Meng-Dawn Cheng

Possible sources and preferred pathways for biogenic and non-sea-salt sulfur for the high Arctic

Sulfate is a major constituent observed in Arctic haze. Sulfur sources include anthropogenic, biogenic, and other natural sources. Previous studies have examined the concentrations and temporal variability of the concentrations of methanesulfonic acid (MSA) and sulfate (SO4=) at Alert, Northwest Territories, Canada. A receptor modeling method called the potential source contribution function (PSCF) combines the concentration data for these species measured in 7-day samples continuously collected between 1980 and 1991 with meteorological information in the form of air parcel back trajectories into conditional probability maps indicating the possible source areas and/or the preferred pathways that give rise to the observed high-concentration samples. After examination of the time series for MSA and SO4=, the data were segregated into time periods representing the spring, summer, and winter months and the PSCF analyses performed based on criterion values of the annual average species concentration. The potential source contribution method has been found to be effective in identifying possible source locations and the preferred pathways of MSA and SO4= in samples collected at Alert. Two concentration peaks are typically observed in the time series for MSA. The time series for SO4= is quite different from the series for MSA. The SO4= series only has peaks in the winter caused primarily by anthropogenic emissions. It was found that different regions of the North Atlantic Ocean contribute to the observed MSA concentrations during these different periods in agreement with prior hypotheses. Sources areas for sulfate during the summer and MSA during the winter can only be observed by changing the criterion value to the average during the period.

A receptor-oriented methodology for determining source regions of particulate sulfate observed at Dorset, Ontario

A statistical receptor-oriented model was developed for long-range transport of atmospheric sulfate to Dorset (elevation 320 m, latitude 4513′26″ N and longitude of 7855′52″ W), Ontario. This model computes the potential for sources within 1 latitude by 1 longitude grid cells across North America that contribute to the airborne concentrations measured at the ground station at Dorset. Airborne concentration data and air parcel backward trajectories were incorporated explicitly in the model calculation to identify the geographical areas of potential contributing sources. The present model is qualitative in nature; however, it provides a reasonable receptor-oriented approach to examine the long-range transport of atmospheric species. In order to fully understand the methodology and in a hope to optimize it, several aspects of the PSCF methodology have been examined in detailed in this study. Results of this study are presented that suggest interpolation of trajectory endpoints to increase the counting statistics for the potential source contribution function (PSCF) values is not reliable. The average concentration provides a reasonable criterion value; however, using the fiftieth percentile value as the criterion point provides an opportunity for identifying source areas that cannot be previously found by using the average concentration. The fiftieth percentile value may be a better choice for the particulate sulfate data in this case since Dorset is a relatively clean background site. Using the seventy-fifth percentile, which is generally larger than the average, may not be suitable because it reduces the number of degrees of freedom. This could render the model to behave like a regular trajectory analysis model that has been used commonly for analyzing episodic pollution events. Separation of data into summer and winter periods is useful to illustrate the effects of photochemistry and meteorology on the PSCF results. Invoking the total probability concept and examining the trajectory arrival at different heights directly above the sampling site, the total PSCF was computed. This resultant function thus provides a time-integrated geographical map useful for identifying sources of airborne particulate sulfate in a receptor-oriented manner.

ARM Southern Great Plains Site Observations of the Smoke Pall Associated with the 1998 Central American Fires

Drought-stricken areas of Central America and Mexico were victimized in 1998 by forest and brush fires that burned out of control during much of the first half of the year. Wind currents at various times during the episode helped transport smoke from these fires over the Gulf of Mexico and into portions of the United States. Visibilities were greatly reduced during favorable flow periods from New Mexico to south Florida and northward to Wisconsin as a result of this smoke and haze. In response to the reduced visibilities and increased pollutants, public health advisories and information statements were issued by various agencies in Gulf Coast states and in Oklahoma. This event was also detected by a unique array of instrumentation deployed at the U.S. Department of Energys Atmospheric Radiation Measurement (ARM) program Southern Great Plains Cloud and Radiation Testbed and by sensors of the Oklahoma Department of Environmental Quality/Air Quality Division. Observations from these measurement devices sugg...

Transport patterns and potential sources of total gaseous mercury measured in Canadian high Arctic in 1995

Abstract Trajectory cluster analysis and the potential source contribution function (PSCF) model have been used to investigate the source–receptor relationship for the total gaseous mercury (TGM) measured in the Canadian High Arctic (Alert, 82.5°N, 62.3°W) during 1995. Cluster analysis of 10-day back-trajectories in 1995 shows that the synoptic flows arriving at Alert are dominated by the air masses from the north. Long-range transport only occurs in the cold seasons while summertime flows tend to circulate in the Arctic Ocean. The potential source regions identified by the PSCF modeling include Eurasia and populated areas in the North America and Europe. Based on the modeling results, it is suggested that the elevated TGM concentrations found in the Arctic summer should be of geological origins, mainly from the evasion of volatile Hg 0 from earths surfaces. In the autumn and winter, mercury is transported to the receptor site from remote anthropogenic sources. The preferred sources of TGM in the spring cannot be clearly determined due to the Arctic springtime mercury depletion, which significantly reduces the number of trajectories contributing to PSCF values. Using TGM data of higher temporal resolution improves the sensitivity of the PSCF modeling results.

Aerosol Measurement by Laser-Induced Plasma Technique: A Review

Literature on laser-induced plasma spectroscopy (LIPS) published since the 1960s is reviewed and presented in this report, although LIPS of solid samples has been emphasized in the past. The LIPS is found to be the most convenient technique for in-situ and real-time measurement of metal species in the gaseous and aerosol phases. This technique is a strong candidate for the develop ment of a next-generation field portable instrument for characterizing metal species from the emission sources as well as ambient environments. The instru ment can provide a highly resolved spatial and temporal data of significance to environmental and health research on metal and particle toxicity. An instrument based on LIPS can be a viable tool for continuously monitoring toxic metal emissions at an industrial source, for example. The wide range of lasers used and other experimental and theoretical factors to be considered in the design of a LIPS instrument for aerosol measurements was discussed in this report. Experimental r...

Detection of Chromium Aerosol Using Time-Resolved Laser-Induced Plasma Spectroscopy

Time-resolved laser-induced plasma spectroscopy (LIPS) has been used as a tool for the detection of chromium in aerosol. In this article, LIPS has been used to achieve the lowest limits of detection for chromium (400 ng/dscm) in droplets. A comparison with other LIPS instruments and inductively coupled plasma atomic emission spectroscopy (ICP-AES) shows that the limits of detection for chromium metal in aerosol range from 12 to 60 μg/dscm and 200 ng/dscm for LIPS and ICP-AES, respectively. We have studied the effects of laser wavelength, excitation energy, and optimum spectrometer delay time to optimize these low limits of detection. A Nd:YAG laser with output wavelengths of 1064, 532, and 266 nm has been used to study the effects of wavelength on laser energy and aerosol interactions—specifically, plasma initiation and efficiency of ionization in the detection of elemental species. Measured time-resolved spectra are used to establish the most appropriate time delay producing an optimum signal-to-background ratio.

Potential source contribution function analysis and source apportionment of sulfur species measured at Rubidoux, CA during the Southern California Air Quality Study, 1987

During the Southern California Air Quality Study (SCAQS) in summer and fall of 1987, specially designed SCAQS samplers were used to collect particles and gaseous species. Ion chromatography (IC) and colorimetry were employed to analyze the gaseous and particulate ionic species while the trace elements in the particles were analyzed using x-ray fluorescence (XRF). Potential source contribution function (PSCF) analysis was applied to the chemistry data of the acidic species collected by the SCAQS samplers at the Burbank, Claremont and Rubidoux sites and the meteorology data in the form of air parcel backward trajectories. The results are presented as gridded conditional probability maps showing source areas that have a potential to contribute to the high concentrations of acidic species observed at the receptor sites. In order to quantitatively determine the mass contributions of acidic species from these identified source areas to the receptor sites, a source apportionment method was developed that utilizes the PSCF analysis results and the ground and elevated level emission inventories. One result is a gridded joint probability map showing the quantities of emitted acidic species from source areas that were transported to the three receptor sites with and/or without undergoing chemical transformations during the transport. Another result is a gridded map for each single receptor site showing the possible maximum amounts of emitted acidic species from source areas that were transported to that receptor site with and/or without undergoing chemical transformations. The potential source areas identified by the PSCF analysis and the amount of transported emissions identified by the source apportionment method are generally well correlated with the emission inventories. The receptor modeling results of SO2 and SO2−4 are presented to illustrate the methodology.

Effects of Nanophase Materials (≤20 nm) on Biological Responses

Abstract Nanophase materials have enhanced properties (thermal, mechanical, electrical, surface reactivity, etc.) not found in bulk materials. Intuitively, the enhancement of material properties could occur when the materials encounter biological specimens. Previous investigations of biological interactions with nanometer-scale materials have been very limited. With the ability to manipulate atoms and molecules, we now can create predefined nanostructures with unprecedented precision. In parallel with this development, improved understanding of the biological effects of the nanophase materials, whatever those may be, should also deserve attention. In this study, we have applied precision aerosol technology to investigate cellular response to nanoparticles. We used synthetic nanoparticles generated by an electrospray technique to produce nanoparticles in the size range of 8–13 nm with practically monodispersed aerosol particles and approximately the same number concentration. We report here on the potency of nano-metal particles with single or binary chemical components in eliciting interleukin-8 (IL-8) production from epithelial cell lines. For single-component nanoparticles, we found that nano-Cu particles were more potent in IL-8 production than nano-Ni and nano-V particles. However, the kinetics of IL-8 production by these three nanoparticles was different, the nano-Ni being the highest among the three. When sulfuric acid was introduced to form acidified nano-Ni particles, we found that the potency of such binary-component nanoparticles in eliciting IL-8 production was increased markedly, by about six times. However, the acidified binary nano-Na and -Mg nanoparticles did not exhibit the same effects as binary nano-Ni particles did. Since Ni, a transition metal, could induce free radicals on cell surfaces, while Na and Mg could not, the acidity might have enhanced the oxidative stress caused by radicals to the cells, leading to markedly higher IL-8 production. This result indicates the complexity of biological responses to nanoparticles. We believe that the exposure methodology and aerosol technology employed in our research will provide an effective means to systematically investigate cellular responses to nanoparticles, structured or unstructured, in ongoing research projects. Different cell lines, chemicals, and particle morphology can also be investigated using such a methodology.

The effect of sampling duration on the ability to resolve source types using factor analysis

The effects of sampling duration on source identification using factor analysis method were examined in this paper. Principal factor analyses were performed on the data collected as part of the Philadelphia Regional and Local Sulfur Aerosol Concentrations Study conducted from July to October 1982. The data were mass concentrations of 22 trace elements analyzed by proton induced x-ray emission (PIXE) analysis and their associated analytical uncertainties that are a measure of the precision of the measurements. A weighting scheme is applied to the concentrations of the elements to emphasize the precisely measured elements for factor analysis. Furthermore, a new method was used to eliminate the problem of Heywood cases in the factor analyses. Results show the influence of sampling duration on the number of resolvable factors as well as the amount of variance explained by the factors. The analyses show that reducing the sampling duration can increase the number of sources identified by the model. Idiosyncrasies not found in the total data are shown on the separate analyses on daylight and non-daylight data.

Monitoring cellular responses of engine-emitted particles by using a direct air-cell interface deposition technique

The impacts of ultrafine airborne particles generated by diesel or gasoline engines on human lung cells have been investigated using a new in vitro cellular exposure technique. This technique enables direct deposition of the gasoline engine exhaust particles (GEP) and diesel engine exhaust particles (DEP) on human lung cells located at the air-cell interface on a transwell membrane in an exposure apparatus. The cellular responses to particle exposure were measured by the levels of IL-8 chemokines produced as a function of exposure time. The findings suggest that GEP and high-sulfur DEP induced the production of similar levels of IL-8 by unprimed A549 cells. The level of IL-8 produced by unprimed A549 cells in response to low-sulfur DEP was found lower than that produced in response to high-sulfur DEP and GEP. When cells were primed, simulating predisposed conditions, significant levels of IL-8 were produced. GEP triggered a much higher level of IL-8 production than DEP did. Furthermore, the time profile of IL-8 production induced by GEP was markedly different from that induced by DEP. The findings indicate that GEP could induce the production of higher levels of chemokines (i.e., IL-8) than DEP did, implying that exposure to GEP could be a greater health risk than exposure to DEP.