Revisiting the size selective performance of EPA's high-volume total suspended particulate matter (Hi-Vol TSP) sampler

<p>Under the National Ambient Air Quality Standard (NAAQS) for airborne lead, measurements are conducted by means of a high-volume total suspended particulate matter (Hi-Vol TSP) sampler. In the decade between 1973 and 1983, there were 12 publications that explored the sampling characteristics and effectiveness of the Hi-Vol TSP, yet there persists uncertainty regarding its performance. This article presents an overview of the existing literature on the performance of the Hi-Vol TSP, and identifies the reported sampler effectiveness with respect to four factors: particle size (reported effectiveness of 7%–100%), wind speed (−36% to 100%), sampler orientation (7%–100%), and operational state (107%–140%). Effectiveness of the Hi-Vol TSP was evaluated with a solid, polydisperse aerosol in a controlled wind tunnel setting. Isokinetic samplers were deployed alongside the Hi-Vol TSP to investigate three wind speeds (2, 8, and 24 km h⁻¹), three sampler orientations (0°, 45°, 90°), and two operational states (on, off) for aerosols with aerodynamic diameters from 5 to 35 µm. Results indicate that particle diameter was the largest determining factor of effectiveness followed by wind speed. Orientation of the sampler did not have a significant effect at 2 and 8 km h⁻¹ but did at 24 km h⁻¹. In a passive state, the Hi-Vol TSP was collected between 1% and 7% of available aerosol depending on particle size and wind speed. Results of this research do not invalidate results of previous studies but rather contribute to our overall understanding of the Hi-Vol TSP's size-selective performance. While results generally agreed with previous studies, the Hi-Vol TSP was found to exhibit less dependence on these four factors than previously reported.</p> <p>© 2017 American Association for Aerosol Research</p

Summary of PM_2.5 Measurement Artifacts Associated with the Teledyne T640 PM Mass Analyzer Under Controlled Chamber Experimental Conditions Using Polydisperse Ammonium Sulfate Aerosols and Biomass Smoke

Particulate matter (PM) is a major primary pollutant emitted during wildland fires that has the potential to pose significant health risks to individuals/communities who live and work in areas impacted by smoke events. Limiting exposure is the principle measure available to mitigate health impacts of smoke and therefore the accurate determination of ambient PM concentrations during wildland fire events is critical to protecting public health. However, monitoring air pollutants in smoke impacted environments has proven challenging in that measurement interferences or sampling conditions can result in both positive and negative artifacts. The EPA has performed research on methods for the measurement of PM2.5 in a series of laboratory based studies including evaluation in smoke. This manuscript will summarize the results of the laboratory based evaluation of federal equivalent method (FEM) analyzers for PM2.5 with particular attention being given to the Teledyne-API Model T640 PM Mass analyzer, as compared to the filter-based federal reference method (FRM). The T640 is an optical-based PM analyzer and has been gaining wide use by state and local agencies in monitoring for PM2.5 U.S. National Ambient Air Quality Standards (NAAQS) attainment. At present, the T640 (includes both T640 and T640X) comprises ~40% of the PM2.5 FEM monitors in U.S. regulatory monitoring networks. In addition, the T640 has increasingly been employed for the higher time resolution comparison/evaluation of low-cost PM sensors including during smoke impacted events. Results from controlled non-smoke laboratory studies using generated ammonium sulfate aerosols, demonstrated a generally negative T640 measurement artifact that was significantly related to the PM2.5 concentration and particle size distribution. Results from biomass burning chamber studies demonstrated positive and negative artifacts significantly associated with PM2.5 concentration and optical wavelength dependent absorption properties of the smoke aerosol. Implications The results detailed in this product will provide state and local air monitoring agencies with the tools and knowledge to address PM2.5 measurement challenges in areas frequently impact by wildland fire smoke. The observed large positive and negative artifacts in the T640 PM mass determination has the potential to result in false exceedances of the PM2.5 NAAQS or in the disqualification of monitoring data through an exceptional event designation. In addition, the observed artifacts in smoke impacted air will have a detrimental effect on providing reliable public information when wildfires occur and also in identifying reference measurements for small sensor evaluation studies. Other PM2.5 FEMs such as the BAM-1022 perform better in smoke and are comparable to the filter based FRM. Care must be taken in choosing high time resolution FEM monitors that will be operated at smoke impacted sites. Accurate methods, such as the FRM and BAM-1022 will reduce the burden of developing and reviewing exceptional event request packages, data loss/disqualification, and provide states with tools to adequately evaluate public exposure risks and provide accurate public health messaging during wildfire/smoke events. Implications The results detailed in this product will provide state and local air monitoring agencies with the tools and knowledge to address PM2.5 measurement challenges in areas frequently impact by wildland fire smoke. The observed large positive and negative artifacts in the T640 PM mass determination has the potential to result in false exceedances of the PM2.5 NAAQS or in the disqualification of monitoring data through an exceptional event designation. In addition, the observed artifacts in smoke impacted air will have a detrimental effect on providing reliable public information when wildfires occur and also in identifying reference measurements for small sensor evaluation studies. Other PM2.5 FEMs such as the BAM-1022 perform better in smoke and are comparable to the filter based FRM. Care must be taken in choosing high time resolution FEM monitors that will be operated at smoke impacted sites. Accurate methods, such as the FRM and BAM-1022 will reduce the burden of developing and reviewing exceptional event request packages, data loss/disqualification, and provide states with tools to adequately evaluate public exposure risks and provide accurate public health messaging during wildfire/smoke events.</p

Trends in the oxidation and relative volatility of chamber-generated secondary organic aerosol

<p>The relationship between the oxidation state and relative volatility of secondary organic aerosol (SOA) from the oxidation of a wide range of hydrocarbons is investigated using a fast-stepping, scanning thermodenuder interfaced with a high-resolution time-of-flight aerosol mass spectrometer (AMS). SOA oxidation state varied widely across the investigated range of parent hydrocarbons but was relatively stable for replicate experiments using a single hydrocarbon precursor. On average, unit mass resolution indicators of SOA oxidation (e.g., AMS <i>f</i>₄₃ and <i>f</i>₄₄) are consistent with previously reported values. Linear regression of H:C vs. O:C obtained from parameterization of <i>f</i>₄₃ and <i>f</i>₄₄ and elemental analysis of high-resolution spectra in Van Krevelen space both yield a slope of ∼−0.5 across different SOA types. A similar slope was obtained for a distinct subset of toluene/NO<i>_x</i> reactions in which the integrated oxidant exposure was varied to alter oxidation. The relative volatility of different SOA types displays similar variability and is strongly correlated with SOA oxidation state (_C). On average, relatively low oxidation and volatility were observed for aliphatic alkene (including terpenes) and <i>n-</i>alkane SOA while the opposite is true for mono- and polycyclic aromatic hydrocarbon SOA. Effective enthalpy for total chamber aerosol obtained from volatility differential mobility analysis is also highly correlated with _C indicating a primary role for oxidation levels in determining the volatility of chamber SOA. Effective enthalpies for chamber SOA are substantially lower than those of neat organic standards but are on the order of those obtained for partially oligomerized glyoxal and methyl glyoxal.</p> <p>© 2018 American Association for Aerosol Research</p

Photochemical Conversion of Surrogate Emissions for Use in Toxicological Studies: Role of Particulate- and Gas-Phase Products

The production of photochemical atmospheres under controlled conditions in an irradiation chamber permits the manipulation of parameters that influence the resulting air-pollutant chemistry and potential biological effects. To date, no studies have examined how contrasting atmospheres with a similar Air Quality Health Index (AQHI), but with differing ratios of criteria air pollutants, might differentially affect health end points. Here, we produced two atmospheres with similar AQHIs based on the final concentrations of ozone, nitrogen dioxide, and particulate matter (PM_2.5). One simulated atmosphere (SA-PM) generated from irradiation of ∼23 ppmC gasoline, 5 ppmC α-pinene, 529 ppb NO, and 3 μg m^–3 (NH₄)₂SO₄ as a seed resulted in an average of 976 μg m^–3 PM_2.5, 326 ppb NO₂, and 141 ppb O₃ (AQHI 97.7). The other atmosphere (SA-O₃) generated from 8 ppmC gasoline, 5 ppmC isoprene, 874 ppb NO, and 2 μg m^–3 (NH₄)₂SO₄ resulted in an average of 55 μg m^–3 PM_2.5, 643 ppb NO₂, and 430 ppb O₃ (AQHI of 99.8). Chemical speciation by gas chromatography showed that photo-oxidation degraded the organic precursors and promoted the de novo formation of secondary reaction products such as formaldehyde and acrolein. Further work in accompanying papers describe toxicological outcomes from the two distinct photochemical atmospheres

Effects of Simulated Smog Atmospheres in Rodent Models of Metabolic and Immunologic Dysfunction

Air pollution is a diverse and dynamic mixture of gaseous and particulate matter, limiting our understanding of associated adverse health outcomes. The biological effects of two simulated smog atmospheres (SA) with different compositions but similar air quality health indexes were compared in a nonobese diabetic rat model (Goto-Kakizaki, GK) and three mouse immune models (house dust mite (HDM) allergy, antibody response to heat-killed pneumococcus, and resistance to influenza A infection). In GK rats, both SA-PM (high particulate matter) and SA-O₃ (high ozone) decreased cholesterol levels immediately after a 4-h exposure, whereas only SA-O₃ increased airflow limitation. Airway responsiveness to methacholine was increased in HDM-allergic mice compared with nonallergic mice, but exposure to SA-PM or SA-O₃ did not significantly alter responsiveness. Exposure to SA-PM did not affect the IgM response to pneumococcus, and SA-O₃ did not affect virus titers, although inflammatory cytokine levels were decreased in mice infected at the end of a 7-day exposure. Collectively, acute SA exposures produced limited health effects in animal models of metabolic and immune diseases. Effects of SA-O₃ tended to be greater than those of SA-PM, suggesting that gas-phase components in photochemically derived multipollutant mixtures may be of greater concern than secondary organic aerosol PM