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A method for evaluating sample bias in field measurements is presented. Experiments were performed in the field and laboratory to quantify the bias as a function of particle size for the scanning mobility particle sizer and the aerodynamic particle sizer. Sources of bias and sample loss considered in this work were sampling line loss, instrumental differences and inlet efficiencies. Measurement of the bias and sample loss allow for correction of the data acquired in the field, so as to obtain more representative samples of atmospheric concentrations. Substantial losses of fine and ultrafine particle count were observed, with sampling line losses ranging from 10–50 %, dependent on particle size. Only minor line losses were observed for coarse particles (approximately 5 %) because the sampling line was oriented vertically. Please note: corrected DOI, in print wrong DOI (10.1002/ppsc.200400939)

Laser optical particle spectrometers have been used to obtain real-time particle counts and infer mass information over a substantial portion of the PM2.5 mass range by means of dynamic aerosol calibrations. The theoretical response of such instruments is quite calculable, as many authors have demonstrated, but the total response still has some problem areas. This article addresses the theoretical response, comparing the calculations to the instrument calibration and other experimental data. Other instrument characteristics, particularly the particle path through the instrument, affect the total response. When the whole instrument is considered, theoretical predictions of response with changes of index of refraction can be made with some confidence. The calculated response of such spectrometers is nonmonotonic with particle size for most indices of refraction, making inversion of the acquired data difficult. A data inversion algorithm has been devised to incorporate all the response effects and overcome t...

Continuous measurements of aerosol size distributions were made in El Paso, TX, for a 21 day period in winter 1999. Size distribution measurements were performed at two urban locations in El Paso using two pairs of the scanning mobility particle sizer and the aerodynamic particle sizer. Complementary measurements also were performed for gas phase pollutants (CO, NO, NO 2 , O 3 ) and meteorological conditions. Throughout the study, the mean ultrafine particle (those smaller than 0.1 μm in diameter) number concentration was 14,400 particles cm −3 . There was a significant correlation between CO and both ultrafine and accumulation mode (those between 0.1 and 1 μm in diameter) particle count, with the Pearson correlation coefficient ( r ) values of 0.81 and 0.87, respectively. The correlation between NO and both ultrafine and accumulation mode particle count is also significant, but not as strong as the correlation of CO and the particle concentrations. Most pollutants were found to vary on diurnal cycles and to follow one of two different trends, either vehicular traffic schedules or sunlight intensity. Wind direction was found to have an influence not only on pollutant concentrations, but also on the correlation between pollutants. With southerly winds, CO, NO and NO 2 concentrations were 25–140% greater than when the wind was coming from the north. Likewise, ultrafine and accumulation mode particle concentrations were approximately 100% greater for southerly than for northerly winds.

Personal exposures, indoor and outdoor concentrations, and questionnaire data were collected in three retirement center settings, supporting broader particulate matter (PM)--health studies of elderly populations. The studies varied geographically and temporally, with populations studied in Baltimore, MD in the summer of 1998, and Fresno, CA in the winter and spring of 1999. The sequential nature of the studies and the relatively rapid review of the mass concentration data after each segment provided the opportunity to modify the experimental designs, including the information collected from activity diary and baseline questionnaires and influencing factors (e.g., heating, ventilation, and air-conditioning (HVAC) system operation, door and window openings, air exchange rate) measurements. This paper highlights both PM2.5 and PM10 personal exposure data and interrelationships across the three retirement center settings, and identifies the most probable influencing factors. The current limited availability of questionnaire results, and chemical speciation data beyond mass concentration for these studies, provided only limited capability to estimate personal exposures from models and apportion the personal exposure collections to their sources. The mean personal PM2.5 exposures for the elderly in three retirement centers were found to be consistently higher than the paired apartment concentrations by 50% to 68%, even though different facility types and geographic locations were represented. Mean personal-to-outdoor ratios were found to 0.70, 0.82, and 1.10, and appeared to be influenced by the time doors and windows were open and aggressive particle removal by the HVAC systems. Essentially identical computed mean PM2.5 personal clouds of 3 micrograms/m3 were determined for two of the studies. The proposed significant contributing factors to these personal clouds were resuspended particles from carpeting, collection of body dander and clothing fibers, personal proximity to open doors and windows, and elevated PM levels in nonapartment indoor microenvironments.

Two 1999 Fresno exposure studies took place in February (winter season) and April/May (spring season) for periods of four weeks each. During that time, nearly continuous measurements of outdoor aerosol concentrations were made with a TSI Scanning Mobility Particle Sizer (SMPS) and a PMS optical particle counter (LASX). These instruments provide particle size distribution information from about 0.01 to 3

Particle size distributions were measured indoors and outdoors of a single, detached residence during the Fresno particulate matter exposure studies in winter (February 1-28, 1999) and spring (April 18-May 16, 1999). Data was collected for particle sizes ranging from about 0.01 to 2.5

Rotating spark gap devices for switching high voltage direct current (DC) into a corona plasma reactor can achieve pulse rise times in the range of tens of nanoseconds. The fast rise times lead to vigorous plasma generation without sparking at instantaneous applied voltages higher than can be obtained with DC. The resulting energetic plasma is effective for destroying a variety of molecules. The spark gap circuit configuration plays an important role in the effectiveness of the plasma generation. A single-gap circuit is effective for generating moderate peak voltages, but is limited by a multiple sparking phenomenon. A double-gap circuit can achieve equal peak voltages with every spark, but with a reduced number of pulses, compared to the single gap. Both configurations have an upper voltage imposed by the changing impedance of the reactor as voltage and frequency are varied. The pulse characteristics are reported for both types of circuits. The general performance of the reactors for destruction of some compounds with both circuits is also reported.

Ozone emissions from a short wire-plate precipitator and three commercial electronic air cleaners were measured. Ozone generation was most strongly affected by the corona current and the polarity of the discharge electrode. To a lesser extent, the type of corona (i.e. whether tuft or glow) was also important. Water vapor seems to reduce the ozone emission rate for negative corona, but ozone emissions from positive coronas are relatively unaffected. Ozone emission rate was also affected by the radius of the discharge electrode, but the measured values did not fit Castle's model (see G.S.P. Castle et al. Trans. IEEE, vol.5, no.4, p.489-96 (1969), and M.B. Awad and G.S.P. Castle, J. APCA, vol.25, no.4, p.369-74 (1975)). >

A dynamic chamber (8 m{sup 3}) was designed and constructed for the investigation of particulate emissions from appliances and office equipment and their impact on indoor air quality. The supply air incorporated high efficiency particle filters to provide a near-zero particle background in a low turbulence flow. The flow rate could be varied from 2 to 80 m{sup 3}/min. For testing operating appliances, such as vacuum cleaners, the dimensions of the chamber were chosen to allow an operator to use an appliance over a floor area of about 2 m{sup 2}. The need for low particle backgrounds dictated that the chamber be operated in an overpressure mode, so that all leaks were from the inside and would only affect the total flow measurements. The flow converges into an outlet tube 20 cm in diameter where velocity and concentration measurements could be made in multiple ports. The chamber was furnished with interior lights and electrical outlets. Recently, the chamber has been modified with carbon filters on the inlet to allow for sampling of volatile organic compounds (VOCs), such as from floor wax. The filters remove the VOC background to a level below that detectable by the sorbent cartridges/analysis system used formore » sampling. The chamber has even been pressed into service as a small cleanroom for some operations that required its unique characteristics. The chamber has been successfully operated in both a closed-loop mode and in an open-loop mode. The main advantage of the closed loop mode is that the backgrounds can be reduced to zero more quickly, but the disadvantage is that humidity and carbon dioxide concentrations grow because they are not removed by the filters.« less

The US Environmental Protection Agency recently conducted the Detroit Exposure and Aerosol Research Study (DEARS). The study began in 2004 and involved community, residential, and personal-based measurements of air pollutants targeting 120 participants and their residences. The primary goal of the study was to evaluate and describe the relationship between air toxics, particulate matter (PM), PM constituents, and PM from specific sources measured at a central site monitor with those from the residential and personal locations. The impact of regional, local (point and mobile), and personal sources on pollutant concentrations and the role of physical and human factors that might influence these concentrations were investigated. A combination of active and passive sampling methodologies were employed in the collection of PM mass, criteria gases, semivolatile organics, and volatile organic compound air pollutants among others. Monitoring was conducted in six selected neighborhoods along with one community site using a repeated measure design. Households from each of the selected communities were monitored for 5 consecutive days in the winter and again in the summer. Household, participant and a variety of other surveys were utilized to better understand human and household factors that might affect the impact of ambient-based pollution sources upon personal and residential locations. A randomized recruitment strategy was successful in enrolling nearly 140 participants over the course of the study. Over 36,000 daily-based environmental data points or records were ultimately collected. This paper fully describes the design of the DEARS and the approach used to implement this field monitoring study and reports select preliminary findings.

When graphing or plotting count data from particle sensors, there is always the problem of handling zero values if a logarithmic scale is desired. The one plotting (or programming) may skip the offending values, leaving all values equal to 1 across the bottom of the graph. Or, a constant may be added to all the counts to provide an offset from zero. We offer an approach with the advantage of changing only one label on the graph, yet allowing all values between 0 and 1 to be plotted automatically. The change is simple to program and can be equally easily used in manual plotting.

Two laboratory-scale plasma reactors, an alternating-current-energized ferroelectric (high-dielectric ceramic) packed-bed reactor and a nanosecond pulsed corona reactor, were constructured. The aim was to develop baseline engineering data to demonstrate the feasibility of applying plasma reactors to the destruction of various volatile organic compounds (VOCs). Gas retention time, concentration, and corona power were varied to determine the effect on destruction efficiency, using gas chromatography for each VOC. Complete destruction was obtained for toluene. Conversions of methylene chloride at 95% and trichlorotrifluoroethane (known as CFC-113) at 67% were achieved. The conversion was dependent on the electron energy of the reactor and was also related to how strongly the halogen species were bonded with carbon. >

A number of incremental improvements in electrostatic precipitator modeling have been made. The improvements have been in particle charging, particle collection, electrical wave form effects, ion mobility, space charge interactions, rapping and nonrapping reentrainment, and back corona effects. These have been incorporated into a single computer model, ESPM, at the Electric Power Research Institute. The resulting program has been compared with measured performance of several ESPs with very good results and has been used to better understand phenomena that occur in precipitators. It brings a fully predictive ESP model closer to realization. The new model improvements are described in detail, since many have not been published. The overall structure of the program is also described, because it closely simulates the operation of an ESP and contributes to the improved performance of the model. >

Germanium and silicon needles were tested as emitter electrodes for use in low-particle-generating static eliminators. The materials were found to oxidize with minimal incorporation of nitrogen, and the negative polarity emitters oxidized at a greater rate than the positive polarity emitters. The negative polarity silicon emitters generated several orders of magnitude greater particle emissions than any of the other emitters tested. The mean particle size was about 0.015 μm. Although the germanium emitters oxidized, little evidence was found to indicate particles were shed from this material. Preliminary data indicates the emitters perform equally well in Class 100 cleanroom air, and lowest particle generation is achieved when germanium electrodes are purged with dry air.

As the result of the Clean Air Act Amendments of 1990, emissions of volatile organic compounds (VOCs) into the air became an increasing environmental concern. The understanding and subsequent development of technologies for controlling these streams has been mandated. The conventional technologies for VOC control are carbon adsorption, catalytic oxidation, and thermal incineration. These technologies are widely accepted and well understood. However, with respect to some parameters, such as concentration and compounds treated, cost, and energy requirements, conventional technologies have practical limitations. For these reasons, an alternating current (ac) energized ferroelectric packed-bed reactor and a nanosecond pulsed-corona reactor have been investigated as alternative technical approaches to control these pollutants at parts per million (ppm) levels.

We experienced repeated failures of carbon vane pumps in an aerosol counter when sampling from nitrogen gas. The nature of the problem and a cure are presented.

An earlier point-to-plane geometry corona device with a rectangular cross section demonstrated low decomposition efficiencies. The numerical simulation of this device suggested that three were zones of low electron density and electric field significant decrease in resulting in electrical sneakage which caused a significant decrease in the kinetic rate coefficients in the chemical reaction process. A triangle-shaped DC corona discharge device was developed to improve the electrical sneakage problem, and a semiempirical mathematical model was developed to describe the detailed electrical characteristics and to refine estimates on the optimum shape of the device. The preliminary experimental results indicated that the decomposition efficiency was much improved. >