Normal Air Composition

 

                  SPECIES                                                                                   CONCENTRATION

 

                  N2                                                                                                      78.1% by volume

                  O2                                                                                                      20.9

                                    total                                                                                                98.9%

                  H2O                                                                                                  variable, but on the order of 1%

 

Trace Species

 

                  Noble Gases

 

                  Ar                                                                                                      0.9%

                  Ne                                                                                                     18 ppmv

                  Kr                                                                                                      1 ppmv

                  Xe                                                                                                     100 ppbv

                  He                                                                                                     5.0 ppmv

 

                  Others

 

                  CO2                                                                                                  360 ppmv

                  CH4                                                                                                  1.67 ppmv

                  H2                                                                                                      0.6 ppmv

                  N2O                                                                                                  300 ppbv

                  NO, NO2                                                                                      <1 - 1000 ppbv

 

                                                                                          Clean Trop                           Polluted Trop

                  CO                                                                120ppbv                                 1000 - 10,000 ppbv

                  SO2                                                               1 - 10                                        20 - 200

                  NO                                                               0.01 - 0.05                           50 - 750

                  NO2                                                              0.05 - 0.5                              50 -250

                  O3                                                                  20 - 80                                     100 - 500

                  HNO3                                                         0.02 - 0.3                              1 - 100+

                  CH2O                                                          0.5                                              20 - 50

                  NH3                                                              1                                                   10 -1 100+

                  PAN                                                                                                                  5 - 35

                  NMHC                                                                                                            500 - 1200

 

air density at STP (1 atm=101.3kPa, 298°K) is 2.46 x 1019 molecules/cm3

 

1 ppbv = 10-9 of air density

1 ppmv = 10-6 of air density