Determination of Fine Particulate Semi-Volatile Organic Material at Three Eastern U.S. Sampling Sites

ABSTRACT

Correct assessment of fine particulate carbonaceous material as a function of particle size is, in part, dependent on the determination of semi-volatile compounds, which can be lost from particles during sampling. This study gives results obtained for the collection of fine particulate carbonaceous material at three eastern U.S. sampling sites [Philadelphia, PA; Shenandoah National Park, VA; and Research Triangle Park (RTP), NC] using diffusion denuder technology. The diffusion denuder samplers allow for the determination of fine particulate organic material with no artifacts, due to the loss of semi-volatile organic particulate compounds, or collection of gas-phase organic compounds by the quartz filter during sampling. The results show that an average of 41, 43, and 59% of fine particulate organic material was lost as volatilized semi-volatile organic material during collection of particles on a filter at Philadelphia, RTP, and Shenandoah, respectively. The particle size distribution of carbonaceous material retained by a filter and lost from a filter during sampling was obtained for the samples collected at Philadelphia and Shenandoah. The carbonaceous material retained by the particles during sampling was found predominantly in particles smaller than 0.4 μm in aerodynamic diameter. In contrast, the semi-volatile organic material lost from the particles during sampling had a mass median diameter of ~0.5 μm.     

Passive Sampling for Ozone

The Brigham Young University (BYU) organic sampling system (BOSS) and the high flow rate multi-system BYU organic sampling system (BIG BOSS), which use multichannel diffusion denuder sampling techniques, were both used to collect samples of atmospheric fine particulate organic material. Both systems were used at the Meadview sampling site located at the western boundary of the Grand Canyon National Park in northwestern Arizona for the Project MOHAVE summer intensive sampling program in August 1992. The concentrations of total fine particulate carbonaceous material determined by temperature programmed volatilization for BOSS collocated replicate samples were in agreement with an uncertainty of ±14%. A comparable agreement was seen between the BOSS and BIG BOSS samples. Carbonaceous material collected by the second of two sequential quartz filters was shown to have originated from organic material lost from particles during sampling. About one-half of the fine particulate organic material was lost from particles during sample collection. These semi-volatile organic compounds lost from particles during sampling were characterized by GC/MS analysis. The concentrations of n-alkanes, n-fatty acids, n-fatty methyl esters, and phthalic acid as a function of fine particulate size were obtained for compounds both retained by and lost from particles during sampling. The possible sources of fine particulate semi-volatile organic material collected at Meadview, and the particle size distribution of fine particulate organic material, n-alkanes, n-fatty acids, and n-fatty esters are discussed.     

Determination of PM2.5 Sulfate and Nitrate with a PC-BOSS Designed for Routine Sampling for Semi-Volatile Particulate Matter

ABSTRACT

Ambient particles contain substantial quantities of material that can be lost from the particles during sample collection on a filter. These include ammonium nitrate and semi-volatile organic compounds. As a result, the concentrations of these species are often significantly in error for results obtained with a filter pack sampler. The accurate measurement of these semi-volatile fine particulate species is essential for a complete understanding of the possible causes of health effects associated with exposure to fine particles. Past organic compound diffusion denuder samplers developed by the authors (e.g., the Brigham Young University Organic Sampling System [BOSS]) are not amenable to routine field use because of the need to independently determine the gas-phase semi-volatile organic material efficiency of the denuder for each sample. This problem has been eliminated using a combined virtual impactor, particle-concentrator inlet to provide a concentrated stream of 0.1-2.5-μm particles. This is followed by a BOSS diffusion denuder and filter packs to collect particles, including any semi-volatile species lost from the particles during sampling. The samp ler (Particle Concentrator-Brigham Young University Organic Sampling System [PC-BOSS]) contains a post-denuder multifilter pack unit to allow for the routine collection of several sequential samples. The PC-BOSS can be used for the determination of both fine particulate nitrate and semi-volatile organic material without significant “positive” or “negative” sampling artifacts. Validation of the sampler for the determination of PM_2.5 sulfate and nitrate based on comparison of results obtained at Riverside, CA with collocated PC-BOSS, annular denuder, and Chem Spec samplers indicates the PC-BOSS gives accurate results for these species with a precision of ±5-8%. An average of 33% of the PM_2.5 nitrate was lost from the particles during sampling for both denuder and single filter samplers.     

Fine Particulate Organic Material in the Los Angeles Basin - I: Assessment of the High-Volume Brigham Young University Organic Sampling System,BIG BOSS

ABSTRACT

A multi-system, high-volume, parallel plate diffusion dénuder Brigham Young University Organic Sampling System (BIG BOSS) was tested using collocated samplers at the Pico Rivera Monitoring Station of the South Coast Air Quality Management District, South Coast Air Basin, in September 1994. Six-hr daytime and 9-hr nighttime samples were collected with a flow of about 200 L/min through each of the three systems designed to collect particles smaller than 2.5, 0.8, and 0.4 mm in a diffusion denuder sampler. Efficiency for the removal of gas phase organic compounds by the diffusion denuder was evaluated using both theoretical predictions and field measurements. Both measured and calculated data indicate high denuder efficiency for the removal of gas phase aromatic and paraffinic compounds. The precision of the BIG BOSS was evaluated using collocated samplers. The precision of determination of total carbon and elemental carbon retained by a quartz filter or of semi-volatile carbonaceous material lost from particles during sampling averaged ±7%. The precision of determination of individual organic compounds averaged ±10%. An average of 42 and 62% of the particulate organic material was semi-volatile organic compounds (SVOCs) lost from particles during sampling for daytime and nighttime samples, respectively. This “negative” sampling artifact was an order of magnitude larger than the “positive” quartz filter artifact due to adsorption of gas phase organic material. Daytime concentrations of fine particulate elemental carbon and nonvolatile organic carbon were higher than nighttime concentrations, but nighttime fine particles contained more semi-volatile organic material than daytime.     

Semi-volatile species in PM2.5: comparison of integrated and continuous samplers for PM2.5 research or monitoring

Fine particles in urban atmospheres contain substantial quantities of semi-volatile material [e.g., NH4NO3 and semi-volatile organic compounds (SVOCs)] that are lost from particles during collection on a filter. Several diffusion denuder samplers have been developed for the determination of both NO3- and organic semi-volatile fine particulate components. The combination of technology used in the BOSS diffusion denuder sampler and the Harvard particle concentrator has resulted in the Particle Concentrator-Brigham Young University Organic Sampling System (PC-BOSS) for the 24-hr (or less) integrated collection of PM2.5, including NH4NO3 and semi-volatile organic material. Modification of the BOSS sampler allows for the weekly determination of these same species. Combination of BOSS denuder and tapered element oscillating microbalance (TEOM) monitor technology has resulted in the real-time ambient mass sampler (RAMS) for the continuous measurement of PM2.5, including the semi-volatile components. Comparison of the results obtained with the BOSS and with each of the newly developed modifications of the BOSS indicates that the modified versions can be used for the continuous, daily, or weekly monitoring of PM2.5, including semi-volatile species, as appropriate to the design of each sampler.     

Evaluation of the RAMS continuous monitor for determination of PM2.5 mass including semi-volatile material in Philadelphia,PA

The real-time ambient mass sampler (RAMS) is a continuous monitor based on particle concentrator, denuder, drier, and tapered element oscillating microbalance (TEOM) monitor technology. It is designed to measure PM2.5 mass, including the semi-volatile species NH4NO3 and semi-volatile organic material, but not to measure PM2.5 water content. The performance of the RAMS in an urban environment with high humidity was evaluated during the July 1999 NARSTO-Northeast Oxidant and Particles Study (NEOPS) intensive study at the Baxter water treatment plant in Philadelphia, PA. The results obtained with the RAMS were compared to mass measurements made with a TEOM monitor and to constructed mass obtained with a Particle Concentrator-Brigham Young University Organic Sampling System (PC-BOSS) sampler designed to determine the chemical composition of fine particles, including the semi-volatile species. An average of 28% of the fine particulate material present during the study was semi-volatile organic material lost from a filter during particle collection, and 1% was NH4NO3 that was also lost from the particles during sampling. The remaining mass was dominantly nonvolatile (NH4)2SO4 (31%) and organic material (37%), with minor amounts of soot, crustal material, and nonvolatile NH4NO3. Comparison of the RAMS and PC-BOSS results indicated that the RAMS correctly monitored for fine particulate mass, including the semivolatile material. In contrast, the heated filter of the TEOM monitor did not measure the semi-volatile material. The comparison of the RAMS and PC-BOSS data had a precision of +/-4.1 microg/m3 (+/-9.6%). The precision of the RAMS data was limited by the uncertainty in the blank correction for the reversible adsorption of water by the charcoal-impregnated cellulose sorbent filter of the RAMS monitor. The precision of the measurement of fine particulate components by the PC-BOSS was +/-6-8%.     

Evaluation of the RAMS Continuous Monitor for Determination of PM2.5 Mass Including Semi-Volatile Material in Philadelphia,PA

Abstract

The real-time ambient mass sampler (RAMS) is a continuous monitor based on particle concentrator, denuder, drier, and tapered element oscillating microbalance (TEOM) monitor technology. It is designed to measure PM_2.5 mass, including the semi-volatile species NH₄NO₃ and semi-volatile organic material, but not to measure PM_2.5 water content. The performance of the RAMS in an urban environment with high humidity was evaluated during the July 1999 NARSTO-Northeast Oxidant and Particles Study (NEOPS) intensive study at the Baxter water treatment plant in Philadelphia, PA. The results obtained with the RAMS were compared to mass measurements made with a TEOM monitor and to constructed mass obtained with a Particle Concentrator-Brigham Young University Organic Sampling System (PC-BOSS) sampler designed to determine the chemical composition of fine particles, including the semi-volatile species. An average of 28% of the fine particulate material present during the study was semi-volatile organic material lost from a filter during particle collection, and 1% was NH₄NO₃ that was also lost from the particles during sampling. The remaining mass was dominantly nonvolatile (NH₄)₂SO₄ (31%) and organic material (37%), with minor amounts of soot, crustal material, and nonvolatile NH₄NO₃. Comparison of the RAMS and PC-BOSS results indicated that the RAMS correctly monitored for fine particulate mass, including the semi-volatile material. In contrast, the heated filter of the TEOM monitor did not measure the semi-volatile material. The comparison of the RAMS and PC-BOSS data had a precision of ±4.1 μg/m³ (±9.6%). The precision of the RAMS data was limited by the uncertainty in the blank correction for the reversible adsorption of water by the charcoal-impregnated cellulose sorbent filter of the RAMS monitor. The precision of the measurement of fine par-ticulate components by the PC-BOSS was ±6-8%.     

Modifications to the Sunset Laboratory Carbon Aerosol Monitor for the Simultaneous Measurement of PM2.5 Nonvolatile and Semi-Volatile Carbonaceous Material

Abstract

Semi-volatile organic carbonaceous material (SVOC) in fine particles is not reliably measured with conventional semicontinuous carbon monitors because semi-volatile carbonaceous material is lost from the collection media during sample collection. Two modifications of a Sunset Laboratory carbon aerosol monitor allowing for the determination of semi-volatile fine particulate organic material are described. Collocated conventional and modified instruments were operated simultaneously using a common inlet. Comparisons were made with integrated PC-BOSS data for quartz filter retained nonvolatile organic carbon (NVOC) and elemental carbon (EC), SVOC, and total carbon (TC = SVOC + NVOC + EC) and good agreement was observed between TC concentrations during studies conducted in Rubidoux, CA. Precision of the comparison was σ=±1.5 μg-C/m³ (±8%). On the basis of experiments performed with the modified Sunset monitor, a dual-oven Sunset monitor was developed and extensively tested in Lindon, UT; Riverside, CA; and in environmental exposure chambers. The precision for the measurement of TC with the dual-oven instrument was σ = ±1.4 μg-C/m³ (±13%).     

Fine particulate chemical composition and light extinction at Meadview, AZ

The concentration of fine particulate nitrate, sulfate, and carbonaceous material was measured for 12-hr day-night samples using diffusion denuder samplers during the Project Measurement of Haze and Visibility Effects (MOHAVE) July to August 1992 Summer Intensive study at Meadview, AZ, just west of Grand Canyon National Park. Organic material was measured by several techniques. Only the diffusion denuder method measured the semivolatile organic material. Fine particulate sulfate and nitrate (using denuder technology) determined by various groups agreed. Based on the various collocated measurements obtained during the Project MOHAVE study, the precision of the major fine particulate species was +/- 0.6 microg/m3 organic material, +/- 0.3 microg/m3 ammonium sulfate, and +/- 0.07 microg/m3 ammonium nitrate. Data were also available on fine particulate crustal material, fine and coarse particulate mass from the Interagency Monitoring of Protected Visual Environments sampling system, and relative humidity (RH), light absorption, particle scattering, and light extinction measurements from Project MOHAVE. An extinction budget was obtained using mass scattering coefficients estimated from particle size distribution data. Literature data were used to estimate the change in the mass scattering coefficients for the measured species as a function of RH and for the absorption of light by elemental carbon. Fine particulate organic material was the principal particulate contributor to light extinction during the study period, with fine particulate sulfate as the second most important contributor. During periods of highest light extinction, contributions from fine particulate organic material, sulfate, and light-absorbing carbon dominated the extinction of light by particles. Particle light extinction was dominated by sulfate and organic material during periods of lowest light extinction. Combination of the extinction data and chemical mass balance analysis of sulfur oxides sources in the region indicate that the major anthropogenic contributors to light extinction were from the Los Angeles, CA, and Las Vegas, NV, urban areas. Mohave Power Project associated secondary sulfate was a negligible contributor to light extinction.     

Measurement of fine particulate matter nonvolatile and semi-volatile organic material with the Sunset Laboratory Carbon Aerosol Monitor

Semi-volatile organic material (SVOM) in fine particles is not reliably measured with conventional semicontinuous carbon monitors because SVOM is lost from the collection media during sample collection. We have modified a Sunset Laboratory Carbon Aerosol Monitor to allow for the determination of SVOM. In a conventional Sunset monitor, gas-phase organic compounds are removed in the sampled airstream by a diffusion denuder employing charcoal-impregnated cellulose filter (CIF) surfaces. Subsequently, particles are collected on a quartz filter and the instrument then determines both the organic carbon and elemental carbon fractions of the aerosol using a thermal/optical method. However, some of the SVOM is lost from the filter during collection, and therefore is not determined. Because the interfering gas-phase organic compounds are removed before aerosol collection, the SVOM can be determined by filtering the particles at the instrument inlet and then replacing the quartz filter in the monitor with a charcoal-impregnated glass fiber filter (CIG), which retains the SVOM lost from particles collected on the inlet filter. The resulting collected SVOM is then determined in the analysis step by measurement of the carbonaceous material thermally evolved from the CIG filter. This concept was tested during field studies in February 2003 in Lindon, UT, and in July 2003 in Rubidoux, CA. The results obtained were validated by comparison with Particle Concentrator-Brigham Young University Organic Sampling System (PC-BOSS) results. The sum of nonvolatile organic material determined with a conventional Sunset monitor and SVOM determined with the modified Sunset monitor agree with the PC-BOSS results. Linear regression analysis of total carbon concentrations determined by the PC-BOSS and the Sunset resulted in a zero-intercept slope of 0.99 +/- 0.02 (R2 = 0.92) and a precision of sigma = +/- 1.5 microg C/m3 (8%).     

Fine Particulate Chemical Composition and Light Extinction at Meadview,AZ

Abstract

The concentration of fine particulate nitrate, sulfate, and carbonaceous material was measured for 12-hr day-night samples using diffusion denuder samplers during the Project Measurement of Haze and Visibility Effects (MOHAVE) July to August 1992 Summer Intensive study at Meadview, AZ, just west of Grand Canyon National Park. Organic material was measured by several techniques. Only the diffusion denuder method measured the semivolatile organic material. Fine particulate sulfate and nitrate (using denuder technology) determined by various groups agreed. Based on the various collocated measurements obtained during the Project MOHAVE study, the precision of the major fine particulate species was ±0.6 μg/m³ organic material, ±0.3 μg/m³ ammonium sulfate, and ±0.07 μg/m³ ammonium nitrate. Data were also available on fine particulate crustal material, fine and coarse particulate mass from the Interagency Monitoring of Protected Visual Environments sampling system, and relative humidity (RH), light absorption, particle scattering, and light extinction measurements from Project MOHAVE. An extinction budget was obtained using mass scattering coefficients estimated from particle size distribution data. Literature data were used to estimate the change in the mass scattering coefficients for the measured species as a function of RH and for the absorption of light by elemental carbon. Fine particulate organic material was the principal particulate contributor to light extinction during the study period, with fine particulate sulfate as the second most important contributor. During periods of highest light extinction, contributions from fine particulate organic material, sulfate, and light-absorbing carbon dominated the extinction of light by particles. Particle light extinction was dominated by sulfate and organic material during periods of lowest light extinction. Combination of the extinction data and chemical mass balance analysis of sulfur oxides sources in the region indicate that the major anthropogenic contributors to light extinction were from the Los Angeles, CA, and Las Vegas, NV, urban areas. Mohave Power Project associated secondary sulfate was a negligible contributor to light extinction.     

Comparison of speciation sampler and PC-BOSS fine particulate matter organic material results obtained in Lindon, Utah, during winter 2001-2002

The Particle Concentrator-Brigham Young University Organic Sampling System (PC-BOSS) has been previously verified as being capable of measuring total fine particulate matter (PM2.5), including semi-volatile species. The present study was conducted to determine if the simple modification of a commercial speciation sampler with a charcoal denuder followed by a filter pack containing a quartz filter and a charcoal-impregnated glass (CIG) fiber filter would allow for the measurement of total PM2.5, including semi-volatile organic material. Data were collected using an R&P (Rupprecht and Pastasnik Co., Inc.) Partisol Model 2300 speciation sampler; an R&P Partisol speciation sampler modified with a BOSS denuder, followed by a filter pack with a quartz and a CIG filter; a Met One spiral aerosol speciation sampler (SASS); and the PC-BOSS from November 2001 to March 2002 at a U.S. Environmental Protection Agency (EPA) Science to Achieve Results (STAR) sampling site in Lindon, UT. Total PM2.5 mass, ammonium nitrate (both nonvolatile and semi-volatile), ammonium sulfate, organic carbon (both non-volatile and semi-volatile), and elemental carbon were determined on a 24-hr basis. Results obtained with the individual samplers were compared to determine the capability of the modified R&P speciation sampler for measuring total PM2.5, including semi-volatile components. Data obtained with the modified speciation sampler agreed with the PC-BOSS results. Data obtained with the two unmodified speciation samplers were low by an average of 26% because of the loss of semi-volatile organic material from the quartz filter during sample collection.     

The measurement of fine particulate semivolatile material in urban aerosols

Ammonium nitrate and semivolatile organic material (SVOM) are significant components of fine particles in urban atmospheres. These components, however, are not properly determined with methods such as the fine particulate matter (PM2.5) Federal Reference Method (FRM) or other single filter samplers because of significant losses of semivolatile material (SVM) from particles collected on the filter during sampling. The R&P tapered element oscillating microbalance (TEOM) monitor also does not measure SVM, because this method heats the sample to remove particle bound water, which also results in evaporation of SVM. Recent advances in monitoring techniques have resulted in samplers for both integrated and continuous measurement of total PM2.5, including the particle concentrator-Brigham Young University organic sampling system (PC-BOSS), the real-time total ambient mass sampler (RAMS), and the R&P filter dynamics measurement system (FDMS) TEOM monitor. Results obtained using these samplers have been compared with those obtained with either a PM2.5 FRM sampler or a TEOM monitor in studies conducted during the past five years. These studies have shown the following: (1) the PC-BOSS, RAMS, and FDMS TEOM are all comparable. Each instrument measures both the nonvolatile material and the SVM. (2) The SVM is not retained on the heated filter of a regular TEOM monitor and is not measured by this sampling technique. (3) Much of the SVM is also lost during sampling from single filter samplers such as the PM2.5 FRM sampler. (4) The amount of SVM lost from single filter samplers can vary from less than one-third of that lost from heated TEOM filters during cold winter conditions to essentially all during warm summer conditions. (5) SVOM can only be reliably collected using an appropriate denuder sampler. (6) A PM2.5 speciation sampler can be easily modified to a denuder sampler with filters that can be analyzed for semivolatile organic carbon (OC), nonvolatile OC, and elemental carbon using existing OC/elemental carbon analytical techniques. The research upon which these statements are based for various urban studies are summarized in this paper.     

Fine particulate (PM2.5) composition in Atlanta, USA: assessment of the particle concentrator-Brigham Young University organic sampling system, PC-BOSS, during the EPA supersite study

Aerosol concentrations of carbonaceous material, sulfate, and nitrate for samples obtained using a newly designed PC-BOSS are reported. The results indicated that PM_2.5 composition in Atlanta was dominated by sulfate and organic material, with low concentrations of particulate nitrate. Observed average particulate component concentrations for the 26-day study period were: sulfate, 12.2 μg/m³ (17.0 μg/m³ as ammonium sulfate); non-volatile organic material, 11.4 μg OM/m³ (assumes organic material, OM, is 61% C); semi-volatile organic compounds (SVOC) lost from particles during sampling, 5.3 μg OM/m³; filter retained nitrate, 0.1 μg/m³ (0.2 μg/m³ as ammonium nitrate); nitrate lost from particles, 0.3 μg/m³ (0.4 μg/m³ as ammonium nitrate); and soot (elemental carbon), 1.5 μg/m³. The PC-BOSS particle concentrator efficiency was obtained by comparison of the PC-BOSS sulfate data with sulfate data obtained from the Federal Reference Method (FRM) sampler. A modification of the PC-BOSS design to allow independent determination of this parameter is recommended.     

A fabric denuder for sampling semi-volatile species

A new style of diffusion denuder has been evaluated specifically for sampling HNO3. A coated fabric is used as the denuder substrate, which can be loaded directly into a standard filter holder. This approach allows direct denuder sampling with no additional capital costs over filter sampling and simplifies the coating and extraction process. Potential denuder materials and coatings were evaluated in the laboratory to test the removal efficiency. NaCl coatings were used to assess more than 20 materials for HNO3 collection efficiency. Particle retention, which would cause a denuder to have a positive bias for gas concentration measurements, was evaluated by ambient air sampling using particulate sulfate as the reference aerosol. Particle retention varied from 0 to 15%, depending on the denuder material tested. The best performing material showed an average particle retention of less than 3%. Denuder efficiency of four fabric materials was tested under ambient conditions to determine removal efficiency. The fabric denuder method was compared with a long path-length Fourier transform infrared (FTIR) spectrometer, a tunable diode laser absorption spectrometer (TDLAS), and a denuder difference sampler to independently measure HNO3. HNO3 collection efficiency was typically 90% for the denuders, whether coated with NaCl or not. For 10-L/min sampling rates with the fabric denuder, the square of the correlation coefficient with the FTIR spectrometer was 0.73, compared to 0.24 with the TDLAS.     

A Fabric Denuder for Sampling Semi-Volatile Species

ABSTRACT

A new style of diffusion denuder has been evaluated specifically for sampling HNO₃. A coated fabric is used as the denuder substrate, which can be loaded directly into a standard filter holder. This approach allows direct denuder sampling with no additional capital costs over filter sampling and simplifies the coating and extraction process.

Potential denuder materials and coatings were evaluated in the laboratory to test the removal efficiency. NaCl coatings were used to assess more than 20 materials for HNO₃ collection efficiency. Particle retention, which would cause a denuder to have a positive bias for gas concentration measurements, was evaluated by ambient air sampling using particulate sulfate as the reference aerosol. Particle retention varied from 0 to 15%, depending on the denuder material tested. The best performing material showed an average particle retention of less than 3%.

Denuder efficiency of four fabric materials was tested under ambient conditions to determine removal efficiency. The fabric denuder method was compared with a long path-length Fourier transform infrared (FTIR) spectrometer, a tunable diode laser absorption spectrometer (TDLAS), and a denuder difference sampler to independently measure HNO₃. HNO₃ collection efficiency was typically 90% for the denuders, whether coated with NaCl or not. For 10-L/min sampling rates with the fabric denuder, the square of the correlation coefficient with the FTIR spectrometer was 0.73, compared to 0.24 with the TDLAS.     

Precision and Accuracy in the Determination of Sulfur Oxides,Fluoride, and Spherical Aluminosilicate Fly Ash Particles in Project MOHAVE

The precision and accuracy of the determination of particu-late sulfate and fluoride, and gas phase SO₂ and HF are estimated from the results obtained from collocated replicate samples and from collocated comparison samples for high-and low-volume filter pack and annular diffusion denuder samplers. The results of replicate analysis of collocated samples and replicate analyses of a given sample for the determination of spherical aluminosilicate fly ash particles have also been compared. Each of these species is being used in the chemical mass balance source apportionment of sulfur oxides in the Grand Canyon region as part of Project MOHAVE, and the precision and accuracy analyses given in this paper provide input to that analysis. The precision of the various measurements reported here is ±1.8 nmol/m³ and ±2.5 nmol/m³ for the determination of SO₂ and sulfate, respectively, with an annular denuder. The precision is ±0.5 nmol/m³ and ±2.0 nmol/m³ for the determination of the same species with a high-volume or low-volume filter pack. The precision for the determination of the sum of HF(g) and fine particulate fluoride is ±0.3 nmol/m³. The precision for the determination of aluminosilicate fly ash particles is ±100 particles/m³. At high concentrations of the various species, reproducibility of the various measurements is ±10% to ±14% of the measured concentration. The concentrations of sulfate determined using filter pack samplers are frequently higher than those determined using diffusion denuder sampling systems. The magnitude of the difference (e.g., 2-10 nmol sulfate/m³) is small, but important relative to the precision of the data and the concentrations of particulate sul-fate present (typically 5-20 nmol sulfate/m³). The concentrations of SO₂(g) determined using a high-volume cascade impactor filter pack sampler are correspondingly lower than those obtained with diffusion denuder samplers. The concentrations of SO_x (SO₂(g) plus particulate sulfate) determined using the two samplers during Project MOHAVE at the Spirit Mountain, NV, and Hopi Point, AZ, sampling sites were in agreement. However, for samples collected at Painted Desert, AZ, and Meadview, AZ, the concentrations of SO_x and SO₂(g) determined with a high-volume cascade impactor filter pack sampler were frequently lower than those determined using a diffusion denuder sampling system. These two sites had very low ambient relative humidity, an average of 25%. Possible causes of observed differences in the SO₂(g) and sulfate results obtained from different types of samplers are given.     

Particulate organic compounds emitted from motor vehicle exhaust and in the urban atmosphere

The emission rate of particle-phase petroleum biomarkers in vehicular exhaust compared to the concentrations of these biomarkers in ambient air is used to determine the particulate organic compound concentration due to primary particle emissions from motor vehicles in the southern California atmosphere. A material balance on the organic particulate matter emitted from motor vehicle traffic in a Los Angeles highway tunnel first is constructed to show the proportion which is solvent-extractable and which will elute from a GC column, the ratio of resolved to unresolved compound mass, the portion of the resolved material that can be identified as single organic compounds, and the contribution of different classes of organic compounds to the overall identified fraction. It is shown that the outdoor ambient concentrations of the petroleum biomarkers track primary emissions measured in the highway tunnel, confirming that direct emissions of these compounds from vehicles govern the observed ambient petroleum biomarker concentrations. Using organic chemical tracer techniques, the portion of fine organic particulate matter in the Los Angeles atmosphere which is attributable to direct particle emissions from vehicle exhaust is calculated to vary from 7.5 to 18.3% at different sites throughout the air basin during a summertime severe photochemical smog episode. A similar level of variation in the contribution of primary motor vehicle exhaust to fine particulate organic matter concentrations during different times of day is seen. While peak atmospheric concentrations of fine particulate organic carbon are observed during the 1200–1600 PDT afternoon sampling period, only 6.3% of that material is apportioned to the directly emitted particles from vehicle exhaust. During the morning traffic peak between 0600–1000 PDT, 19.1% of the fine particulate organic material is traced to primary emissions from motor vehicles.     

Optimization of the coating layer for the measurement of ammonia by diffusion denuders

The performance of citric acid, oxalic acid and phosphorous acid as denuder coating layers for the determination of atmospheric ammonia have been studied by means of laboratory and field tests. The parameters evaluated during the study include: collection efficiency, selectivity of the coating layer, stability of the reaction product, operative capacity and stability of the coating layer. The results of this study show that phosphorous acid is a suitable coating layer for a denuder line intended to determine both gaseous ammonia and particulate ammonium in the atmosphere. It has been found that the citric acid coating suffers from an insufficient strength of the bond between collected ammonia and the coating layer, which causes a release of the collected ammonia both towards the air flow and towards the active sites of the denuder glass. The performance of oxalic acid was very good in the determination of gaseous ammonia, but this coating showed to be unsuitable for denuder sampling lines which are intended also for the determination of atmospheric ammonium. The volatilisation of oxalic from the denuder surface, in fact, causes a displacement of nitrate from the Teflon filter and an excess of nitrate ion on the back-up filter.Phosphorous acid-coated denuders were added to the sampling line employed in the EMEP station of Montelibretti. Reliable and interesting results were obtained, which allowed us to detect the presence of gaseous ammonia adsorbed on atmospheric particles.     

Indoor/outdoor relationships for ambient PM2.5 and associated pollutants: epidemiological implications in Lindon, Utah

Outdoor and indoor fine particulate species were measured at the Lindon Elementary School in Lindon, Utah, to determine which components of ambient fine particles have strong indoor and outdoor concentration correlations. PM2.5 mass concentrations were measured using tapered element oscillating microbalance (TEOM) monitors and by gravimetric analysis of Teflon filter samples. Gas-phase HNO3, sulfur dioxide, particulate nitrate, strong acid, and particulate sulfate were measured using annular denuder samplers. Soot was measured using quartz filters in filter packs. Total particulate number was measured with a condensation nucleus counter (CNC). Total particulate number and fine particulate sulfate and soot were correlated for ambient and indoor measurements. Indoor PM2.5 mass showed a low correlation with outdoor PM2.5 mass because of the influence of coarse material from student activities on indoor PM2.5. Fine particle acidity and the potentiation of biological oxidative mechanisms by iron were not correlated indoors and outdoors.