Week 3

Question 1

What does the box represent in a box model?

Answer 1

Small parcel of air or the entire globe

Question 2

What do we assume within a box model?

Answer 2

That the box is well mixed

Question 3

What is another way of thinking of the lifetime t of X in the box?

Answer 3

The average time that a molecule of X remains in the box

Question 4

Equation to workout lifetime t of X in the box

Answer 4

t= m/Fout+L+D

Question 5

What does P represent in atmospheric box?

Answer 5

Chemical production

Question 6

What does L represent in box model?

Answer 6

Chemical loss

Question 7

What does E represent in box model?

Answer 7

Emission

Question 8

What does D represent in box model?

Answer 8

Deposition

Question 9

What is lifetime?

Answer 9

The average/median time that a molecule of X remains in the box

Question 10

Residence time

Answer 10

When the loss terms are physical loss e.g. Fout or D

Question 11

Generalised chemical rate constant is chemical loss rate is:

Answer 11

Fout+ L +D=(kout+kL+kD)=km

Question 12

Chemical rate constant equation:

Answer 12

kout=1/tout

Question 13

What is the concept of mass balance?

Answer 13

Mass is conserved- what is produced in one place must be lost elsewhere

Question 14

Sources in a box model

Answer 14

Inflow (Fin), Emission and Chemical production

Question 15

Sinks within box model:

Answer 15

Chemical loss, deposition and Outflow (Fout)

Question 16

Overall Source rate Equation:

Answer 16

S = Fin+E+P

Question 17

The cycling of what compounds are central to the production of O3

Answer 17

NOx and HOx and VOCs

Question 18

Expression describing the steady state concentration of CO from the oxidation background CH4 if the mean rate constants for CH4 and CO by OH in the atmosphere are K1 and K2 respectively

Answer 18

K1[CH4][OH]=K[CO][OH]

Question 19

What are initiation reactions?(HOx)

Answer 19

Reactions producing HOx (OH and HO2) from non HOx species introducing new radicals to system

Question 20

What are propagation reactions?(HOx)

Answer 20

Reactions that inter convert OH and HO2 maintaining HOx pool without net production loss

Question 21

What are termination reactions? (HOx)

Answer 21

Reactions removing HOx radicals from system forming stable products

Question 22

Low NOx termination

Answer 22

Dominated by HOx self reactions or reactions with peroxides

Question 23

High NOx termination

Answer 23

Terminsation involving NOx species e.g. nitric acid formation

Question 24

Equation- Initiation for HOx

Answer 24

O(1D)+H2O –> 2OH

Question 25

Equation Low NOx termination

Answer 25

HO2 + HO2 --> H2O2 + O2

Question 26

Equation High NOx termination

Answer 26

NO2 + OH + M --> HNO3

Question 27

Equation propogation examples HOx

Answer 27

CO + OH --> HO2 + CO2 HO2 + NO --> OH + NO2 NO2 +OH + M --> HNO3

Question 28

Which compounds work together to oxidise CO and CH4 leading to ozone production (O3)

Answer 28

HOx and NOx

Question 29

Propagation steps without NOx-

Answer 29

CO + OH* → CO₂ + H* H* + O₂ + M → HO₂* + M

Question 30

Rate law - first order reaction

Answer 30

Rate= k[A] in s^-1

Question 31

Rate law - second order reaction

Answer 31

Rate= k[A]^2 or k[A][B]

Question 32

Lifetime- first order reaction

Answer 32

t=1/k

Question 33

Lifetime - second order reaction

Answer 33

t=1/k[A]o

Question 34

Sources of NOx

Answer 34

* Fossil Fuel Combustion * Transport from stratosphere * Biomass burning * NH3 oxidation * Lightning * Aircrafts

Question 35

Production of Thermal NOx via Zeldovich mechanism

Answer 35

O2 <--> O +O O+N2 <--> NO + N N + O2 <--> NO + O

Question 36

Why are NO and NO2 part of the NOx family?

Answer 36

Because they cycle rapidly between each other

Question 37

Equations - cycling of NO and NO2

Answer 37

NO + O3 --> NO2 + O2 NO2 + hv --> NO + O --> O + O2 --> O3

Question 38

Daytime sink of NOx- main loss path

Answer 38

NO2 + OH + M --> HNO3 + M

Question 39

Why is HNO3 lost by precipitation

Answer 39

It is soluble

Question 40

Levels of OH at nightime

Answer 40

Low- other oxidants dominate

Question 41

Storage of NOx- PAN

Answer 41

PAN acts as a reservoir = temporary transport

Question 42

How to HOx and NOX work together to produce ozone?

Answer 42

HOX- initiates oxidation of VOCs or CO and peroxy radicals react with NO converting it to NO2 which then undergoes photolysis to form O3

Question 43

Net effect of VOCs+NOx to form O3

Answer 43

VOCs (or CO) + NOₓ + sunlight → O₃ + other oxidized products

Question 44

Levels of O3 at nightime

Answer 44

O3 is Scarce meaning other oxidants dominate

Question 45

Difference between PAN and HNO3 for NOx transport

Answer 45

PAN is a reservoir - temporary storage whereas HNO3 is more of a permanent sink

Question 46

How is PAN formed

Answer 46

From the oxidation of carbonyl compounds in the presence of NOX

Question 47

Stability of PAN vs HNO3

Answer 47

PAN is stable at colder temperatures- upper troposphere HNO3 is not stable at altitude

Question 48

Transport role of PAN vs HNO3 for O3

Answer 48

PAN is a major carrier of NOx over distance HNO3 transport of NOx is minimal

Question 49

How can temperature effect PAN?

Answer 49

PAN can thermally decompose- at 295k lifetime= 1 hour and at 250K lifetime is several months