Particle Deposition in AERMOD: Overview

Transcription

1 Partcle Deposton n AERMOD: Overvew 2018 Regonal/State/Locals Modelng Workshop Boston, MA James Thurman U.S. EPA/OAQPS/AQAD/AQMG 6/19/2018 U.S. Envronmental Protecton Agency 1

2 Background Recent nterest n AERMOD deposton Polyfluoroalkyl sulfonate (PFAS), perfuorooctanoc acd (PFOA), Perfluorooctanesulfonc acd (PFOS) Hg deposton AERMOD ncorporates dry and wet deposton for partcles and gases Generally not used for regulatory applcatons but can be ncorporated f mportant (Secton of Appendx W) Wll focus only on partcle deposton here 6/19/2018 U.S. Envronmental Protecton Agency 2

3 Dry deposton flux F d =C d xv dep F d =dry deposton flux (mg/m 2 /s) rate at whch a mass s deposted to a surface from the ar over an area C d =concentraton (mg/m 3 ) calculated at z r V dep =deposton velocty (m/s) z r =deposton roughness heght (m)=z o +1 z o =surface roughness (m) from meteorologcal fle 6/19/2018 U.S. Envronmental Protecton Agency 3

4 Wet deposton flux F w =10-3 r p xw p r F w =wet deposton flux (mg/m 2 /hr) r p =column average concentraton (mg/m 3 ) of partculate n ar W p =Washout coeffcent r=precptaton rate (mm/hr) from meteorologcal fle 6/19/2018 U.S. Envronmental Protecton Agency 4

5 METHOD 1 AERMOD methods of partcle dry deposton DEFAULT From ISCST3 Based on Plem et al. (1984) Inputs by sze bn Dameter (mcrons) Method 2 Mass fracton (0 to 1) Densty (g/cm 3 ) Added early 2000 s (Wesely et al., 2002) Smplfed approach when partcle sze dstrbuton not well known Non-default Inputs Fne mass fracton (0 to 1) Mean partcle dameter (mcrons) of fne mass fracton 6/19/2018 U.S. Envronmental Protecton Agency 5

6 Method 1 When do I use? A sgnfcant fracton (> 10%) of total partculate mass has a dameter of 10 mcrons or larger or, The partcle sze dstrbuton s known Method 2 Partcle sze dstrbuton s not well known and, When a small fracton (< 10%) of total partcular mass has a dameter of 10 mcrons or larger See Secton of AERMOD User s gude 6/19/2018 U.S. Envronmental Protecton Agency 6

7 Method 1 How are nput parameters used? Dameter and densty used to calculate numerous varables yeldng deposton veloctes Fracton used n adjustment factor n concentraton and deposton calculatons (see model debug fle) Method 2 Dameter and fracton used to calculate varables yeldng deposton veloctes Fracton used to n adjustment factor n concentraton and deposton calculatons (see model debug fle) 6/19/2018 U.S. Envronmental Protecton Agency 7

8 Modfed Method 1 deposton velocty 1 V = + V + d, g, R + R + R R V a p, a p, g, V dphor V d, = Deposton velocty for bn (m/s) R a = Hourly varyng aerodynamc resstance (s/m) (ndependent of method) R p, = Hourly varyng deposton layer resstance (s/m) for bn * V g, = Gravtatonal settlng velocty (m/s) for bn V dphor = Deposton velocty due to phoretc effects ( m/s) *R p, replaces the R d, varable n the orgnal Method 1 formulaton as recommended by Wesely et al. (2002) 6/19/2018 U.S. Envronmental Protecton Agency 8

9 Method 2 deposton velocty V d1 = R a 1 + R p V d 2 = R a + R p R a R p V d1 = Deposton velocty for fne partcle mode (m/s) V d2 = Deposton velocty for coarse partcle mode (m/s) Vdep= Total deposton velocty (m/s) R a = Hourly varyng aerodynamc resstance (s/m) (ndependent of method) R p = Hourly varyng resstance component (s/m) F fne = Fne mass fracton 0.002= Gravtatonal settlng velocty (m/s) for coarse mode* * Gravtatonal settlng velocty assumed to be 0 m/s for fne mode 6/19/2018 U.S. Envronmental Protecton Agency 9

10 Key dfferences between dry deposton methods No V g for fne mode n Method 2 Assumed V g =0.002 m/s for coarse mode Reasonable compared to Method 1 Vg for coarse partcles No V dphor for Method 2 V g, = g ( )( ) ρ ρ 4 Dam ar 10 S, 18µ 2 CF 6/19/2018 U.S. Envronmental Protecton Agency 10

11 R Key dfferences between dry deposton methods R p calculaton p, 1 = 3 Gadju* ( Schmdt + x ) 2 / (contnued) nert Method 1 (see Appendx for varable calculatons; dameter dependent) R p = 500 u * Method 2 stable (L > 0) 500 R p = u 300 * L ( ( ) 1 Method 2 unstable (L < 0) 6/19/2018 U.S. Envronmental Protecton Agency 11

12 Other dfferences between dry deposton methods Method 1 Concentratons and deposton calculated for each partcle bn Total concentraton s sum across bns Method 2 One concentraton usng the total deposton velocty 6/19/2018 U.S. Envronmental Protecton Agency 12

13 AERMOD method for wet deposton Same for both dry deposton methods Key dfference Partcle bns looped for Method 1 and only 1 partcle sze bn for Method 2 See Appendx for varables and equatons 6/19/2018 U.S. Envronmental Protecton Agency 13

14 Partcle and gas deposton and depleton n AERMOD To calculate deposton use DEPOS, DDEP, or WDEP on MODELOPT lne DEPOS: Total deposton flux calculated (dry+wet) DDEP: Dry deposton flux calculated WDEP: Wet deposton flux calculated Deposton values are not averages but total for the perod, year, day, hour, etc. Default unts of g/m2 for averagng perod Automatcally nvokes dry (DRYDPLT) and/or wet depleton (WETDPLT) 6/19/2018 U.S. Envronmental Protecton Agency 14

15 Partcle and gas deposton and depleton n AERMOD (contnued) Calculate deposton wthout depleton NODRYDPLT and/or NOWETDPLT on MODELOPT lne Calculate depleton wthout deposton calculatons DRYDPLT and/or WETDPLT but not DEPOS, DDP, or WDEP on MODELOPT lne Ether way, you need to enter partcle nformaton on SO pathway 6/19/2018 U.S. Envronmental Protecton Agency 15

16 Example: All fne partculates Assume 1 partcle sze bn for Method 1 and 100% fne for Method 2 Dameter: 1 mcron Densty: 1.5 g/cm 3 Fracton: 1 Use DEPOS, DEPOS, DDEP, WDEP keywords on MODELOPT pathway Use DEPOS keyword wth DEBUGOPT pathway Outputs hourly veloctes and other parameters Hard coded flename PDEP.DAT 6/19/2018 U.S. Envronmental Protecton Agency 16

17 Method 1 Method 2 CO STARTING CO TITLEONE METHOD 1 CO MODELOPT CONC DEPOS DDEP WDEP FLAT CO AVERTIME ANNUAL CO POLLUTID OTHER CO RUNORNOT RUN CO DEBUGOPT DEPOS CO ERRORFIL ERRORS.OUT CO FINISHED SO STARTING SO LOCATION RUR1 POINT SO SRCPARAM RUR SO PARTDIAM RUR1 1.0 SO MASSFRAX RUR1 1.0 SO PARTDENS RUR1 1.5 SO SRCGROUP RUR1 RUR1 SO FINISHED CO STARTING CO TITLEONE METHOD 1 CO MODELOPT CONC DEPOS DDEP WDEP FLAT CO AVERTIME ANNUAL CO POLLUTID OTHER CO RUNORNOT RUN CO DEBUGOPT DEPOS CO ERRORFIL ERRORS.OUT CO FINISHED SO STARTING SO LOCATION RUR1 POINT SO SRCPARAM RUR SO METHOD_2 RUR SO SRCGROUP RUR1 RUR1 SO FINISHED 6/19/2018 U.S. Envronmental Protecton Agency 17

18 PDEP.DAT Method 1 YYMMDDHH ISRC ICAT Method No. Ra Rp Vg() Vdep() OPTIONS: RegDFAULT CONC DEPOS DDEP WDEP ELEV DRYDPLT WETDPLT RURAL METHOD_ E E E E METHOD_ E E E E METHOD_ E E E E-03 PDEP.DAT Method 2 YYMMDDHH ISRC ICAT Method No. Ra Rp Vg() Vdep() OPTIONS: NonDFAULT CONC DEPOS DDEP WDEP FLAT DRYDPLT WETDPLT RURAL METHOD_ E E E E METHOD_ E E E E METHOD_ E E E E-03 6/19/2018 U.S. Envronmental Protecton Agency 18

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20 Annual average concentraton No deposton 6/19/2018 U.S. Envronmental Protecton Agency 20

21 Annual average concentraton Method 1 6/19/2018 U.S. Envronmental Protecton Agency 21

22 Annual average concentraton rato Method 1/No deposton Mnmum rato: Mean rato: Medan rato: Maxmum rato: 1.0 6/19/2018 U.S. Envronmental Protecton Agency 22

23 Annual average concentraton Method 2 6/19/2018 U.S. Envronmental Protecton Agency 23

24 Annual average concentraton rato Method 2/No deposton Mnmum rato: Mean rato: Medan rato: Maxmum rato: /19/2018 U.S. Envronmental Protecton Agency 24

25 Annual average concentraton rato Method 1/Method 2 Mnmum rato: Mean rato: Medan rato: Maxmum rato: /19/2018 U.S. Envronmental Protecton Agency 25

26 Annual deposton (g/m 2 ) Method 1 6/19/2018 U.S. Envronmental Protecton Agency 26

27 Annual deposton (g/m 2 ) Method 2 6/19/2018 U.S. Envronmental Protecton Agency 27

28 Annual dry deposton rato Method 1/Method 2 Mnmum rato: Mean rato: Medan rato: Maxmum rato: Deposton velocty ratos Method 1/Method 2 Mnmum rato: Mean rato: Medan rato: Maxmum rato: R p ratos Method 1/Method 2 Mnmum rato: Mean rato: Medan rato: Maxmum rato: /19/2018 U.S. Envronmental Protecton Agency 28

29 Summary Methods 1 and 2 gve dfferent results for deposton veloctes and deposton flux Concentratons appear to change lttle dependng on whch method used Need more research n how deposton ncorporated n AERMOD 6/19/2018 U.S. Envronmental Protecton Agency 29

30 Useful lnks ISCST3 user s gude volume 2 (METHOD 1) AERMOD user s gude df AERMOD deposton algorthms document (draft) Deposton report 6/19/2018 U.S. Envronmental Protecton Agency 30

31 Appendx Deposton equatons 6/19/2018 U.S. Envronmental Protecton Agency 31

32 6/19/2018 U.S. Envronmental Protecton Agency 32 Ra (aerodynamc resstance) calculatons + = L z z z ku R d o d a 5 ln 1 * + + = ln 1 * L z L z L z L z ku R o d o d a Stable (L>0) Unstable (L < 0) Z d =z o +1 (z o =surface roughness from sfc fle) k=von Karman constant (0.4) u * =surface frcton velocty (from sfc fle) L=Monn-Obukhov length (from sfc fle)

33 Method 1 R p calculatons: Schmdt number calculaton Knematc vscosty of ar (vares hourly; partcle ndependent) X t nu 1 = = u 2 * X nu Ta P ( + ( P Po )) T T o P a =ambent temperature (from sfc fle) o T o =reference temperature ( K) P=surface pressure (from sfc fle) P o =reference pressure (101.3 kpa) Gust adjustment factor (vares hourly; partcle ndependent) Gadj = 1 w * =0 w * =convectve velocty scale (from sfc fle) 2 w * G adj = w 2 * 0 u * =surface frcton velocty (from sfc fle) u* P=surface pressure (from sfc fle) P o =reference pressure (101.3 kpa) Inertal mpacton term for partcle bn ; hourly varyng x nert = 10 3 T stop, t1 Brownan dffusvty of partcle n ar (m 2 /s) for partcle bn ; hourly varyng DB, = TaSCF Dam B, Schmdt number for partcle bn ; hourly varyng X nu Schmdt = D Slp correcton factor for partcle bn I; non-hourly varyng ( a Dam / xmfp ) a 3 2xmfp ( a1 + a2e ) 1 =1.257 SCF, = 1+ a 2 = Dam a 3 =0.55 x mfp =6.5x10-6 Dam =partcle dameter for bn Gravtatonal settlng velocty for partcle bn I; non-hourly varyng 4 2 ρ g( ρ ρ ar )( 10 Dam ) S =densty of partcle bn CF, Vg, = ρ 18µ ar =Ar densty (1.2x10-3 g/cm 3 ) µ=absolute vscosty of ar (1.81x10-4 g/cm/s) Stop tme; non-hourly varyng Vg, Tstop, = g=gravty ( m/s 2 ) g R p, 1 2 / ( Schmdt + x ) = 3 Gadju* nert 6/19/2018 U.S. Envronmental Protecton Agency 33

34 Wet deposton calculatons (vary hourly) Randrop fall speed V = fall Rate p Rate p =precptaton rate (from sfc fle) Stokes number V fall Vg, Stk = Tstop, 0.01RDROP Randrop radus Rate p RDROP = e Reynolds number V R = 0. 01RDROP fall ( + R ) e X Crtcal Stokes number ln( 1+ Re ) Stkc = ln 1.0 nu For each partcle bn =1,n (Method 2, n=1) Dffuson term for scavagng ratos Term 4 1/ Re Schmdt 3 0. ReSchmdt 16 1, = + + ( R Schmdt ) Rato of partcle to randrop dameter (adjusted for unts) 10 6 Dam κ = 0.02RDROP Intercepton term for scavagng ratos 2 ( κ ( 1 R ) Term 2 2, = 4κ + e e Reset crtcal Stokes number to mnmum of Stokes number and crtcal Stokes number Stk c =mnmum(stk,stk c ) Inertal mpacton term for scavagng ratos Term 3, Stk Stk = Stk Stkc + c 1/ Scale by the rato of water (1 g/cm 3 ) to partcle densty (g/cm 3 ) Term 3, = Term 3, Collson effcency 1 ρ ECOLL =mnmum(1,(term 1, +Term 2, +Term 3, )) Washout coeffcent Z pecoll WASHOUT = RDROP Partcle scavengng rato Rate p Pscat, = 1.5ECOLL 2RDROP 3.64 Pscat =0 Z p =Heght of top of the plume (m) Rate p > 0 Rate p = 0 34

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