ATMOSPHERIC TRANSPORT PROCESSES OVER THE … R... · ATMOSPHERIC TRANSPORT PROCESSES OVER THE...

ATMOSPHERICTRANSPORTPROCESSESOVERTHEKATHMANDUVALLEYNEPAL ATMOSPHERICTRANSPORTPROCESSESOVERTHEKATHMANDUVALLEYNEPAL ATMOSPHERICTRANSPORTPROCESSESOVERTHEKATHMANDUVALLEY,NEPAL ATMOSPHERICTRANSPORT PROCESSES OVER THE KATHMANDU VALLEY, NEPAL RPRidLkNJh RamP.RegmiandLokN.Jha Ram P. Regmiand LokN. JhaCentralDepartmentofPhysicsTribhuvanUniversityKathmanduNepalSCIENCE AND TECHNOLOGY 2011 T1P13 TRIBHUVANUNIVERSITYCentral Department of Physics, TribhuvanUniversity, Kathmandu, Nepal.SCIENCE AND TECHNOLOGY 2011: T1-P13 TRIBHUVAN     UNIVERSITY

ABSTRACT5ResultsCVerticalStructureofWindandPotentialTemperatureTemporalandSpatialDistributionofPollutants ABSTRACTThitthtitithKthdllhbtdidtthtildtl

5.ResultsAChtitifNSfLlFl

C.    Vertical Structure of Wind and Potential TemperatureTemporal and Spatial Distribution of Pollutants() TheairmasstransportcharacteristicsovertheKathmanduvalleyhavebeenstudiedtoassessthespatialandtemporal

dbfdlfllhhlflThdhbdhhlfA.Characteristics of Near Surface Local Flows

06:45LST 00:45LST18:00 LST •Pollutants(e.g.,SO2)releasedinthesouthernareabuildshihihd distributionsofdecouplingofvalley'sairmasswiththeregionalflows.Thestudyhasbeencarriedoutwiththeapplicationsof

06:45 LST 00:45 LST Near surface wind at 11:45 LST Near surface wind at 05:45 LSThighconcentrationzoneneartheeasternandthttil fpgfygfyppf

MesoscaleMeteorologicalModel(MM5)WeatherResearchandForecast(WRF)andaChemicalTransportnortheasternmountainslops.

MesoscaleMeteorologicalModel(MM5),WeatherResearchandForecast(WRF)andaChemicalTransportMdlThdlditihbdithbddtThtdlthtKthdlltill

•TheprevailinglocalflowsorganizegeneralmassModels.Themodelpredictionshavebeencomparedwithobserveddata.ThestudyrevealsthatKathmanduvalleytypicallyPa)

Pa)

pgggtransportfromwest/southtoeastintheKathmandu

showsaplateau-basindualnature.Thenighttimenearsurfaceairmassremainslargelycalm.However,theintermittentre (h

e (hP

valleyandchanneloutintoeasternvalley.Thepollutants pTgfgyH,downslopewindsorganizeaweakflowsystemthatoftendevelopsvalleywideanticlockwisecirculationatabout150mabovethessur

ssure

L m)furthermovetowardstheHimalayas.

downslopewindsorganizeaweakflowsystemthatoftendevelopsvalleywideanti-clockwisecirculationatabout150mabovetheflhhllbffldhhllflddhhT

Pres

Pres

SL

m)

MSL

e (km

•SOremainsconstantaround40ppbduringthe floor,whichslowlybuteffectivelyinducesmassexchangeinthelowerlayerofcoldairmassduringthenighttime.TwoveryAM

e (km

m) A

M

ance•SO2remainsconstantaround40ppbduringthenighttimedespiteitscontinuousreleaseinthearea

gentlewindsystems,southwesterlyandnorthwesterly,composedofregionalscaledeepupslopeandplain-to-plateauwinds(m)

ance

n (m

istanighttimedespiteitscontinuousreleaseinthearea(Imadol)duetothewindlesssurfaceandpresenceof gentlewindsystems,southwesterlyandnorthwesterly,composedofregionalscaledeepupslopeandplaintoplateauwinds

llitditthKthdlllttidtitillthltiUifth3ion

Dista

ation

th D(Imadol)duetothewindlesssurfaceandpresenceofsomeintermittentwindatabout150mAGLas regularlyintrudeintotheKathmanduvalleyclosetonoontimeandcontinuetillthelateevening.Upperairfrommorethan3

kbhllddhllflhfSfKhd

evati

th D

leva

Nortsomeintermittentwindatabout150mAGLas

mountain/down‐slopewind.kmabovethemeansealevelcomesdownandsweepsacrossthevalleyfloorintheafternoon.SpringseasonofKathmanduEle

Nort

n El

uth-Nmountain/downslopewind.

ThditibtifllttdttthdilappearstoberelativelywindycomparedtowinterNostrongdecouplingofvalley'sairmasswiththeregionalairflowsappear12:45LST 10:45LST rain

uth-N

errai

Sou•Thedistributionofpollutantsdemonstratethediurnalidiitiittiththhtiti appearstoberelativelywindycomparedtowinter.Nostrongdecouplingofvalleysairmasswiththeregionalairflowsappear

titfth2hiddthllThditittillthtd12:45 LST 10:45 LST

Terr

Sou

Te Speriodicityinconsistentwiththecharacteristicmeteorology topersistformorethan24hoursorsoinandaroundthevalley.Thesurroundingmountaintops,particularly,theeasternand

hbhblflbkdl

Tmeteorology.

southeasternmountaintopsappeartobethemostsuitablesitesforregionalbackgroundaerosolconcentrationmeasurements.•Pollutantsmayspreadoverthemixedlayerofabout1.2 pppfgg

1Idi

Pa)

Pa)kmoverthevalleyjustbeforetheintrusionofthelocal1.  Introductione (hP

e (hP

flows.

Mt. ShivapuriMt. Nagarkot TheatmospherictransportprocessesovertheKathmandussure

ssure

•IntheeveningHNO3richairmasscomesbackovertheMt. Phulchoki

2660 m2250 m TheatmospherictransportprocessesovertheKathmanduvalleylocatedintheMiddleHillsoftheCentralHimalayaP

res

Pres

West-EastDistance(km) West-East Distance (km)IntheeveningHNO3richairmasscomesbackovertheKathmanduvalleyandremainsfloatingatabout350 2762 m valley,locatedintheMiddleHillsoftheCentralHimalaya,

offersratherdifferentcharacteristicsoflocalflowfieldsin

P P West-East Distance (km)

Nearsurfacewindat14:45LSTNearsurfacewindat17:45LSTKathmanduvalleyandremainsfloatingatabout350metersabovethevalleyfloor. offersratherdifferentcharacteristicsoflocalflowfieldsin

comparisontothegeneralmountainvalleywindsystemInNear surface wind at 14:45 LSTNear surface wind at 17:45 LSTmetersabovethevalleyfloor.

comparisontothegeneralmountainvalleywindsystem.Inthisregionthelocalcirculationsassociatedwithalarge thisregion,thelocalcirculationsassociatedwithalargenumberofsmallscalesubdivisionsandsubclimatesinteract numberofsmall‐scalesubdivisionsandsub‐climatesinteractinacomplicatedmannerPresentstudyassessesthe inacomplicatedmanner.PresentstudyassessestheatmosphericconditionsprevailingovertheKathmanduvalley17:45LST atmosphericconditionsprevailingovertheKathmanduvalleyandthenexaminestheextentofdecouplingofsurfaceair

17:45 LST 14:45 LST

L m)

m)

andthenexaminestheextentofdecouplingofsurfaceairiddthKthdlliththilM

SL

(km

MSL

(km

D3 TheonlyValleyOutletmassinandaroundtheKathmanduvalleywiththeregionalfldithdddititbl

AM

nce

) AM

nce

D3 The only Valley OutletBagmatiRiver Gorge flowsduringthedryseasonandrecommendssitessuitable

fil/lbllbkdttiPa)

Pa)

(m)

stan

n (m)

stan

forregional/globalaerosolbackgroundconcentrationtWeakStability e (hP

(hP

on (

h Dis

tion

Dis

measurement.StableLayer(1km)

Weak Stability

ssure

sure

vatio

orth

evat

rth

Stable Layer(~1km)

Pres

Press

Elev

th-N

n Ele

Nor

P P

in E

Sout

rrain

uth-

View in AutumnHimalayasrrai S

Ter

Sou

Tihiht()AMSL

yC TeS

Terrain height (m) AMSL3DTopographicViewofKathmanduValleyandItsSurroundingsShllthtl

CB

3‐D Topographic View of Kathmandu Valley and Its Surroundings.()

Shallow southwesterly

hhllfl()dd(l) BhimsenTower (54m high)Northwest‐Southeast cross‐sectional plot of potential temperature (contours) and wind vector (along A—B)

S 17:45 LST West-East Distance (km)West-East Distance (km)

KathmanduremainrelativelycleanduringAutumn

()()Near surface wind at 20:45 LST

Kathmandu remain relatively clean during AutumnConceptual flow diagram

Vtildiifllttiltiita)

Vertical dispersion of pollutants in late morning winter

(hPa

Himalayan range as seen from Kathmanduure (

Hundreds of emitters in operation

ressuPr

SL

m)

AM

e (km

(m)

ance

SodarsiteNthtlflbthtl ion

ista

Northwesterly flows above southwesterly

evati

th D

Southwest‐Northeast cross‐sectional plot of potential temperature ()()

Photographs of wind/dust storm (upper left picture) and highly  Ele

Nort

Smokeflowpatternintheafternoon Fogandpollutant’slayerblanketingtheKathmanduValley(contours) and wind vector (along C—D)localized destructions caused by wind storm in last March.

rain

uth-N

Smoke flow pattern in the afternoon Fog and pollutants layer blanketing  the Kathmandu Valley 

2GllitiftfKthdll•Bothsouthwesterlyandnorthwesterlyshowthenatureofthecooldensity•Therelativelycoolersouth‐westerlycappedbythewarmer Terr

Sou

2.   General climatic feature of Kathmandu valleyyyy

flow;theyintrudeintothemixedlayerdevelopedovertheKathmanduyyppy

northwesterlyandthedevelopmentofstablelayeraloftjustT S

TheKathmanduvalleypossessesawarmtemperatesemi‐tropicalandvalley.abovethesurroundingmountaintopsthatcoversthewhole TheKathmanduvalleypossessesawarmtemperatesemitropicalandseasonableclimate.Thewinterclimateischaracterizedasdrywithan•Thesouthwesterlyisdrivenbyacombinationofbothupslopeandplain

Kathmanduvalleyandbeyondsetsthebasicmeteorological yaveragemaximumandminimumtemperaturesof17and2°C,

•Thesouthwesterlyisdrivenbyacombinationofbothup‐slopeandplain‐to‐plateauwinds

backgroundforairpollutiontransportoverthevalley. gp,respectively.Duringthewinterseason,thevalleyremainsmostlyclear

to‐plateauwinds.•Thislayeringflowstructureoverthevalleyseverelylimitsthe pyg,yy

initsskieswithcalmorwindlessnightsfollowedbyearlymorning•ThenorthwesterlyexecuteahydraulicjumplikeflowanditridesovertheThislayeringflowstructureoverthevalleyseverelylimitstheverticaldispersionofpollutantsandleadstotheformationof WestEastDistance(km)

densefoglingeringupto09or10LocalStandardTime(LST).Verycoolsouthwesterlythedepthofwhichisabout250m.verticaldispersionofpollutantsandleadstotheformationofmultiplelayeringofpollutants.

West-East Distance (km)

gentlewindroutinelystartstoblowclosetothenoontimeand•Thewindstormgenerallyoccurslateafternoonandearlyeveningthatmultiplelayeringofpollutants.

Thidllldl700800bhNighttime Wind Fields at 02:45 LST at 150m AGL Near surface Potential Temperature at 16:45 LST

7ObservedLocalFlowCharacteristicsinandAroundtheValley LocalFlowsandObservedPollutantDistribution continuetilltheevening.ThesurfacewindspeedshavebeenfoundtoThewindstormgenerallyoccurslateafternoonandearlyeveningthatcoincideswiththedevelopmentofstablelayerjustabovethesurrounding•Themixedlayergenerallydevelopsupto700to800mabovethe

llflithftdithd

7.   Observed Local Flow Characteristics in and Around the Valley  Local Flows and Observed Pollutant Distribution

becalm(<1ms‐1)forabout75%ofthetimeofadaywithmax.windpyjg

mountaintops.valleyfloorintheafternoonduringthedryseason.Wind Speed at Thankot (March)

10.01-Mar2M

Wind Speed at NAST (March)6.01-Mar

Wind speed at western mountain passWind speed at southern area

speedgenerallyaround5ms‐1intheafternoon,butcouldreachashighp

DEmissionSourceDistributioninDrySeason9.0

2-Mar3-Mar4-Mar

2-Mar3-Mar4-Mar

as15ms‐1inthelatespring.SpringmonthsarecharacterizedbyD.   Emission Source Distribution in Dry Season8.0

a5-Mar6-Mar7-Mar

5.04Mar5-Mar6-Mar7Mar

showeryandrelativelywindyweather,increasinglyhigherhumiditydhdihilhilWidNOTSP SO

7.0

7-Mar8-Mar9-Mar10Mar40

7-Mar8-Mar9-Mar10M

andpre‐monsoonthunderstormswithoccasionalhail.Winterandlihditthtidth

NOxTSP SOx )6.0 m/s)10-Mar

11-Mar12-Mar

4.0

m/s)10-Mar

11-Mar12-Mar

earlyspringshowersmaydepositsnowonthemountainsaroundthedfthllThidttldftill(km

m)5.0 peed (13-Mar

14-Mar15-Mar3.0 peed (m

13-Mar14-Mar15-Mar

edgesofthevalley.Thewindpatterns,cloudformation,valleyventilationvisibilityaswellastheairmassdispersioncharacteristicsnce (

e (k

4.0

Wind sp15Mar

16-Mar17-Mar18-MarW

ind Sp15Mar16-Mar17-Mar18-Mar

ventilation,visibilityaswellastheairmassdispersioncharacteristicsoverthevalleyindryseasonappearsdistinctlydifferentfromthewetAil stan

ance

3.0

W18-Mar19-Mar20-Mar21M

2.0

W18-Mar19-Mar20-Mar21Mar overthevalleyindryseasonappearsdistinctlydifferentfromthewet

seasonThesummermonsoonoccursaseasterndisturbancesTheAprilApril

h Dis

Dista

2.021-Mar22-Mar23-Mar

10

21-Mar22-Mar23-Mar24M season.Thesummermonsoonoccursaseasterndisturbances.The

annualrainfallgenerallyexceeds1300mmofwhich70to80%rainfallsorth

rth D

1.024-Mar25-Mar26-Mar

1.024-Mar25-Mar26-Mar

annualrainfallgenerallyexceeds1300mmofwhich70to80%rainfallsduringthesummermonsoonmonthsMonsoonrainshaveatendencyh-N

-Nor

0.0

000000000000

26Mar27-Mar28-Mar29Mar0.0

27-Mar28-Mar29-Mar duringthesummermonsoonmonths.Monsoonrainshaveatendency

tobemorefrequentatnightwhereasthedaylighthoursaremostlySout

uth-0:00

2:00

4:00

6:00

8:00

10:00

12:00

14:00

16:00

18:00

20:00

22:00

LlStddTi(h)

29-Mar30-Mar31-MarA

0:00

2:00

4:00

6:00

8:00

10:00

12:00

14:00

16:00

18:00

20:00

22:0029Mar30-Mar31-MarAverage tobemorefrequentatnightwhereasthedaylighthoursaremostly

sunnyOvercastisratherrareoverthevalleyThedryseasongenerally

S

SouLocal Standard Time (hr.)AverageLocal Standard Time (hr.)Average

sunny.Overcastisratherrareoverthevalley.Thedryseasongenerallypersistsfor9months(OctobertoJune)withmuchlessprecipitation

Wind Speed at Babarmahal (March)4.51-Mar

2M

Wind Speed at Budanilakantha (March)5.01-Mar Wind speed at northern area Wind speed at central area persistsfor9months(OctobertoJune)withmuchlessprecipitation

(only10–20%oftheannualtotal).4.0

2-Mar3-Mar4-Mar4.5

a2-Mar3-Mar4-Mar (only1020%oftheannualtotal).

35

4.05-Mar6-Mar7-Mar4.0

4-Mar5-Mar6-Mar7Mar

3.   Purpose30

3.57Mar8-Mar9-Mar10Mar

3.5

7-Mar8-Mar9-Mar10M

•TounderstandthemechanismofdevelopmentoflocalflowsovertheKathmanduvalley25

3.0

(m/s)10-Mar

11-Mar12-Mar13M

3.0 m/s)10-Mar

11-Mar12-Mar

•TounderstandthemechanismofdevelopmentoflocalflowsovertheKathmanduvalley.Tdtdhifilltittdthidithll

2.5

peed (13-Mar14-Mar15-Mar2.5 peed (13-Mar

14-Mar15-Mar

•Tounderstandmechanismofairpollutiontransportandtheirdynamicsoverthevalley.Tdtdthltihibtthllfldftifthllttfildithll

FebruaryFebruary  WestEastDistance(km)

2.0

Wind S16-Mar

17-Mar18-Mar

2.0

Wind S15Mar

16-Mar17-Mar18Mar

•Tounderstandtherelationshipbetweenthelocalflowsandformationofthepollutantfieldsinthevalley.Thildldiibifdlifll’iihhilfl

West-East Distance (km)West-East Distance (km)1.5 W18-Mar19-Mar20-Mar21Mar

1.5

W18-Mar19-Mar20-Mar21M

•Toassessthespatialandtemporaldistributionsofdecouplingofvalley’sairmasswiththeregionalflows.ff21 21 MoreLargeScaleFlow

1.021-Mar22-Mar23-Mar24M

1.021-Mar22-Mar23-Mar

ObdNOdSOllfllthiltdll•Kathmanduvalleyremainscalmduringlateeveninguntil

•Toidentifythesuitablesitesforregionalbackgroundaerosolconcentrationmeasurement.NOx(kg-NO2 km-2day-1)TSP (kgkm-2day-1) SOx(kg-SO2km-2day-1) More Large Scale Flow0.524-Mar25-Mar26-Mar

0.524-Mar25-Mar26-Mar

•Observed NO2and SO2closely follows the simulated local fl

thenoonformingadeepcoldairlakeatnightthatmay

4Methodologyx2

EVisibleTransportProcesses 4.MethodologyNearSurfaceWindFieldsat14:45LST0.0

000000000000

26Mar27-Mar28-Mar29-Mar

0.0

000000000000

26Mar27-Mar28-Mar29Mar

flows. reach400minitsdepthintheearlymorning.4.MethodologyE.   Visible Transport Processes 4.   MethodologyNear Surface Wind Fields at 14:45 LST

0:00

2:00

4:00

6:00

8:00

10:00

12:00

14:00

16:00

18:00

20:00

22:0029-Mar30-Mar31-MarAverage

0:00

2:00

4:00

6:00

8:00

10:00

12:00

14:00

16:00

18:00

20:00

22:00

LlStddTi(h)

29-Mar30-Mar31-MarA •TheAprilconcentrationsaresignificantlyhigherthanthe •Intrusionofcoolerairmassesclosetothenoontimefrom

NagarkotHilltopLocal Standard Time (hr.)AverageLocal Standard Time (hr.)Average TheAprilconcentrationsaresignificantlyhigherthanthe

Februarybutthedistributionpatternremainsthesame. theIndianPlainandthewesternvalleythatmergeintoa

A.Air pollutionNagarkotHilltop

•UpwardtransportofsmokeatthefrontoflocalflowsrevealtheFebruarybutthedistributionpatternremainsthesame.Thismayindicatetheatmosphericconditionsdrivingthe•Diurnalvariationoftheobservedwindoverthevalleyfloorcanbecharacterizedwitha westerlyformingconvergencealongcentralwest‐east p

DtilfildtfNO2dSO2

Upwardtransportofsmokeatthefrontoflocalflowsrevealthepassageofthefrontclosetothenoontime.

Thismayindicatetheatmosphericconditionsdrivingthelocalflowsareratherstableduringthedryseasonandthus

longperiodofthecalmsituation,from20:00LSTto10:00LSTonthenextday,andonset line.•DetailfieldmeasurementofNO2andSO2,

dPM10kli

passageofthefrontclosetothenoontime.localflowsareratherstableduringthedryseasonandthuslocalflowstendtorepeatregularly

ofthewindataround12:00LST,whichcontinuestoaround18:00LST. •Thewarmernorthwesterlyflowsoverthecoolersouth‐andPM10atkeylocations

kkd•Thepollutantsreleasedintothesouthwesterlyaretrappedinits )

localflowstendtorepeatregularly.•Thecalmsituationcorrespondstothestablystratifiedcoldairlakeduringthenighttime, westerlyinthelateafternoon.•Emissionestimation1kmx1kmgridnet.shallowlayerbelow250mhighandmigratetowardtheeasternpartof T(m

)

•VeryhighconcentrationoftheNO2andSO2inAprilandtheunsetofwindrepresentsarrivalofacombinedvalleyandtheplain‐to‐plateaudfhhblldhhl

y•Combinedplain‐toplateauandvalleywindfromthe

•NumericalsimulationwithChemicalTransportModel.yggp

thevalleyT

on (

measurementcomparedtoFebruarysuggeststhewindsformtheneighboringvalleyandthesouthernplain.ThflhkblddiiliAbli

ppysouthernplain(southwesterly)andnorthwesterlyform

BMeteorologyNagarkotHilltop

thevalley.

KSatio

advectionofregionalpollutantsintothevalleywithlocal•Thepatternsofmeteorologyhavearemarkableday‐to‐daysimilarity.Anyabnormalitytitildldttlltiftti

p(y)ythewesternvalleystronglydominatetheflowsystemof B.MeteorologyNagarkotHilltop •Thenorthwesterlycapturestheurbanpollutantsinthewesternpartof Keva

flows.apparentinaparticulardayrarelyordoesnotatallcontinueevenfortwoconsecutived

thewesternvalleystronglydominatetheflowsystemofKathmanduvalley(K).

•SodarobservationusingMonostaticFlatArraySodar.yppp

thevalleyandflowsoverthesouthwesterlylayer. n Eldays.

6SitfRilBkdAl

Kathmanduvalley(K).•Flowsplitintheeasternvalley(S)appearsratherweak

•SurfaceobservationsinandaroundtheKathmanduvalley.thevalleyandflowsoverthesouthwesterlylayer.

ain6.    Sites for Regional Background Aerosol 8Conclusions

Flowsplitintheeasternvalley(S)appearsratherweakanddoesnotpenetrateKathmandu y

•NumericalSimulationoflocalflowswithMM5andWRF.•Asaresult,multiplepollutantlayersdevelopintheeasternareaofthe

TerrConcentration Measurement8.   Conclusions anddoesnotpenetrateKathmandu.

•LocalflowsappeartofollowtheterrainelevationKTMvalleyclosetothesunset.

Te

TribhuvanUniversityNagarkotHilltop•LocalflowsappeartofollowtheterrainelevationKTMvalley(K)1350mSunkoshi(S)800mTrishuli(T)600mvalleyclosetothesunset.TribhuvanUniversityNagarkotHilltop•Kathmanduvalleyregularlydevelopsadeepcalmcoldairpoolduringthenighttime. valley(K)1350m,Sunkoshi(S)800m,Trishuli(T)600mvalleys;southernplain(~100m)AMSL

FinestDomain(D3) 45050FChilTtCllti

HattibanHilltop•Twocharacteristicslocalflows(southwesterlyandnorthwesterly)regularlyintrudeintothe valleys;southernplain(~100m)AMSL.Itittttiididti Finest Domain (D3) 450TirshuliF.    Chemical Transport Calculations

hflllfllfll

pvalleyclosetothenoontimeandcontinuetilltheevening. •Intermittentmountainwindsmayorganizedananti‐

lkikfltthllb150Daytime Characteristic of Pollutant Transport Role of Local Flows for Pollutant Transport•Thereislittleday‐to‐dayvariationinthelocalflowsoverthevalleyduringthedryseason.clockwiseweakflowsystemoverthevalleyabove150mkihibllidl

07:00LST12:00LST15:00 LST15:00 LSTyyygy

•Thelocalflowsshowthenatureofcooldensityflowsintrudingintotheweaklydevelopedkeepingtheairmassbelowalmostwindless.

hdlll/bdl07:00 LST12:00 LST

m)

m) 36040Mt. Shivapuri

WestEastDistance(km)

ygypmixedlayeroverthevalley. •Kathmanduvalleyexecutesplateau/basindualnature

(km

(kmTNWest‐East Distance (km)mixedlayeroverthevalley.•Therelativelywarmernorthwesterlyflowsoverthecoolerandshallowsouthwesterly

duringdayandnighttime.

ce   

ce (

BUMtNagarjunFulchokiMountaintop

Therelativelywarmernorthwesterlyflowsoverthecoolerandshallowsouthwesterlyduringthelateafternoonleadingtotheformationofinternalthermalboundarylayersin BComparisonwithObservation

anc

tanc

Mt. EverestNEPAL 27030

TL MH BAMt. Nagarjunpduringthelateafternoonleadingtotheformationofinternalthermalboundarylayersin

thecentralandeasternarea

B. Comparison with Observation

Dist

Dist N E P A L 27030

TIA THBTMtNagarkot

Kathmanduthecentralandeasternarea.Thifth3kbthlllldd

th D

th D

KathmanduTIA

KLBS MA

BTDAMt. NagarkotBhaktapur D3

•Theupperairfrommorethan3kmabovethemeansealevelregularlycomesdownandthllflithft

Nort

Nort

BKTI KRPUBS MABhaktapur

Patan D3sweepsacrossthevalleyfloorintheafternoon.f

h‐N

th‐N

D2 18020BN BK

IM HCNK Mt. Champadevi•Thedownslopewindscanorganizeaweakflowsystematabout150mabovethevalley •FulchokiMountaintop(2762AMSL),locatedinthe

X2 outh

out D2 18020LU IM HC

Banepafloorthatslowlybuteffectivelyinducemassexchangeinthelowerlayerofcoldairmass southeasternedgeoftheKathmanduvalleyappearstobe

18:00LST 15:00LSTX2

SoSo

CH

Banepa•Duringthenighttimepollutantaccumulatesintheshallowlayer.duringthenighttime. mostsuitablefortheregionalaerosolmeasurement.

18:00 LST 15:00 LST CHRiverGorge

Duringthenighttimepollutantaccumulatesintheshallowlayer.

lldiidlhidllfi•Kathmanduvalleyregularlyflushesitsnighttimestagnatedairmasstotheeastern •ThesitessuchasNagarkotHilltopandHattibanHilltopand

ibhiilbbliblf 9010Mt.FulchokiRiver Gorge•Pollutantsdisperserapidlyasthemixedlayerevolvesaftersunrise

ttdiiittitthneighboringvalleyintheearlyafternoonthatfurthermovestowardstheHimalayas. TribhuvanUniversityalsoappeartobereasonablysuitablefor

itithilbkdttifi

Kthdll INDIAMt. Fulchokiattendingaminimumconcentrationatthenoon.

ggyyy•Thewesternpartofthevalleyappearstobefreefromdaytimestratification.

monitoringtheregionalbackgroundconcentrationofspecieslikdiit Kathmandu valley D1•Intrusionofthecoolersouthwesterlytrapsthepollutantreleasedwithin

pyppy•Occasionaldecouplingofvalley’ssurfaceairmassdoesnotsustainformorethan24hours.

likeradioxenonisotopes.

360

yppitsshallowboundaryrapidlybuildingupnearsurfaceconcentration.

Occasionaldecouplingofvalleyssurfaceairmassdoesnotsustainformorethan24hours.•Thepollutantsfromtheeasternvalleyintheeveningremainfloatingoverthewholevalley

WtEtDit(k)901802703604501020304050•Thefictitiouspollutants(X1andX2)concentrationdistributioncontours

Thepollutantsfromtheeasternvalleyintheeveningremainfloatingoverthewholevalleyatabout250mabovethevalleyflooruntilthedevelopmentofmixedlayernextday Akldt West‐East Distance (km) West‐East Distance   (km)•Thefictitiouspollutants(X1andX2)concentrationdistributioncontours

clearlydemonstratethedoublelayeringstructureofthesouthwesterlyatabout250mabovethevalleyflooruntilthedevelopmentofmixedlayernextday. Acknowledgment:

•TohsihiroKitadaToyohashiUniversityofTechnologyJapanMM5/WRF/CTM Simulation Domain System D1, D2, and D3 (left) and Air Quality Sampling Sites (Black Circle).

clearlydemonstratethedoublelayeringstructureofthesouthwesterlyandnorthwesterlywindsandformationofthelayeredpollutantsover

•TohsihiroKitada, Toyohashi University of Technology, Japan•HarryMileyPacificNWNationalLaboratoryUSA

Blue and Red boxes show emission areas (right) for the hypothetical species X1 and X2,  respectively.andnorthwesterlywindsandformationofthelayeredpollutantsoverthecentralandeasternareaoftheKathmanduvalley

•Harry Miley, Pacific NW National Laboratory, USA.•AndersRingbonSwedishDefenseResearchAgencySwedenContact:regmirp@hotmailcom (g)ypppythecentralandeasternareaoftheKathmanduvalley.•Anders Ringbon, Swedish Defense Research Agency, Sweden.Contact:  regmi_rp@hotmail.com