Josef Podzimek

Potential role of nuclei in cloud element formation at high altitudes

Abstract The role of aerosols in providing a heterogeneous nucleation contribution to cirrus cloud ice crystal formation has long been an unresolved question. A mobile aerosol sampling facility was employed on the NCAR Sabreliner research aircraft to take aerosol samples from the vicinity of cirrus clouds over Colorado and Wyoming. Tandem electrostatic classifier and impactor technique were used to measure aerosol size distribution, hydration capability and composition information. The results suggest that aerosol related heterogeneous nucleation processes are active in cirrus cloud processes.

The university of missouri-rolla, absolute aitken nucleus counter

The authors discuss the expansion cloud chamber system known as the University of Missouri-Rolla-absolute Aitken nucleus counter. A review of the properties of an expansion chamber and how it creates a supersaturation are given and a critical examination is made of the assumptions in its operation, e.g. adiabaticity of the expansion. The design of the chamber is described in detail and an analysis of the propagation of errors is given for quantities measured and calculated. A short review of the performance of the chamber and some general comments relative to comparisons with other Aitken nucleus counting instruments are given. The chamber is capable of making measurements on aerosols of number concentration up to 106 nuclei/cm3 to an accuracy of about 10–15% at any desired supersaturation ratio up to the ion limit. Finally mention is made of other expansion chambers developed in this laboratory for measurements of homogeneous nucleation rates.

Combustion aerosol scavenging

Abstract As an aerosol ages, the larger particles may scavenge smaller particles in the system. Here we study the scavenging of combustion aerosols by larger particles with a relatively high critical supersaturation. Combustion particles are not composed of pure elemental carbon particles which would be hydrophobic, but rather are composed of mixed soluble and insoluble materials. In this experiment the aerosols soluble fraction was enhanced through the addition of a small amount of ethyl disulfide to the original fuel. Measurements are made of scavenging rates for the combustion aerosols by the larger particles using the changes which the combustion particles induce in the scavengers when deposition occurs. The presence of the small combustion particle dramatically lowers the critical supersaturation of the composite particle, and this allows the differentiation between the large pure particles and those which have collected a small one. The scavenging is found to occur at faster rates than those predicted by Brownian scavenging theory. The mixed particles resulting from scavenging behave as large inert particles with point activation sites on their surfaces.

Upper-Tropospheric Aerosol Sampled during Project FIRE IFO II

Abstract During the FIRE IFO II project, aircraft were available for airborne sampling in and around cirrus cloud. Aerosols can play a role in the cloud formation process through the heterogeneous nucleation mechanism, and in turn, once formed, cirrus clouds can impact the ambient aerosol through scavenging and other collection mechanisms. University of Missouri aerosol sampling facilities were employed on these aircraft for in situ collection and characterization of the particulates near cirrus cloud level. Tandem differential mobility analyzer and impactor techniques were used to measure aerosol size distribution, hydration capability, and particle composition information. Evidence of aerosol layering was observed near the tropopause, and there was a tendency toward depletion of the ambient aerosol at both ends of the condensation nuclei (CN) size distribution. A large variability in the fine particle CN concentration was found, ranging from several tens to several thousands per cubic centimeter. The si...

Physical properties of coarse aerosol particles and haze elements in polluted urban-marine environment

Abstract Measurements of coarse particles (with r ≥ 1.0 μm) with the aid of a cascade impactor and of particle (droplet) identification in sensitized gelatine layers reveal their mean concentration of about 1.5 cm −3 during the months of May and June 20 km west from Napoli in Italy. Haze particles (droplets) are usually featured by insoluble core and many small particles deposited on their surface. Sea salt aerosol does not play a dominant role in the haze element formation at this site of measurement.

Aitken nuclei measurements in the lower stratosphere

A report is presented on Aitken nuclei (AN) measurements between 6 km and 19 km with the new Stratospheric Aitken Nuclei Detection System (SANDS) which was installed in the nose section of the WB-57F aircraft. Measurements were made between 48ON and 9s latitudes over the U.S.A., Gulf of Mexico, Central and South America between March, 1974, and February, 1975. Evaluation of 18 flights led to the following conclusion: The vertical profdes of AN concentration are similar to those found by Junge et al. (1961). However, the AN concentrations at altitudes above 17 km are higher by several tens of AN cm-". Horizontal flights showed a low AN concentration above 18 km over the tropical regions (below 20 AN cm-"), and an influence of the Rocky Mountains and the Andes Mountains on the AN measurements at 18 km altitude. Usually, several km above the tropopause, a negative correlation between AN, and ozone concentration was found.

Measurement of the concentration of large and giant chloride condensation nuclei during flight

РезюмеВ работе рассматривается способ применения чувствительных желатинных слоев (метод Виттори) для определения концентрации гигантских хлоридных ядер конденсации, а также влияние физических свойств среды на величину данных, полученных в результате измерений. Был разработан простой метод полетных измерений, который был проверен в течение семи полетов. При скорости движения самолета 150км/ч, гигантские ядра наталкиваются на стеклышка с чувствительным слоем (AgNO3) и оставляют на них следы, соответствующие величине ядер. При одной и той же скорости полета величина следа на стеклышке различна в зависимости от величины частиц. Путем измерений одной и той же полосы в центре стеклышка можно получить спектр величины ядер, предполагая, что нам известен фактор увеличения, который нам позволит произвести пересчет величины следа на действительную величину ядра (в данном случае он лежит в пределах 5,7–6,6). На основании измерений можно сделать следующие заключения: Использованный метод применим в метеорологии. Он довольно прост и точен для определения концентрации гигантскых ядер конденсации на различных уровнях атмосферы над землей. Общие концентрации гигантскых ядер обычно не достаточны для обьяснения эффективного процесса коагуляции, а в силу этого—и для обьяснения возникновения осадков из чисто водяных облаков над территорией ЧСР. Распределение концентрации ядер на различных высотах наводит на мысль о двояком происхождении ядер. В приземном слое в большом количестве преобладают частицы континентального происхождения, в то время как на более значительных высотах обнаруживается небольшое количество гигантских ядер морского происхождения. Над низкой облачностью было обнаружено мало ядер, так что здесь можно говорить о какомто “фильтрующем” воздействии облаков. Концентрация частиц и спектр их величины на определенной высоте над землей зависят от температурного расслоения атмосферы. Микрофотографии (кружков) подтвердили то, что здесь часто мы имеем дело с нерастворимыми ядрами в воде на поверхности которых сохранились активные частицы.

Droplet Concentration and Size Distribution in Haze and Fog

Fog (haze) droplet concentrations and size distributions were measured at five sampling sites representing rural and urban regions and a highly polluted marine-urban environment. Droplet imprints in a thin gelatine layer were evaluated and compared to the measurement by light scattering instruments. This enabled conditions for the application of the logarithmic-normal size distribution and for the classification of typical fog droplet size distributions to be established. In particular, the parameters featuring the width and asymmetry of a size distribution were suggested and calculated. Advantages and drawbacks of the applied droplet sampling and evaluation technique are discussed in more detail.

Experimental determination of the “capacity” of ice crystals

РезюмеРассмотрены вопросы, связанные с изучением „емкостей” различных форм моделей кристаллов льда при помощи измерений электрического тока в сосуде с электролитом. Несколько примеров показывает, что использованный метод позволяет с довольет с довольно хорошей точностью определить „емкость” самых сложных форм кристаллов.

Condensation nuclei activation or deactivation by deposited insoluble particles

Abstract Laboratory experiments have been performed in order to determine to what extent the deposition of, e.g. carbon particles doped by ethyl disulfide can affect the activation of well defined pure condensation nuclei such as sodium chloride and to study the way in which the carbon particles are distributed within the solution droplets. A significant effect was found for NaCl nuclei (dry particle diameter D = 0.425 μ m) after several hours of exposure to the carbon aerosol ( D c = 0.05–0.07 μ m) generated by a blowtorch. The critical supersaturation of sodium chloride with deposited doped carbon particles was slightly lowered in all samples. Analysis of micrographs shows that carbon particles are deposited on the droplet surface and in the core as well. A simple model of a droplet with insoluble deposited particles is suggested.