Sulfur dioxide (SO2) concentration in troposphere
0.1-0.5 ppm common urban concentration
Less than 1 ppb far from industri
More than 2 ppm in highly polluted areas
Nitrous oxide
dinitrogen oxide N2O
greenhouse gas
unknown effects
Nitric oxide
NO
Main source of nitrous oxide in atmosphere:
Microbal reduction of nitrate (NO3 -) occurs in soils and waters with low oxygen contents.
Nitrous oxide is broken down:
In stratosphere: (2 reactions)
- 2N2O + hv = 2N2 + O2 (sunlight)
- N2O + O* = 2NO (Highly reactive atomic oxygen from ozone reaction, exited)
Photodissociation of ozone in Stratosphere:
O3 + hv (lambda - 325nm) = O* + O2
Describe CFCs
- Freons used as coolants, propellants and solvents.
- Destroys the ozone layer
- Greenhouse gas
(- decresing due to Montreal protocol)
Describe HFC
- Sustitute to freons/CFCs
- Not bad for ozone
- Also a greenhouse gas
What does the Nitrogen molecule in air look like?
N2 - Tripple bond
3 covalent bonds
6 shared electrons
Very strong!
pH of seawater?
8-10 (alkaline) becomming more acidic
pH rain?
- Unpolluted 5.5 (CO2 makes it naturaly acidic)
- Polluted 4.5 (polluted surface water)
What is mole?
- the amount of a substance that contains 6.0225210^23 particles, Avogadros number
m_a = n_aM_a - m_a: mass of substance [g]
- n_a: number of mole [mole]
- M_a: molar mass of emelemnt or molecule [g/mol]
What is Molarity?
- the concentration of a substance in a certain volume of
another substance very common (like water) [mole/L]
How much of the Atmospheric mass is found in the troposphere?
90%
What molecules can absorb IR (are GHG):
Only di-pol molecules like:
- H2O, CO2, CH4, NOx, halocarbons etc
Photodissociation of ozone in Troposphere:
O3 + hv (lambda < 310nm) -> O* + O2
How is methane broken down in troposphere?
O* + CH4 = OH + CH3
OH + CH4 = H2O + CH3
O* from ozone break down
How are OH radicals made in troposphere?
- O* + CH4 = OH + CH3
- O* + H2O = 2OH
O* from ozone break down
Why is tropospheric hydroxyl (OH) good?
- It reacts with CO, CH4 and other VOC
cleaning up the atmosphere of pollutants.
OH production during day or night?
production of OH is a daytime reaction. Needs the sunlight to break down ozone.
Why do we need NO3 when NOx is so harmful?
NO3 is needed in troposphere to remove pollutants in cities during nighttime.
- created from NO2 by removing tropospheric ozone.
Where does sulphur pollutants come from?
- Volcanos
- Domestic and industriel combustion of fossil fuel (petroleum and Coal)
Where does nitrogen oxides come from?
- Microbial activity in soil and lightning
- High temperature processes (combustion)
Where does Volatile Organic Compounds (VOC) come from?
- isoprene rubber, vegitation (non methane)
- Solvents, fuel from petroleum
What is London smog?
- H2SO4
- formed during cold winter nights
- from SO2, fog and soot particles.
(- Deadly in high concentrtions.)
What is photochemical (LA) smog?
- Aldehydes, PAN, ozone
- formed sunny days with car traffic
- from NOx, VOC, unburned fuel from cars.
What is a free radical?
- And atom, molecule or ion with an unpaired valence electron.
- Highly reactive.
What is the problem with NOx and ozone?
They can be part of the rection that produces tropospheric ozone, and they can also act as X and OX in the reaction of ozone destruction in the stratosphere.
How is the daily distribution of photochemical smog?
- morning: NO, Hydrocarbons (cars)
- NO2
- lunchtime: ozone, aldehydes (sunlight)
End product when nitrogen gets oxidized in atmosphere?
- There is no real end so to say, since the nitrogen cykle is a chain of continous reactions, thanks to the sunlight that keeps reducing the oxidized nitrogen. N2 is a very stable product (no oxidation) but even that is broken down by lightning or bacteria in soil.
Terminator for clorine atom reactions?
CH4 + Cl = CH3 + HCl (Hydrocloric acid)
End product for Methane in atmosphere?
- It’s a very slow process but one can say that the end product of methane in the atmosphere is:
CO2
Acid rain:
SO4(2-) (aq)
- from HSO3(-)(aq) + H2O … (+ O3) …
Formula for Gibbs free constant:
dG = dH - T*dS G = Gibbs free energy H = Entalpy (tables) S = Entropy (tables)
dG <> 0 :
dG < 0 -> sontaneuos
dG > 0 -> NOT spontaneous
What can prevent spontaneous reactions from occuring?
High activation energy, Ea
Leighton’s relationship:
1: NO + O3 = NO2 + O2
2: NO2 + h*ny = NO + O
3: O + O2 + M = O3 + M
Occurs naturally, not net prod of ozone.
Main primary pollutants in acid rain:
- NOx and SO2
Main secondary pollutants in acid rain:
H2SO4, HNO3
sulphur acid, nitric acid
svavelsyra, salpetersyra