Lecture No. : Ozone
 
 
1. Ozone Formation
 (1) photolysis of NO2
  NO2 + hv ----> NO + O
  O + O2 + M ----> O3
 (2) cycle of carbon monoxide, methane, and other hydrocarbons
  A. NO + HO2 ----> OH + NO2
  B. reduce NO destruction on ozone.
2. Stratospheric Ozone
 (1) source: downward movement by turbulent diffusion.
 (2) latitudinal variation: 
  A. 3 concentration maxima.
  (A) 60 degree latitude
 a. The gap between polar and mid-latitude tropopause.
 b. Most pronounced maximum.
  (B) 30 degree latitude
 The gap between the tropical and middle latitude  
 tropopause.
  (C) 45 degree latitude
 Frontal and jet activities.
  B. Mean vertical distribution
  (A) Lower stratosphere (tropopause to 20 km, 250-30 mb)
 a. Polar (arctic and antarctic) maxima and equatorial 
  minimum 
  (a) Consequence of transport processes:
  Ozone is transported from the pole to the equator
  (b) More pronounced in spring.
 b. The ozone maximum appears at considerably greater
  height and is more strongly developed in the arctic
  than in antarctic.
 c. Tropical tropopause (15 km, 100 mb):
  lowest ozone concentration because of strong vertical
  mixing of air from below containing less ozone.
 d. Arctic maximum at 20 km (50 mb).
 e. Stronger ozone concentration in April than in October.
 f. Tropics: lack of seasonal variation.
 g. Greater ozone in Northern Hemisphere than in
  Southern Hemisphere.
  (B) Middle stratosphere (20-40 km, 30-3mb)
 a. Equatorial maximum and polar minimum.
  photochemical processes dominates over the equator.
 b. Higher ozone in Northern Hemisphere.
 c. Maximum ozone concentration in the middle troposphere
  (20-25 km).
 d. Variation in ozone concentration (total ozone in an  
  air column) is the reflection of variation in this  
  layer.
 e. 15-30 km : 60% of the total ozone in this air column.
 f. 10 km (tropopause) and above (stratosphere): 93% of
  total ozone.
 g. Variations in height and thickness of the maximum  
  ozone layer(20-25 km).
  (a) High latitudes: lower and thicker in winter and
 spring.
  (b) Tropics: higher and thinner during all seasons.
  (C) Upper stratosphere (40-50 km, 3-1 mb, stratopause)
 a. Weak polar maximum and tropical minimum.
 b. Small latitudinal variation.
 c. Higher ozone in Northern Hemisphere.
 C. Seasonal Variation
  (A) Lower stratosphere (Figs. 12 e-h, 31-176 mb)
 a. Polar, arctic, and antarctic areas:
  spring maximum, summer and fall minimum (more    
   vertical mixing?).
 b. Tropics: lack of seasonal variation.
 c. Southern Hemisphere at 31-44 mb (upper lower  
  stratosphere)
  Maximum ozone in middle latitude in spring 
  (September - October).
  (B) Middle stratosphere (Figs. 12 b-d, 4-22 mb)
 a. Polar, arctic, and antarctic areas:
  higher ozone in winter than in summer.
 b. Middle latitudes (30-60 degrees):lack of seasonal  
 variation.
 c. Tropics: winter and spring maximum.
  (C) Upper stratosphere (Figs. 12a)
 a. Polar, arctic, and antarctic area:
  higher ozone concentration in winter.
 b. Stronger seasonal variation.
  (D) Overall concentration
 a. Ozone in stratosphere is higher in Northern   
 Hemisphere than in Southern hemisphere.
 b. Annual range: larger in Northern Hemisphere.
 D. Day to Day Variations (Figs. 13 and 14)
  (A) Most pronounced in the middle latitude because of day to
 day weather variations.
  (B) Largest variation in the lower stratosphere in the
 neighborhood of 100 mb.
  (C) Middle stratosphere variation in connection with a  
 sudden middle stratosphere warming.
 E. Year to Year Variations (Fig. 15)
  (A) most strongly in the lower stratosphere.
  (B) trend:
 a. Ozone has declined since 1960.
 b. correlation with sunspot (r=0.7) with phase shift of  
  2 years.
3. Tropospheric Ozone
 (1) Classical (Chapman, 1930) photochemistry theory
 A. Ground surface is a sink of stratospheric ozone.
 B. Ozone is transported downward through the tropopause gaps and
  is destroyed at the ground surface by contact with various
  substance, mainly organic matters.
 C. The most pronounced ozone Maximum is below the tropopause gap   
  nearest to polar regions.
 D. Very low ozone concentration over the equator:
  strong updraft in the troposphere.
 (2) Modern theory of photochemical reactions in the troposphere:
 HOx - NOx - CH4 oxidation chains may have significant influence  
 On global ozone values.
 
 (3) The earth's surface is a sink for stratospheric ozone.
 A. The maximum ozone concentration in the troposphere is 1-2    
 Month lag behind the total ozone concentration      
   (stratosphere).
 B. Residence time of ozone in the troposphere
  (A) 1-2 month by observation.
  (B) 1-2 year by calculation (Junge, 1963).
 C. Ozone destruction in the troposphere
  (A) Ozone loss rate: 780 x 106 tons/year at the earth's
 surface.
  (B) Reaction chains
 a. Photolysis
  (a) UV (ultraviolet, wavelength < 0.32µ)
 O3 + hv ----> O* + O2
  (b) Hartley and Chappuis bands
 visible light (wavelengths between 0.45 and 0.7  
 µ).
 O3 + hv ----> O + O2
  Destroy half of the tropospheric ozone before it  
  reaches the ground surface.
 b. Hydrolysis (reaction with water vapor)
  O3 + H2O + hv ----> O2 + 2OH
 c. Reaction with free radicals
  O3 + OH ----> HO2 + O2
  O3 + HO2 ----> OH + 2O2
 d. Reaction with nitrogen oxides in rain and fog
  NO2 + O3 ----> NO3 + O2
  NO + O3 ----> NO2 + O2
  Nitrogen Oxides include nitrous oxide (N2O),
  nitric oxide (NO), and nitrogen dioxide (NO2).
 e. Reaction with sulfur dioxide in rain and fog
  Sulfates and nitrates collected from precipitation
  Reach a maximum concentration in spring, when ozone  
  concentration is minimum.
  (C) Ozone destruction rate in Northern Hemisphere is three
 times more than that in Southern Hemisphere: downward  
 flux of ozone over land is much larger than over ocean  
 because of larger convective activity over land. 
 (4) Troposphere is also a source of ozone.
 A. higher ozone concentration in Northern Hemisphere than in
  Southern Hemisphere.
  (A) Unequal influx of ozone through the tropopause gaps as a 
 consequence of the difference in the general circulation.
  (B) Less CO concentration in Southern Hemisphere.
 CO attacks NO that reacts with ozone and therefore  
 allowing ozone to build up.
 B. CO, NO, and HC concentrations are higher in Northern
  Hemisphere.
 (5) Influx of stratospheric ozone to troposphere (Figs. 17a and b)
 A. occurs in a single discrete intrusions (not a smooth    
 Continuous process) 
 B. strong intrusions in the jet stream region in connection with   
  developing disturbances.
 (6) Local Influences On Surface Ozone
 A. Valley near Zurich Hills(400-500 m)
  (A) Nighttime destruction of ozone (minimum concentration). 
 a. Ground destruction.
 b. Inhibition of replacement by vertical turbulence
  transport (stable air preventing vertical mixing),
  (B) High nighttime destruction rate
 downward flux = 1012 molecules/cm2sec.
  (C) High afternoon concentration of ozone in the boundary
 layer (the lowest layer of atmosphere where friction  
  exerts a significant influence on air motion,  
 approximately from ground surface to 1 km height):
 a. Influenced by nearby Zurich City.
 b. 60 ppb v.s. background concentration of 40 ppb.
 B. Hill Top (Arosa, Switzerland)
  (A) 2000 m surrounded by high mountains.
  (B) Smaller diurnal range.
  (C) Maximum ozone concentration at night peaking at sunrise:
 downward flux of ozone carried by mountain winds. 
  (D) Soon after sunrise:
 valley winds along the sun exposed slope bring air with  
 low ozone concentration to the observing site.
  (E) Diurnal range: 70 m-atm cm.
  (F) Day to day range in winter and spring: 250 m-atm cm.
  (G) Interannual variation: 100 m-atm cm.
4. Global Distribution (Fig. 4)
 (1) Equator: minimum.
 (2) Maximum concentration: arctic and antarctic (66o N and S).
  Transport of ozone from primary production region in the 
   equatorial upper stratosphere to the lower and middle
  stratospheres in arctic and antarctic where ozone is
  relatively inert photochemically.
 (3) Arctic ozone concentration > antarctic ozone concentration.
  Stronger horizontal ozone mixing in Northern Hemisphere due  
  To more lands.
 (4) The average total ozone is about 2% higher in the Northern
  than in the Southern Hemisphere: effect of the stronger     
  poleward transport of ozone in the Northern Hemisphere.
  A. Northern Hemisphere
 mean = 302 m-atm cm.
  B. Southern Hemisphere
 mean = 295 m-atm cm.
5. Seasonal Distribution (Fig. 5)
 (1) Maximum concentration in Northern Hemisphere
  A. Late March and April at 70o N.
  B. 460 m-atm cm.
 (2) Maximum concentration in the Southern Hemisphere
  A. Late spring (October and November).
  B. Less pronounced (400 m-atm cm).
 (3) Minimum concentration
  all seasons at the equator.
6. Secular Variations (1958-1977)
 (1) Northern Hemisphere
  Ozone has declined since 1967.
 (2) Southern Hemisphere
  Ozone has declined since 1963.
7. Normal Ozone Concentration in an air column/cm2
 (1) 8 x 1018 ozone molecules/cm2.
 (2) 0.3 cm at standard air temperature and pressure (STP) or 300
 m-atm cm.
8. Meaning of ozone
 (1) Ozein: to smell.
 (2) Odor.
9. Instruments
 (1) Indirect methods
  A. Gotz-Umkehr method.
  B. Dobson Spectrometer (1924)
 (A) Total amount of ozone in an air column from the
 observing site up to the external light source
 (normally sun).
 (B) Two wavelengths
  a. Hartly-Huggins bands (300-360 nm).
  b. Chappuis ozone absorption bands (440-760 nm).
  c. Standard instrument adopted by WMO.
  C. M-83
   Used by Russia and Eastern European countries since 1957.
 (2) Direct methods
  A. Optical method
 (A) heavy and expensive.
 (B) cloud and haze could cause errors.
 (C) better vertical resolution.
  B. Chemical method
 chemiluminescent.
   C. KI method
 2KI + O3 + H2O + 2Ag ---> 2AgI + 2KOH + O2
  D. UV method.
  
 Please click the following URL to reach Ozone website  
 
   http://www.epa.gov/air/oaqps/index.html
  http://www.epa.gov/oar/oaqps/peg_caa/pegcaa06.html#topic6
  http://www.epa.gov/oar/oaqps/gooduphigh/good.html#1