Published on February 20, 2008
Slide1: Mihaela Mircea1, Massimo D'Isidoro1, Alberto Maurizi1, Maria Gabriella Villani1, Andrea Buzzi1, Sandro Fuzzi1, Francesco Tampieri1 Gabriele Zanini2, Fabio Monforti2, Lina Vitale2 1Istituto di Scienze dell’Atmosfera e del Clima, CNR, Bologna, Italy 2ENEA,Italian Agency for New Technologies, Energy and the Environment, Via Martiri di Monte Sole 4, 40129 Bologna, Italy Ozone modeling over Italy: a sensitivity analysis to precursors using BOLCHEM air quality model Objectives: Objectives to investigate the sensitivity of ozone concentration to the reduction of NOx and VOC for few periods during the years 1999 and 2003 over the whole Italy to asses the relative importance of precursors in reducing the ozone levels identifying the regions of Italy where local emissions strategies could not be effective Motivation: Motivation there is no such study – only studies over Northern Italy in some areas, the ozone concentrations can be controlled by transboundary processes and that it cannot be ruled out by simulating a small area. the topography of Italy is very complex and leads to very complicate circulations features. Italy is in a geographic position (from ca. 37o to 47o lat North) that lead to various climate features. The ozone episodes to simulate were chosen for the year 1999 because it is used as a reference year in meteorological studies and for the summer 2003 because it was characterized by very high temperatures for a many days. Slide4: BOLCHEM flow chart Gas Chemistry (SAPRC90/CB4) Emissions Dry Deposition Meteorological Model (BOLAM) Winds, T, q Transport/dispersion Chemistry&transport model (CTM) Photochemical mechanisms: Photochemical mechanisms CB-IV (Gery et al., 1989) : lumped-structure condensed mechanism -85 reactions and 30 chemical species -organics are grouped according to bond type (for example, as carbon single bonds, carbon double bounds or carbonyl bounds) -organic species are treated explicitly (e.g. formaldehyde, ethene, isoprene), represented by carbon bond (PAR – single bonded one carbon atom, OLE –two carbon atoms) or molecular (TOL and XYL aromatic hydrocarbons) surrogates according with their chemistry or importance in the environment. SAPRC90 (Carter, 1990) : lumped-molecular condensed mechanism -131 reactions with 35 chemical species -calculate the kinetic and mechanistic parameters for lumped species in the mechanism created for representative emissions profile (mole-weighted approach) -organics species are treated explicitly (e.g. formaldehyde, acetaldehyde, etc) or represented by molecules as alkane, alkenes, aromatics, etc. Chemistry is coupled “online” with meteorology : Chemistry is coupled “online” with meteorology Meteorology and chemistry use: same transport scheme (WAF (Weighted Average Flux) 3-d advection scheme) same grid: horizontal and vertical components (the vertical coordinate system is terrain-following (s), with variables distributed on a non-uniformly spaced staggered Lorenz grid. the horizontal discretization uses geographical coordinates on an Arakawa C-grid) same physics for the subgrid-scale transport (for example vertical diffusion in surface layer and PBL parameterization depend on the Richardson number) same time step Emissions, initial and boundary conditions: Emissions, initial and boundary conditions The chemical fields are driven by hourly surface emissions and 3 hourly lateral boundary conditions after the initialisation. Emissions, initial and boundary conditions are produced by Thoscane model (Zanini et al., 2004). The emission inventory includes the ship emissions and the point source emissions are also considered in the simulations. Slide8: Model configuration and meteorological inputs The model domain extends between: NW (20.77, 47.55); NE (4.82 - 47.55); SW (6.17 - 35.79); SE (19.42 – 35.79). The horizontal resolution used in the simulations is of 20 km. The vertical resolution includes 33 sigma vertical layers from surface to the tropopause. The lower layer is approximately 20m thick above the surface. The meteorological fields are supplied by ECMWF. The lateral boundary conditions are updated every 6 hours. The weather fields were re-initialized every 48 hours with the analyses in order to avoid an excessive error growth in the meteorological forecast. Evaluation of model performance: Evaluation of model performance The model runs are on an grid between fine and coarse, therefore the model results are only compared with observations at rural and semi-rural locations. 1999: 4 clear sky periods selected based on Meteosat Images of Europe: January: 20-25 June: 1-4 July: 1-5 August: 5-8 Time series of observed and predicted O3 mixing ratio of gases at sites (1): Time series of observed and predicted O3 mixing ratio of gases at sites (1) Atmospheric Chemistry Slide11: Atmospheric Chemistry Time series of observed and predicted O3 mixing ratio of gases at sites (2) Quantitative performance statistics for hourly concentrations of O3: Quantitative performance statistics for hourly concentrations of O3 Slide13: NOx reduced(-35%) VOC reduced(-35%) Base case Differences in ozone concentrations: DO3=O3(65%VOC)-O3(65%NOx) : Differences in ozone concentrations: DO3=O3(65%VOC)-O3(65%NOx) CB4 DO3 > 0 NOx limited area DO3 <0 VOC limited area SAPRC90 ppb Chemical regimes over Italy ppb Areas selected for the analysis: Areas selected for the analysis Slide16: NOx reduced(-35%) VOC reduced(-35%) DO3=local-global reductions DO3(ppb) CB4 SAPRC90 Extreme summer 2003: Extreme summer 2003 DO3=O3(65%VOC)-O3(65%NOx) Fraction of VOC or NOx limited area: Fraction of VOC or NOx limited area O3 increase due to the increase in isoprene emissions: O3 increase due to the increase in isoprene emissions ppb Preliminary conclusions: Preliminary conclusions The differences in the predicted ozone concentrations due to the photochemical mechanisms are comparable to those obtained by reducing the emissions of NOx or VOC The distribution and the “intensity” (differences in ozone concentration) of VOC or NOx limited areas depend on the photochemical mechanism. For example, in the same meteorological and environmental conditions, a region can be VOC or NOx sensitive according with the photochemical mechanism used. The local reduction of VOC was efficient for Milano and Venice areas. In the other regions, significant increase in ozone concentration was observed by reducing locally both the NOx or VOC emissions. The increase of isoprene leads to substantial increase in the concentration of ozone at some locations (up to 25%), therefore, the uncertainties in isoprene emissions can bias the air quality design. ACKNOWLEDGEMENTS: Atmospheric Chemistry – ISAC (CNR) ACKNOWLEDGEMENTS GEMS and ACCENT: EU-projects ICTP Programme for Training and Research in Italian Laboratories”, Trieste, Italy
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