Aerosol size distributions and optical properties found in the marine boundary layer over the Atlantic Ocean

Abstract

Measurements and analyses of the aerosol size distributions and optical properties found in the marine boundary layer (MBL) during the 1983 USNS Lynch cruise from Charleston, South Carolina, to Scotland via Canary Islands are presented. The data given are the most extensive and accurate measurements of the submicron marine aerosol size distribution to date and are supplemented by extensive meteorological observations. Eight detailed case studies of the evolution of the size distribution that occurred under different meteorological conditions are presented and discussed. The data indicate that repeated cycling of MBL air through nonprecipitating clouds at the top of the MBL is a major factor in shaping the size distribution and that new particle formation by heteromolecular, homogeneous nucleation is the most likely mechanism for sustaining the particle concentration below 0.04‐μm radius. Calculations of the scattering and extinction coefficients and optical depth of the MBL as a function of wavelength directly from the measured size distribution and MBL vertical structure are compared to measured values of the scattering coefficient and optical depth. These measured and calculated optical properties correlate well throughout the cruise and the results give a relatively consistent picture of the relationship between the aerosol size distribution and electromagnetic properties in the MBL.

An exploration of aqueous oxalic acid production in the coastal marine atmosphere

“…Calculation of the predicted oxalate using the observed glyoxylate cloud water concentrations and Eq. (2), assuming a residence time (t) of six to eight days based upon the observed size distributions of oxalate and the calculations of Hoppel (1990). The observed vertical fraction of the MBL occupied by the stratocumulus cloud deck used in the calculations varied from 0.40 to 0.75.…”

“…For specific cases, f can be estimated as the vertical fraction of the marine boundary layer occupied by the stratocumulus cloud deck determined using the FSSP and CAPS hotwire probe vertical profile measurements of total aerosol volume. A value of 6-8 days was assigned to t based upon similar size distributions of the aerosols containing sulfate and oxalate and the calculations by Hoppel et al (1990) for atmospheric residence time of aerosols of a given diameter. Using the suggested rate constant and the concentration of glyoxylic acid observed in the cloud water samples collected during CARMA I a concentration of 0.47-1.17 mmol cl À1 oxalic acid is predicted for the samples.…”

Columnar aerosol single‐scattering albedo and phase function retrieved from sky radiance over the ocean: Measurements of Saharan dust

“…Angstrom exponents are usually less than 0.5 for pure Saharan dust [Eck et al, 1999;Reddy et al, 1990;Smirnov et al, 1998;Tanré et al, 1988]. In contrast, values for smaller maritime aerosols generally fall between 1 and 2 [Hoppel et al, 1990;Reddy et al, 1990;von Hoyningen-Huene and Wendisch, 1994]. Optical depths and Angstrom exponents observed during the experiment are summarized in Table 1.…”

Deep convection as a source of new particles in the midlatitude upper troposphere

“…[8] The observations presented here were made from the NASA DC-8 aircraft as part of the Subsonic Assessment: Hegg et al [1990] midlat MBL (Pac), above, in clean stratus 6,000 Hoppel et al [1990] midlat MBL (Atl), cloud free 20,000 Hegg [1991] midlat MBL (Pac), in marine stratus 600 Radke and Hobbs [1991] midlat cont, near cumulus 12,000 Covert et al [1992] midlat clean MBL, broken cloud layer 3, 200 Clarke [1992200 Clarke [ , 1993 UT (Pac), especially above cloud 80,000 Gras [1993] Antarctic coast, surface 600 Hofmann [1993] midlat cont UT 25, 000 Hoppel et al [1994] MBL and FT (Pac), especially above cloud 6,000 Perry and Hobbs [1994] midlat, downwind of marine cumulus 4, 200 Brock et al [1995] tropical UT 30, 000 Ferek et al [1995] Arctic over ocean 5, 400 Weber et al [1995] Pac MBL/FT boundary (Hawaii) 140 Covert et al [1996] Pac MBL (produced in FT?) 2,000 Clarke et al [1997] midlat free trop (Atl) 6,000 O'Dowd et al [1997] Weddell Sea MBL (Antarctic) 4,300 Raes et al [1997] subtropical free trop, cloud free 4,000 Schröder and Ström [1997] midlat cont UT 10,000 Thornton et al [1997] tropical UT, near convection 18,000 Weber et al [1997] and Eisele and McMurry [1997] midlat clean cont, free trop air 600…”