eas6792eas6792air pollution meteorologyair pollution meteorology

Term PaperTerm Paper

Diurnal vertical concentration Diurnal vertical concentration profile of CO in an urban profile of CO in an urban

environmentenvironment

byby

BurBurççak Kaynakak Kaynak

IntroductionIntroductionAir quality in urban areas

connection between air pollution and human health emissions and concentrations of primary pollutants

shows extremely strong spatial and temporal variations

characterization of urban air pollution is fairly complicated

CO and other pollutants may concur in several chemical processes,

contributing to the formation of other pollutants (o3)

have injurious effects on the health damage vegetation and materials, alter temperature and wind distribution,

generally affect urban climates

IntroductionIntroduction

Concentrations of pollutants in urban areas balance between pollutant accumulation and dispersion

Strong gradients of gaseous and particulate pollutants (in the vertical and horizontal direction) mainly due to

activities of emission sources rapid mixing dilution of emissions

CO is a good indicator to understand the dispersion and advection processes in the urban areas

IntroductionIntroductionThe diurnal vertical profile of CO in a suburban area will be calculated by Euler explicit method and compared with the actual measurements

assumptions:velocity (u) and eddy diffusion coefficient (Kz) profiles for typical urban atmospherediurnal emission profiles of CO, scaled according to the max. emissionsboundary layer heights for 2 cases: day time(1200m), night time (200m)no sources or sinks (long lifetime of CO)

Measurements for Measurements for comparisoncomparison

“Wintertime vertical profiles of air pollutants over a suburban area in central

Taiwan” (Chen et al., 2002.)

Vertical CO profiles through 1200 m

Assumptions_Assumptions_input datainput data

0

0.2

0.4

0.6

0.8

1

1.2

0 3 6 9 12 15 18 21 24

Local time

emis

sio

n r

atio

(er

/er_

max

)

Measurements_Measurements_CO diurnal CO diurnal profilesprofiles

Measurements_Measurements_CO vertical CO vertical profilesprofiles

System equationSystem equationδC/δt = Kz(z)*δ2C/δz2 +u(z)*(Co-C)/ δz

 

By using Taylor series, at steady state 

0 = Kz(z)[ C(z+Δz)-2 C(z)+ C(z-Δz)]/ Δz2 + (u(z)C(z))/Δz

 

say C(z+Δz) =Ci+1C(z) =CiC(z-Δz) =Ci-1

 

0 = Kz i[ Ci+1 - 2Ci + Ci-1]/ Δz2 + (u i Ci)/Δz

So Ci+1 = [ 2Ci - Ci-1] - (u i Ci)*Δz/Kz i

Findings_Findings_vertical profile for day vertical profile for day @max.em.@max.em.

0

200

400

600

800

1000

1200

0 200 400 600 800 1000 1200

CO (ppm)

z (m

)

disp. without u

u addition

2 nd disp.

Expected outcomesExpected outcomesthe average vertical profile of vehicular pollutant conc.s the general exponential form (rather than simple exponential function or Gaussian distribution)

Maximums morning hours w/ relatively high traffic and low mixing

Good correlation between traffic load and mechanical mixing

Decreasing CO concentrations with height

ProblemsProblems

The concentrations are going to “zero” or “-” values immediately

Possible reasons could be:The explicit method is unstableThe velocities assumed are too high that they swept all the COProblems in writing the algorithm or in coding in the Mathlab program

Future workFuture work

Finding the problems in the solutionObtaining a reasonable vertical profileComparison of the day and night profilesEffect of the traffic emission loads on vertical profilesComparison of the numerical solution with the measurements in the reference noted

Thanks for listening…any questions ???