Integrating Plate Method Research Articles

Comparison between XRF and IBA techniques in analysis of fine aerosols collected in Rijeka, Croatia

The new system for energy dispersive X-ray fluorescence (EDXRF) analysis has been installed at the Laboratory for Elemental Micro-Analysis (LEMA) at the University of Rijeka. Currently the key application of this new XRF system is in the field of environmental science, i.e.in the analysis of fine airborne particles. In this work, results of initial multi-elemental analysis of PM2.5 fraction is reported for the first time in the region of Rijeka, Croatia. Sampling was performed at the Rijeka City center, during a continuous 9-day period in February/March 2012. All samples were collected on stretched Teflon filters in 12h periods. To check the reliability of the new XRF system, results of XRF analysis are compared with the results obtained by the well-established Ion Beam Analysis (IBA) laboratory at Australian Nuclear Science and Technology Organisation (ANSTO). The concentrations of H, Na, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br and Pb were determined. In addition, black carbon was determined by Laser Integrating Plate Method (LIPM). Very good agreement between XRF and IBA techniques is obtained for all elements detected by both techniques. Elemental concentrations were correlated with the traffic volume and wind speed and direction. The summary of our findings is presented and discussed in this paper.

Size-resolved elemental composition of aerosol particles in greater Sydney in 2002–2003

Environmental context Atmospheric aerosols may either scatter or absorb solar radiation, potentially cooling or warming the planet. The warming–cooling effects of aerosols are determined by their optical properties, which depend on chemical composition. To better predict aerosol effects we need a good understanding of aerosol chemistry across a wide size range and geographic area. We report results of a study designed to increase understanding of the chemical composition of fine and coarse aerosols in Sydney. Abstract Between November 2002 and December 2003 samples of PM2.5 and PM10 (particulate matter less than 2.5- and 10-μm aerodynamic diameter) aerosols were collected at four sites in the Sydney Basin in order to determine the spatial and seasonal variation of size-resolved aerosol chemical composition in the Sydney region and relate this to aerosol optical properties. Accelerator-based ion beam analysis was used to determine the elemental composition and black carbon (BC) was determined using the laser integrating plate method. Aerosol species were determined by multiplying a marker element by a factor based on molecular weight ratios. Mass concentrations at the rural sites were lower than at the urban sites with an average PM2.5/PM10 mass ratio of 0.5–0.6 for all sites although at the urban sites it was 0.2–0.25 in summer. For all sites BC was the dominant element, followed by Na. For the urban sites this was followed by Cl suggesting sea salt and then the soil elements Al and Si. For the rural sites the soil elements Al, Si and Ca were more important than Cl, which was found to decrease away from the coast. Analysis of aerosol species shows that BC accounts for a larger portion of PM2.5 than PM10 and sea salt and sulfate levels are higher in summer than in winter.

Black Carbon Measurement using Laser Integrating Plate Method

An intensive study to test and validate the Laser Integrating Plate Method (LIPM) of determining absorption coefficient and black carbon mass was carried out. Measurements by LIPM were compared to Smoke Stain Reflectometer measurements and Mie calculations based on accelerator ion beam analysis (IBA) elemental composition measurements. Results show that the value of mass absorption coefficient ϵ = 10 m2g− 1 previously used for mass determination, and widely accepted for black carbon generated by combustion processes, is an inappropriate choice for the type of carbon measured in Sydney. A value of ϵ = 7 m2g−1 for soot and ambient aerosol particles was found to be more appropriate.

A study of the aerosol of Santiago de Chile III: Light absorption measurements

The light absorption coefficient of the aerosol of Santiago de Chile has been measured by means of the integrating plate method. Values ranging between 0.01 and 0.2 km −1 have been found. Variations of the absorption coefficient by a factor of 8 within a few hours have frequently been found and have their causes in the specific meteorology of the Santiago air basin. In the summer a minimum occurs between 1 and 4 a.m. and a maximum between 8 and 10 a.m., whereas in the winter a maximum is found during the night and minimum values are in the afternoon with a smaller amplitude. Similar variations of the light absorption coefficient have been found also inside uninhabited rooms, since the aerosol was transported there almost without any losses. The daily pattern is similar but delayed and has a lower mean value and amplitude. When converting the light absorption to mass of black carbon, concentrations of elemental carbon of 1.3–25 μg m −3 were obtained. This is similar to other large cities, where a considerable part of the mobile sources are equipped with diesel motors. The light absorption contributes to about 15% of the light extinction of the aerosol, and considering an equal scattering of the soot particles, the contribution of soot to light attenuation in the atmosphere is about 30%. The single scattering albedo of the aerosol is 0.85, thus the heating effect of the absorption dominates. The light absorption coefficient is wavelength dependent with an average relationship of σ a = k( λλ 0) − α , the exponent being α = 0.92. The exponent of the wavelength dependence of the extinction coefficient of the aerosol was 1.22.

Experimental calibration for aerosol light absorption measurements using the integrating plate method—Summary of the data

The determination of the light absorption coefficient by means of the integrating plate method is a very simple and reproducible procedure frequently used in various configurations. In this work it was calibrated with laboratory generated aerosol of different absorption and scattering properties generated from internal and external mixtures of carbon and a transparent substance. The light absorption coefficient was determined by an independent method which can be considered free of systematic errors.The light absorption coefficient determined by the integrating plate method was always higher than the value obtained by the reference method. It was strongly dependent on the ratio of light absorption coefficient to extinction coefficient of the aerosol. For weakly absorbing aerosols the integrating plate method gave excessively high values. For example, when absorption contributed 5% to the extinction, the absorption coefficient determined by the integrating plate method was too high by a factor of 2.8. Calibration factors for a variety of aerosols are given.The deviations can be explained by considering the transmission, scattering and absorption of light in the slab of deposited particles. Radiative transfer calculations show the same trend as the experimental values. It turns out that this deviation is inherent to all methods which determine the light absorption coefficient by transmission with simultaneous integration of the scattered light.

Comment on “Measurement of Aerosol Absorption Coefficient from Teflon Filters using the Integrating Plate and Integrating Sphere Techniques” by D. Campbell, S. Copeland and T. Cahill

Campbell et al. (1995) present a study of the light transmitted by and reflected from Teflon filters, and claim that the Laser Integrating Plate Method (LIPM), a variant of the Integrating Plate Method (IPM; Lin et al., 1973), provides accurate determination of the light absorption coefficient of the particles deposited on the filters. Close examination of the paper reveals that it is an incomplete evaluation of a technique that is inappropriately compared to a questionable facsimile of an established method (IPM), and that the authors have not demonstrated that the LIPM technique provides accurate measurements of aerosol absorption coefficient. As a result of the lack of corrections for multiple scattering and absorption in the Teflon filters, data obtained with the LIPM (e.g., Malm et al., 1994) may significantly overestimate the true aerosol absorption coefficient.

Measurement of Aerosol Absorption Coefficient from Teflon Filters Using Integrating Plate and Integrating Sphere Techniques

Optical transmission of aerosol samples collected on Teflon filters measured by the integrating plate method (IPM) has been used as a means of determining the aerosol absorption coefficient, b ap, by the Air Quality Group at Crocker Nuclear Lab for over 9 years. The results of an intensive quality assurance program, using an integrating sphere photometer configured for measurement of the transmission of filters, demonstrate that the IPM is highly precise (±1%) and does not suffer from inherent overestimation of particle absorption due to internal scattering, a problem commonly attributed to IPM measurements of aerosols collected on Nuclepore filters. If the appropriate correction is applied when filter loading exceeds a monolayer of particles, b ap can be accurately determined by the IPM for aerosol samples collected on Teflon filters.

Determination of elemental concentrations in atmospheric aerosols in mexico city using proton induced x-ray emission, proton elastic scattering, and laser absorption

A study of the concentrations of elements present in atmospheric aerosols at two different sites in Mexico City was done with samples taken during September 1990 and February 1991. The samples were taken daily during 6 h periods (from 6:00 to 12:00 hr), using a Stacking Filter Unit (SFU) of the Davis design. This allowed the separation of particles with sizes ranging from 2.5 to 15 μm (coarse mass), and smaller than 2.5 μm (fine mass). Analyses of the samples with Proton Induced X-ray Emission (PIXE) gave information on elements heavier than Ne, Proton Elastic Scattering Analysis (PESA) on hydrogen contents, and the Laser Integrating Plate Method (LIPM) was used on the fine fraction to determine soot contents. Cluster Analysis is applied to the sample set in order to identify the emission sources of the elements. Additionally, the relationship to several meteorological variables is presented. Comparisons with previous studies are also provided.

Absorption coefficients and mass concentrations of the urban aerosol of Vienna, Austria, during the years 1985 and 1986

Nearly every day aerosol absorption coefficients and mass concentrations were measured at the physics building of the University of Vienna, located approximately 1.5 km from the city center. The aerosol was deposited on Nuclepore filters with 0.2 μm pore size, which were analyzed both gravimetrically for mass concentration c m and by the integrating plate method for absorption coefficients (σ a ). The overestimation of the method was corrected for using calibration factors derived from Hitzenberger (1993) and Hitzenberger and Puxbaum (1993). A statistical analysis showed marked seasonal changes of both σ a and c m with lowest values in summer (σ a below detection limit, c m =21.1 μg/m3) and highest in winter (σ a =0.574 km−1, c m = 543.1 μg/m3).The monthly averages ranged from σ a =0.014 km−1 (July 85) to σ a =0.127 km−1 (Dec. 85). The monthly mean mass concentration had a low in June 85 (44.5 μg/m3) and a maximum of 159 μg/m3 in February 85. A marked dependence on the wind direction was found for both σ a and c m , although the wind directions of the maximum values do not match. An estimate of the black carbon (BC) content using a value of the specific absorption coefficient B a for BC of 8 m 2/g showed that mean winter BC-concentrations were higher by a factor of 5.2 than in summer, although mass concentrations were increased by only a factor of 2. From seasonal and weekly variation patterns it can be estimated that heavy duty diesel traffic contributes 63 % of the absorbing aerosol in summer. In winter the main BC source is space heating (54 % during the week, 85 % on Sundays); followed by heavy duty traffic (27 % during the week, absent on Sundays). Mean single scattering albedos ω 0 in winter were as low as 0.70 and in summer as high as 0.94, although individual days had ω 0 below the critical value of 0.85.

Comparison of measurements of aerosol optical absorption by filter collection and a transmissometric method

Light-absorbing aerosol particles are present in the atmosphere all over the world, and they play an important role in the energy transfer to the atmosphere. The main substance causing light absorption in the atmosphere is graphitic (black) carbon, the major constituent of soot. It is generated at any kind of combustion, and in source regions soot particles are mostly mixed externally with other particles. After some time the soot particles may become attached to other particles, thus becoming mixed internally. Many methods for the determination of the light absorption by particles exists. The integrating plate technique offers a fast and reproducible way to determine light absorption coefficients of aerosol particles deposited on filters. Comparisons of this method with other determinations of light absorption coefficients have given partially agreement and partially disagreement. Therefore a comparison with an absolute method has been performed in order to determine possible inaccuracies. An externally mixed aerosol was made by independently generating a light-absorbing aerosol and a non-light-absorbing aerosol and mixing them such that within the measuring period coagulation was negligible. The light-absorbing aerosol was generated by a spark discharge between carbon electrodes. The sizes of the particles were small, usually more than 90% of the particle mass was below 50 nm. The non-absorbing was generated by a constant output atomizer. For small carbon particles the light extinction is dominated by the light absorption, therefore a measurement of the light extinction coefficient in a long path photometer provides an absolute method to determine the absorption coefficient. A comparison with the absorption coefficient determined simultaneously with the integrating plate method permits the estimation of the error. For pure carbon the light absorption coefficient determined by the integrating plate method is approximately 20% higher than the “true” value. For mixed aerosols the deviation depends on the mixing rate, but the integrating plate method always overestimates the light absorption coefficient.

TWO YEAR STUDY OF ELEMENTAL COMPOSITION OF ATMOSPHERIC AEROSOLS IN MEXICO CITY

As the second part of a wide project, we have carried out a study of airborne particulates in Mexico City, collected during two time periods (from 7:00 to 11:00, and from 11:00 to 15:00 Hrs.), one day of every week between March 1988 and February 1990. Elemental concentrations were determined by Proton Induced X-ray Emission (PIXE) for elements Na to Pb, while soot content was measured by means of Laser Integrating Plate Method (LIPM). As expected, the concentrations show an increase during the months October to March, due to frequent thermal inversions and dry weather. Moreover, the pollutant levels are higher during earlier hours, while the soil and anthropogenic origin of the elements can be better determined for the mid-day period, as seen from the grouping in the respective dendograms.

SEASONAL STUDY OF THE COMPOSITION OF ATMOSPHERIC AEROSOLS IN MEXICO CITY

Elemental analysis of airborne particulates collected in a site near downtown Mexico City have been performed. The samples were taken during one week of every season in 1988, Twenty three elements, from sodium to lead, were detected by Proton Induced X-ray Emission (PIXE). In addition, soot contents was determined by laser Integrating Plate Method (LIPM). Concentrations of these elements show hourly variations during the day, with maximum values in the period from 6 to 12 A.M. An overall tendency toward maximum elemental concentrations is observed in the winter season, especially for primary anthropogenic pollutants, as was anticipated based upon the frequency of thermal inversions.

Properties of atmospheric aerosols inverted from optical remote sensing

A new approach is proposed for optical remote sensing of atmospheric aerosols. A multiwavelength radiometer was used to measure direct solar radiation and sky radiation on the solar almucantar. The scattering phase function, the atmospheric optical depth, and their variation with wavelength were inverted simultaneously. A ‘reserve’ method was used to obtain the size distribution and refractive index of atmospheric aerosols. The results indicated that in Beijing city, the minimum total optical depth was 0.33 measured in September and October, and the maximum was 0.462 measured in March. The average value of the imaginary part of refractive index was 0.034 (0.532 μm) measured in winter (heating periods), and was only 0.016 (0.532 μm) measured in nonheating periods. A parallel observation was made to check the remote method, in which the aerosol size distribution was measured with a cascade sampler and the absorption coefficient of aerosols was obtained with the integrating plate method. The agreement of the results showed that the approach proposed was useful.

Experimental determination of the accuracy of light absorption measurements with the integrating plate method

Experimental determination of the accuracy of light absorption measurements with the integrating plate method

Absorption and mass absorption coefficients measured with the integrating plate method

Absorption and mass absorption coefficients measured with the integrating plate method

Absorption Coefficient of the Vienna Aerosols: Comparison of Two Methods

The absorption coefficient of the atmospheric aerosol over Vienna has been determined by two independent methods: the integrating plate method and by subtracting the light scattering coefficient obtained with an integrating nephelometer from the light extinction coefficient obtained by telephotometer. The raw data are highly correlated and, both for the summer aerosol with an average 20% light absorption and for the winter aerosol with an average of 40% light absorption, they agree almost perfectly. When considering small corrections owing to truncation in the nephelometer, the light absorption measured by the integrating plate is consistently too high by 30%–40%. This is in agreement with previously published results for other locations.

A Processor-Controlled Multisample Soot Photometer

The technique of the integrating plate method for the measurement of aerosol light absorption has been expanded significantly in a multisample soot photometer. The instrument consists of a double-beam, single detector, digital measurements, and control system. Transmission changes due to particle absorption on the order of 10 −4 can be detected with the new instrument, corresponding to a few nanograms of elemental carbon per sample. The photometer has been calibrated with known amounts of a well-characterized reference soot. The usefulness of the instrument is demonstrated with field results of three areas of application: aerosol light absorption at a Swedish remote area station, soot in cloud water, and light-absorbing particles in an Arctic ice core.

Particulate monitoring at US National Parks using PIXE

In order to help the United States National Park Service understand the causes of visibility impairment at various national parks throughout the United States, the Crocker Nuclear Laboratory at the University of California, Davis, has been collecting samples of coarse and fine particles at 35 sites continuously since 1982. At these remote sites most visibility impairment is due to the scattering of light by fine particles, between 0.2 and 1 μm. We are responsible for all aspects of the monitoring program, including designing and maintaining the particulate samplers, handling and analyzing the filters, and presenting and interpreting the results. A successful monitoring program requires strict adherence to carefully prepared procedures at all stages, with numerous quality assurance checks. All the samples are analyzed for mass by microbalance and for elemental composition by PIXE. PIXE is well-suited to particulate monitoring in terms of accuracy, cost, range of elements, and spatial resolution. The concentration of fine hydrogen is measured by proton elastic scattering operated simultaneously with the PIXE analysis. We also measure the optical absorption by fine soot particles using the integrating plate method. Because the sites arc remote and the sampling is almost continuous, most of the measured variables show well-defined regional patterns when averaged over the seasons of the year. The wide range of elements permits a good characterization of the fine particles. There are wide differences in the overall composition for different regions. In the eastern US the fine mass is dominated by ammonium sulfate. In some regions of the western US, fine soil and organics are important components to the aerosol. For visibility, fine sulphur is the most single important element measureable by PIXE. For most regions sulfur is largest in summer, although in some regions the maxima are in spring or fall. The average sulfur concentration varies widely over the US. with values in the east ten times those in some regions of the west. The concentrations of other variables, such as potassium, lead, zinc, copper, hydrogen, silicon are also important in understanding the composition of fine particles.

Optical and chemical properties of roadside aerosols

Roadside aerosols have been monitored by a variety of techniques. Optical reflectance of Whatman No. 1 filters gave the British Standard smoke value. The optical absorption coefficient was measured by the integrating plate method after collection on Nuclepore filters. As expected there is a good correlation between optical absorption and smoke concentrations but a somewhat poorer correlation of these values with the mass concentration determined gravimetrically. To distinguish between local traffic emissions and the general urban background simultaneous monitoring was undertaken at a rooftop site away from the road. The specific absorption coefficient values were higher at the roadside than on the rooftop reflecting the higher proportion of carbonaceous material near to traffic. To assess the importance of the elemental and organic carbon content of the aerosol to the optical properties, two further measurements were made. The fraction of volatile matter in the aerosol was determined by thermal desorption and the carbon content of the non-volatile remainder was determined using an elemental analyser. The fraction of volatile matter, which includes hydrocarbons and some inorganic species such as NH 4NO 3, was found to be in the range 24–73% and to be slightly higher away from the road. The non-volatile carbon was found to be in the range 6–25% by the road. The specific absorption increases with the fraction of non-volatile carbon.

Measurement of Light Absorption Extinction in Denver

Simultaneous measurements of b ext (teleradiometer), b sp (integrating nephelometer), and b ag (N02 monitor) were used to obtain particle absorption extinction coefficients b ap for the Denver atmosphere during January 1982. The average of the ratio b ap/b sp was measured to be 0.185 ± 0.015 at 530 nm, which is 2–3 times smaller than previous measurements. Supplementary data included b ap measurements by the integrating plate method, which yielded values systematically higher by about 35%, and elemental carbon (black soot) aerosol concentration, from which a value of 8.0±0.6 m2 g−1 was obtained for the mass-specific absorption coefficient of elemental carbon.