Specify the aerosol type in the lower 2 km of the atmosphere as  

aerosol_haze type

 
where type is an integer identifying the following aerosol types:

1

Rural type aerosols.

2

Maritime type aerosols.

5

Urban type aerosols.

6

Tropospheric type aerosols.

For a description of the different aerosol types see shettle89.