O’LEVEL CHEMISTRY: MCQ

Berko Sierau

Description

• exposé

Model Questions Biochemistry Olympiad - 2010 University of Dhaka S.S.C./O-level (A Bengali version of the question paper will be provided in the final examination) Directions: Each of the questions or incomplete statements below is followed by four suggested answers or completions. Select the best answer in each case. Answer All questions: Question 1: Matter has ___________. (a) no mass but occupies space (b) mass but occupies no space (c) mass and occupies space (d) no mass and occupies no space Answer: (c) Question 2: In

• transport chain
• lead sulphate
• kinetic energy of molecules
• base pairs of dna
• lactic acid
• plant cells
• reaction
• carbon dioxide
• answer

Sujets

• Exposé
• Answer
• Energy
• Réaction
• Molécule
• Carbón

Informations

• Publié par: ribul
• Nombre de lectures: 30
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

weather modification

Weather modification

Nucleation scavenging

Cloud chemistry and weather modification

Cloud chemistry and

Impaction scavenging

Berko Sierau (IACETH)

Cloud chemistry and weather modification

Weather modification

Impaction scavenging

Weather modification

In- and near-cloud processes

Nucleation scavenging

Berko Sierau (IACETH)

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Dec 20, 2011

Graphic by Victor Koen; Courtesy of Ana Cirisan

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Impaction scavenging

Nucleation scavenging

Berko Sierau (IACETH)

Cloud chemistry

Cloud chemistry related to aerosols

Here concentrate only on (2)

Dec 20, 2011

Cloud chemistry and weather modification

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[Courtesy Dean Hegg]

Cloud chemistry

1.Chemical constituents found in cloud and rain water and in meltwater of snow 2.Mechanism by which the constituents enter cloud and precipitation particles, both inside and below a cloud (in-cloud and below-cloud scavenging) 3.Mechanism by which these constituents are deposited on the ground.

Cloud chemistry

Cloud chemistry

Nucleation scavenging

Impaction scavenging

Weather modification

Scavenging of aerosol particles by cloud drops, raindrops and ice particles Impaction scavenging (cloud droplet, rain drop or ice particle already I exists), only mechanism to act below cloud base Nucleation scavenging (cloud drop develops) realized as efficiency. I E.g. about 80-99% of sulfate aerosol mass is scavenged, and 10-90% of the aerosol number. All aerosols withr>0.2µm undergo nucleation scavenging. What is more important for scavenging?Rain or snow? I

I What is more important for scavenging?Nucleation or impaction scavenging?

Berko Sierau (IACETH)

Cloud chemistry

Cloud chemistry and weather modification

Nucleation scavenging

Impaction scavenging

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Weather modification

Nucleation scavenging Nucleation scavenging: Activation and subsequent growth of aerosol I particles that become activated. Mass scavenging ratioF m : I C m,cloud C m,0 −C m,int F m (1)= = C m,0 C m,0 where C m,0 is the concentration (mass per volume of air) before cloud formation and C m,int is the interstitial aerosol conc. I F m has been determined from measurements of sulfate aerosols to be between 0.1 and 11,why? I Number scavenging ratioF N : N 0 −N int F N = (2) N 0 whereN 0 is the aerosol number conc. before cloud formation and N int is the interstitial aerosol number conc. Berko Sierau (IACETH) Cloud chemistry and weather modification Dec 20, 2011 5 / 26

Cloud chemistry

Berko Sierau (IACETH)

Nucleation scavenging

Impaction scavenging

Cloud chemistry and weather modification

Weather modification

Dec 20, 2011

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Cloud chemistry

Nucleation scavenging

Impaction scavenging

Cloud processing [Wurzler et al., JGR, 2000]

Berko Sierau (IACETH)

Cloud chemistry

Cloud chemistry and weather modification

Nucleation scavenging

Impaction scavenging

Impaction scavenging

Weather modification

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Weather modification

Brownian diffusion (B) I Thermophoresis (Th): A gradient in molecular energies that is I associated with a macroscopic temperature gradient.Thcause aerosols to diffuse to an evaporating colder droplet (aerosol sink) Diffusiophoresis (Df): occurs in the presence of a gradient of vapour I molecules.Dfcause aerosols to diffuse away from an evaporating cloud droplet and vice versa for a growing droplet I Inertial capture (H): 1.Gravitational or hydrodynamic inertia due to large terminal velocity of collector drop. Air is not able to move aerosols around drop. 2.Turbulent shear and turbulent inertial capture.

Berko Sierau (IACETH)

Cloud chemistry

Cloud chemistry and weather modification

Nucleation scavenging

Scavenging efficiencies

Impaction scavenging

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Weather modification

I Loss of aerosols with radiusrper unit volume of air by impaction scavenging: Z ∂ −n(r,t) =n(r,t)K(r,a)n d (a,t)da(3) ∂t wherea= droplet radius,r= aerosol radius,n d = cloud droplet conc.,K = impaction kernel I Define scavenging coefficient (Λ) [1/s]: Z 1∂ Λ(r,t)≡ −n(r,t) =K(r,a)n d (a,t)da(4) n∂t

I Local rate of removal is treated as a first-order process, i.e. scavenging is irreversible: rate of removal depends linearly on the aerosol conc. independent of previously scavenged material. I Thus the scavenging problem boils down to determine the different collection kernels:K B ,K Th ,K Df ,K H .

Berko Sierau (IACETH)

Cloud chemistry and weather modification

Dec 20, 2011

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Cloud chemistry

Nucleation scavenging

Impaction scaven

in

Impaction scavenging

P&K 17-12

Weather modification

3 Figure: Collection kernel (cm /s) for a water drop (a=10µm) collecting an aerosol particle by Brownian diffusion (B), thermophoresis (T), diffusiophoresis (D) and net effect (N) for 100.3% RH (g), 98% RH (e). dashed: negative values

Berko Sierau (IACETH)

Cloud chemistry

Cloud chemistry and weather modification

Nucleation scavenging

Hydrodynamic

Impaction scavenging

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Weather modification

inertia (= Aerodynamic effects)

I Start with the collection kernelK H analogous to the one introduced in eq. (10) of the warm cloud microphysics lecture. I Neglect fall velocity and size of the aerosol particle (AP)

2 K H =πa V t (a)E(r,a)

(5)

WhereE(r,a) = fraction of AP with radiusrcontained within the I collision volume of a drop with radiusa;V t (a) = fall velocity of drop EAll AP in collision volume will be collected by the drop.= 1: I NormallyE<1, butE>1 is possible if electrical forces are present. I If AP don’t stick to drops, thenE=E coll ∙E stick assume. Here E stick = 1.

Berko Sierau (IACETH)

Cloud chemistry

Cloud chemistry and weather modification

Nucleation scavenging

Impaction scavenging

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Weather modification

Empirical collision efficiencyE [Seinfeld&Pandis, Eq. 20.56] h i 4 1/2 1/3 1/2 1/2 E= 1 + 0.4Re Sc+ 0.16Re Sc(6) ReSc     3/2 ∗ r St−S rµ a 1/2 +4 (1 + 2Re) + (7) ∗ aµ w a St−S+ 2/3 where 1.2 + 1/12ln(1 +Re) ∗ S= (8) 1 +ln(1 +Re) Re= Reynolds number of raindrop: aV t ρ a Re= (9) 2µ a Sc= Schmidt number of the aerosol particle: µ a Sc= (10) 2ρ a r St= Stokes number of the aerosol withτ= characteristic relaxation time 2τ∗(V t −v t )m w C c St= ;τ= (11) a6πµ a a Berko Sierau (IACETH) Cloud chemistry and weather modification Dec 20, 2011 12 / 26

Berko Sierau (IACETH)

Nucleation scavenging

Cloud chemistry and weather modification

(12)

Weather modification

Nucleation scavenging

Scavenging by rain

E

= =

−3−7 6∙10 + 4.1∙0 (10 + AP= 0.01µm) −5−4 9∙110 + .4∙10 + 0 (AP= 1µm)

=

E

Impaction scavenging

Impaction scavenging

Berko Sierau (IACETH)

Cloud chemistry

Nucleation scavenging

Impaction scavenging

Weather modification

(13) (14)

Weather modification

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Cloud chemistry and weather modification

Dec 20, 2011

(Slinn, 1977)

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Collision efficiencyE

Cloud chemistry

where the terms in eq. (13) are: I 1.Brownian diffusion 2.Interception: Aerosol hits raindrop if it is sufficiently large for contact to occur when streamlines take it around raindrop (capture from the side). This normally occurs when the aerosol is located within the collector drop radius 3.Inertial impaction (capture from below)

Cloud chemistry

Berko Sierau (IACETH)

I Characteristic minimum inE(called Greenfield gap): for accumulation mode aerosols which are too large to have an appreciable Brownian diffusivity, yet too small to be collected effectively by impaction or interception.

Collision efficiencyE

h i 4 1/2 1/3 1/2 1/2 1 + 0.4Re Sc+ 0.16Re Sc ReSc     3/2 ∗ rµ a r St−S 1/2 +4 (1 + 2Re) + ∗ aµ w a St−S+ 2/3

Cloud chemistry and weather modification

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I Example for 1 mm diameter raindrop and an aerosol particle of 0.01µm and 1µm: ∗ −5−1−1 Re = 152, S = 0.6, T = 273 K,µ a = 1.7 10skg m , I −3−1−1 µ w = 1.8 10kg m s:

Berko Sierau (IACETH)

Impaction scavenging

I A snowflake of 640µm maximum length corresponds to a droplet with a melted radius r=108µm (from P&K Table 2.2a using P1a shape) I Radius r (aerosol) = 0.1µm and RH=95% −4 I E(r,a) rain ∼8×10 −2 E(r,a) snow ∼10 I I Using the empirical fall velocities of rain and melted snow: v(rain with a radius of 108µm) = 0.9 m/s I I v(snow with a melted diameter of 216µm) = 0.5 m/s 2 I Yields collection kernels (K H =πa V t (a)E(r,a)) of: −11 3 rain:K H = 2.6×10m/s I −10 3 snow:K H = 1.83×10m/s I I For this example the snow crystal is 7×as efficient as a water drop for scavenging of a 0.1µm aerosol particle.

Weather modification

Cloud chemistry and weather modification

Nucleation scavenging

Weather modification

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snow

Scavenging by rain vs.

Berko Sierau (IACETH)

Cloud chemistry

Cloud chemistry

Scavenging by snow

Dec 20, 2011

Cloud chemistry and weather modification

Nucleation scavenging

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Weather modification

Dec 20, 2011

Impaction scavenging

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Impaction scavenging

Cloud chemistry

Scavenging by

snow (Slinn, 1977)

Nucleation scavenging

Cloud chemistry and weather modification

Berko Sierau (IACETH)

seeding

Cloud

Nucleation scavenging

Berko Sierau (IACETH)

Cloud chemistry and weather modification

Figure:www.urbanhonking.com/universe/SeedingEffects.jpg

Impaction scavenging

Impaction scavenging

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Berko Sierau (IACETH)

Weather modification

Dec 20, 2011

Weather modification

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Cloud chemistry and weather modification

Berko Sierau (IACETH)

Cloud chemistry

Nucleation scavenging

Cloud chemistry and weather modification

Cloud chemistry

Nucleation scavenging

modification

Dec 20, 2011

Weather

Weather modification

Rain/snow

How to modify the original cloud? I

Hail suppression (prevention of hail damage) I I Rain/snow enhancement (crops/water) I Fog dissipation (airports) Cloud dissipation (outdoor events) I

enhancement

I How?

What must be changed? I

Why? I

Impaction scavenging

Cloud chemistry

Impaction scavenging

What must be changed?

Cloud

Cloud chemistry and weather modification

Nucleation scavenging

Cloud chemistry

Snomax

Berko Sierau (IACETH)

How?

How to modify the original cloud?

Nucleation scavenging

Cloud chemistry and weather modification

Impaction scavenging

How to modify the original cloud?

Berko Sierau (IACETH)

Cloud chemistry

dissipation

Weather modification

Dec 20, 2011

Weather modification

I

Why?

I

I

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I

dissipation

I

I

I

I

Fog

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Cloud chemistry and weather modification

Impaction scavenging

Figure: www.kennislink.nl/upload/107464 962 1075386229670−sneeuw snomaxkanon.JPG

Berko Sierau (IACETH)

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Dec 20, 2011

Weather modification

Dec 20, 2011

What must be changed?

How?

Cloud chemistry

Why?

Nucleation scavenging

Cloud chemistry

Nucleation scavenging

Does it work?

Impaction scavenging

Weather modification

I China has 35,000 people in the “Weather modification” industry I Mexico and Russia have built cloud seeding “plants”; they estimate an annual increase in rain of 30-35% I This suggest that weather modification works. But is that true? I Look at hail suppression. How would we tell if it works or not?

Berko Sierau (IACETH)

Cloud chemistry

Cloud chemistry and weather modification

Nucleation scavenging

To consider...

Impaction scavenging

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Weather modification

Are people making a profit from weather modification impartial in I their claims that it has a clear cause-and-effect? I Is it better to do nothing than to do something? How can be decouple variability from cause-and-effect? I Where should limited reach money be spent? I What are the drawbacks? I

Note: these are no answers, only considerations

Berko Sierau (IACETH)

Cloud chemistry and weather modification

Dec 20, 2011

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