Residence times of sulfate aerosols in the atmosphere

Atmospheric aerosol size distributions consist basically of three modes nuclei mode ( 0.1 -pm diameter), accumulation mode ( 2.0-pm diameter, but 0.1-pm diameter) and coarse particle mode ( 2.0-pm diameter). Depending on their source there may be from one to three 

Therefore, if we consider the sulfate aerosols in terms of the naturally occurring radioactive aerosols (e.g., Pb-aerosols), the following equation applies  

Using the data on radon decay product aerosols, Papastefanou and Bondietti (1991) reported a mean residence time, xr, of 8 days for aerosols of 0.3-pm activity median aerodynamic diameter (AMAD) size as determined from Bi/ Pb activity ratios. From the decay scheme of 2 Po T /2 = 3.05 min), because of the relatively short half-lives of the product radionuclides after two a-decays and two /S-decays, Pb-aerosols are produced. From 32 experiments for radon decay product aerosols ( °Pb-aerosols), Papastefanou and Bondietti (1991) calculated average values of fractions F and F2 of about 76.11 and 21.32, respectively. From 12 measurements of sulfate aerosols, Bondietti and Papastefanou (1993) calculated in the same manner average values of fractions F and F2 of about 68.67 and 12.63, respectively. According to Equation (4.12) and the above mentioned data, a mean residence time, xr, SO , of about 12 days would apply to sulfate aerosols of 0.3-pm mass median aerodynamic diameter (MMAD) size. 

Balkanski, P.J., Jacob, D.J., Gardner, G.M., Graustein, W.C., Turekian, K.K. (1993). Transport and residence times of tropospheric aerosols inferred from a global three-dimensional simulation of Pb. J. Geophys. Res. 98 (Oil), 

Baskaran, M., Shaw, G.E. (2001). Residence time of arctic haze aerosols using the concenttations and activity ratios of Po, Pb and Be. J. Aerosol Sci. 32, 443-452. 

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The column burden of sulfate aerosol, m Q2, can be estimated from the global source strength of SO2, 0sO i the average fractional conversion of SO2 to sulfate in the atmosphere, vso, the mean residence time of sulfate aerosol in the atmosphere, t q , and the area, A, of the geographical region over which the estimate is performed (e.g. the entire globe, the Northern Hemisphere, etc.), as... 

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