The aerosol spectrometer (A.S.) separates quantitatively airborne particles in the diameter range 3 μ – 0.03 μ from the atmosphere in the form of a size-spectrum, that is, a continuous band-shaped deposit. The position of a particle thereon is indicative of its ‘Stokes' diameter' while it was airborne, and independent of physical changes incurred after its separation from the suspending air. This size-classified separation results from the exposure of a laminar, continuous air flow to a large centrifugal field (up to 26,000 g), the flow rates vary between 3.3 and 7.4 lit/min. The size (and mass) distribution of the aerosol is derived from the typical variation of the deposit density along the spectrum, either by microscopic count (down to 0.1 μ) or by micro-photometric recording of the light scattered by the particles under reflected dark-field illumination in a special micro-analyzer. A brief description of the instruments and the mathematical basis of the analytical procedure is presented, also its application to a “model” aerosol of polystyrene latex, consisting of equal-sized particles in various states of agglomeration. From the size definition in terms of the Stokes' diameter, a relationship between the locus of deposition of dry and hydrated hygroscopic nuclei is derived and subsequently supported experimentally for NaCl aerosols. The A.S. has been applied to the analysis of natural and artificial aerosols in the submicron range. Samples of natural (off-shore and mountain) aerosol spectra are presented; they follow in general the pattern determined by previous authors but show a fine structure which appears to be due to traces of organic matter. The artificial generation and conditioning of NaCl aerosols and the so resulting size distribution is described, particularly the strong effect of the presence of traces of organic vapors (turpentine, pinene) during the hydration and dehydration of the salt nuclei. It is apparent that such traces prevent or delay the equilibrium of the nucleus when the humidity of its gaseous environment is altered.

This paper describes the nature of nanometer particles involving considerations of the kinetic theory of gases, quantum mechanics, and aerosol dynamics. It is shown that particles in the size range below about 5nm contain only few molecules with a high proportion at the surface. Hence, the structure of such particles cannot be regarded as a continuum and the traditional concepts of particle volume and surface area are no longer prime parameters. The electronic state of the particle is determined by the electronic states of the individual constituent molecules. Their configuration is extremely important in the particle interactions with other entities, including molecules, other particles, and biological cells. It is acknowledged that the physics of very, very small particles and their interactions are currently understood only for very simple systems. But, in view of the profound implications for many areas of practical interest, it is expected that during the years ahead multidisciplinary research will lead to rapid advances in our understanding.

AUPHEP was started in 1999 as a 5 years program to investigate the situation of the atmospheric aerosol with respect to effects on human health. At four different sites in Austria (3 urban and one rural site) an extended monitoring program was conducted for PM1, PM2.5 and PM10 as well as particle number concentration for 12 months each. Beside continuous measurements using TEOM and beta attenuation high-volume sampling of PM2.5 and PM10 provided samples for chemical analyses of various ions, heavy metals and organic compounds. Furthermore, carbonaceous material (TC, EC, OC) year round and PAHs on selected days were analyzed. From collocated public monitoring stations also pollutant gases (SO2, NO, NO2, O3, CO) and meteorological components are available. In winter and summer campaigns aerosol size spectra including chemical components were measured for at least one week each. All data are collected in a project data base (CD-ROM). While extensive data analysis will be presented in following papers, some general results are presented within this paper: annual averages for PM1 are between 10 and 20 μg m−3, for PM2.5 between 15 and 26 mg m−3 and for PM10 between 20 and 38 μg m−3. Number concentrations are between 10,000 and 30,000 cm−3. Urban concentrations are usually higher in winter, rural concentrations in summer. PM2.5 is in average around 70% of PM10, for PM1 this fraction is about 57%. Several studies on health effects are included in this project: a cross-sectional study on preschool and school children regarding lung function measurements and questionnaires about respiratory impairment in the surrounding area of the monitoring sites as well as time series studies on mortality and respiratory morbidity on the general population.

The monitoring data for the PM mass fractions of PM1, PM2.5, PM10 and TSP as well as the particle number concentrations at four sites in Austria (3 urban and 1 rural) and over a 1 year period are presented within this paper. The mass concentrations discussed are mostly based on TEOM measurements, but beta absorption and HiVol gravimetric sampling has been used in parallel. The data are compared with other European and world wide information available so far—for PM1 the data base still is very poor. Generally the data fit into the Central European context as far as the long-term averages and the daily and seasonal pattern and the ratios between the various fractions are concerned. Annual means of mass concentrations for PM1, PM2.5 and PM10 are in the order of 16, 20 and 28μgm−3 at the urban sites and a little bit lower at the rural site. In average PM1 counted for about 50–60% and PM2.5 for about 70% of PM10.The number concentrations at the urban sites are in the upper European level and show a distinct seasonal cycle. At the rural site no seasonal influence can be seen.

On several days during the 1 year measurement period the 24 h average EU concentration limit for PM10 of 50 μg m−3 was exceeded at the urban site AUPHEP1 as well as at the rural site AUPHEP2. The exceedances occurred generally during the winter half-year, however, during the summer period the elevated values were recorded as well. At the urban site several days with concentrations above 70 μg m−3 were observed. The highest 24-h concentration reached 130 μg m−3 on 1 January 2000. Regional transport processes of polluted air mass were the influencing factor for the elevated PM burden at both sites, however, the rural site was often additionally polluted by the Vienna metropolitan area. The high pollution events generally occurred under weather condition with prevailing SE–SW air flow. The chemical composition of the PM fractions during "high PM" was clearly different than that during the days with "low PM" burden. The chemical composition obviously reflects different source regions, paths of the air masses as well as weather patterns.

The measurements of PM2.5 and PM10 at two sites—an urban site in Vienna (AUPHEP-1) and a rural site considered local background (AUPHEP-2)—indicated only low aerosol generation activity in the city on an annual basis. Defining the term "urban impact" as the difference between observations at the urban and the local background site we find an annually averaged urban impact for PM2.5 of 3.4 μg m−3 and for PMC of 3.3 μg m−3 (the coarse fraction PMC=PM10−PM2.5). The relative increase of the particulate matter (PM) concentration at the urban site compared to the background site (AUPHEP-2) is annually averaged only 19% for PM2.5, but 60% for PMC. The chemical main constituents of the PM2.5 urban impact are black carbon (BC), organic carbon (OC), and sulfate; the main constituents of the PMC urban impact are OC and indicators for mineralic aerosol (Fe, Ca, Mg, Na, K). The BC/TC ratio of the PM2.5 urban impact is typical as for combustion sources, e.g. automotive traffic, oil or coal combustion. Urban coarse OC is considered to originate from non-pyrogenic sources. From the trace metals investigated (As, Cd, Co, Cu, Cr, Mn, Ni, Pb, V, Zn) only Cd, Ni, Pb, and Zn exhibited a slight cold season enrichment in the urban airshed. From the weak signal of a seasonality of oil or coal combustion indicators we conclude that local domestic heating sources are using "clean fuels".

Measurement methods for continuous monitoring of the mass concentration of particulate matter (PM) frequently yield data which differ from standardized manual gravimetric methods. The data set from a 1 year measurement period at four sites in Austria was used to analyze the results from gravimetric (high volume sampling) and automated methods (TEOM® and beta-attenuation). Grouping of the data according to season (average temperature) and chemical composition (in particular nitrate) showed good agreement of the various methods for summer and even better for low nitrate content. Correction for nitrate from experimental data and also from modeled nitrate improved the agreement also for winter data and higher nitrate concentrations. At least for the situation in Central Europe adequate conversion factors can be derived from information about the nitrate content of PM between data based on different measuring methods.

Mass size distributions of atmospheric aerosols have been sampled in the region of Vienna, a typical city in central Europe, at an urban and a rural site. The aerosol was collected simultaneously by cascade impactors. Two experiments which had a duration of 4 weeks each, were performed in August 1999 and in January/February 2000. Daily sampling periods were from 8:00 to 20:00, and from 20:00 to 8:00.An evaluation of the mass size distributions is represented in this paper. Emphasis is on the relationships of different aerosol components in a local and a regional context. The main results are as follows. The main components of the atmospheric aerosol are a fine aerosol, the accumulation aerosol, and a coarse aerosol. Specific coarse modes with modal diameters of 4.7 mum average and geometric standard deviations of about 3 occur at the urban and at the rural site, some times surprisingly strong. The fine and the coarse modes are very likely related to motor-car traffic. Usually the PM2.5 and PM10 aerosols are regionally strongly correlated. Occasionally, this correlation is effectively disturbed by local and/or regional emissions. Time series of correlation coefficients reveal an episodic character of the atmospheric aerosol. Periods of strong inter-site correlations of PM2.5 and PM10 indicate the dominance and the co-variation of the accumulation aerosols or the dominance and the co-variation of the coarse modes. (C) 2004 Elsevier Ltd. All rights reserved.

Total aerosol particle number concentrations, as measured by means of 16 different measurement systems, have been quantitatively compared during an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (ICCP-IUGG). The range of measuring instruments includes Pollak counters (PCO) in use already for several decades, presently available commercial particle counters, as well as laboratory prototypes. The operation of the instruments considered was based on different measurement principles: (1) adiabatic expansion condensation particle counter, (2) flow diffusion condensation particle counter, (3) turbulent mixing condensation particle counter, (4) laser optical particle counter, and (5) electrostatic particle measurement system. Well-defined test aerosols with various chemical compositions were considered: DEHS, sodium chloride, silver, hydrocarbons, and tungsten oxide. The test aerosols were nearly monodispersed with mean particle diameters between 4 and 520 run, the particle number concentrations were varied over 10(6) cm(-3) a range from about 4 x 10(1) to 7 x A few measurements were performed with two-component aerosol mixtures. For simultaneous concentration measurements, the various instruments 4 considered were operated under steady state conditions in a linear flow system. A series of at least 10 single concentration measurements was performed by each individual instrument at each set of test aerosol parameters. The average of the concentration data measured by the various instruments was defined as a common reference. The number concentrations obtained from the various instruments typically agreed within a factor of about two over the entire concentration range considered. The agreement of the measured concentrations is notable considering the various different measurement principles applied in this study, and particularly in view of the broad range of measurement instruments used. Significant deviations and nonlinear response were observed only in a few cases and are possibly related to calibration errors. For certain conditions, a dependence of aerosol counter response on particle composition has been found. The scatter of the number concentrations obtained from each individual instrument during measurements with constant test aerosol typically did not 10(3) cm(-3) exceed 20% to 25%. At concentrations below however, several of the instruments, including electrostatic particle measurement systems, tend to show increased experimental scatter. (C) 2002 Elsevier Science B.V. All rights reserved.

During an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (IAMAS-IUGG), 10 instruments for aerosol number concentration measurement were studied, covering a wide range of methods based on various different measuring principles. In order to investigate the detection limits of the instruments considered with respect to particle size, simultaneous number concentration measurements were performed for monodispersed aerosols with particle sizes ranging from 1.5 to 50 nm diameter and various compositions.