Page 205 - Fundamentals of Air Pollution 3E

III. Gas-Phase Chemical Reaction Pathways 17!

TABLE 12-4
Classes and Examples of Atmospheric Compounds
Hydrocarbons Oxygenated hydrocarbons
Alkenes Aldehydes
Formaldehyde HCHO
Ethene C 2H 4
Acetylaldehyde CH 3CHO
Propene C 3H 6
frans-2-Butene Other aldehydes ECHO
Alkanes Acids
Methane CH 4 Formic acid HCOOH
Ethane C 2H 6 Acetic acid CH 3COOH
Alkynes Alcohols
Methanol CH 3OH
Acetylene C 2H 2
Aromatics
Toluene QH 6
m-Xylene C 6H 10
Oxides of nitrogen Oxides of sulfur
Nitric oxide NO Sulfur dioxide SO 2
Nitrogen dioxide NO 2 Sulfur trioxide SO 3
Nitrous acid HNO 2 Sulfuric acid H 2SO 4
Nitric acid HNO 3 Ammonium bisulfate (NH 4)HSO 4
Nitrogen trioxide NO 3 Ammonium sulfate (NH 4) 2SO 4
Dinitrogen pentoxide N 2O 5
Ammonium nitrate NH 4NO 3
Free radicals Oxidants
Atomic oxygen O PAN CH 3COO 2NO 2
Atomic hydrogen H Ozone O 3
Hydroxyl OH
Hydroperoxyl HO 2
Acyl RCO
Peroxyacyl RCOO 2

295 nm through the visible region. The absorption of photons at these
different wavelengths causes the NO 2 molecule to enter an excited state.
For longer wavelengths, transitions only in the rotational-vibrational states
occur, whereas for shorter wavelengths changes in electronic states may
occur. The process of photoabsorption for NO 2 is expressed as

where hv represents the photon of solar radiation of energy and NO 2* is
the NO 2 molecule in the excited state. The excited NO 2 molecule can follow
several pathways:
Fluorescence
Collisional deactivation where X 2 is
N 2 or O 2