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Supplemental digital content is available in the text. Objective: Clinical trials assessing the efficacy of botulinum toxin in treating recalcitrant lateral epicondylitis have demonstrated varied results and differed greatly in methodology. The objective of this systematic review was to demonstrate injection location as a significant contributor to outcome heterogeneity. Design: Two reviewers independently conducted a systematic review using Scopus, Embase, and PubMed for randomized controlled trials assessing botulinum toxin in the treatment of lateral epicondylitis. After applying inclusion/exclusion criteria to abstracts and reviewing the full-text articles, seven studies were found representing six separate injection locations. Reduction in visual analog scale pain and change in grip strength were the principal outcomes of interest. Results: The largest reduction in pain was seen in injection at 1/3 of the length of the forearm from the lateral epicondyle at 16-wk follow-up, whereas the smallest reduction was seen at 12-wk follow-up after injection at the 0-cm mark. Differences were also identified in grip strength, although all studies reported return to baseline strength by weeks 12–18. Conclusions: This study demonstrates injection location as a potential source of heterogeneity. This clinical question warrants further evaluation with direct comparison of outcomes at different injection locations while controlling for dosage, toxin type, and ultrasound/electromyographic guidance. [ABSTRACT FROM AUTHOR]

Presents a study that described a model proposed for lock-on in gallium arsenide (GaAs) photoconductive switches based on avalanche breakdown from impact ionization of deep EL2 traps. Capability of the model; Description of a GaAs photoconductive switch; Result from irradiating the GaAs with neutrons.

Oil and gas activities have occurred in the Bakken region of North Dakota and nearby states and provinces since the 1950s but began increasing rapidly around 2008 due to new extraction methods. Three receptor-based techniques were used to examine the potential impacts of oil and gas extraction activities on airborne particulate concentrations in Class I areas in and around the Bakken. This work was based on long-term measurements from the Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring network. Spatial and temporal patterns in measured concentrations were examined before and after 2008 to better characterize the influence of these activities. A multisite back-trajectory analysis and a receptor-based source apportionment model were used to estimate impacts. Findings suggest that recent Bakken oil and gas activities have led to an increase in regional fine (PM2.5—particles with aerodynamic diameters <2.5 µm) soil and elemental carbon (EC) concentrations, as well as coarse mass (CM = PM10-PM2.5). Influences on sulfate and nitrate concentrations were harder to discern due to the concurrent decline in regional emissions of precursors to these species from coal-fired electric generating stations. Impacts were largest at sites in North Dakota and Montana that are closest to the most recent drilling activity. Implications: The increase in oil and gas activities in the Bakken region of North Dakota and surrounding areas has had a discernible impact on airborne particulate concentrations that impact visibility at protected sites in the region. However, the impact has been at least partially offset by a concurrent reduction in emissions from coal-fired electric generating stations. Continuing the recent reductions in flaring would likely be beneficial for the regional visual air quality. [ABSTRACT FROM AUTHOR]

Abstract: Ammonia and ammonium are important atmospheric trace constituents that affect particulate matter concentrations and contribute to reactive nitrogen deposition. We refer to and measure the sum of ammonia and ammonium as NHx. To better understand concentrations of NHx in remote areas, the Interagency Monitoring of Protected Visual Environments (IMPROVE) fine particulate matter (<2.5 μm) sampler was modified to measure NHx at a subset of locations in the routine IMPROVE network. To sample NHx, an additional IMPROVE PM2.5 sampler was installed. Samples were collected on phosphorous acid impregnated cellulose filters held in polypropylene filter holders. While the standard IMPROVE filter holder is made of Delrin (polyoxymethylene, POM), reactions between collected NHx and formaldehyde released by phosphorous acid degradation of the POM holder produced substantial amounts of artifact methylamine, especially during warm sampling periods. This artifact did not occur with the new polypropylene holder design, and no methylamine was measured above the method detection limit of 0.003 μg/m3. Samples collected using the new IMPROVE NHx sampling system were evaluated against samples collected with a collocated URG annular denuder/filter-pack module for 6 weeks; the observed bias was −7%. The NHx monitors were deployed at a total of nine sites in the U.S. Rocky Mountain and Great Plains regions and to the east, and at Bondville, Illinois, from April 2011 to August 2012. Collocated samplers at Rocky Mountain National Park, Colorado, and Bondville, Illinois, demonstrated excellent measurement precision. The data revealed a pattern of increasing NHx concentrations in late spring/early summer (June) and a decrease in winter, starting in September for most of the sites. This pattern is consistent with expected seasonal patterns in agricultural emissions of ammonia. Sites closer to agricultural sources at Bondville and Cedar Bluff (Kansas), however, still exhibit quite abundant winter NHx, which may reflect continued local agricultural emissions trapped within a shallower winter boundary layer. A probable impact of wildfires on NHx concentrations was observed for Bandelier NM, Chiricahua NM, and Yellowstone NP during summer/fall 2011. [Copyright &y& Elsevier]

Abstract: Increasing rates of nitrogen deposition are a concern in many protected ecosystems. Understanding the sources influencing these regions can be a challenge as there are often few observations available to understand the transport of key species. Several field campaigns were conducted in and around Rocky Mountain National Park (RMNP) from 2006 to 2009 to assess the impacts of various reactive nitrogen sources and regional meteorology on reactive nitrogen deposition. Measurements of ammonia, ammonium, nitric acid, and nitrate at ground-level sites across northern Colorado were used to examine spatial gradients in atmospheric reactive nitrogen concentrations, the influence of wind direction on reactive nitrogen transport in the regional atmosphere, and anthropogenic contributions to reactive nitrogen concentrations in RMNP. The highest concentrations of reduced nitrogen occurred on the eastern plains of Colorado while oxidized nitrogen concentrations were highest along the Front Range urban corridor. Both regions lie east of RMNP. Upslope (easterly) winds associated with mountain–valley wind patterns and larger, synoptic scale forcing, transport emissions from these sources westward up the eastern slope of the Rockies and into RMNP; the highest ammonium and nitrate concentrations in RMNP were clearly associated with this upslope transport pattern. Concentrations of key reactive nitrogen species east of the Continental Divide in RMNP were, on average, more than 50% higher than those observed at a background site located west of the park, further indicating large contributions from sources east of the park. These observations highlight the need to focus on controlling reactive nitrogen emissions east of the park as part of ongoing efforts to reduce reactive nitrogen deposition in RMNP. [Copyright &y& Elsevier]

Abstract: Observation and appreciation of scenic landscape features, airport runway visibility, and the earth''s radiation balance are all dependent on the radiative properties of the atmosphere, which in turn are dependent on the scattering and absorption characteristics of ambient aerosols. Atmospheric scattering and, to a lesser degree, absorption characteristics are highly dependent on the amount of water vapor absorbed by aerosols under ambient relative humidity (RH) conditions. Water vapor absorptive properties of inorganic aerosols have been extensively measured and modeled; however, hygroscopic properties of organic aerosols are less understood, especially as they occur in the ambient atmosphere. Therefore, an aerosol characterization study was conceived and implemented at Yosemite National Park, which is highly impacted by carbonaceous aerosols. The overall objective of the study was to characterize the physical, chemical, and optical properties of a carbon-dominated aerosol, including the ratio of total organic matter weight to organic carbon, organic mass scattering efficiencies, and the hygroscopic characteristics of a carbon-laden ambient aerosol. The study was conducted during July, August, and the first week of September at Turtleback Dome on the south rim of the entrance to Yosemite Valley. The ratio of the scattering coefficient at some RH divided by the scattering coefficient at some minimum RH () was measured over a wide range of RHs. f(85&#60;RH&#60;90) decreased from about 2.0 to &#60;1.2 as the organic carbon mass (OMC/(NH4)2(SO4)) ratio increased from a low of 0.57 to 11.15, implying that the f(RH) associated with organics is small, possibly on the order of 1.1 or less. Furthermore, modeling f(RH) as a function of RH suggested that ambient organic mass aerosols may be weakly hygroscopic with an f(RH) at RH=85–90% of about 1.1. [Copyright &y& Elsevier]

The hygroscopic nature of atmospheric fine aerosol was investigated at a rural site in the Great Smoky Mountains National Park during July and August 1995. Passing the sample aerosol through an inlet, which housed an array of Perma Pure diffusion dryers, controlled the sample aerosol's relative humidity (RH). After conditioning the aerosol sample in the inlet, the light scattering coefficient and the aerosol size distribution were simultaneously measured. During this study, the conditioned aerosol's humidity ranged between 5% < RH < 95%. Aerosol response curves were produced using the ratio b[subspw] / b[subspd]; where b[subspw] is the scattering coefficient measured at some RH greater than 20% and b[subspd] is the scattering coefficient of the "dry" aerosol. For this work, any sample RH values below 15% were considered dry. Results of this investigation showed that the light scattering ratio increased continuously and smoothly over the entire range of relative humidity. The magnitude of the ratio at a particular RH value, however, varied considerably in time, particularly for RH values greater than approximately 60%. Curves of the scattering coefficient ratios as a function of RH were generated for each day and compared to the average 12-hour chemical composition of the aerosol. This comparison showed that for any particular RH value the ratio was highest during time periods of high sulfate concentrations and lowest during time periods of high soil or high organic carbon concentrations. [ABSTRACT FROM AUTHOR]

The eastern United States national parks experience some of the worst visibility conditions in the nation. To study these conditions, the Southeastern Aerosol and Visibility Study (SEAVS) was undertaken to characterize the size-dependent composition, thermodynamic properties, and optical characteristics of the ambient atmospheric particles. It is a cooperative three-year study that is sponsored by the National Park Service and the Electric Power Research Institute and its member utilities. The field portion of the study was carried out from July 15 to August 25, 1995. The study design, instrumental configuration, and estimation of aerosol types from particle measurements is presented in a companion paper. In the companion paper, we compare measurements of scattering at ambient conditions and as functions of relative humidity to theoretical predictions of scattering. In this paper, we make similar comparisons, but using statistical techniques. Statistically derived specific scattering associated with sulfates suggest that a reasonable estimate of sulfate scattering can be arrived at by assuming nominal dry specific scattering and treating the aerosols as an external mixture with ammoniation of sulfate accounted for and by the use of Tang's growth curves to predict water absorption. However, the regressions suggest that the sulfate scattering may be underestimated by about 10%. Regression coefficients on organics, to within the statistical uncertainty of the model, suggest that a reasonable estimate of organic scattering is about 4.0 m²/g. A new analysis technique is presented, which does not rely on comparing measured to model estimates of scattering to evoke an understanding of ambient aerosol growth properties, but rather relies on measurements of scattering as a function of relative humidity to develop actual estimates of f(RH) curves. The estimates of the study average f(RH) curve for sulfates compares favorably with the theoretical f(RH) curve for... [ABSTRACT FROM AUTHOR]

The Southeastern Aerosol and Visibility Study (SEAVS) was undertaken to characterize the size-dependent composition, thermodynamic properties, and optical characteristics of the ambient atmospheric particles in the southeastern United States. The field portion of the study was carried out from July 15 to August 25, 1995. As part of the study a relative humidity controlled inlet was built to raise or lower the relative humidity to predetermined levels before the aerosol was passed into an integrating nephelometer or particle-sizing device. Five other integrating nephelometers were operated in various configurations, two of which were fitted with a 2.5 µm inlet. Fine particle < 2.5 µm) samplers were operated to measure concentrations of sulfate, nitrate, and ammonium ions, organic and elemental carbon, and fine soil. Mass size distributions were measured with an eight-stage, single orifice cascade impactor. Four different strategies for estimating scattering were used. First, an externally mixed model with constant specific scattering coefficients, sulfate ion mass interpreted as ammonium bisulfate, and ammonium bisulfate growth as a function of relative humidity, is assumed. Second, an externally mixed aerosol model, assuming constant dry specific scattering but with sulfate ammoniation and associated composition-dependent hygroscopicity explicitly accounted for, is used. Third, an externally mixed aerosol model, but with sulfate ammoniation, associated growth as a function of relative humidity, and sulfate size distributions, is applied. Fourth, an internally mixed aerosol model with measured sulfur size distributions and estimated size distributions for other species is used with the growth characteristics of the mixture being estimated using the Zdanovskii-Stokes-Robinson (ZSR) assumptions. Only ionic species were considered to be hygroscopic. The second, third, and fourth approaches yield similar results with reconstructed scattering comparing... [ABSTRACT FROM AUTHOR]

Reports on the seasonal changes in aerosol composition and acidity at Shenandoah and Great Smoky Mountains National Parks in the United States. Measurement of the acidity of atmospheric aerosols; Impact of acidic particulate on health and visibility; Method of determining degree of neutralization of sulfate.

Dinosaur National Monument (DINO) is located near the northeastern edge of the Uinta Basin and often experiences elevated levels of wintertime ground-level ozone. Previous studies have shown that high ozone mixing ratios in the Uinta Basin are driven by elevated levels of volatile organic compounds (VOCs) and nitrogen oxides (NOx) from regional oil and gas development coupled with temperature inversions and enhanced photochemistry from persistent snow cover. Here, we show that persistent snow cover and temperature inversions, along with abundant ammonia, also lead to wintertime haze in this region. A study was conducted at DINO from November 2018 through May 2020 where ozone, speciated fine and coarse aerosols, inorganic gases, and VOCs were measured. Three National Ambient Air Quality Standards (NAAQS) ozone exceedances were observed in the first winter, and no exceedances were observed in the second winter. In contrast, elevated levels of particulate matter were observed both winters, with 24-h averaged particle light extinction exceeding 100 Mm−1. These haze events were dominated by ammonium nitrate, and particulate organics were highly correlated with ammonium nitrate. Ammonium nitrate formation was limited by nitric acid in winter. As such, reductions in regional NOx emissions should reduce haze levels and improve visibility at DINO in winter. Long-term measurements of particulate matter from nearby Vernal, Utah, suggest that visibility impairment is a persistent issue in the Uinta Basin in winter. From April through October 2019, relatively clean conditions occurred, with average particle extinction of ~10 Mm−1. During this period, ammonium nitrate concentrations were lower by more than an order of magnitude, and contributions from coarse mass and soil to haze levels increased. VOC markers indicated that the high levels of observed pollutants in winter were likely from local sources related to oil and gas extraction activities. Implications: Elevated ground-level ozone and haze levels were observed at Dinosaur National Monument in winter. Haze episodes were dominated by ammonium nitrate, with 24-h averaged particle light extinction exceeding 100 Mm−1, reducing visual range near the surface to ~35 km. Despite elevated ammonium nitrate concentrations, additional gas-phase ammonia was available, such that any increase in NOx emissions in the region is likely to lead to even greater haze levels. [ABSTRACT FROM AUTHOR]

The National Park Service (NPS) has a need to measure real-time PM2.5 and haze levels across its many park units to inform the public of unhealthy air and track visual degradation of park scenic vistas. To fulfill this need, the NPS deployed PurpleAir monitors (PA) in several park units. PA monitors are inexpensive monitors promoted as particle counters capable of measuring particle size distributions. Each PA is equipped with two Plantower (PMS) particle counters and a temperature, relative humidity (RH) and pressure sensor. In 2022, the NPS initiated a field study to evaluate PA limitations, uncertainties, and how the measurements relate to particle light scattering. The study was conducted in Fort Collins, CO where five nephelometers, particle sizing instruments, semi-continuous ion concentration measurements, and seven PAs were deployed. One nephelometer and two PA's sampled air from an RH controlled chamber with RH ≤ 40%. The PA temperatures were accurate, but the PA RH measurements were systematically underreported RH by ∼28% and it is recommended to scale these data by 1.35. The PMS reported size distributions are shown to be invalid. PA instruments mounted without protection from wind exhibited biases of ±160% for wind speeds exceeding 5 mph. Hourly CH1 data were precise, with errors of ∼100% at low concentrations of 30 #/dl and 15% for concentrations ≥1000 #/dl. Normalizing all PMS sensors to each other reduced the errors to 20% and 8% for low and higher particle concentrations respectively. The reported total particle count, i.e. ≥0.3 μm channel (CH1), was biased low, and the bias decreased linearly with mean scattering diameter (MSD). The ratio of measured ≥0.3 μm to PA CH1 channel increases linearly with MSD. The overall normalized mean deviation (NMD) between the two measurements is 121.8%. The CH1 channel also increases as a function of RH primarily due to the growth of hygroscopic aerosols. On average, the relationship between the atmospheric scattering coefficient (b sp) and the PMS ≥0.3 μm CH1 channel is described by the equation b sp = 0.015 × CH1 for MSD levels less than 0.35 μm. The PMS CH1 response decreases linearly with MSD. The NMD between ambient PMS derived b sp and measured ambient b sp is 27.0%. Recommendations are made for PA network deployment. • When the Purple Air monitor is mounted without a wind shield meteorological conditions can cause over or underestimation of reported air quality parameters by factors of ±1.6. • When multiple PMS sensors are normalized to each other the precision of the instruments was near 10% for number concentration greater than about 200 #/dl. • The Plantower sensor does not measure a true particle size number concentration distribution. • As the median scattering diameter increases from 0.34 to 0.42 μm the ratio of b sp to PMS derived b sp increases by about 30%. [ABSTRACT FROM AUTHOR]

Integrating nephelometers are designed to measure the scattering coefficient, b sp , of an aerosol introduced into its sampling chamber. They have been and are used extensively in laboratory studies and short-term intensive aerosol characterization studies to validate and improve optical aerosol models. They are used to measure long-term temporal and spatial trends of the particle scattering coefficient, and to measure trends in the scattering enhancement factor, f(RH). The National Park Service (NPS) has operated Optec NGN nephelometers with an open sampling chamber, referred to as NGN ambient , designed to measure total (coarse plus fine) particle scattering at near ambient relative humidity (RH). However, the NGN is no longer manufactured and will be replaced with Ambilabs 2WIN nephelometers. An intercomparison study was initiated to compare the NGN ambient , an enclosed heated NGN, two 2WIN nephelometers, one held at RH ≤ 40% and another modified to sample at near ambient RH, and a TSI (Shoreview, MN, USA). The objective of the study was to evaluate the suitability of the 2WIN to replace the NGN ambient and more generally to assess the suitability of the 2WIN instrument to be used to track long term trends in bsp and f(RH) values. The two 2WIN's, TSI and the heated NGN have enclosed sampling chambers with PM2.5 inlets. Measurements of particle physical and chemical properties and sampling chamber RH allowed for an assessment of the inter-comparability of relationships between optical models and nephelometer measurements. Heating of the sampling chamber to reduce RH to less than 40% did not significantly volatilize particle nitrate but heating to reduce the RH to near 20% did. It was also determined that measurement of the scattering enhancement function, f(RH) , was underestimated in this study, by about 20% for RH levels of 70% or greater, when the reference RH nephelometer was held at RH ≤ 40% compared to when the RH ≤ 10%. The study highlighted the importance of careful calibration of the instrument and careful documentation of the sampling chamber environment in which the measurement is made. Knowing precisely the RH in the sensor volume is critical to the interpretation of measured b sp levels. Monitoring of long-term temporal and spatial trends should be done either with the sampling chamber at or near ambient RH to track changes in ambient b sp or at RH ≤ 10% to understand changes in particulate mass concentrations contributing to b sp. Understanding changes in f(RH) over time and space should be done with the reference b sp at RH ≤ 10%. The lower RH levels should be achieved by some method other than heating the chamber to avoid volatilization of the aerosol species such as ammonium nitrate. Key Points. • When atmospheric particle size and physical and chemical characteristics are known it is possible to estimate particulate scattering as measured by a nephelometer if operation of the nephelometer does not inadvertently modify the aerosol, for example heating the aerosol such that volatile species are lost. • Even though nephelometers are easily and accurately calibrated the measurement of particulate scattering is very sensitive to temperature and RH in the sampling chamber. Therefore, to track long-term spatial and temporal trends in aerosol scattering it is critical to control the humidity in the sampling chamber, preferably at relative humidity levels near 20% or less and by some method other than heating the aerosol. • All commercially available nephelometers modify the aerosol because of inadvertent heating and modifications must be made to the nephelometers to operate at near-ambient conditions. • Slight heating of the aerosol such that relative humidity did not exceed 40% in this study apparently did not volatilize ammonium nitrate particles. [ABSTRACT FROM AUTHOR]

Rocky Mountain National Park is experiencing reduced visibility and changes in ecosystem function due to increasing levels of oxidized and reduced nitrogen. The Rocky Mountain Atmospheric Nitrogen and Sulfur (Ro- MANS) study was initiated to better understand the origins of sulfur and nitrogen species as well as the complex chemistry occurring during transport from source to receptor. As part of the study, a monitoring program was initiated for two 1-month time periods-one during the spring and the other during late summer/fall. The monitoring program included intensive high time resolution concentration measurements of aerosol number size distribution, inorganic anions, and cations, and 24-hr time resolution of PM2.5 and PM10 mass, sulfate, nitrate, carbon, and soil-related elements concentrations. These data are combined to estimate high time resolution concentrations of PM2.5 and PM10 aerosol mass and fine mass species estimates of ammoniated sulfate, nitrate, and organic and elemental carbon. Hour-by-hour extinction budgets are calculated by using these species concentration estimates and measurements of size distribution and assuming internal and external particle mixtures. Summer extinction was on average about 3 times higher than spring extinction. During spring months, sulfates, nitrates, carbon mass, and PM10 - PM2.5 mass contributed approximately equal amounts of extinction, whereas during the summer months, carbonaceous material extinction was 2-3 times higher than other species. [ABSTRACT FROM AUTHOR]

Abstract: Atmospheric particulate matter can be strongly affected by smoke from biomass combustion, including wildfires, prescribed burns, and residential wood burning. Molecular source tracer techniques help determine contributions of biomass smoke to particle concentrations if representative source profiles are available. Various wood smoke source profiles have been generated for residential wood burning; however, few emission data are available for the combustion of biomass under open-burning conditions. Anhydrosugars, produced as thermal degradation products of cellulose and hemicellulose, are typically analyzed by gas chromatography-mass spectrometry (GC-MS) after chemical derivatization. A simpler alternative analytical method, based on high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD), was developed here and utilized to measure several isomeric anhydrosugars (levoglucosan, mannosan, and galactosan) in primary smoke aerosol from various types of biomass and from different combustion conditions representative of prescribed and wildfires. Highly varying patterns were observed in the emission profiles of various molecular markers as a function of fuel type and combustion conditions. Emission factors of levoglucosan were a strong function of fuel type, combustion phase, and uphill versus downhill burn direction, varying from 36 to 1368μgmg−1 organic carbon. Fuel type was the most important determinant, causing variations in emission factors of levoglucosan over an order of magnitude, while combustion phase and burn direction generally affected emission factors by a factor of 2–3. Mannosan and galactosan showed emission trends similar to levoglucosan. Levoglucosan emission factors from selected samples were compared to data obtained by two independent analytical methods, high-performance liquid chromatography (HPLC-MS) and GC-MS, showing rather good agreement. The HPAEC-PAD analytical method offers a simple alternative to GC-MS for future studies of aerosol concentrations of anhydrosugars, enabling more accurate estimates of contributions from biomass combustion to ambient particle concentrations. [Copyright &y& Elsevier]

Abstract: Observations of aerosol physical, chemical, and optical properties made at 38 locations in Washington, Oregon, and California are presented to show the regional-scale influence of wildfire smoke during the summer of 2002. Aerosol measurements made during an intensive field campaign conducted in July, August, and September 2002 in Yosemite National Park indicated that smoke-impacted aerosols were present at the park during frequent haze episodes. In addition, backward trajectory analyses showed that large-scale meteorological conditions during the study were dominated by transport from western and southern Oregon, a region with high fire activity during the summer of 2002. Observations of aerosol properties at the Yosemite NP site were remarkably similar, with similar temporal variations, to data from a second monitoring site at Blodgett Forest Research Station in the Sierra Nevada, approximately 150km to the NNW. Further similarities to the temporal changes in aerosol properties as measured by monitoring networks with numerous sites in California and Oregon confirmed the regional nature of the haze, which had elevated fine aerosol particle mass concentrations compared with typical summertime average concentrations. The observations suggest that emissions from wild fires can have strong and sustained regional impacts on aerosol concentrations, air quality, and visibility. [Copyright &y& Elsevier]

Abstract: The influence of particulate organic material (POM) and the contribution of biomass smoke on air quality and visibility remain a paramount issue in addressing regional haze concerns in US national parks. Measurements during the Yosemite Aerosol Characterization Study (July–September 2002) indicated an aerosol dominated by POM (∼70% of identified species) and strongly influenced by biomass smoke. Here we report aerosol size hygroscopic growth measurements for dry (RH&#60;5%) aerosol diameters of 100 and 200nm as measured with a controlled relative humidity tandem differential mobility analyzer. Hygroscopic growth was found to be negligible for relative humidity (RH) &#60;∼40% within the sensitivity of the method. For RH>40%, particle size typically increased smoothly with RH, and overall hygroscopic growth at high RH was low to moderate in comparison to the range of values reported in the literature. For RH>80%, both monomodal and bimodal growth profiles were observed during the study, with 200nm particles more often splitting into bimodal profiles (68% of cases), indicating some degree of external mixing. Trimodal growth profiles were observed on two occasions during periods of changing meteorology and aerosol composition. For bimodal profiles for 200nm dry particles, particle diameter growth factors at RH=80% ( where Do is measured at RH&#60;5%) were 1.11±0.04 and 1.29±0.08 for the more and less hygroscopic modes, respectively. Ensemble D/Do was calculated using a cubic-weighted sum of D/Do of individual modes. For 200nm particles, average ensemble was 1.15±0.05 and was 1.31±0.06, and were slightly large for 100nm particles. These growth factors are dramatically lower than those for typical ambient aerosol ionic components such as sulfate, nitrate and sodium salts and sulfuric acid. An inverse relationship between the POM fraction of PM2.5 and hygroscopicity was particularly evident for 200nm particles with approaching ∼1.1 as the POM/ionic mass ratio exceeded 10. Linear correlations with several measurements of POM and select biomass smoke markers were -0.74&#60;R&#60;-0.59 for 200nm and -0.43&#60;R&#60;-0.25 for 100nm particles. The limited hygroscopic growth of the carbon dominated, biomass smoke influenced aerosol at Yosemite has important implications to assessing the role of POM in visibility degradation in national parks. [Copyright &y& Elsevier]

Aerosol water content was determined from relative humidity controlled optical particle counter (ASASP-X) size distribution measurements made during the Southeastern Aerosol and Visibility Study (SEAVS) in the Great Smoky Mountains National Park during summer 1995. Since the scattering response function of the ASASP-X is sensitive to particle refractive index, a technique for calibrating the ASASP-X for any real refractive index was developed. A new iterative process was employed to calculate water mass concentration and wet refractive index as functions of relative humidity. Experimental water mass concentrations were compared to theoretically predicted values assuming only ammonium sulfate compounds were hygroscopic. These comparisons agreed within experimental uncertainty. Estimates of particle hygroscopicity using a rural aerosol model of refractive index as a function of relative humidity demonstrated no significant differences from those made with daily varying refractive index estimates. Although aerosol size parameters were affected by the assumed chemical composition, forming ratios of these parameters nearly canceled these effects. [ABSTRACT FROM AUTHOR]

Aerosol size distributions were measured during the summertime 1995 Southeastern Aerosol and Visibility Study (SEAVS) in Great Smoky Mountains National Park using an Active Scattering Aerosol Spectrometer (ASASP-X) optical particle counter. We present an overview of the experimental method, our data inversion technique, timelines of the size distribution parameters, and calculations of dry accumulation mode aerosol density and refractive index. Aerosol size distributions were recorded during daylight hours for aerosol in the size range 0.1 < Dp < 2.5 µm. The particle refractive index used for the data inversion was calculated with the partial molar refractive index approach using 12-hr measured aerosol chemical composition. Aerosol accumulation mode volume concentrations ranging from 1 to 26 µm³ cm[sup-3] were observed, with an average of 7 ± 5 µm³ cm[sup-3] . The study average dry accumulation mode geometric volume median diameter was 0.27 ± 0.03 µm, and the mean geometric standard deviation was 1.45 ± 0.06. Using an internally mixed aerosol model, and assuming chemical homogeneity across the measured particle distribution, an average accumulation mode dry sulfate ion mass scattering efficiency of 3.8 ± 0.6 m² g[sup-1] was calculated. [ABSTRACT FROM AUTHOR]