Global Distribution, Physical Removal, and Residence Time of the Tropospheric Aerosol

6 Global Distribution, Physical Removal, and Residence Time of the Tropospheric Aerosol 

As for other constituents of the atmosphere, it is possible to set up a mass budget of the aerosol and to calculate its residence time. The main problem is to characterize the global distribution of particulate matter in order to determine its total mass in the troposphere. One may then apply the emission estimates of Table 7-11 to calculate the tropospheric residence time ta with the help of Eq. (4-11). This approach will be discussed in the first part of this section. Subsequently, we consider an independent method for estimating the residence time, which results from the use of radioactive tracers. Finally, the removal of aerosol particles by sedimentation and impactation at the Earth surface will be discussed. 

The model used here is based on the ground-level concentrations given in Table 7-1. The vertical distribution of continental and marine aerosols are illustrated in Fig. 7-26. The decline of concentrations with height follows from the adopted scale heights and is expressed as 

Assuming an average tropopause height of 12 km, one obtains by integration over height the following approximate column densities. 

The total burden of particulate matter in the troposphere is then obtained by applying the surface areas Acont = 1.49 x 1014 m2 and Asca = 3.61 x 1014 m2, with the result 

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