1 1 Model studies of some atmospheric aerosols and comparisons with measurements K. G e o r g i e v I P P – B A S, S o f i a, B u l g a r i a

2 2 Introduction DG Joint Research Centre of European Commission Institute for Environment and Sustainability (IES – JRC, Ispra, Italy) M. Krool, F. Dentener, E. Vignati

3 3 Aerosols big and increasing importance for the assessment of air quality and climate forcing; play a crucial role for global temperature modifications; research of aerosols in the surface layer is mainly motivated of their impact on human health and possible ecological effects.

4 4 Aerosols Aerosols are defined as relatively stable suspensions of solid or liquid particles in a gas. The aerosols can be classified as primary (those that are emitted in particulate form directly from sources) and secondary (particles produced in the atmosphere).

5 5 Aerosols The formation of the secondary aerosols can be done mainly by : reaction of gases to form low–vapor–pressure products; reaction of gases on the surfaces of existing particles to form condensed phase products; chemical reactions within the aerosol itself (for example, SO2, oxidation to sulfate)

6 6 TM5 Model TM5 TM5 – 3D global chemistry Transport Model Allows two-way nested zooming which leads to possibility to run the model on relatively very fine space grid (1  1  ) (longitude x latitude) over selected regions (Europe is most often used but North America, Africa, Asia and South America can be treated separately or in combinations) The coarsest space resolution is (6  4  ) and between these two is a grid (3  2  )

7 7 Zooming Europe

8 8 Zooming Africa

9 9 Zooming Asia

10 Zooming North America

11 Vertical resolution Dashed lines – the 60 hybrid sigma-pressure (terrain following) levels of the operational ECMWF model; Solid lines – the subset employed by the 25 layer European zoom model; five layers –boundary layer ten layers –free troposphere ten layers – stratosphere

12 The model The TM5 model is designed for Global studies of atmospheric chemistry such as intercontinental and interhemispheric exchange; effects of grid refinement on the budgets of chemically active compounds.

13 The model The TM5 model is an offline model, using preprocessed meteorological fields from ECMWF.

14 The model Splitting The basic model operations (advection, convection, sources, chemistry) are solved by symmetrical operator splitting

15 The model Splitting Symmetrical splitting can not always be presented in an zooming algorithm Note: X and Y – horizontal advection Z – vertical advection V– vertical diffusion and convection C– chemistry (incl. emissions and depositions)

16 The model Splitting Let  – the parents write the boundary conditions to their children  –the parents are updated with the information by their children

17 The model – splitting Three-region European-focused TM5 version t ………………………………………………………………..t + ΔT/2 Region 1  X  YZ……………………………………………………………...VC Region 2 ……..  X  YZ…………………..VC CVZ  Y  X…………………  Region 3 ……………...XYZVC CVZYX  ……………….CVZYX XYZVC  t + ΔT/2 …………………………………………………………….. t + ΔT Region 1 CVZ  Y  X………………………………………………………………….. Region 2 ………… CVZ  Y  X……………………  X  YZ……………………VC  Region 3 ……………………… CVZYX XYZVC  XYZVC CVZYX  ……

18 The model Chemistry Gas phase chemistry is calculated using the CBM-IV chemical mechanism solved by means of the EBI method. Photochemistry and aerosols are coupled in the IPCC version of the TM5 model.

19 The model Aerosol Chemistry Aerosols are assumed internally mixed and in an accumulation mode size distribution for the calculations of both scavenging and depositions. They can contain sulphate, ammonium and nitrate and are described using bulk approach.

20 The model Aerosol Chemistry The water attached to the particles is determined from the ambient relatively humidity. Sulphate is reduced to its aerosol phase. It is obtained by the oxidation of sulphur dioxide in the gas phase by OH radical. In the aqueous phase this oxidation is done by H2O2 and ozone.

21 Aerosol studied sulfate (SO4,); ammonium (NH4); nitrate (NO3) sulfur dioxide (SO2), ammonia (NH3), nitric acid (HNO3) (due to some chemical transformations which play an essential role in creation and the live cycle of SO4, NH4, NO3)

22 Aerosol measurements There are relatively enough EMEP stations (57) with measurements for sulfate and sulfur dioxide. The stations with available measurements for ammonium and ammonia are 23 while the stations presenting measurements for nitrate and nitric acid are only 14 and not all of them have measurements for both.

23 Aerosol measurements The measurements reported by the EMEP network stations are surface measurements. The model output predictions which are discussed and used for the comparisons are taken in the first model layer.

24 Results vs measurements for sulphate

25 Results vs measurements for sulphate The correlation between measurements end model results is relatively good. The model results underestimate the measurements in the most of the stations (65 %).

26 Results vs measurements for sulphate and sulphur dioxide

27 Results vs measurements for sulphate In total: 65 %  corr. coeff. > 0.5 >13 %  > 0.75 “GB” : > 90%  corr. coeff. > %  corr. coeff. > 0.75 “North” + “Central”: 50%  corr. coeff. > 0.5

28 Results vs measurements for sulphate and sulphur dioxide TM5 model overpredicts sulphur dioxide and underpredicts sulphate

29 Results vs measurements for ammonium and ammonia TM5 model overestimate ammonium and underestimate ammonia

30 Results vs measurements for nitrate and nitric acid TM5 model overpredicts nitrate and underpredicts nitric acid

31 Implementation TM5 program has been coded in Fortran 90 Implemented and tested on: IBM p690+ SGI Origin 3800 MAC OSX SUN Cluster