Global measurements of aerosols in remote continental and marine regions: Concentrations, size distributions, and optical properties

Abstract

The phase I Gametag (Global Atmospheric Measurements Experiment of Tropospheric Aerosols and Gases) aerosol measurements were designed to provide an initial assessment of the levels, types, and optical effects of tropospheric aerosols in remote marine and continental regions and to examine the possible causal relationships between the observed distributions and the dominant factors controlling aerosol population: chemical and physical transformations, source and sink strengths, and transport. We used size‐number data to determine mass concentrations and to estimate extinction, using nominal optical properties. Filter and impactor data have been used to determine aerosol composition, and correlative aircraft measurements have been used to aid in our data interpretation. Our data have been used to generate latitudinal profiles along our Pacific flight tracks. Our continental measurements, in general, show bimodal aerosol size distributions that reflect different source for each mode. The aerosol population consists primarily of crustal aerosols with r ≥ 0.5 μm and sulfate and combustion aerosols with r < 0.5 μm, with only a minor sea salt component. Owing to vertical mixing, there are no qualitative differences between the boundary layer and the free troposphere. Our data indicate that crustal aerosols represent a significant component of a background tropospheric aerosol in western North America and suggest that the possible contribution of the crustal aerosol to extinction should not be ignored. Pacific marine measurements show a qualitative difference between the boundary layer and the free troposphere. The boundary‐layer aerosol population is dominated by a bimodal sea spray aerosol; optical effects and mass concentration are dominated by a mode with a volume mean radius of ∼1 μm. Our measurements show only a small crustal component of the marine boundary‐layer aerosol. Our data indicate a loss of Cl from the sea spray aerosol, with the greatest loss in the small particles. We have inferred a background concentration of 0.2 ppbm for our measured particles that does not appear to be directly related to the sea spray aerosol. We have identified some of these particles as locally produced secondary aerosols; simultaneous measurements of gaseous species support this interpretation. Our Pacific free tropospheric aerosol measurements show a highly variable aerosol component, with local variations in concentration by 1 order of magnitude within a few kilometers. Our measured total aerosol and crustal component concentrations show a general decrease from north to south. Our lowest mean mid tropospheric concentration was seen south of 20°S; we have identified this mean concentration of 0.08 ppbm as a midtropospheric background aerosol.

Chemical characterization of cloud episodes at a ridge site in Tuscan Appennines, Italy

“…Previous results show that the depletion of Cl À occurs, first of all, in submicron particles and in regions with significant anthropogenic contributions (Martens et al, 1973;Sadasivan, 1978;Patterson et al, 1980). As regards to the SO 4 2À /Na + ratio, which is always higher than the seawater ratio (from 2 to 60 times), it is clear that most sulphate is not of marine origin.…”

The effects of the coastal environment on the atmospheric mercury cycle

“…Sea-salt penetration onto land is greatest in the first few kilometers but can exceed 50 km inland [Gustafsson and Franzen, 2000]. In some cases, sea-salt particles may be transported to the free troposphere as well [Patterson et al, 1980]. Aerosols may continue to scavenge Hg gases throughout their lifetime, as long as they have an associated water phase.…”

Simulation of the Optical Particle Counter Forward Scattering Spectrometer Probe 100 (FSSP-100)

“…Selecting the proper refractive index is more difficult, as only Patterson et al (1980) state a mean value for the continental distribution, while none of the authors reports about the refractive index of the maritime distributions.…”

“…Thus simulations were carried out using additional informations given by the authors or published elsewhere. Patterson et al (1980) show for the GAMETAG experiment some typical size distributions. They show a deep minimum at 0.5-pm radius.…”

“…Because of further limitations, these instruments have developed into a research topic in itself (Pinnick and Auvermann, 1979;Cerni, 1983;Cooper, 1988;Kim and Boatman, 1990; to name a few); the counters are used also for in situ measurements of droplet size distributions in clouds/fogs and other atmospheric aerosols in the same way as the forward scattering spectrometer probe Model 100 (FSSP-100, Particle Measuring Systems, Boulder, CO) Patterson et al, 1980;Borrmann et al, 1987;Kristament et al, 1992). The FSSP works in the nominal particle size range of radius 0.25-23.5-pm.…”