VII. Tropospheric Ozone Catalytic Cycles Terminating the Cycles Initiating Organic Chemistry...
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VII. Tropospheric Ozone Catalytic Cycles Terminating the Cycles Initiating Organic Chemistry Meteorology
Transcript of VII. Tropospheric Ozone Catalytic Cycles Terminating the Cycles Initiating Organic Chemistry...
VII. Tropospheric Ozone
Catalytic CyclesTerminating the CyclesInitiating Organic ChemistryMeteorology
Ozone
Damages lung – hard on kids, the aged, and
anyone
with bad lungs
Concentrations
40-50 ppbv (continental background)
80 ppbv (EPA 8 hour limit)
120 ppbv (old EPA 1 hour limit)
EPA Map of Peak Ozone Concentration
0-60 ppb
61-79 ppb
80-99 ppb
100-110 ppb
111-124 ppb
125+ ppb
No Data
Source of Ground-Level O3
NO2 + h → NO + OO + O2 → O3 NO + O3 → NO2 + O2
NOx = NO + NO2
NOx + sunlight yields O3
These 3 reactions steady state w/limited [O3]
Add CO and HOx Chemistry
OH + CO → H + CO2
H + O2 → HO2
HO2 + NO → OH + NO2
NO2 + h → NO + O
O + O2 → O3
CO + 2 O2 → CO2 + O3
CO
CO2
OH
HO2NO
NO2
h
OO3 O2
Add Organic Compounds…
OH + CH4 → CH3 + HOH
CH3 + O2 → CH3OO
CH3OO + NO → CH3O + NO2
CH3O + O2 → CH2=O + HO2
HO2 + NO → OH + NO2
2{NO2 + h → NO + O}
2{O + O2 → O3}
CH4 + 4 O2 → CH2=O + 2 O3 + H2O
NOx Concentrations
Urban 5-20 ppbvRural 0.1 – 5 ppbvRemote 0.005 -0.1 ppbv
[HOO] ≈ Sum over [ROO] << [NOx] except for Remote
k(ROO + NO) ≈ k(HOO + NO) ≈ k(ROO + HOO)
So HOO and ROO mostly react with NO
Termination of Cycles
RO
RH + OH, O2 → ROONO
NO2
h
RONO2
Limits NOx Cycling and organic radical chem.
Termination of Cycles at High [NO2]
NO2
RCH3
RCH=O
OH
HO2NO
NO2
h
HONO2
Stops HOx Cycling
Termination of Cycles at low [NOx]
RO
ROO
NO
NO2
h
HOO
ROOH
2 HOO →HOOH + O2
organic radical chem.
HOx cycling
Contour of Maximum [O3]
VOC (ppmC)
NO
x (p
pb
)
[O3]max
160 ppb
120 ppb
80 ppb
NOx : VOC
≈ 1:7downtown
downwind
Fate of Organic Compounds- OH
vacuum cleaner of the atmosphere
OH + RH → R + HOH
OH + RCH=CH2 → RCHCH2OH or RCH(OH)CH2
OH Production photochemical (daylight)
O(1D) + HOH → 2 OH
HONO + h → OH + NO
HOO + NO → OH + NO2
HOO from CH2=O + h and organic
radicals
NO3 + RCH=CH2 → RCHCH2ONO2 or RCH(ONO2)CH2
NO3 Production
NO + O3 → NO2 + O2
NO2 + O3 → NO3 + O2 (slower than NO2 + h)
NO2 + NO3 → N2O5
NO3 + h → NO2 + O or NO + O2 ( = seconds)
[NO3] only significant in the dark !!
Fate of Organic Compounds- NO3
Fate of Organic Compounds- O3
O3
OO
O
OO O
CH2=O CH2
OO
+
++
-
++
-
OH (in variable yield)
Consider this mechanism: cm3 molecule-1 s-1 1) C3H8 + OH C3H7 + H2O k1 = 1.1 x 10-12 2) C3H7 + O2 C3H7O2 k2 = 1 x 10-12 3) C3H7O2 + NO C3H7O + NO2 k3 = 9 x 10-13 4) C3H7O + O2 C3H6O + HO2 k4 = 8.5 x 10-15 [C3H8] = 2 ppbv = 5 x 1010 molecules cm-3 [O2] = 0.21 atm = 5 x 1018 molecules cm-3 [NO] = 1 ppbv Calculate the steady state concentrations of: C3H7, C3H7O2, and C3H7O.
Activity
Meteorology and Air Pollution“Dilution is the Solution to Pollution”
Dispersing vs. Trapping pollutants
Planetary Boundary Layer- region influenced by surface (convection)- vertical mixing time scale of 1 hour- 1st 100 m – 2 km- diurnal (daily) cycle
Planetary Boundary Layer
0422 0758 1324 1700 2037
Ozone and Topography
Topography and Meteorology
Pacific Ocean (km) San Bernadino Mtns
Topography and Meteorology
Pacific Ocean (km) San Bernadino Mtns
Topography and Meteorology
Inversion Layer
• Warmer above than below, so air is trapped• time limited, specific geography
Key Points
• Sunlight, NOx, and Organics
• Cycles in HOx and NOx
• NOx is globally limiting reagent
• OH removes organics (O3, NO3)
• Kinetics calculations - steady state concentrations
- fate of species• Topography (meteorology)
