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New IMPROVE algorithm to calculate light extinction

Aerosol Light Extinction (Bep):   The attenuation of light due to scattering and absorption of aerosols.

Aerosol Ext = 2.2 * fS(RH) * [small sulfate] + 4.8 * fL(RH) * [large sulfate] + 2.4 * fS (RH) * [small nitrate] + 5.1 * fL(RH) * [large nitrate] + 2.8 *fS(RH) * [small organic mass] + 6.1 * fL(RH) * [large organic mass] + 10 * [elemental carbon] +1 * [fine soil] + 1.7 * fSS(RH) * [sea salt] + 0.6 * [coarse mass]

where the concentrations of the major chemical components are calculated using the equations listed in the table below.  The units of Bsp and the concentrations of major light scattering aerosol components are Mm-1 and mg m-3, respectively.

The apportionment of the total concentration of sulfate compounds into the concentrations of the small and large size fractions is accomplished using the following equations.

                  

                         

 

The same equations are used to apportion total nitrate and total organic mass concentrations into the small and large size fractions.

(In the following table the brackets [ ] denote concentrations of that chemical species)

Species

Formula

Assumption

Possible Sources

Sulfate in PM2.5

4.125[S]

All elemental S is from sulfate.  All sulfate is from ammonium sulfate.

Fossil fuel combustion

Nitrate in PM2.5

1.29[NO3]

Denuder efficiency is close to 100%.  All nitrate is from ammonium nitrate.

Industrial and automobile emissions, organic decomposition

Organic Mass by Carbon (OMC) in PM2.5

1.8 * OC

Average organic molecule is 56% carbon.

Biomass burning, automobile emissions, fossil fuel combustion, gas-to-particle conversion of hydrocarbons

Elemental Carbon (EC) or Light absorbing Carbon (LAC) in PM2.5

EC1+EC2+EC3-OP

 

Incomplete combustion of fossil and biomass fuels

Soil  in PM2.5 (Fine Soil)

2.2[Al]+2.49[Si]+1.63[Ca]+2.42[Fe]+1.94[Ti]

[Soil K]=0.6[Fe].  FeO and Fe2O3 are equally abundant. A factor of 1.16 is used for MgO, Na2O, H2O, CO2.

Desert dust, construction, road dust

Sea Salt in PM2.5

1.8*[Cl-]

Sea salt is calculated as 1.8 x [Chloride], or 1.8 x [Chlorine] if the chloride measurement is below detection limits, missing or invalid

 

Coarse Mass (CM)

[PM10] - [PM2.5]

Consists only of insoluble soil particles.

Crushing or grinding operations, dust from paved or unpaved roads

The algorithm uses three water growth adjustment term as shown in the Table below.  They are for use with the small size distribution and the large size distribution of sulfate and nitrate compounds and for sea salt (fS(RH), fL(RH) and fSS(RH) respectively).

RH (%)

fS(RH)

fL(RH)

fSS(RH)

 

RH (%)

fS(RH)

fL(RH)

fSS(RH)

 

RH (%)

fS(RH)

fL(RH)

fSS(RH)

0 to 36

1.00

1.00

1.00

 

56

1.78

1.61

2.58

 

76

2.60

2.18

3.35

37

1.38

1.31

1.00

 

57

1.81

1.63

2.59

 

77

2.67

2.22

3.42

38

1.40

1.32

1.00

 

58

1.83

1.65

2.62

 

78

2.75

2.27

3.52

39

1.42

1.34

1.00

 

59

1.86

1.67

2.66

 

79

2.84

2.33

3.57

40

1.44

1.35

1.00

 

60

1.89

1.69

2.69

 

80

2.93

2.39

3.63

41

1.46

1.36

1.00

 

61

1.92

1.71

2.73

 

81

3.03

2.45

3.69

42

1.48

1.38

1.00

 

62

1.95

1.73

2.78

 

82

3.15

2.52

3.81

43

1.49

1.39

1.00

 

63

1.99

1.75

2.83

 

83

3.27

2.60

3.95

44

1.51

1.41

1.00

 

64

2.02

1.78

2.83

 

84

3.42

2.69

4.04

45

1.53

1.42

1.00

 

65

2.06

1.80

2.86

 

85

3.58

2.79

4.11

46

1.55

1.44

1.00

 

66

2.09

1.83

2.89

 

86

3.76

2.90

4.28

47

1.57

1.45

2.36

 

67

2.13

1.86

2.91

 

87

3.98

3.02

4.49

48

1.59

1.47

2.38

 

68

2.17

1.89

2.95

 

88

4.23

3.16

4.61

49

1.62

1.49

2.42

 

69

2.22

1.92

3.01

 

89

4.53

3.33

4.86

50

1.64

1.50

2.45

 

70

2.26

1.95

3.05

 

90

4.90

3.53

5.12

51

1.66

1.52

2.48

 

71

2.31

1.98

3.13

 

91

5.35

3.77

5.38

52

1.68

1.54

2.50

 

72

2.36

2.01

3.17

 

92

5.93

4.06

5.75

53

1.71

1.55

2.51

 

73

2.41

2.05

3.21

 

93

6.71

4.43

6.17

54

1.73

1.57

2.53

 

74

2.47

2.09

3.25

 

94

7.78

4.92

6.72

55

1.76

1.59

2.56

 

75

2.54

2.13

3.27

 

95

9.34

5.57

7.35

 

 

 

 

 

 

 

 

 

 

 

Total Light Extinction (Bext): The attenuation of light due to scattering and absorption as it passes through a medium.

Bext = Aerosol Ext (Bep) + Site specific Rayleigh light extinction (annual average)

Units: inverse distance, e.g. inverse mega meters (Mm-1)

Benefit:  Light extinction can be directly related to gaseous and aerosol concentrations.

Drawback:  Light extinction is non-linearly related to a person perception of changes in haze.  For example, a 10 Mm-1 increase in bext will have a larger perceived impact on a scene at Bext = 20 Mm-1 than at Bext = 100 Mm-1

Deciview (DV): A metric of haze proportional to the logarithm of the atmospheric extinction (Bext).

Units: Unitless

Benefit: Under many circumstances a change in one deciview will be perceived to be the same on clear and hazy days.

Drawback:  Deciview is not easily related to gaseous and aerosol concentrations

Relationships:

DV = 10*ln(Bext/10)

DV = 10*ln(K/V.R./10) 

Standard Visual Range (V.R.):The greatest distance at which an observer can just see a black object viewed against the horizon sky.   

Units:  Distance, e.g. kilometers (km)

Benefit:  This metric is most useful in situation where only the distance that one can see is important, such as for aviation.

Drawback:  Does not account for changes in scene, such as loss of textures and discoloration as haze increases.

Relationships:

V.R. = K/Bext
Where K is the Koschmieder Coefficient – the log of the contrast threshold of the human eye,  K = 3.91