Open AccessProcesses determining the relationship between aerosol number and non‐sea‐salt sulfate mass concentrations in the clean and perturbed marine boundary layer
Author(s) -
Van Dingenen Rita,
Raes Frank,
Putaud JeanPhilippe,
Virkkula Aki,
Mangoni Monica
Publication year - 1999
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/1998jd100059
Subject(s) - aerosol , sulfate , entrainment (biomusicology) , sea salt , sea salt aerosol , atmospheric sciences , environmental science , dilution , radiative forcing , boundary layer , mass concentration (chemistry) , pollution , radiative transfer , environmental chemistry , meteorology , chemistry , physics , thermodynamics , ecology , organic chemistry , rhythm , acoustics , biology , quantum mechanics
An evaluation of the indirect radiative forcing by aerosols requires knowledge about aerosol number densities, and more particularly the number of particles that can be activated in clouds. In this study we present a data set relating the total number ( N TOT ) and the number of particles with dry diameter > 80 nm ( N >80 ) to the aerosol volume and non‐sea‐salt (nss) SO 4 = mass ( M SO4 ). The data refer to submicron aerosol and have been obtained in both clean and polluted conditions in the North Atlantic marine boundary layer (MBL). Over this whole range, the relationships of both N TOT and N >80 versus M SO4 are close to linear. Detailed aerosol dynamics modeling shows that dilution of the initial pollution aerosol by entrainment of free tropospheric (FT) aerosol is the major process determining these relationships. Entrainment further explains our observation that the contribution of nss‐sulfate (i.e., (NH 4 ) x (SO 4 ) y ) to the dry MBL aerosol mass decreases from over 85% near the continent to 45–70% in more remote and clean conditions, as smaller contributions of sulfate to the FT aerosol mass have been observed. Finally, the linear relationships between aerosol number and M SO4 suggest that the observed nonlinear relation between the number of cloud droplets and M SO4 must be mainly ascribed to nonlinearities in the cloud activation process.