module 9 photochemistry. mcen 4131/5131 2 preliminaries exams back, will go over on thursday, fcqs?...
TRANSCRIPT
Module 9Module 9
Photochemistry
MCEN 4131/5131
2
PreliminariesPreliminaries• Exams back, will go over on Thursday, • FCQs?• Thanks for coming to the Pizza Party!• Final here in this classroom, Tues 10:30
MCEN 4131/5131
3
Review
Module 8 Educational Module 8 Educational ObjectivesObjectives
• General circulation patterns– Coriolis force
• Stability and vertical mixing– Temperature gradient in
atmosphere
• Lapse rate• Temperature inversions
MCEN 4131/5131
4
LearningObjectivesfor Today Module 9 Educational Module 9 Educational
ObjectivesObjectives
• Photochemical smog– How it forms, key ingredients
• Photolysis– Photolytic cycle
• Role of reactive organics• Control of smog• EKMA model
MCEN 4131/5131
5
Clicker Question?Clicker Question?
• What are the three essential ingredients for creating photochemical smog?
a. Methane, reactive organics, oxygen, sun
b. Nitric acid, reactive organics, high RHc. Nitrogen oxides, sun, reactive
organicsd. High T, carbon dioxide, nitrogen
oxides
LearningObjectives
Photochemical smogPhotolysisReactive organicsControlEKMA model
MCEN 4131/5131
6
Health effectsHealth effects
• Reduce lung function• irritate the respiratory
system• aggravate asthma• inflame and damage the linin
g of the lungThis photo shows a healthy lung air way (top) and an inflamed lung air way (bottom). Ozone can inflame the lung's lining, and repeated episodes of inflammation may cause permanent changes in the lung.
LearningObjectives
Photochemical smogPhotolysisReactive organicsControlEKMA model
MCEN 4131/5131
7
Typical Smog EpisodeTypical Smog Episode
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
LearningObjectives
Photochemical smogPhotolysisReactive organicsControlEKMA model
MCEN 4131/5131
8
PhotolysisPhotolysis
• Energy for reaction comes from an absorbed photon– Only certain species photolyze– In troposphere, photolysis is initiated for light
of 280–730 nm wavelengths
• Example: NO2 dissociation– NO2 + h --> NO + O* (kmax = 0.5 min-1)– h = Planck’s constant (6.63 x 10-34 J s) – = frequency of photon (=c/, where c = 3 x
108 m/s)– Dissociation only occurs if photon possesses
enough energy to break molecular bonds, < 430 nm for NO2
LearningObjectives
Photochemical smogPhotolysisReactive organicsControlEKMA model
MCEN 4131/5131
9
Primary photolytic Primary photolytic CycleCycle
• Group Question: Which of the following is part of the photolytic cycle?
– a. NO + hv --> N + O
– b. O + NO --> NO2
– c. O3 + NO --> NO2 + O2
NO2 + h --> O(3P)*+ NO
O(3P)* + O2 + M --> O3 + M
O3 + NO --> NO2 + O2
1
2
3
Main source of ozone in troposphere
LearningObjectives
Photochemical smogPhotolysisReactive organicsControlEKMA model
MCEN 4131/5131
10
Ozone is higher than Ozone is higher than photolytic reactions photolytic reactions
predict!predict!• Assuming photostationary state
for O and O3, then we can derive equation for O3 formation:
• When NO2 ~ NO, ozone is predicted by above to be around 20 ppb
• But in reality it is much higher by as much as an order of magnitude - WHY?
O3[ ]=k1 NO2[ ]k3 NO[ ]
LearningObjectives
Photochemical smogPhotolysisReactive organicsControlEKMA model
MCEN 4131/5131
11
Role of Reactive Role of Reactive OrganicsOrganics
• Hydrocarbons are source of radicals that convert NO to NO2 – Increase rate at which O3 is produced by
increasing NO2
– Decrease rate at which O3 is scavenged by decreasing NO
O3
NO2
O
NO
O2& M
h
RO2
Reactive organic RO2 provides a shortcut to NO2 production that does not consume ozone - so ozone accumulates
LearningObjectives
Photochemical smogPhotolysisReactive organicsControlEKMA model
MCEN 4131/5131
12
Control of SmogControl of Smog
• Question: Is smog a ?a. Secondary air pollutant b. Primary air pollutant
• Must control emissions of precursors to control smog: HCs, NOx– source of HCs: solvents, cars, lighter fluid,
industrial sources– source of NOx: cars, all combustion, power
plants, etc
• System is highly nonlinear• Analyze system using EPA’s Empirical
Kinetic Modeling Approach (EKMA)– Relates changes in HCs and NOx emissions to
changes in maximum ozone
LearningObjectives
Photochemical smogPhotolysisReactive organicsControlEKMA model
MCEN 4131/5131
13
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
MCEN 4131/5131
14
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
MCEN 4131/5131
15
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.