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.

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 Energy's 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 suggest elevated levels of aerosol loading and ozone concentrations during May 1998 when prevailing winds were favorable for the transport of the Central American smoke pall into Oklahoma and Kansas. In particular, aerosol extinction profiles derived from the ARM Raman lidar measurements revealed large variations in the vertical distribution of the smoke.

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.

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 development of a next-generation ® eld portable instrument for characterizing metal species from the emission sources as well as ambient environments. The instrument can provide a highly resolved spatial an d temporal data of signi® cance 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 results from different studies on the high-energy laser interaction with aerosols an d breakdown thresholds as a function of particle size, particle density, and wavelength are presented and the physical processes are discussed. Although it is not meant to be an exhaustive survey, this review serves as the basis for our ongoing development of a miniaturized LIPS-based instrument at the Oak Ridge National Laboratory.

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A new DMA column has been designed with the capability of simultaneously extracting monodisperse particles of different sizes in multiple stages. We call this design a multistage DMA, or MDMA. A prototype MDMA has been constructed and experimentally evaluated in this study. The new column enables the fast measurement of particles in a wide size range, while preserving the powerful particle classification function of a DMA. The prototype MDMA has three sampling stages, capable of classifying monodisperse particles of three different sizes simultaneously. The scanning voltage operation of a DMA can be applied to this new column. Each stage of MDMA column covers a fraction of the entire particle size range to be measured. The covered size fractions of two adjacent stages of the MDMA are designed somewhat overlapped. The arrangement leads to the reduction of scanning voltage range and thus the cycling time of the measurement. The modular sampling stage design of the MDMA allows the flexible configuration of desired particle classification lengths and variable number of stages in the MDMA. The design of our MDMA also permits operation at high sheath flow, enabling high-resolution particle size measurement and/or reduction of the lower sizing limit. Using the tandem DMA technique, the performance of the MDMA, i.e., sizing accuracy, resolution, and transmission efficiency, was evaluated at different ratios of aerosol and sheath flowrates. Two aerosol sampling schemes were investigated. One was to extract aerosol flows at an evenly partitioned flowrate at each stage, and the other was to extract aerosol at a rate the same as the polydisperse aerosol flowrate at each stage. We detail the prototype design of the MDMA and the evaluation result on the transfer functions of the MDMA at different particle sizes and operational conditions.

Abstract. The potential source contribution function (PSCF) is a receptor modeling technique for identifying emission sources and transport pathways. This technique has been widely used in the determination of potential emission sources and preferred transport pathways of a variety of air pollutants for more than a decade. However, the model has not been objectively evaluated against well-documented real-world data and the performance of the model is virtually untested. In this study we verified the PSCF model and tested the model performance by taking the opportunity of the 1998 Central America smoke events that produced elevated levels of aerosols detected at the Southern Great Plains site operated by the U.S. Department of Energy's Atmospheric Radiation Measurement. Our results show that the PSCF model could correctly identify the emission source locations and transport pathways of the smoke particles. However, one cannot take the PSCF results for granted without further examination of back trajectories that are responsible for the transport. False positives could result from the tailing of the back trajectories that travel over the true source locations. Model performance analysis suggests that using the mean or median as the criterion value yielded satisfactory PSCF results. Use of a high criterion value (e.g., the 90th percentile) and a larger database could improve the resolution of PSCF source identification. Trajectory arrival height above the surface sampling station should be carefully chosen to be within the column mixing height to ensure an effective coupling of transport and surface measurement.

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