G. Garland Lala

On the Production of Aitken Nuclei from Breaking Waves and Their Role in the Atmosphere

Abstract A laboratory model of a breaking wave or whitecap was constructed, and the aerosol produced by it was investigated intensively. Submicron- and even Aitken-sized particles were produced: the presence of salt particles of mass <10−17 g(r<0.01 μm) could be inferred. The evidence strongly suggests that the submicron fraction is composed of film drops, derived primarily from bubbles larger than 1 mm in diameter. The shape of the CCN spectrum and overall mass distribution of the model-produced aerosol were similar to what is observed in clean marine air. Whether or not the production rate of such small particles is globally significant when the model results are applied to the oceans depends to a large extent on the set of assumptions one makes concerning aerosol residence time and fraction of sea surface covered by whitecaps. However, there are realistic choices of these parameters which suggest that appreciable fractions of both CCN and CN in the lower marine atmosphere are produced directly by the sea.

Semicontinuous PM2.5 sulfate and nitrate measurements at an urban and a rural location in New York: PMTACS-NY summer 2001 and 2002 campaigns.

Abstract Several collocated semicontinuous instruments measuring particulate matter with particle sizes ≤2.5 μm (PM2.5) sulfate (SO4 22−) and nitrate (NO3 −) were intercompared during two intensive field campaigns as part of the PM2.5 Technology Assessment and Characterization Study. The summer 2001 urban campaign in Queens, NY, and the summer 2002 rural campaign in upstate New York (Whiteface Mountain) hosted an operation of an Aerosol Mass Spectrometer, Ambient Particulate Sulfate and Nitrate Monitors, a Continuous Ambient Sulfate Monitor, and a Particle-Into-Liquid Sampler with Ion Chromato-graphs (PILS-IC). These instruments provided near realtime particulate SO4 2− and NO3 − mass concentration data, allowing the study of particulate SO4 2−/NO3 − diurnal patterns and detection of short-term events. Typical particulate SO4 2− concentrations were comparable at both sites (ranging from 0 to 20 μg/m3), while ambient urban particulate NO3 − concentrations ranged from 0 to 11 μg/m3 and rural NO3 − concentration was typically less than 1 μg/m3. Results of the intercomparisons of the semicontinu-ous measurements are presented, as are results of the comparisons between the semicontinuous and time-integrated filter-based measurements. The comparisons at both sites, in most cases, indicated similar performance characteristics. In addition, charge balance calculations, based on major soluble ionic components of atmospheric aerosol from the PILS-IC and the filter measurements, indicated slightly acidic aerosol at both locations.

Climatological Aspects of Radiation Fog Occurrence at Albany, New York

Abstract We present a detailed investigation of the local radiation fog climatology, carried out in support of our ongoing field program to study radiation fog mechanisms at Albany, New York. At Albany, a distinct ”radiation fog season” is observed during September and October. We show that this late-summer/early-autumn maximum in radiation fog observations is primarily due to a sufficient period of nocturnal cooling coupled with an adequate moisture supply. Five critical surface synoptic patterns are responsible for initiating the radiation fog process. In addition, radiation fog life cycles are generally confined to a modest time window centered on sunrise. Key parameters necessary for forecasting the onset time of fog are shown to be the initial relative humidity and nocturnal cooling rate.

Fog-82: A Cooperative Field Study of Radiation Fog

The Cloud Physics Section of the Atmospheric Sciences Research Center-State University of New York at Albany conducted a cooperative field study (FOG-82) during the autumn of 1982 as part of an ongoing radiation-fog research program. A computer-controlled data-acquisition system consisting of sophisticated soil, surface, and boundary-layer sensors, as well as contemporary aerosol and droplet probes was developed. These data are being used to address a variety of critical problems related to radiation-fog evolution. Scientists from 10 universities and research laboratories participated in portions of FOG-82. Research objectives included studies of fog mesoscale meteorology, radiation studies, low-level water budget, vertical fog structure, fog supersaturation, condensation nuclei, and fog-water chemistry, as well as radiation-fog life cycles. A comprehensive description of the FOG-82 program and objectives is presented.

Measurements of Visual Range and Radiation-Fog (Haze) Microphysics

Abstract An extensive boundary-layer field program was conducted which included simultaneous measurements of visibility and particle size distributions during fog and haze. Several empirical expressions relating changes in visibility to characteristics of the aerosol (droplet) size spectrum and relative humidity are presented and evaluated. Detailed analysis of one evolving dense fog revealed several points of interest regarding the behavior of drop size spectra, including a scheme for approximating fog supersaturation.

Development, Operation and Applications of an Aerosol Generation, Calibration and Research Facility

An aerosol generation, calibration, and research facility has been developed with the major purpose of evaluating aerosol instrumentation, including quality assurance testing, intercomparison, performance evaluation, and calibration of aerosol sizing, bulk, and speciated mass-measuring instruments. The aerosol facility also provides excellent opportunities for basic aerosol research. Polydisperse test aerosols are generated most often through spray atomization of solutions. Monodisperse test aerosols can be produced by mobility classification of polydisperse aerosols, by a vibrating orifice aerosol generator, by an electrospray aerosol generator, or by nebulization of polystyrene latex (PSL) particle suspensions. Generated inorganic, organic, and mixed aerosol particles range in size from 0.005 to greater than 1 micrometer. Physical characterization of the test aerosols is done using scanning mobility particle sizers, condensation particle counters, and an aerodynamic particle sizer. The facility includes a 450 l cylindrical glass slow-flow chamber that is used mainly for the dilution, equilibration, and controlled humidification of generated primary aerosol particles larger than 50 nm as well as for the generation of secondary aerosols through the choice of appropriate precursor reactants. Test aerosols can also be subjected to controlled concentrations of pollutant gases (O3, NOx, SO2, and VOCs). Smaller particles can also be generated and sampled either from a fast-flow chamber or a static chamber. The well-characterized aerosol environment produced in the slow-flow chamber is used to evaluate the performance of various instruments designed to measure aerosol mass, composition, and size over a range of ambient conditions. Instruments evaluated to date include an R&P standard TEOM mass monitor; a SES TEOM mass monitor; a Differential TEOM mass monitor with an electrostatic precipitator (ESP); R&P Ambient Particulate Sulfate, Nitrate, and Carbon monitors; a Particle-Into-Liquid Sampler with IC (PILS-IC); an Aerodyne Aerosol Mass Spectrometer (AMS); TSI scanning mobility particle sizers (SMPSs); and condensation particle counters (CPCs). Several examples of applications of the aerosol facility involving the TEOM mass monitors and the AMS are also discussed in this article.

A Numerical Evaluation of Radiation Fog Variables

Abstract A numerical model of radiation fog was developed in order to test the sensitivity of variables comprising the model, and evaluate its capability for forecasting the onset of fog from standard radiosonde weather data. Four case studies were considered that included both fog and no-fog occurrences. The variables examined–initial surface temperature and moisture conditions, eddy exchange profiles, radiative flux divergence, and dew formation–were all found to influence critically the models performance. Prediction of fog occurrence and temperature were reasonably encouraging provided a judicious (though somewhat arbitrary) choice of eddy mixing values was made.

Numerical Estimates of Humidity in a Membrane–Filter Ice Nucleus Chamber

Abstract A one-dimensional model was developed to examine humidity fields within a conditioning chamber for measuring ice nucleus concentrations on millipore filters. Representative concentrations of ice and cloud condensation nuclei were assumed, and the interplay among these growing particles (vapor sinks), the supply flux of vapor, and the resultant relative humidity at and above the filter surface investigated. The model suggests that water saturation is not achieved under typical operating conditions of such chambers. Maximum humidifies reached decrease with increasing numbers of either condensation or ice nuclei, thereby offering another possible explanation of the filter volume effect. Most favorable operating conditions for achieving highest chamber humidities are delineated. The results suggest that this technique is capable of detecting mixed condensation-freezing nuclei, deposition nuclei and some contact nuclei, with the former perhaps being most common not only in filter measurements but also...

Field Evaluation of a TSI Model 3034 Scanning Mobility Particle Sizer in New York City: Winter 2004 Intensive Campaign

A new “single box” Scanning Mobility Particle Sizer (TSI SMPS Model 3034) was deployed and operated during a period of four weeks as a part of the PMTACS-NY Winter 2004 intensive study in Queens College, New York City. The SMPS 3034 is an alternative to a conventional multi-component TSI SMPS and houses a Differential Mobility Analyzer and butanol-based Condensation Particle Counter in one cabinet. The SMPS 3034 operates at a fixed 1 l/min sample flow rate (4 l/min sheath flow rate) and measures size distributions within a 10–487 nm size range. One size scan is produced every 3 minutes. Four other measurement systems (a conventional TSI SMPS with a Nano Differential Mobility Analyzer, an Aerodynamic Particle Sizer, a stand-alone Condensation Particle Counter, and an R&P Inc. Filter Dynamic Measurement System (FDMS) TEOM mass monitor) were operated side-by-side with the SMPS 3034. It is shown that total particle number concentrations measured by the SMPS 3034 are highly correlated with those from the conventional Nano SMPS, the Condensation Particle Counter and the FDMS TEOM monitor, and that the number median diameters measured by the SMPS 3034 and the Nano SMPS agree within 3 nm.

Comments on 'Rocket effluent - Its ice nucleation activity and related properties'

Parungo and Allee (1978) reported ice nucleus (IN) measurements made from an aircraft in stabilized ground clouds from Titan III launches at KSC. They concluded from the measurements that the SGC contained IN. After an examination of the data the present authors (Hindman and Lala) argue that the filter devices were unable to detect IN in the SGC. In a reply Parungo and Allee attempt to refute this conclusion.