Processes determining the relationship between aerosol number and non‐sea‐salt sulfate mass concentrations in the clean and perturbed marine boundary layer

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 (NTOT) and the number of particles with dry diameter > 80 nm (N>80) to the aerosol volume and non-sea-salt (nss) SO4= mass (MSO4). 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 NTOT and N>80 versus MSO4 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., (NH4)x(SO4)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 MSO4 suggest that the observed nonlinear relation between the number of cloud droplets and MSO4 must be mainly ascribed to nonlinearities in the cloud activation process.

[1]  D. Lenschow,et al.  Bidirectional mixing in an ACE 1 marine boundary layer overlain by a second turbulent layer , 1998 .

[2]  Y. Kaufman,et al.  Measurements of the relationship between submicron aerosol number and volume concentration , 1998 .

[3]  P. Hobbs,et al.  Airborne measurements of carbonaceous aerosols on the East Coast of the United States , 1997 .

[4]  Philip B. Russell,et al.  Chemical apportionment of aerosol column optical depth off the mid‐Atlantic coast of the United States , 1997 .

[5]  P. V. Velthoven,et al.  Observations of aerosols in the free troposphere and marine boundary layer of the subtropical Northeast Atlantic: Discussion of processes determining their size distribution , 1997 .

[6]  S. Jennings,et al.  Aerosol and trace gas measurements during the mace head experiment , 1996 .

[7]  N. Jensen,et al.  Observation of DMSO and CH3S(O)OH from the gas phase reaction between DMS and OH , 1996 .

[8]  A. Clarke,et al.  Lagrangian evolution of an aerosol column during the Atlantic Stratocumulus Transition Experiment , 1996 .

[9]  J. Putaud,et al.  Assessment of dimethylsulfide sea‐air exchange rate , 1996 .

[10]  B. Huebert,et al.  Sulfate, nitrate, methanesulfonate, chloride, ammonium, and sodium measurements from ship, island, and aircraft during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol Gas Exchange , 1996 .

[11]  H. Maring,et al.  Results of the pre-ace 2 campaigns in the subtropical North Atlantic , 1996 .

[12]  R. Van Dingenen,et al.  Evidence for anthropogenic impact on number concentration and sulfate content of cloud‐processed aerosol particles over the North Atlantic , 1995 .

[13]  S. Schwartz,et al.  Field observations in continental stratiform clouds: Partitioning of cloud particles between droplets and unactivated interstitial aerosols , 1995 .

[14]  C. Bretherton,et al.  Cloudiness and Marine Boundary Layer Dynamics in the ASTEX Lagrangian Experiments. Part II: Cloudiness, Drizzle, Surface Fluxes, and Entrainment , 1995 .

[15]  Andrea Saltelli,et al.  Uncertainty and sensitivity analyses of OH-initiated dimethyl sulphide (DMS) oxidation kinetics , 1995 .

[16]  Olivier Boucher,et al.  The sulfate‐CCN‐cloud albedo effect , 1995 .

[17]  F. Raes.  Entrainment of free tropospheric aerosols as a regulating mechanism for cloud condensation nuclei in the remote marine boundary layer , 1995 .

[18]  J. Gras.  CN, CCN and particle size in Southern Ocean air at Cape Grim , 1995 .

[19]  D. Hegg.  Cloud condensation nucleus-sulphate mass relationship and cloud albedo , 1994 .

[20]  Stephen E. Schwartz,et al.  Sulfate over the North Atlantic and adjacent continental regions: Evaluation for October and November 1986 using a three-dimensonal model driven by observation-derived meteorology , 1994 .

[21]  D. L. Roberts,et al.  A climate model study of indirect radiative forcing by anthropogenic sulphate aerosols , 1994, Nature.

[22]  D. W. Johnson,et al.  The Measurement and Parameterization of Effective Radius of Droplets in Warm Stratocumulus Clouds , 1994 .

[23]  R. Dingenen,et al.  Modelling formation and growth of H2SO4-H2O aerosols: Uncertainty analysis and experimental evaluation , 1992 .

[24]  George A. Isaac,et al.  The relationship between cloud droplet number concentrations and anthropogenic pollution : observations and climatic implications , 1992 .

[25]  A. Berner,et al.  A new electromobility spectrometer for the measurement of aerosol size distributions in the size range from 1 to 1000 nm , 1991 .

[26]  J. W. Fitzgerald,et al.  Aerosol size distributions and optical properties found in the marine boundary layer over the Atlantic Ocean , 1990 .

[27]  M. Hoffmann,et al.  Atmospheric chemistry of peroxides: a review , 1990 .

[28]  Ian Barnes,et al.  Kinetics and mechanisms of the reaction of OH radicals with dimethyl sulfide , 1988 .

[29]  J. Hudson,et al.  Cloud droplet nucleation and cloud scavenging of aerosol sulphate in polluted atmospheres , 1986 .

[30]  M. Molina,et al.  Chemical kinetics and photochemical data for use in stratospheric modeling , 1985 .