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Abstract
The simultaneous operation of two NCAR ice nuclei counters and an integrating nephelometer at Mauna Loa Observatory over a period of 9 months shows concentration changes in the ice nuclei population that vary in direct relation to the atmospheric light scattering coefficient. Furthermore, both of these atmospheric parameters are strongly correlated with local climatology. 1) lowest values of ice nuclei concentrations and Rayleigh scattering exist when subsiding air or a strong temperature inversion prevents the advection of sub-inversion air to the monitoring site; 2) an increased frequency of higher ice nuclei counts and Increased light scattering over a period of several hours are found when mesoscale atmospheric mixing occurs; and 3) the highest number of ice nuclei and maximum light scatter are encountered when a thermally induced air flow advects sub-inversion air to the Observatory site. These findings suggest the absence of extraterrestrial sources for light scattering and ice nucleating material, and point toward the existence of sources for both on Hawaii.
Abstract
The simultaneous operation of two NCAR ice nuclei counters and an integrating nephelometer at Mauna Loa Observatory over a period of 9 months shows concentration changes in the ice nuclei population that vary in direct relation to the atmospheric light scattering coefficient. Furthermore, both of these atmospheric parameters are strongly correlated with local climatology. 1) lowest values of ice nuclei concentrations and Rayleigh scattering exist when subsiding air or a strong temperature inversion prevents the advection of sub-inversion air to the monitoring site; 2) an increased frequency of higher ice nuclei counts and Increased light scattering over a period of several hours are found when mesoscale atmospheric mixing occurs; and 3) the highest number of ice nuclei and maximum light scatter are encountered when a thermally induced air flow advects sub-inversion air to the Observatory site. These findings suggest the absence of extraterrestrial sources for light scattering and ice nucleating material, and point toward the existence of sources for both on Hawaii.
Abstract
Solar radiation transmission data taken at Mauna Loa exhibit a seasonal variation with the minimum in summer. On the basis of Barrett's model for the depletion of solar radiation by aerosols, it is suggested that these variations are due to the seasonal generation of organic aerosols by the biosphere. It is suggested that the naturally produced atmospheric background aerosol of organic origin causes the typical seasonal turbidity variations. Furthermore, changes in the amplitude or phase of transmission data could be used to indicate whether aerosols from anthropogenic sources would influence the earth's albedo.
Precipitable water calculations suggest that humidity data above Mauna Loa are not accurate enough to make a quantitative estimate of the effect of atmospheric water vapor on Mauna Loa radiation data. However, water vapor apparently cannot account for these variations on the basis of phase angle considerations.
Abstract
Solar radiation transmission data taken at Mauna Loa exhibit a seasonal variation with the minimum in summer. On the basis of Barrett's model for the depletion of solar radiation by aerosols, it is suggested that these variations are due to the seasonal generation of organic aerosols by the biosphere. It is suggested that the naturally produced atmospheric background aerosol of organic origin causes the typical seasonal turbidity variations. Furthermore, changes in the amplitude or phase of transmission data could be used to indicate whether aerosols from anthropogenic sources would influence the earth's albedo.
Precipitable water calculations suggest that humidity data above Mauna Loa are not accurate enough to make a quantitative estimate of the effect of atmospheric water vapor on Mauna Loa radiation data. However, water vapor apparently cannot account for these variations on the basis of phase angle considerations.
Abstract
Nephelometry, in conjunction with a tube furnace and an Aitken nuclei counter, has been applied to the investigation of the volatile component of the aerosol budget at Cape Kumukahi, Hilo. and Mauna Loa Observatory, Hawaii. It was found that heating of the incoming air sample resulted in a decrease in light scattering above 100C due to the loss of organics and other easily volatilized compounds, and a drastic increase in Aitken nuclei counts at temperatures above 150C in the presence of ammonium sulfate. In the marine aerosol, a decrease in light mattering at about 45C was observed which is probably due to the loss of moisture during the phase transition from droplet to crystal. A second decrease near 120C is probably caused by the volatilization of organics from the droplet aerosol. In heating to 150C, the amount of light-scattering decrease was found to depend on the air mass. On occasions when volcanic effluent was apparently present, an increase in Aitken nuclei was noted in the heated air. Total aerosol mass deduced from light-scattering measurements before heating was in good agreement with aerosol mass measurements determined by standard high-volume filter sampling techniques. The total amount of aerosols in the air mass above the trade inversion is comparable to the quantity found in the marine air man. After penetrating the trade inversion, however, the cation content of the air is significantly reduced and the aerosol volatility is increased.
Abstract
Nephelometry, in conjunction with a tube furnace and an Aitken nuclei counter, has been applied to the investigation of the volatile component of the aerosol budget at Cape Kumukahi, Hilo. and Mauna Loa Observatory, Hawaii. It was found that heating of the incoming air sample resulted in a decrease in light scattering above 100C due to the loss of organics and other easily volatilized compounds, and a drastic increase in Aitken nuclei counts at temperatures above 150C in the presence of ammonium sulfate. In the marine aerosol, a decrease in light mattering at about 45C was observed which is probably due to the loss of moisture during the phase transition from droplet to crystal. A second decrease near 120C is probably caused by the volatilization of organics from the droplet aerosol. In heating to 150C, the amount of light-scattering decrease was found to depend on the air mass. On occasions when volcanic effluent was apparently present, an increase in Aitken nuclei was noted in the heated air. Total aerosol mass deduced from light-scattering measurements before heating was in good agreement with aerosol mass measurements determined by standard high-volume filter sampling techniques. The total amount of aerosols in the air mass above the trade inversion is comparable to the quantity found in the marine air man. After penetrating the trade inversion, however, the cation content of the air is significantly reduced and the aerosol volatility is increased.
Abstract
Aitken nuclei and ice nuclei concentrations in the smoke plume from an oil well fire near Glenrock, Wyo., on 14 December 1973, were found to be elevated by at least an order of magnitude as compared with the surrounding atmosphere. The composition of most particles in the plume was suggestive of the clay minerals; these could account for the increased ice nuclei concentrations.
Abstract
Aitken nuclei and ice nuclei concentrations in the smoke plume from an oil well fire near Glenrock, Wyo., on 14 December 1973, were found to be elevated by at least an order of magnitude as compared with the surrounding atmosphere. The composition of most particles in the plume was suggestive of the clay minerals; these could account for the increased ice nuclei concentrations.
Abstract
To assess the influence of anthropogenic aerosols on the physics and chemistry of clouds in the northeastern United State, aerosol and cloud-drop size distributions, elemental composition of aerosols as a function of size, and ionic content of cloud water were measured on Whiteface Mountain, New York, during the summers of 1981 and 1982. In several case studies, the data were cross-correlated with different air mass types—background continental, polluted continental, and maritime—that were advected to the sampling site. The results are the following (1) Anthropogenic sources hundreds of kilometers upwind cause the small-particle (accumulation) mode number to increase from hundreds to thousands per cubic centimeter and the mass loading to increase from a few to several tens of micrograms per cubic meter, mostly in the form of sulfur aerosols. (ii) A significant fraction of anthropogenic sulfur aerosols appears to act as cloud condensation nuclei (CCN) to affect the cloud drop concentration. (iii) Clouds in Atlantic maritime air masses have cloud drop spectra that are markedly different from those measured in continental clouds. The drop concentration is significantly lower, and the drop size spectra are heavily skewed toward large drops. (iv) Effects of anthropogenic pollutants on cloud water ionic composition are an increase of nitrate by a factor of 50, an increase of sulfate by more than one order of magnitude, and an increase of ammonium ion by a factor of 7. The net effect of the changes in ionic concentrations is an increase in cloud water acidity. An anion deficit even in maritime clouds suggests an unknown, possibly biogenic, source that could be responsible for a pH below neutral, which is frequently observed in nonpolluted clouds.
Abstract
To assess the influence of anthropogenic aerosols on the physics and chemistry of clouds in the northeastern United State, aerosol and cloud-drop size distributions, elemental composition of aerosols as a function of size, and ionic content of cloud water were measured on Whiteface Mountain, New York, during the summers of 1981 and 1982. In several case studies, the data were cross-correlated with different air mass types—background continental, polluted continental, and maritime—that were advected to the sampling site. The results are the following (1) Anthropogenic sources hundreds of kilometers upwind cause the small-particle (accumulation) mode number to increase from hundreds to thousands per cubic centimeter and the mass loading to increase from a few to several tens of micrograms per cubic meter, mostly in the form of sulfur aerosols. (ii) A significant fraction of anthropogenic sulfur aerosols appears to act as cloud condensation nuclei (CCN) to affect the cloud drop concentration. (iii) Clouds in Atlantic maritime air masses have cloud drop spectra that are markedly different from those measured in continental clouds. The drop concentration is significantly lower, and the drop size spectra are heavily skewed toward large drops. (iv) Effects of anthropogenic pollutants on cloud water ionic composition are an increase of nitrate by a factor of 50, an increase of sulfate by more than one order of magnitude, and an increase of ammonium ion by a factor of 7. The net effect of the changes in ionic concentrations is an increase in cloud water acidity. An anion deficit even in maritime clouds suggests an unknown, possibly biogenic, source that could be responsible for a pH below neutral, which is frequently observed in nonpolluted clouds.
Abstract
Using an airborne lidar, we have measured atmospheric aerosol backscatter coefficients (differential backscatter cross section per unit volume) for 10.6 μm wavelength laser radiation as a function of height to 5200 m for a number of meteorological conditions over the United States high plains. Airborne in situ samplers measured the particle size distribution at the same time and altitude as the lidar measured backscatter. One backscatter coefficient profile at 10.6 μm was compared with a 0.694 μm lidar backscatter profile as well as with the particle size distribution profile. The average infrared backscatter coefficient ranged from ∼8 × 10−9 m−1 sr−1 at the surface to 1 × 10−10 sr−1 at 5200 m altitude.
Abstract
Using an airborne lidar, we have measured atmospheric aerosol backscatter coefficients (differential backscatter cross section per unit volume) for 10.6 μm wavelength laser radiation as a function of height to 5200 m for a number of meteorological conditions over the United States high plains. Airborne in situ samplers measured the particle size distribution at the same time and altitude as the lidar measured backscatter. One backscatter coefficient profile at 10.6 μm was compared with a 0.694 μm lidar backscatter profile as well as with the particle size distribution profile. The average infrared backscatter coefficient ranged from ∼8 × 10−9 m−1 sr−1 at the surface to 1 × 10−10 sr−1 at 5200 m altitude.
Abstract
A focused cavity aerosol spectrometer aboard a NASA ER-2 high-altitude aircraft provided high-resolution measurements of the size of the stratospheric particles in the 0.06–2.0-µm-diameter range in flights following the eruption of Mount Pinatubo in 1991. Effects of anisokinetic sampling and evaporation in the sampling system were accounted for by means adapted and specifically developed for this instrument. Calibrations with monodisperse aerosol particles provided the instrument's response matrix, which upon inversion during data reduction yielded the particle size distributions. The resultant dataset is internally consistent and generally shows agreement to within a factor of 2 with comparable measurements simultaneously obtained by a condensation nuclei counter, a forward-scattering spectrometer probe, and aerosol particle impactors, as well as with nearby extinction profiles obtained by satellite measurements and with lidar measurements of backscatter.
Abstract
A focused cavity aerosol spectrometer aboard a NASA ER-2 high-altitude aircraft provided high-resolution measurements of the size of the stratospheric particles in the 0.06–2.0-µm-diameter range in flights following the eruption of Mount Pinatubo in 1991. Effects of anisokinetic sampling and evaporation in the sampling system were accounted for by means adapted and specifically developed for this instrument. Calibrations with monodisperse aerosol particles provided the instrument's response matrix, which upon inversion during data reduction yielded the particle size distributions. The resultant dataset is internally consistent and generally shows agreement to within a factor of 2 with comparable measurements simultaneously obtained by a condensation nuclei counter, a forward-scattering spectrometer probe, and aerosol particle impactors, as well as with nearby extinction profiles obtained by satellite measurements and with lidar measurements of backscatter.
