to 50°E & 15°N to 65°N • No emissions from Europe included! • FLEXPART control parameters • Atmospheric half-lifetime is set to 2 days

  6. FLEXPART:: Output • 1°x1° lat-lon grid, 10 vertical levels (1km resolution) • 3h averages every 3 hours (15:00UT is plotted as it corresponds with the transatlantic overpass-time of OMI) • Plot1: Total columns (molec/cm2) in Lon-Lat domain • Plot2: Lon-Altitude plot, highest concentration (molec/cm3) along each Longitudinal band

  7. FLEXPART:: Example 1 • Plot1: Total columns (molec/cm2) in Lon-Lat domain

  8. FLEXPART:: Example 2 • Plot2: Maximal concentration (molec/cm3) along the Longitudinal band

  9. Trajectories: Limits • Yearly averaged NOx emission as a representative for time dep. NO2 emissions • Uniform NOx half-lifetime over entire domain • No chemistry or Temperature/Altitude dependence! • Wind field errors & limited resolution • Interpolation errors • wind data are only available at discrete locations in time and space • Truncation errors

  10. Trajectories: Future Improvements • Better NOx emission climatology • Better NOx half-lifetime parameter • Detailed OMI FLEXPART intercomparison • Forecasting abilities using either ECMWF or GFS windfield data • Seasonality and Receptor-region analysis

  11. Trajectories: Summary • FLEXPART output generates a useful tool to visualise and (eventually) predict LRT events • One should keep in mind the inherent limitations of this product • The real strength of these simulations lie in their synergic use with OMI (or other satellites) data products • (More on this during Bas’ presentation)

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