TEMIS user workshop, Frascati, 8-9 October 2007

Long range transport of air pollution service:

Part 1: Trajectories

Bart Dils, M. De Mazière, J. van Geffen, M. Van Roozendael

TEMIS user workshop, Frascati, 8-9 October 2007

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)

TEMIS user workshop, Frascati, 8-9 October 2007

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

TEMIS user workshop, Frascati, 8-9 October 2007

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

TEMIS user workshop, Frascati, 8-9 October 2007

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

TEMIS user workshop, Frascati, 8-9 October 2007

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

TEMIS user workshop, Frascati, 8-9 October 2007

FLEXPART:: Example 1

• Plot1: Total columns (molec/cm2) in Lon-Lat domain

TEMIS user workshop, Frascati, 8-9 October 2007

FLEXPART:: Example 2

• Plot2: Maximal concentration (molec/cm3) along the Longitudinal band

TEMIS user workshop, Frascati, 8-9 October 2007

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

TEMIS user workshop, Frascati, 8-9 October 2007

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

TEMIS user workshop, Frascati, 8-9 October 2007

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)