Paul A. Solomon

Airborne Particulate Matter and Human Health: A Review

Results of recent research show that particulate matter (PM) composition and size vary widely with both space and time. Despite the variability in PM characteristics, which are believed to influence human health risks, the observed relative health risk estimates per unit PM mass falls within a narrow range of values. Furthermore, no single chemical species appears to dominate health effects; rather the effects appear to be due to a combination of species. Non-PM factors such as socioeconomic status and lifestyle are also believed to affect the health risk, although accounting for these confounding factors is challenging. Airborne PM is also responsible for a number of effects aside from human health, such as alterations in visibility and climate. Because the PM problem is associated with a range of societal issues such as energy production and economic development, making progress on reducing the effects of PM will require integrated strategies that bring together scientists and decision makers from different disciplines to consider tradeoffs holistically.

The Changing Paradigm of Air Pollution Monitoring

The air pollution monitoring paradigm is rapidly changing due to recent advances in (1) the development of portable, lower-cost air pollution sensors reporting data in near-real time at a high-time resolution, (2) increased computational and visualization capabilities, and (3) wireless communication/infrastructure. It is possible that these advances can support traditional air quality monitoring by supplementing ambient air monitoring and enhancing compliance monitoring. Sensors are beginning to provide individuals and communities the tools needed to understand their environmental exposures with these data individual and community-based strategies can be developed to reduce pollution exposure as well as understand linkages to health indicators. Each of these areas as well as corresponding challenges (e.g., quality of data) and potential opportunities associated with development and implementation of air pollution sensors are discussed.

Breakdown in silicon oxide−A review

A review is given concerning measurement techniques and experimental results obtained on electrical breakdown in SiO2. Breakdown dependence on parameters such as time, thickness, temperature, and electrode material are covered, as well as the effect of various high‐temperature processing steps and the effect of ion implantation. The effects of sodium in causing time‐dependent breakdown are also reviewed. Special attention is given to the intrinsic breakdown mechanism in MOS capacitors where mechanisms involving impact ionization and positive charge buildup in the insulator are favored.

Comparison of scientific findings from major ozone field studies in North America and Europe

Abstract During the past decade, nearly 600 million dollars were invested in more than 30 major field studies in North America and Europe examining tropospheric ozone chemistry, meteorology, precursor emissions, and modeling. Most of these studies were undertaken to provide new or refined knowledge about ozone accumulation and to assist in the development of economical and effective emissions management practices for ozone. In this paper, we describe a selection of field research programs conducted under a wide range of geographical and climatological conditions in North America and Europe. The designs of these studies were generally similar, employing a combination of ground-based observation networks, upper-air sampling, and meteorological observations. Analysis and interpretation of the resulting data were combined with improved inventories of ozone precursor emissions and air quality modeling to develop new or enhanced knowledge about photochemical processes under various tropospheric conditions. The scientific results from these studies contained few surprises; in fact, they generally affirmed the conclusions in the review by the US National Research Council (NRC, 1999). Key findings include: (1) reaffirmation that tropospheric ozone is a multi-scale phenomenon extending to continental boundaries; (2) aerometric conditions aloft are important to ground-level ozone; (3) biogenic sources make important contributions to VOC and NOx emissions in parts of eastern North America and southern Europe; (4) emissions estimates are among the more uncertain components of predictive models for ozone; (5) recirculating flow over complex terrain and large water bodies are universally important factors affecting accumulation of ozone at the ground; (6) nonlinearities in ozone response to precursor changes create important degrees of freedom in management strategies – VOC and NOx sensitivities vary extensively in urban and rural areas, making decisions about emissions management complicated; (7) measurement methods for many precursors, intermediates, and products of photochemical reactions have improved greatly; and (8) additional analysis and interpretation of existing data from many of these field studies should pay handsome dividends at relatively modest cost.

The nitric acid shootout: field comparison of measurement methods

Eighteen instruments for measuring atmospheric concentrations of nitric acid were compared in an eight day field study at Pomona College, situated in the eastern portion of the Los Angeles Basin, in September 1985. The study design included collocated and separated duplicate samplers, and the analysis by each laboratory of a set of quality assurance filters, so that the experimental variability could be distinguished from differences due to measurement methods. For all sampling periods, the values for nitric acid concentrations reported by the different instruments vary by as much as a factor of four. The differences among measurement techniques increase with nitric acid loading, corresponding to a coefficient of variation of 40%. In contrast, samplers of the same design operated by the same group show variability of 11–27 %. Overall, the highest reported concentrations are observed with the filter packs and lower concentrations are observed by the annular denuders and tunable diode laser absorption spectrometers. When the nitric acid concentrations are high enough to be detected by the FTIR, the FTIR values are close to those obtained by the denuder difference method and to the mean value from the other sampler groups. In the absence of a reference standard for the entire study, measurement methods are compared to the average of four denuder difference method samplers (DDM). Filter pack samplers are higher than the DDM for both daytime and night-time sampling. Two different filter packs using Teflon® prefilters are higher than the DDM by factors of 1.25 and 1.4. The results from the three annular denuders do not agree; the ratios of means to the DDM value are 1.0,0.8 and 0.6. For the transition flow reactor method and for two dichotomous samplers operated as denuder difference samplers, the ratio of means to the DDM are 1.09 and 0.93, respectively. The tunable diode laser absorption spectrometers gave lower daytime and higher night-time readings compared to the DDM, especially during the last three days of the study. Averaged over the entire measurement period, the daytime ratio of TDLAS to DDM is 0.8 and the night-time ratio is 1.7.

Trends in Fine Particle Concentration and Chemical Composition in Southern California

ABSTRACT Airborne fine particle mass concentrations in Southern California have declined in recent years. Trends in sulfate and elemental carbon (EC) particle concentrations over the period 1982-1993 are consistent with this overall improvement in air quality and help to confirm some of the reasons for the changes that are seen. Fine particle sulfate concentrations have declined as a strict sulfur oxides (SOx) emission control program adopted in 1978 was implemented over time. Fine particle elemental (black) carbon concentrations have declined over a period when newer diesel engines and improved diesel fuels have been introduced into the vehicle fleet. Organic aerosol concentrations have not declined as rapidly as the EC particle concentrations, despite the fact that catalyst-equipped cars having lower particle emission rates were introduced into the vehicle fleet alongside the diesel engine improvements mentioned above. This situation is consistent with the growth in population and vehicle miles traveled in the air basin over time. Fine particle ammonium nitrate in the Los Angeles area atmosphere contributes more than half of the fine aerosol mass concentration on the highest concentration days of the year, emphasizing both the need for accurate aerosol nitrate measurements and the likely importance of deliberate control of aerosol nitrate as a part of any serious further fine particle control program for the Los Angeles area.

Semicontinuous aerosol carbon measurements: Comparison of Atlanta Supersite measurements

[1] An intensive field campaign of the Atlanta Supersite Experiment was carried out at a ground-based measurement site on Jefferson Street in midtown Atlanta, Georgia, from 3 August to 1 September 1999. This paper examines the semicontinuous particulate organic and elemental measurements that were made as a part of the experiment. Measurements were made using a Rutgers University/Oregon Graduate Institute in situ thermal-optical carbon analyzer, Rupprecht and Patashnick 5400 ambient carbon particulate monitor, Radiance Research particle soot absorption photometer, Aerosol Dynamics flash vaporization carbon analyzer, and Magee Scientific AE-16 Aethalometer. The intersampler precision with which semicontinuous particulate total carbon (TC), organic carbon (OC), and elemental carbon (EC) were measured is 7, 13, and 26%, expressed as pooled coefficients of variation of 2, 3, and 4 instruments, respectively. Correlations between pairs of OC measurements are moderate (R 2 = 54-73%), and correlations between pairs of EC measurements are high (R 2 = 74-97%). Differences in reported OC concentrations are small compared to differences in EC concentrations; intersampler EC concentration differences result from differences (1) in the operational definitions of OC and EC, (2) in the calibration of optical instruments, and (3) because EC values are closer to limits of detection. This agreement between semicontinuous samplers is quite good, especially in light of previous particulate carbon comparisons. Reasons for measurement differences and benefits of automated time-resolved measurements are discussed.

Chemical Characteristics of PM10 Aerosols Collected in the Los Angeles Area

A PM_(10) monitoring network was established throughout the South Coast Air Basin (SOCAB) in the greater Los Angeles region during the calendar year 1986. Annual average PM_(10) mass concentrations within the Los Angeles metropolitan area ranged from 47.0 µg m^(-3) along the coast to 87.4 µg m^(-3) at Rubldoux, the furthest inland monitoring station. Measurements made at San Nicolas Island suggest that regional background aerosol contributes between 28 to 44 percent of the PM_(10) aerosol at monitoring sites In the SOCAB over the long term average. Five major aerosol components (carbonaceous material, NO- _3, SO=_4, NH+_4, and soil-related material) account for greater than 80 percent of the annual average PM_(10) mass at all on-land monitoring stations. Peak 24-h average mass concentrations of nearly 300 µg m^(-3) were observed at inland locations, with lower peak values (˜130–150 µg m^(-3)) measured along the coast. Peak-day aerosol composition was characterized by increased NO-_3 Ion and associated ammonium ion levels, as compared to the annual average. There appears to be only a weak dependence of PM_(10) mass concentration on season of the year. This lack of a pronounced seasonal dependence results from the complex and contradictory seasonal variations in the major chemical components (carbonaceous material, nitrate, sulfate, ammonium ion and crustal material). At most sites within the Los Angeles metropolitan area, PM_(10) mass concentrations exceeded both the annual and 24-h average federal and state of California PM_(10) regulatory standards.

Intercomparison of near real time monitors of PM2.5 nitrate and sulfate at the U.S. Environmental Protection Agency Atlanta Supersite

[1] Five new instruments for semicontinuous measurements of fine particle (PM2.5) nitrate and sulfate were deployed in the Atlanta Supersite Experiment during an intensive study in August 1999. The instruments measured bulk aerosol chemical composition at rates ranging from every 5 min to once per hour. The techniques included a filter sampling system with automated water extraction and online ion chromatographic (IC) analysis, two systems that directly collected particles into water for IC analysis, and two techniques that converted aerosol nitrate or sulfate either catalytically or by flash vaporization to gaseous products that were measured with gas analyzers. During the one-month study, 15-min integrated nitrate concentrations were low, ranging from about 0.1 to 3.5 μg m -3 with a mean value of 0.5 μg m -3 . Ten-minute integrated sulfate concentrations varied between 0.3 and 40 μg m -3 with a mean of 14 μg m -3 . By the end of the one-month study most instruments were in close agreement, with r-squared values between instrument pairs typically ranging from 0.7 to 0.94. Based on comparison between individual semicontinuous devices and 24-hour integrated filter measurements, most instruments were within 20-30% for nitrate (∼0.1-0.2 μg m -3 ) and 10-15% for sulfate (1-2 leg m -3 ). Within 95% confidence intervals, linear regression fits suggest that no biases existed between the semicontinuous techniques and the 24-hour integrated filter measurements of nitrate and sulfate;, however, for nitrate, the semicontinuous intercomparisons showed significantly less variability than intercomparisons amongst the 24-hour integrated filters.

U.S. National PM2.5 Chemical Speciation Monitoring Networks—CSN and IMPROVE: Description of networks

The U.S. Environmental Protection Agency (EPA) initiated the national PM2.5 Chemical Speciation Monitoring Network (CSN) in 2000 to support evaluation of long-term trends and to better quantify the impact of sources on particulate matter (PM) concentrations in the size range below 2.5 μm aerodynamic diameter (PM2.5; fine particles). The network peaked at more than 260 sites in 2005. In response to the 1999 Regional Haze Rule and the need to better understand the regional transport of PM, EPA also augmented the long-existing Interagency Monitoring of Protected Visual Environments (IMPROVE) visibility monitoring network in 2000, adding nearly 100 additional IMPROVE sites in rural Class 1 Areas across the country. Both networks measure the major chemical components of PM2.5 using historically accepted filter-based methods. Components measured by both networks include major anions, carbonaceous material, and a series of trace elements. CSN also measures ammonium and other cations directly, whereas IMPROVE estimates ammonium assuming complete neutralization of the measured sulfate and nitrate. IMPROVE also measures chloride and nitrite. In general, the field and laboratory approaches used in the two networks are similar; however, there are numerous, often subtle differences in sampling and chemical analysis methods, shipping, and quality control practices. These could potentially affect merging the two data sets when used to understand better the impact of sources on PM concentrations and the regional nature and long-range transport of PM2.5. This paper describes, for the first time in the peer-reviewed literature, these networks as they have existed since 2000, outlines differences in field and laboratory approaches, provides a summary of the analytical parameters that address data uncertainty, and summarizes major network changes since the inception of CSN. Implications Two long-term chemical speciation particle monitoring networks have operated simultaneously in the United States since 2001, when the EPA began regular operations of its PM2.5 Chemical Speciation Monitoring Network (IMPROVE began in 1988). These networks use similar field sampling and analytical methods, but there are numerous, often subtle differences in equipment and methodologies that can affect the results. This paper describes these networks since 2000 (inception of CSN) and their differences, and summarizes the analytical parameters that address data uncertainty, providing researchers and policymakers with background information they may need (e.g., for 2018 PM2.5 designation and State Implementation Plan process; McCarthy, 2013) to assess results from each network and decide how these data sets can be mutually employed for enhanced analyses. Changes in CSN and IMPROVE that have occurred over the years also are described.