Atmospheric models. Chem Christoph Knote - NCAR Spring 2013

Transcription

1 Atmospheric models Chem 55 - Christoph Knote - NCAR Spring 203 based on: Introduction to Atmospheric Chemistry, D. Jacob, Princeton Press, 999 Prof. Colette Heald s course total change in over time Continuity equation dt = F + E + P L D Nothing is ever lost. The change of a quantity over time is the net result of sources minus sinks. Source and sink terms depend on the application. 2

2 total change in over time Transport dt = F + E + P L D transport Example ( == water) inflow Fin (inflow) - Fout (outflow) in this example outflow 3 total change in over time Transport dt = F + E + P L D transport Example ( == water) + Hoover dam inflow before inflow after (>>0) 0 outflow outflow 4

3 Clicker question Did the transport term F (on average) change after construction of the Hoover dam? A. yes, it is now > 0.0 B. yes, it is now < 0.0 C. no D.yes, it is now == 0.0 E. I don t know 5 Clicker question Did the transport term F (on average) change after construction of the Hoover dam? A. yes, it is now > 0.0 B. yes, it is now < 0.0 C. no D.yes, it is now == 0.0 E. I don t know C no (on average), because the reservoir would overflow if the term is still positive once the reservoir is full. transport is always: Fin - Fout 6

4 total change in over time Emissions = F + E + P dt emissions L D based on emission factors and activity rates: E = EF A = 368 kg CO2 emitted Example: 368 g CO2 / km biogenic animals (CH4, NH3) plants (VOCs, debris) algae (DMS).000 km driven geogenic dust, sea salt (aerosols) volcanos (SO2) lightning (NOx) anthropogenic cars, aircrafts, industry (CO2, NOx,VOCs) 7 Emission inventories global regional national METEOTEST continental TNO/MACC Belastungskarten/NO2/2000/4_3_2000.jpg different datasets on different grids for certain species, multiple (overlapping) datasets for a single species C2SM Center for Climate NWP seminar - MeteoSchweiz - Christoph Knote - christoph.knote@empa.ch Systems Modeling 8

5 total change in over time Chemical reactions dt = F + E + P L D e.g. tropospheric ozone (photostationary state) production loss chemical Production / Loss NO 2 + h! NO + O( 3 P ) O( 3 P )+O 2 + M! O 3 + M NO + O 3 k! NO2 + O 2 in our model e.g.: = J NO2 [NO 2 ]+f([o( 3 P )], [O 2 ], [M]) k NO,O3 [NO][O 3 ] 9 total change in over time Deposition dt = F + E + P L D evaporating droplets wet dry deposition ra aerodynamic multi-phase chemistry activation to CCN impaction scavenging evaporating rain rb rc quasi-laminar layer surface wet deposition 0

6 Calculation of dry dep. flux based on resistance analogy F = 3 2 r a = 2 r b = 0 r c = 3 0 r tot Resistance approach F = v dep [] deposition velocity r total = v dep ra concentration of 3 aerodynamic = 3 (F r b + ) r a 2 = 3 (F r b + F r c ) r a F = r a + r b + r c typical values of vdep for gases: 0.5 cm/s see also: Wesely and Hicks, Atm. Env., 34, 2000 resistances in series v dep = r a + r b + r c rb rc quasi-laminar layer surface 0 = 0 Box models Fin inflow P E chemical production and loss emissions and deposition L D Fout outflow adapted from Introduction to Atmospheric Chemistry, D. Jacob All variables (e.g. ) and environmental conditions (temperature, pressure,...) are homogeneous within the box: well-mixed assumption 2

7 Fin inflow P E chemical production and loss emissions and deposition L D Fout outflow Lifetime dt = sources atmospheric lifetime: adapted from Introduction to Atmospheric Chemistry, D. Jacob mass balance: sinks = Fin F out + E + P L D = F out + L + D (s) lifetimes add in parallel: = + outflow chemical loss + deposition loss rates relate to lifetime: k = (s- ) 3 Clicker question Box of x x m. No transport. 20 ppbv of compound in the box at steady state. Chemical production of : 0. ppbv/s. Chemical loss (first order k): /s. Emissions of 0.5 ppbv/s. Deposition: ppbv/s. Lifetime of against chemical loss? A s B. 200 s C. 60 s D s E. I don t know 4

8 Clicker question Box of x x m. No transport. 20 ppbv of compound in the box at steady state. Chemical production of : 0. ppbv/s. Chemical loss (first order k): /s. Emissions of 0.5 ppbv/s. Deposition: ppbv/s. Lifetime of against chemical loss? A s B. 200 s C. 60 s D s E. I don t know = + outflow = F out + L + D chemical loss + chemical loss = Lx 20 ppbv B ppbv s = L = 4000 s deposition 5 Two-box models F2 F2 2 adapted from Introduction to Atmospheric Chemistry, D. Jacob simple transfer process: diffusion F2>0 F2<0 2 F2 = -F2 6

9 Two-box models F2 F2 2 adapted from Introduction to Atmospheric Chemistry, D. Jacob extended continuity eq. for assume flux is mass times transport coefficient (k) dt dt = E + P L D + F 2 F 2 = E + P L D + k 2 2 k 2 system of coupled ODEs (analytically solvable if in steady state) 7 Examples of box models reservoirs: GtC rates: GtC yr - adapted from hemispheric exchange studies, emission estimates lifetime and lifecycle assessments for longer lived species (e.g. CO2, HFCs, CH4) 8

10 Clicker question What is the lifetime of C in the atmosphere? A..6 yrs B. 3.4 yrs C. 2.8 yrs D.4.9 yrs E. I don t know reservoirs: GtC rates: GtC yr - adapted from 9 Clicker question What is the lifetime of C in the atmosphere? A..6 yrs B. 3.4 yrs C. 2.8 yrs D.4.9 yrs E. I don t know reservoirs: GtC rates: GtC yr - B. = 730 =3.45 yrs adapted from 20

11 box models Fin P E L D Fout Lagrangian models Eulerian models 2 Puff models t=t0+δt t=t0+2δt t=t0+3δt t=t0+4δt t=t0+5δt t=t0+6δt t=t0 box follows wind vector, continuity eq.: dt = E + P L D k dil( env ) dilution term - air in box mixes with surroundings Large uncertainties in transport and dilution possible! (additionally to uncert. in chemistry, emissions, removal) 22

12 Lagrangian models follow individual trajectories deal with uncertainties in puff models: release large number of boxes + computationally efficient - no mixing between individual boxes (chemistry!) - statistical undersampling away from source 23 release at Trinidad Head (CA) Example residence time x emissions = sensitivity adapted from Figure 3 in Cooper, O. R., et al. (2005), A springtime comparison of tropospheric ozone and transport pathways on the east and west coasts of the United States, J. Geophys. Res., 0, D05S90, doi:0.029/2004jd

13 box models Fin P E Lagrangian models L Fout D Eulerian models 25 Eulerian 3D models system of coupled ODEs (for each box) ~06 boxes are computationally feasible currently typical box sizes: km (global), -00 km (regional) vertical extent: surface to hpa Empa Medientechnik 26

14 SO4 2- (z km) Eulerian model example cloud ph processes seen here: transport, convection (F) wet deposition (D) aq.-phase chem. (P) dt = F + E + P L D 27 Lagrangian models Eulerian models! output of Eulerian model ( weather forecast ) necessary for wind vector! boxes follow wind vector, transport term == 0 +computationally efficient +no numerical diffusion - no mixing (chemistry) - statistical undersampling large # of boxes at fixed positions +complex chemistry, interactions possible - expensive computation - numerical diffusion 28

15 Box models Final overview Column models Fin P E L D Fout Lagrangian models Eulerian models various types of models, you decide depending on question you want to answer 29