6 th INTERNATIONAL WORKSHOP ON SAND/DUSTSTORMS AND ASSOCIATED DUSTFALL 7-9 September 2011, Athens, Greece

Transcription

1 6 th INTERNATIONAL WORKSHOP ON SAND/DUSTSTORMS AND ASSOCIATED DUSTFALL

2 Motivations Importance of Numerical Prediction Models to mineral dust cycle evaluation of dust effects over Italian region Identify the PM 10 natural contribution: in some episode it can play a fundamental role in the exceedance of limit values estabilished by European Union (Directive 2008/50/EC) Here is presented the case study June 2006, where an intense episode of dust affected Mediterranean Basin (Italy). 2

3 Numerical model A 3D comprehensive modelling system is developed. It is based on three different modules: the atmospheric model (RAMS), the dust emission model (DUSTEM) and the transport/deposition model (CAMx). 3

4 Numerical model overview NCEP REA II MODIS SSTs Land use Dust Emissions DUSTEM emission model RAMS meteorological model RAMS meteo fields soil moisture friction velocity wind fields CAMx dispertion model Dust Concentr. 4

5 Meteorological model - RAMS Regional atmospheric model constructed around the full set of nonhydrostatic, compressible equations atmospheric dynamics and thermodynamics conservation equations for scalar quantities a large selection of parameterizations for turbulent diffusion, solar and terrestrial radiation, moist processes, cumulus convection, etc. Physiographic dataset needed to represent the atmospheric dynamical behaviour: Land cover (Joint Research Centre, GLC2000 ) Sea surface temperature (NASA-PODAAC SST archive: AVHRR Pathfinder SST & MODIS AQUA/TERRA SST ) Atmospheric input providing initial and boundary condition: Main atmospheric fields from NCEP-NCAR Reanalysis II spatial resolution 2.5 5

6 Emission model - DUSTEM The emission model estimates the emission rate of 4 different dimensional classes of mineral particle lifted in atmosphere by wind. DUSTEM is a modification of the DREAM model, developed by Insular Coastal Dynamics, MALTA (ICoD) (Nickovic et al., 2001) The model estimates the dust emission rates using empirical equation based on: soil type, land cover, soil moisture, friction velocity and boundary layer turbolence. TYPE NAME Typical Particle Diameter (µm) Typical Particle Radius (µm) Particle Density (g/cm 3 ) Erodible Fraction Clay CCR Silt, small CCR Silt, large CCR Sand CCR

7 Transport/deposition model - CAMx The CAMx model developed by ENVIRON International Corporation ( is a photochemical eulerian dispersion model. oblique stereographic coordinate 30 degree horizontal resolution 18 vertical levels Only the two first dimensional classes are considered (because long range transport) 1µm-20µm CAMX Version 4.31 Temporal extension 25 th May 5 th July 2006 Time step Domain hourly 30km x 30km Stereographic coordinate with pole lat 40 -lon 5 Numer vertical levels 18 (from 10m to 10500m) Dry deposition Slinn & Slinn (1980) Wet deposition Seinfeld & Pandis (1998) Classes (aerodynamic diameter) Input Output CCR1 : 1 µm -2 µm CCR2 : 2 µm -20 µm CCR3 : 20 µm -50 µm CCR4 : 50 µm -100 µm hourly meteorological fields hourly dust emission rates hourly mean dust concentrations for each class 7

8 The simulated episode The simulation results were compared with: The daily maps provided by GOCART global model developed by the Georgia Institute of Technology-Goddard: daily dust aerosol column optical depths (550 nm) The in-situ PM 10 daily measurements, collected during the PATOS Project, which was funded by the Tuscany Regional Government to investigate the aerosol composition and to identify its sources 8

9 Analysis of the episode June, 7 th GOCART model 9

10 Analysis of the episode June, 15 th GOCART model 10

11 Analysis of the episode June, 24 th GOCART model 11

12 Analysis of the episode June, 28 th GOCART model 12

13 Comparison with in-situ measurements In-situ measurements of PM10 available from 15 th to 28 th of June 2006 in 3 cities of Central Italy. Measures are based on PIXE (Particle Induced X-ray Emission) technique, in order to measure the concentrations of all the main characteristic elements of the crustal component (Na, Mg, Al, Si, K, Ca, Ti, Mn, Fe, Sr, Zr) that can be used as markers of Saharan dust intrusions. Friday 9 th presentations by S. Nava & S. Becagli 6 th INTERNATIONAL WORKSHOP ON SAND/DUSTSTORMS AND ASSOCIATED DUSTFALL

14 Comparison with in-situ measurements The simulation considered hourly PM 20, while the measure are daily PM 10 qualitatively comparison Period extension: model identifies the episode from the 16 th of June to the 1 st of July in the inland cities (Florence and Lucca), shifting the onset of the dust outbreak by two days with respect to measurements. in the coastal city (Grosseto) these periods are coincident. In all the sites, both modelled and observed time series showed a good agreement in the right representation of the concentration s decrease of 24 th -25 th June, and the following increasing phase, up to the end of the episode. inland cities simulations values greater than measurements ( PM 10 meas. vs. PM 20 simul. ) coastal city simulations values lower than measurements 6 th INTERNATIONAL WORKSHOP ON SAND/DUSTSTORMS AND ASSOCIATED DUSTFALL 14

15 Vertical profiles inland Florence & Grosseto vertical cross section of dust concentration Between 1000m and 5000m there is the most part of dust concentration different behaviour on soil concentration Hmix Need of vertical profile measurements coastal 6 th INTERNATIONAL WORKSHOP ON SAND/DUSTSTORMS AND ASSOCIATED DUSTFALL 15

16 Hmix Comparing inland hourly dust concentration with Hmix there is a good correlation: the peaks have the same period (dust about 3 hours in advance to Hmix) the major part of dust concentration is located above boundary layer: during the day Hmix is growing up to 1000 m and the dust incomes in the lower level. The finest fraction remain suspended in atmosphere while the coarser fraction settled more quickly. In coastal cities, the simulated Hmix is lower because of the sea proximity (cell resolution: 30km x 30 km), obstructing dust intrusion from higher to lower levels. 6 th INTERNATIONAL WORKSHOP ON SAND/DUSTSTORMS AND ASSOCIATED DUSTFALL 16

17 Comparison with in-situ measurements Probable reason for lower values simulated near the coast: model representation of the boundary layer vertical extent, which could be underestimated obstructing the dust intrusions from higher to lower levels. ( introduce a nested grid with higher resolution) A further more detailed investigation could be done using hourly measurements instead of daily one 6 th INTERNATIONAL WORKSHOP ON SAND/DUSTSTORMS AND ASSOCIATED DUSTFALL 17

18 Conclusions The overall dynamics of aerosols extraction and transport, from local to large scale, in the Mediterranean is captured. The simulation results (1-20µm) are in a general good agreement with the in-situ measurements both in terms of concentrations near the surface and timing of peaks. Near the sea, the HPBL is not well resolved nested grid better resolution on target zone (about 10km x 10 km) Future planning: use WRF (operational at our institute) to develop a forecast model chain for dust intrusions. 6 th INTERNATIONAL WORKSHOP ON SAND/DUSTSTORMS AND ASSOCIATED DUSTFALL 18