Semi-volatile Particulate Matter Research Articles

Role of semi-volatile particulate matter in gas-particle partitioning leading to change in oxidative potential.

Atmospheric semi-volatile organic compounds (SVOCs) are complex in their chemical and toxicological characteristics with sources from both primary combustion emissions and secondary oxygenated aerosol formation processes. In this study, thermal desorption of PM2.5 in association with online measurement of reactive oxygen species (ROS) was carried out to study the role of SVOCs in its gas-particle partitioning. The mass concentrations of PM2.5, black carbon (BC) and p-PAHs downstream of a thermodenuder were measured online at different temperature settings (25, 50, 100, and 200°C) to characterize PM physico-chemical properties. While the mass concentrations of PM2.5 and p-PAHs reduced to ∼34% at 200°C compared to that in ambient temperature, BC mass concentration has decreased by 30% at the highest temperature. Furthermore, the submicron particle size distribution showed reduced particle number concentration in Aitken mode at 200°C heating. The ROS, measured by Particle-into-Nitroxide-Quencher, also showed reduction and followed a similar trend with PM measurements, where the total ROS decreased by 12%, 31%, and 53% at 50°C, 100°C, and 200°C, respectively, compared to the ambient sample. When a HEPA filter was included in the upstream of samples, 39% of gas phase ROS reduction was observed at 200°C. This provided a good estimate of the contribution of SVOCs in ROS production in PM2.5, where decreased SVOCs concentration at 200°C increased the percentage of particle surface area. This concludes that the surface chemistry of these organic coatings on the particles is important for assessing the health impacts of PM.

Mode-specific, semi-volatile chemical composition of particulate matter emissions from a commercial gas turbine aircraft engine

We measured and characterized semi-volatile chemical composition of particulate matter (PM) in aircraft engine exhaust plumes in a dedicated aircraft PM emission study (NASA's AAFEX 1 field measurement campaign). Mode-specific organic and sulfate components were observed with a compact time-of-flight aerosol mass spectrometer (C-ToF-AMS). Nitrate components in both the nucleation and soot mode particles were negligible. The organic composition for the nucleation mode particles decreases with increasing engine power. For the soot mode, organic fraction initially decreases with increasing engine power but then slightly increases again above 45% engine thrust, probably due to the increasing contribution from lubrication oil emissions. These results show that an appreciable amount of semi-volatile PM can be generated in the exhaust plumes from a commercial aircraft engine. Thus, volatile PM must be studied as carefully as non-volatile soot emissions to fully address local air quality and human health impacts of aviation.

Investigation of alternative metrics to quantify PM mass emissions from light duty vehicles

We evaluated the performance of six alternative particulate matter (PM) metrics relative to the regulatory gravimetric method during chassis dynamometer testing of five light-duty vehicles over the Federal Test Procedure (FTP) and Supplemental FTP (US06) cycles. Alternative metrics included three mass-based metrics including black carbon (BC), two suspended PM mass using integrated particle size distribution (IPSD) method, and three number/surface-based metrics including total particle number (PN), solid particle number (SPN), and particle active surface area (PS). The results showed PM emissions over the FTP cycle were dominated by solid particles on a mass basis (BC to PM ratio = 0.6 ± 0.5), whereas over the US06 cycle were dominated by semi-volatile particles (BC to PM ratio = 0.2 ± 0.2). Moderate to strong correlations were reported between the gravimetric method and the six alternative metrics for FTP and US06 cycles separately (R2 = 0.69–0.91), i.e. the best-fit lines were strongly dependent upon the cycle. On the other hand, the six alternative PM mass and number metrics exhibited moderate to strong correlations regardless of the test cycle (R2 = 0.66–0.98). We attribute the observed cycle dependency between alternative metrics and the gravimetric mass method to the greater gravimetric sensitivity to organic and semi-volatile PM than for most alternative metrics.

A comparative analysis of chemical components and cell toxicity properties of solid and semi-volatile PM from diesel and biodiesel blend

Alternative fuel has raised increasing attention in recent years for better fuel economy and emission reduction. The biodiesel fuel is natively produced from vegetable and animal oils with large number of organic compounds with varying groups and characteristics. Particulate Matter (PM) emissions from the biodiesel blend are often complicated by the volatility of the different organic components. We here report the chemical and toxicological characterization of solid-PM and semi-volatile PM (SV-PM) from diesel and biodiesel blend (BD30) exhausts, using front and backup filter, respectively. While total PM emission was lower for BD30 in general, it contained 19% higher organic compounds (OC) in SV-PM compared to diesel, which on the other hand noted 24% more solid-PM. These organic compounds were further analyzed with OCEC thermograph to confirm the dominant existence of highly volatile OC in SV-PM. We further extracted water-soluble components from the solid- and SV-PM samples, and subjected to RAW 264.7 macrophage cell exposure. More than 2-fold increase of oxidative potential was observed in SV-PM samples over solid-PM with elevated levels of cellular reactive oxygen species (ROS) and a significant correlation with OC concentration. Instead, non-cellular assay for ROS quantification showed the change in oxidative potential is greatly influenced by solid-PM. And non-cellular ROS due to SV-PM is 2-fold less than cell-based assay. Hence, the semi-volatiles, though produced in small quantities, need great attention in assessing health hazards and could well be a scope for further research.

Atmospheric Processes Influencing Aerosols Generated by Combustion and the Inference of Their Impact on Public Exposure: A Review

Combustion-generated aerosols, especially emissions of heavy and light duty vehicles, are the dominant contributors of ambient particulate matter (PM) in urban environments. This paper reviews the atmospheric processes (such as dilution, nucleation, condensation and coagulation) that dominate the dynamics of combustion aerosols following their emission, with a particular emphasis on PM from mobile sources. Atmospheric dilution affects the dynamic behavior of aerosols by shifting the gas-particle partitioning of the semi-volatile component of these aerosols. Our paper discusses the roles of dilution in changing the physico-chemical properties of the ambient aerosols, such as particle size distribution and number concentration, and the degree to which it affects non-labile and semi-volatile PM components. This information is complemented with a discussion of secondary aerosol formation from atmospheric photochemical reactions that involve precursors emitted from traffic sources. Special focus is devoted to the role of gas-phase vapors formed from the evaporation of the semi-volatile fraction of aerosols during dilution. Adding to the common recognition that volatile organic compounds (VOCs) are the major gaseous precursors, these vapors also actively participate in photochemical reactions and contribute to the formation of secondary aerosols. Following this discussion, we review recent findings that link PM semi-volatile components and their redox activity, and we discuss the influence and importance of PM volatility on particle toxicity. Lastly, this paper discusses possible metrics to regulate PM emissions and establish ambient air quality standards that are pertinent to public health, and suggests future investigations aimed to improve our current understanding of the adverse health effects of population exposure to combustion-generated aerosols.

Malodor as a Trigger of Stress and Negative Mood in Neighbors of Industrial Hog Operations

We evaluated malodor and air pollutants near industrial hog operations as environmental stressors and negative mood triggers. We collected data from 101 nonsmoking adults in 16 neighborhoods within 1.5 miles of at least 1 industrial hog operation in eastern North Carolina. Participants rated malodor intensity, stress, and mood for 2 weeks while air pollutants were monitored. Reported malodor was associated with stress and 4 mood states; odds ratios (ORs) for a 1-unit change on the 0-to-8 odor scale ranged from 1.31 (95% confidence interval [CI] = 1.16, 1.50) to 1.81 (95% CI = 1.63, 2.00). ORs for stress and feeling nervous or anxious were 1.18 (95% CI = 1.08, 1.30) and 1.12 (95% CI = 1.03, 1.22), respectively, for a 1 ppb change in hydrogen sulfide and 1.06 (95% CI = 1.00, 1.11) and 1.10 (95% CI = 1.03, 1.17), respectively, for a 1 microg/m(3) change in semivolatile particulate matter less than 10 microm in aerodynamic diameter (PM(10)). Hog odor, hydrogen sulfide, and semivolatile PM(10) are related to stress and negative mood in disproportionately low-income communities near industrial hog operations in eastern North Carolina. Malodor should be considered in studies of health impacts of environmental injustice.

Field Evaluation of the Differential TEOM Monitor for Continuous PM2.5Mass Concentrations Special Issue ofAerosol Science and Technologyon Findings from the Fine Particulate Matter Supersites Program

The performance of a prototype differential TEOM monitor (Rupprecht and Patashnick Co., NY) and its ability to measure the “actual” ambient near-continuous PM-2.5 mass in an area often high in semivolatile particulate matter has been evaluated. Measurements were made within a mobile particle instrumentation trailer (PIU) located in Claremont, CA—a “receptor” site in the Los Angeles Basin. The Differential TEOM monitor has been developed to directly measure ambient PM mass concentrations while accounting for collection artifacts, including loss of semivolatile aerosols and temperature changes. The Differential TEOM monitors used in this study were self-referencing, providing mass concentration measurements at 5 min intervals. To reference the semicontinuous mass measured by the Differential TEOM monitor, its 24 h time-integrated mass concentrations were compared to those determined by collocated filter-based samplers, i.e., MOUDI (Model 110) and Partisol (Model 2025). A HEADS was used to evaluate ammonium nitrate losses from the time-integrated samplers. The results show that PM-2.5 mass measurements using the Differential TEOM monitor are consistent with those of the MOUDI and Partisol, while differences can be generally explained by loss of ammonium nitrate from the reference samplers. The field results also demonstrate the ability of the Differential TEOM monitor to track adsorption and desorption processes from its sample filter. Although adsorption and evaporation can be dynamic processes, and difficult to estimate, the results of this study also suggest that the Differential TEOM monitor provides a very good estimate of the “actual” ambient particulate mass present on a near-continuous basis.

Trends in PM 2.5 composition at the Department of Energy OST NETL fine particle characterization site in Pittsburgh, PA, USA

This paper reports on the results from the first 6 months (from November 1999 to April 2000) of an ongoing monitoring study of fine particulate air pollutants at the Department of Energy's Office of Science and Technology (OST) NETL sampling site, 30 km southwest of Pittsburgh city center, Pennsylvania. This study is part of a 2-year sampling program for PM characterization, under the auspices of The University Coal Research Program of the National Energy Technology Laboratory (NETL), US Department of Energy in Pittsburgh, PA, USA. Samples were collected daily with a Particle Concentrator-Brigham Young University Organic Sampling System (PC-BOSS) to determine PM 2.3 composition, including the semi-volatile organic compounds (SVOC) and ammonium nitrate lost from particles during sampling. Average fine particulate composition during the 6-month period was: constructed PM 2.3, 19.4 μg m −3; ammonium sulfate 4.3 μg m −3; non-volatile organic material, 6.9 μg m −3; elemental carbon, 0.4 μg m −3; SVOC lost from particles during sampling, 6.1 μg m −3; retained ammonium nitrate, 1.4 μg m −3; lost ammonium nitrate, 0.3 μg m −3. Results from the PC-BOSS sampler are also compared with those obtained from a Federal Reference Method PM 2.5 sampler, and a Tapered Element Oscillating Microbalance monitor, both of which tended to not measure the semi-volatile particulate matter. SVOC concentrations were highest in the spring. Episodes of fine particulate non-volatile organic material occurred throughout the 6-month period. Average ammonium sulfate concentrations were higher in November and January than the other months for the study period.

Monitoring of particulate matter outdoors.

Recent studies of the size and composition of atmospheric particulate matter (PM) have demonstrated the usefulness of separating atmospheric PM into its fine and coarse components. The need to measure the mass and composition of fine and coarse PM separately has been emphasized by research in exposure, epidemiology, and toxicology of atmospheric PM. This paper provides a background on the size distribution and properties of PM relevant to the differences between fine and coarse particles. Various decisions that must be made when deciding how to separate, collect, and measure PM are discussed. Techniques for monitoring fine and coarse particles, including the US Federal Reference Method for PM2.5 and several techniques for PM10-2.5, are presented. Problems encountered in collecting semivolatile PM and in weighing atmospheric PM collected on a filter are described. Continuous monitoring methods for PM mass and for PM components (carbon, nitrate, and sulfate) are described and brief descriptions are given of analytical techniques for the chemical characterization of collected PM. This information should be especially useful for environmental workers familiar with monitoring methods for total suspended particles or PM10 but who will need to measure PM2, and PM10-2.5 in the future.

Development of a Reference Standard for Particulate Matter Mass in Ambient Air

Particulate matter (PM) in ambient air is composed of many chemical species of varying vapor pressures. A direct mass measurement of PM mass on filters is the basis of regulatory PM reference methods. The loss of semi-volatile PM mass collected on filters and filter sampling artifacts can produce nonquantifiable biases in reference method measurements depending on the thermodynamic history of the filter; therefore, a reference method cannot be considered a scientific reference standard. A new technique is introduced which has the potential to overcome the difficulties inherent in PM mass measurement and holds the promise of the measurement of PM mass as it exists in ambient air at ambient temperature. While comprehensive laboratory and field studies of the instrument and its components are needed to fully characterize the system, preliminary data have been obtained to provide a basic proof of concept for the technique.