Tropospheric Chemistry

Question 1

Why is O(1D) production slower in troposphere?

Answer 1

Narrower wavelength band that can photolyze to produce O(1D)

Question 2

What do we use to measure [OH] in troposphere?

Answer 2

Methylchloroform, CH2CCl3- only produced anthropogenically, banned in Montreal protocol, lifetime = 1/k[OH]

Question 3

Sinks of OH in troposphere

Answer 3

OH + X –> products

where X is non-radical reduced species

Question 4

Source of OH in troposphere

Answer 4

O3 + hv –> O2 +O(1D)

O(1D) + H2O –> 2OH

Question 5

Key difference between troposphere and stratosphere

Answer 5

lower O3 and O concentrations in troposphere, lower O(1D), lower energy photons

Question 6

Principal sink of NOx in the atmosphere - daytime

Answer 6

NOx + OH –> HNO3

only occurs in the daytime , not much OH at night

Question 7

Three NOx sinks at nighttime

Answer 7

NO2 + O3 → NO3 + O2;
NO3 + NO2 → N2O5;
N2O5+H2O → 2HNO3

Question 8

Why is HNO3 not an effective reservoir for NOx

Answer 8

Precipiates out in wet deposition too quickly

Question 9

Production of PAN

Answer 9

peroxyacytlnitrate
CH3CHO + OH → CH3CO + H2O
CH3CO + O2 + M → CH3C(O)OO + M
CH3C(O)OO+NO2 +M→PAN+M

Question 10

How does PAN function as a reservoir for NOx

Answer 10

PAN can thermally decompose to produce NOx,
PAN –> CH3C(O)OO + NO2
This is very temperature sensitive. PAN can be transported out of an area to later on thermally decompose back into NOx, facilitating the transport of NOx
PAN is most important reservoir

Question 11

Ozone production inside the troposphere

Answer 11

HO2 + NO –> NO2 + OH
CH3O2 + NO –> CH3O + NO2
NO2 + hv –> NO +O3 (in presence of O2)

Question 12

Loss pathways of O3 in troposphere

Answer 12

dry deposition
in remote troposphere: reacting with OH and HO2
O3 –> O(1D) + O2
O(1D) + H2O –> 2OH

Question 13

Increasing NOx or O3- impact on OH

Answer 13

Increases OH

Question 14

Increasing CO or CH4- impact on OH

Answer 14

Decrease OH

Question 15

O3 destruction that is HOx propogation

Answer 15

OH + O3 –> O2 + HO2
HO2 + O3 –> 2O2 + OH
net : 2O3 –> 2O2

Question 16

HOx + O3 cycling stops with loss of HOx radicals. This happens two ways:

Answer 16

In low NOx: peroxyl radicals react with themselves
HO2 + HO2 –> H2O2 +O2

In High NOx: oxidation of NO2
NO2 + OH –> HNO3

Question 17

Why is isoprene the primary hydrocarbon that contributes to ozone production

Answer 17

abundant, has two C=C bonds that OH reacts with very quickly. lifetime of a few hours

Question 18

Ozone production efficiency

Answer 18

ε = PO3/LNOx. How many ozone molecules are produced per molecule NOx consumed.

Question 19

increasing hydrocarbon concentrations does what to ozone production efficiency?

Answer 19

Increases-

Increasing hydrocarbons will decrease OH and extend lifetime of NOx, more O3 per NOx

Question 20

increasing NOx concentrations does what to ozone production efficiency?

Answer 20

Decrease-

Increasing NOx causes OH to increase, decreases lifetime of NOx

Question 21

Typical values of Ozone production efficiency

Answer 21

1-20 mol/mol

Question 22

One reason O3 may be increasing despite air quality constraints

Answer 22

Decreasing particulate matter pollution- particles scavenge HO2 radicals that otherwise would go to ozone production. Less particulate matter- more HO2 forms more ozone.

Question 23

Sources of HO2 in troposphere

Answer 23

Photodissociation of CH2O
CH2O + hv –> H + HCO
H + O2 +M –> HO2 + M
HCO + O2 –> HO2 + CO

from alkoxy radical reactions
RCH2O + O2 –> RCHO + HO2

Question 24

HONO photolysis

Answer 24

HONO + hv –> OH + NO
builds up at night
important source at daybreak
very long wavelength

Question 25

O3 source in troposphere

Answer 25

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

Question 26

Sources of NO3 in troposphere

Answer 26

Oxidation of NO2 NO2 + O3 --> NO3 + O2

Question 27

Sources of chlorine in troposphere

Answer 27

Sea salt chemistry

Question 28

Lifetimes

Answer 28

``` d[M]/dt = -k[X][M] lifetime = 1/k[X] ```

Question 29

Primary nighttime oxidant

Answer 29

NO3

Question 30

peroxy radicals NO oxidation

Answer 30

NO +HO2 --> OH +NO2 | NO + RO2 --> RO + NO2

Question 31

Oxidation of NO2

Answer 31

Daytime- NO2 + OH --> HONO2 nighttime: NO2 + O3 --> NO2 + O2 NO2 + NO3 --> N2O5

Question 32

Source of HONO

Answer 32

OH + NO --> HONO