South Coast Air Quality Management Research Articles

Neighbourhood Electric Vehicles in Mature Suburbs

This is a Report on the first phase of a demonstration of Neighborhood Electric Vehicles (NEVs) in the South Bay Subregion of Los Angeles County. The project is sponsored by the South Bay Cities Council of Governments (SBCCOG) and funded by the South Coast Air Quality Management District (AQMD). Active use of the first demonstration phase began May 1, 2010 and ran for 18 months ending October 31, 2011. This Report, based on the 18 months of data collection and analysis, aims to identify the positive role NEVs can play in addressing the following issues: • Reducing green house gas emissions, criteria air pollutants, and consumption of fossil fuels by passenger vehicles and light trucks. • Informing government plans and policies currently being formulated, including the 2012 Regional Transportation Plan, California Energy Commission’s initiative for electric vehicle readiness, and the California Air Resources Board AB 118 vehicle voucher program. • Implementing the Sustainable South Bay Strategy with its mobility initiative based on transitioning the gasoline fueled passenger vehicle fleet to some form of electric vehicle. Because this study is extremely data rich, a very detailed and scientific analysis has been completed for a somewhat small sample size of 29 participating households. From these findings it is clear that significant GHG and criteria air pollutant reductions could be achieved from wide spread use of NEVs for suburban residential driving. This research has also identified numerous market barriers that prevent wide spread adoption of NEVs as well as strategies to overcome market barriers such as production quality, speed limitations, and NEV prices.

The evolution and impact of testing baghouse filter performance

In 1995, the U.S. Environmental Protection Agency (EPA) initiated the Environmental Technology Verification (ETV) program for the purpose of generating both independent and credible performance verification of innovative technologies and helping to accelerate acceptance of these products into the marketplace to further benefit the environment and protect public health. The EPA has approved a testing protocol under this program to verify the performance of commercially available filtration products for pulse-jet baghouses in removing fine particulate matter (aerodynamic diameter <2.5 μm; PM2.5). This verification testing protocol was later used as a basis for the development of the American Society for Testing and Materials (ASTM) Method D6830-02 and the International Organization for Standardization (ISO) Method 11057. The South Coast Air Quality Management District (SCAQMD) in California and the EPA's Office of Air Quality Planning and Standards (OAQPS) highly encourage the use of ETV/ASTM-verified filtration media. This paper highlights the evolution of the standard test methods, the EPA's and SCAQMD's regulatory activities, the benefits of using verified filtration media, and the importance of including the filter performance testing in future consideration of baghouse permitting, baghouse operation and maintenance (O&M) plans, quality assurance/quality control (QA/QC), and bag monitoring plans. Implications: Environmental engineers, managers, and the public will benefit from the information related to the PM2.5 emissions documented in the EPA's Environmental Technology Verification (ETV) program for baghouse filtration products. The South Coast Air Quality Management District and the EPA's Office of Air Quality Planning and Standards are in support of the ETV program. Baghouse users are recommended to use the ETV-verified filtration products and incorporate the performance testing in their baghouse monitoring program. This action will reduce air pollution and create a positive impact on public health and public relations.

Environmental Justice and Green‐Technology Adoption

AbstractThis paper presents an analysis of an environmental justice (EJ) program adopted by the South Coast Air Quality Management District (SCAQMD) as a part of its regulation to phase out a toxic chemical used by dry cleaners. SCAQMD provided financial incentives to switch early and gave establishments in EJ neighborhoods priority in applying for grants. Despite this pro‐EJ policy, available data show that dry cleaners in low‐income, predominantly minority, and EJ‐designated areas were less likely to be an early adopter of green technologies, and this finding holds even after accounting for firm and market characteristics. Dry cleaners in disadvantaged neighborhoods were also less likely to receive a grant to switch technology despite the district's effort to set aside half of the funding for applicants from EJ areas.

Traffic-Related Air Toxics and Term Low Birth Weight in Los Angeles County, California

Background: Numerous studies have linked criteria air pollutants with adverse birth outcomes, but there is less information on the importance of specific emission sources, such as traffic, and air toxics.Objectives: We used three exposure data sources to examine odds of term low birth weight (LBW) in Los Angeles, California, women when exposed to high levels of traffic-related air pollutants during pregnancy.Methods: We identified term births during 1 June 2004 to 30 March 2006 to women residing within 5 miles of a South Coast Air Quality Management District (SCAQMD) Multiple Air Toxics Exposure Study (MATES III) monitoring station. Pregnancy period average exposures were estimated for air toxics, including polycyclic aromatic hydrocarbons (PAHs), source-specific particulate matter < 2.5 μm in aerodynamic diameter (PM2.5) based on a chemical mass balance model, criteria air pollutants from government monitoring data, and land use regression (LUR) model estimates of nitric oxide (NO), nitrogen dioxide (NO2) and nitrogen oxides (NOx). Associations between these metrics and odds of term LBW (< 2,500 g) were examined using logistic regression.Results: Odds of term LBW increased approximately 5% per interquartile range increase in entire pregnancy exposures to several correlated traffic pollutants: LUR measures of NO, NO2, and NOx, elemental carbon, and PM2.5 from diesel and gasoline combustion and paved road dust (geological PM2.5).Conclusions: These analyses provide additional evidence of the potential impact of traffic-related air pollution on fetal growth. Particles from traffic sources should be a focus of future studies.

Air Pollution and Health: Bridging the Gap from Sources to Health Outcomes

The U.S. Environmental Protection Agency (EPA) has established National Ambient Air Quality Standards (NAAQS) for six principal air pollutants (“criteria” pollutants): carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), particulate matter (PM) in two size ranges [< 2.5 μm (PM2.5) and < 10 μm (PM10)], ozone (O3), and sulfur dioxide (SO2) (U.S. EPA 2010b). Although associations have been identified between these pollutants and adverse health effects, considerable uncertainty remains regarding a) methods and approaches to understanding relationships between air pollution and health effects; b) which components (gas and/or aerosol) and sources are most toxic; c) the mechanisms of actions of the pollutants and causal relationships; d) effect of confounding factors, and e) which populations are susceptible {U.S. EPA 2006a (Pb), 2006b (O3), 2008a [NOx Integrated Science Assessment (ISA)], 2008b (SOx ISA), 2009 (PM), 2010 (CO)}. This holds true especially for PM, because it is composed of many components with significant spatial and temporal variation (U.S. EPA 2009). Air pollution and health research continues to reduce these uncertainties across the source-to-health effects paradigm as described by the National Research Council (NRC) Research Priorities for Airborne Particulate Matter, volumes I–IV, (NRC 1998, 1999, 2001, 2004) and the U.S. EPA (2006a, 2006b, 2008a, 2008b, 2009b, 2010a). Linking air pollution and adverse health effects is complicated and requires expertise across a range of scientific disciplines—from atmospheric to exposure to health sciences, as well as inclusion of air quality managers and policy makers who implement and develop policy to reduce risk from air pollution. Interaction among these groups at different points in time helps to identify gaps in knowledge and suggest future research directions. One such opportunity was the international specialty conference “Air Pollution and Health: Bridging the Gap from Sources to Health Outcomes,” sponsored by the American Association for Aerosol Research (AAAR 2010). The conference, chaired by myself and Maria Costantini (Health Effects Institute), was designed to help disseminate and integrate results from scientific studies that cut across the range of air pollution– and health-related disciplines of the source-to-health effects continuum. The conference addressed the science of air pollution and health within a multipollutant framework, focusing on five key science areas—sources, atmospheric sciences, exposure, dose, and health effects—as identified by the NRC (1998). Eight key policy-relevant science questions that integrated across various parts of these science areas formed the basis of the meeting, and a ninth question addressed the policy implications of the findings (see Appendix). This was the AAAR’s third international specialty conference and extended the findings presented at the AAAR’s first specialty conference “Particulate Matter: Atmospheric Sciences, Exposure, and the Fourth Colloquium on PM and Human Health,” held in Pittsburgh, Pennsylvania, in 2003 (Davidson et al. 2005). Results from the 2010 AAAR Air Pollution and Health conference are being published in Environmental Health Perspectives (EHP); Air Quality, Atmosphere and Health; Aerosol Science and Technology; Atmospheric Environment; and Inhalation Toxicology (Solomon 2010). This issue of EHP includes conference papers on the importance of a multipollutant approach and of individual components of particulate matter to understanding linkages between sources and adverse health outcomes, including respiratory and/or cardiovascular diseases (Ito et al. 2011; Lall et al. 2011; Rohr et al. 2011; Spira-Cohen et al. 2011; Zhou et al. 2011), associated effects, such as inflammation (Alexeeff et al. 2011), and birth outcomes associated with exposures to traffic-related pollution during gestation (Malmqvist et al. 2011). Several air pollution components and sources were evaluated, including elemental carbon and secondary organic aerosol, traffic, local industrial sources, and residential oil and wood burning. Where studied, some effects varied by season and location over sufficient time (specifically, Detroit, MI; Seattle, WA; New York, NY), likely due to the influence of different source impacts. In addition, this issue includes a review of population characteristics related to susceptibility (Sacks et al. 2011), and an accountability study of the feasibility of hybrid regional–local modeling to assess health improvements in small communities (Lobdell et al. 2011).

Baseline in the Sand: Communities for a Better Environment v. South Coast Air Quality Management District

Baseline in the Sand: Communities for a Better Environment v. South Coast Air Quality Management District

Do Environmental Regulations Impede Economic Growth? A Case Study of the Metal Finishing Industry in the South Coast Basin of Southern California

Air pollution emitted from firms and industries in the United States poses a significant threat to human health and the environment. Economists have traditionally opposed environmental regulations based on the argument that regulations reduce economic growth. Some scholars, however, have argued that polluting firms often adjust to environmental regulations through technological innovations that have the opposite effect. This study examines the effects of environmental regulations on economic growth through a case study of the metal finishing industry in the South Coast Basin of Southern California. The industry in the Basin has been regulated since 1988 by the South Coast Air Quality Management District (AQMD) as a result of the industry’s use of hexavalent chromium. Based on a comparative analysis of the metal finishing industries in Chicago and Detroit, it appears that the AQMD regulations have not had a detrimental impact on the growth of the industry in the Basin.

Global Trade Comes Home: Community Impacts of Goods Movement

For many U.S. residents, 2007 was a year of heightened awareness of some of the problems of global trade. Extensive recalls of melamine-tainted pet food in the spring followed by even larger toy recalls in the summer and fall raised consumer concerns about how the United States can ensure the safety of products shipped in from overseas. The Salt Lake Tribune and the Wall Street Journal detailed injuries and illnesses threatening the health of Chinese workers making products for export to the United States. And on 15 December 2007, a New York Times feature detailed the practice of farming fish in toxic Chinese waters for export to the United States and other countries. While these news stories demonstrate some of the pitfalls of globalization, much less attention has focused on air pollution and other community-level impacts in the United States, as toys, electronics, food, and other imports travel through ports, then to trucks, trains, warehouses, and stores in a complex system called “goods movement.” Along the route, residents are exposed to diesel exhaust and other vehicle emissions, noise from truck-congested roads, bright lights from round-the-clock operations, and other potential health threats. Transportation experts refer to these impacts simply as “externalities” of transport, but to community residents they can directly harm the quality of daily life. As ports and goods movement activity expands throughout the United States, a major challenge is how to make its health and community impacts a more central part of policy discussions.

Engine Manufacturer's Association v. South Coast Air Quality Management District: Using Market Participation to Achieve Environment Goals

Engine Manufacturer's Association v. South Coast Air Quality Management District: Using Market Participation to Achieve Environment Goals

Errors in variables and spatial effects in hedonic house price models of ambient air quality

In the valuation of the effect of improved air quality through the estimation of hedonic models of house prices, the potential “errors in variables” aspect of the interpolated air pollution measures is often ignored. In this paper, we assess the extent to which this may affect the resulting empirical estimates for marginal willingness to pay (MWTP), using an extensive sample of over 100,000 individual house sales for 1999 in the South Coast Air Quality Management District of Southern California. We take an explicit spatial econometric perspective and account for spatial dependence and endogeneity using recently developed Spatial 2SLS estimation methods. We also account for both spatial autocorrelation and heteroskedasticity in the error terms, using the Kelejian–Prucha HAC estimator. Our results are consistent across different spatial weights matrices and different kernel functions and suggest that the bias from ignoring the endogeneity in interpolated values may be substantial.

Environmental regulations and the diffusion of clean technologies in the dry cleaning industry

Most dry cleaners in the United States use perchloroethylene, a chemical whose vapors are emitted into the ambient air during the dry cleaning process. Scientific studies have linked perchloroethylene exposure to increased risks for cancer and other health problems. In 2002, the South Coast Air Quality Management District (AQMD) adopted Rule 1421, a regulation requiring the dry cleaning industry in the South Coast Basin of California to adopt alternative technologies to perchloroethylene. In this article I examine how alternative technologies to perchloroethylene have been diffusing throughout the industry in response to Rule 1421. My research reveals that the industry is highly skeptical of alternative technologies on economic and political grounds. Despite these problems, the industry has made progress in substituting alternative technologies for perchloroethylene. The challenge for policy makers is to mitigate barriers to the diffusion process so the full environmental benefits of Rule 1421 can be realised.

Source apportionment of VOCs in the Los Angeles area using positive matrix factorization

Eight 3-h speciated hydrocarbon measurements were collected daily by the South Coast Air Quality Management District (SCAQMD) as part of the Photochemical Assessment Monitoring Stations (PAMS) program during the summers of 2001–03 at two sites in the Los Angeles air basin, Azusa and Hawthorne. Over 30 hydrocarbons from over 500 samples at Azusa and 600 samples at Hawthorne were subsequently analyzed using the multivariate receptor model positive matrix factorization (PMF). At Azusa and Hawthorne, five and six factors were identified, respectively, with a good comparison between predicted and measured mass. At Azusa, evaporative emissions (a median of 31% of the total mass), motor vehicle exhaust (22%), liquid/unburned gasoline (27%), coatings (17%), and biogenic emissions (3%) factors were identified. Factors identified at Hawthorne were evaporative emissions (a median of 34% of the total mass), motor vehicle exhaust (24%), industrial process losses (15%), natural gas (13%), liquid/unburned gasoline (13%), and biogenic emissions (1%). Together, the median contribution from mobile source-related factors (exhaust, evaporative emissions, and liquid/unburned gasoline) was 80% and 71% at Azusa and Hawthorne, respectively, similar to previous source apportionment results using the chemical mass balance (CMB) model. There is a difference in the distribution among mobile source factors compared to the CMB work, with an increase in the contribution from evaporative emissions, though the cause (changes in emissions or differences between models) is unknown.

Interpolation of Air Quality Measures in Hedonic House Price Models: Spatial Aspects

This paper investigates the sensitivity of hedonic models of house prices to the spatial interpolation of measures of air quality. We consider three aspects of this question: the interpolation technique used, the inclusion of air quality as a continuous vs discrete variable in the model, and the estimation method. Using a sample of 115,732 individual house sales for 1999 in the South Coast Air Quality Management District of Southern California, we compare Thiessen polygons, inverse distance weighting, Kriging and splines to carry out spatial interpolation of point measures of ozone obtained at 27 air quality monitoring stations to the locations of the houses. We take a spatial econometric perspective and employ both maximum-likelihood and general method of moments techniques in the estimation of the hedonic. A high degree of residual spatial autocorrelation warrants the inclusion of a spatially lagged dependent variable in the regression model. We find significant differences across interpolators in the coefficients of ozone, as well as in the estimates of willingness to pay. Overall, the Kriging technique provides the best results in terms of estimates (signs), model fit and interpretation. There is some indication that the use of a categorical measure for ozone is superior to a continuous one. RÉSUMÉ Interpolation des Mesures de la Qualité de l'Air dans les Modèles Hédoniste de l'Estimation Immobilière: Aspects Spatiaux Cet article examine la sensibilité de l’évaluation hédoniste des prix de l'immobilier à l'interpolation spatiale des mesures de la qualité de l'air. Nous avons envisagé la question sous trois aspects: la technique d'interpolation utilisée, l'introduction de la qualité de l'air comme variable continue ou discrète dans le modèle et la méthode d'estimation. Nous avons utilisé un échantillon de 115 732 ventes de maisons individuelles, en 1999, dans le district Côte Sud de la gestion de la Qualité de l'Air en Californie du Sud. Nous avons comparé les polygônes de Thiessen, la pondération inversement proportionnelle à la distance, le krigeage et les courbes splines pour mener l'interpolation des mesures ponctuelles de l'ozone, obtenues dans 27 stations de suivi de la qualité de l'air en fonction des lieux où étaient situées les maisons. Nous avons pris une perspective spatiale économétrique et employé aussi bien la probabilité maximale que la méthode générale des moments techniques dans l’évaluation de l'hédonique. Un degré élevé d'auto corrélation spatiale résiduelle garantie l'inclusion d'une variable dépendante spatialement décalée dans le modèle de régression. Nous avons trouvé des différences importantes parmi les interpolateurs dans les coefficients d'ozone, ainsi que parmi les indicateurs de la volonté de payer. Surtout, la technique de krigeage donne les meilleurs résultats pour les estimations (signes), l'ajustement du modèle et l'interprétation. L'utilisation d'une mesure nominale pour l'ozone est supérieure à une mesure continue, semble-t-il. RESUMEN Interpolación de las medidas de la calidad del aire en los modelos de los precios hedónicos de la vivienda: aspectos espaciales En este ensayo investigamos la sensibilidad de los modelos de lo precios hedónicos de la vivienda para la interpolación espacial de medidas de la calidad del aire. Tenemos en cuenta tres aspectos al respecto: la técnica de interpolación utilizada, la inclusión de la calidad del aire como variable continua, en vez de discreta, en el modelo, y el método de cálculo. Con una muestra de 115.732 ventas de viviendas individuales durante 1999 en el Distrito de Gestión de Calidad del Aire de la Costa Sur en California, comparamos los polígonos de Thiessen, la ponderación de la distancia inversa, métodos geoestadísticos o Kriging y métodos basados en splines para llevar a cabo la interpolación espacial de las mediciones puntuales de ozono obtenidas en 27 estaciones de control de calidad del aire en los lugares donde están situadas las viviendas. Desde la perspectiva econométrica espacial empleamos las técnicas de la probabilidad máxima del método general de momentos en el cálculo de precios hedónicos. Debido a un alto grado de autocorrelación espacial residual debemos incluir una variable dependiente espacialmente rezagada en el modelo de regresión. Se observan diferencias importantes entre los interpoladores en los coeficientes del ozono y en los cálculos de la disposición a pagar. En general, la técnica Kriging da los mejores resultados en cuanto a los cálculos (señales), la idoneidad del modelo y la interpretación. Hay indicios de que es mejor usar una medida categórica para el ozono en vez de una continua.

Stationary Sources of Airborne Lead: A Comparison of Emissions Data for Southern California

Estimates for the air releases of lead from stationary point sources are considered for the South Coast Air Basin of California. We have examined four databases published by U.S. Environmental Protection Agency, the California Air Resources Board, and the South Coast Air Quality Management District. Our analysis indicates that none of the databases includes every emitting facility in the South Coast Air Basin of California and that other discrepancies among the databases exist. Additionally, the data have been analyzed for temporal variation, and some of the California Air Resources Board data are not current. The South Coast Air Quality Management District inventory covers 12 times more facilities in 2001 than in 1996. From this analysis, we conclude that all four of the databases would beneflt by sharing data, increasing transparency, analyzing uncertainty, and standardizing emission estimation methods.

Ports in a Storm

In many parts of the world, shipping-related emissions have already exceeded or are expected to soon exceed those from land-based sources. Shipping emissions can be reduced substantially by using some of the same technologies being applied to land-based sources, including cleaner engines and fuels, exhaust control methods, and operational modifications. Various ports are testing the feasibility of these mechanisms with varying degrees of success. What is perhaps most greatly needed is expedited creation of better regulations at all levels, from the International Maritime Organization to port city authorities.

Laboratory and Field Evaluation of Instrumentation for the Semicontinuous Determination of Particulate Nitrate (and Other Water-Soluble Particulate Components)

Studies conducted at the U.S. Environmental Protection Agency facility in Research Triangle Park, NC, and at a field study in Southern California have demonstrated the capability for the semicontinuous determination of particulate nitrate (and other water-soluble ionic species). Two instruments, an R&P Series 8400N Ambient Particulate Nitrate Monitor (8400N) and an ion chromatography (IC)-based prototype monitor developed at Texas Tech University, were evaluated both in the laboratory using aqueous standards and simulated ambient aerosols and in the field during a 3-week (July 1–21, 2003) joint ambient comparison study with Brigham Young University and the South Coast Air Quality Management District (SCAQMD). The field study was conducted at the SCAQMD Rubidoux field site near Riverside, CA. During initial (before the field study) laboratory studies, both instruments were responsive to changes in the simulated aerosol concentration. However, potential problems were discovered involving both instruments during the laboratory-based studies both before and after the Rubidoux study, and these problems are currently being addressed. During the 3-week field study period, 15-minute average particulate nitrate concentrations approaching 30 μg/m3 were observed. Because of malfunctioning IC components (concentrator columns) of the Texas Tech University prototype monitor, limited data were obtained from this instrument during the 3-week sampling period. Initial ambient comparisons show general agreement between the 8400N and IC-based prototype instrument for the semicontinuous determination of ambient particulate nitrate at lower nitrate concentrations (<15 μg/m3) and an underdetermination by the 8400N at higher concentrations (>15 μg/m3). A decreased molybdenum converter efficiency in the pulse analyzer of the 8400N discovered during postfield study laboratory evaluation may explain the negative bias observed at higher nitrate concentrations. Semicontinuous results obtained from U.S. Environmental Protection Agency-operated instruments were averaged and compared with integrated sampler results obtained by Brigham Young University and SCAQMD.

Calculations of Incremental Secondary Organic Aerosol Reactivity

The incremental secondary organic aerosol reactivity (ISOAR) of a species j is defined as the relative incremental change in secondary organic aerosol (SOA) formed per relative incremental change in the amount of species jemitted. The California Institute of Technology three-dimensional air quality model is used in conjunction with the Caltech Atmospheric Chemistry Mechanism (CACM) and the Model to Predict the Multiphase Partitioning of Organics to calculate spatially and temporally averaged ISOAR values for the South Coast Air Basin of California (SoCAB). The base case SOA concentrations are derived for September 9, 1993. The South Coast Air Quality Management District of California provided emission and meteorological data. ISOAR values are calculated for the lumped surrogate compounds considered by CACM: isoprene, low-yield monoterpenes, high-yield monoterpenes, high-yield aromatics, etc. This work presents basin-wide ISOAR values determined through regression analysis. In addition, ISOAR values are reported at individual locations within the SoCAB. Modeled data are compared with ISOAR values calculated using smog chamber data. Results indicate that long-chain alkanes present the highest ISOAR. On the other hand, short-chain organics present the lowest ISOAR.

Locational Adjustments to Pollution Regulations: The South Coast Air Quality Management District and the Furniture Industry

Since the 1960s, environmental regulations have played an increasingly large role in regulating the activities of private businesses that generate pollution. There has been little research, however, on the effects of environmental regulations on the location decisions of firms and industries. This article attempts to bridge this gap by examining the impact of air pollution regulations implemented by the South Coast Air Quality Management District in 1988 on the wood household furniture industry in southern California. The regulations created a great deal of uncertainty within the industry. Some firms relocated to Mexico to avoid compliance. Other firms remained in the region and attempted to adjust through product and process innovations. Over time, and with the help of institutions, the industry adjusted through a process of “learning by doing.” A challenge for community economic development practitioners is to build institutions that foster the learning process by which firms adjust to environmental regulations.

A cohort‐based approach for characterizing lifetime inhalation cancer risk from time‐varying exposure to air toxics from ambient sources

AbstractIn recent years, the U.S. EPA as well as state and local agencies have released a number of risk characterizations addressing potential inhalation cancer risks from exposure to ambient sources of air toxics (e.g., U.S. EPA's 1993 Motor Vehicle‐Related Air Toxics Study, the South Coast Air Quality Management District's MATES‐II study, the U.S. EPA's National Scale Air Toxics Assessment). In these assessments, quantitative estimates of cancer risk are often presented as point estimates and/or distributions of individual upper‐bound lifetime risks. The individual upper‐bound lifetime cancer risk is the probability that an individual in a given population will contract cancer if exposed continuously to a given concentration of an airborne carcinogen over an assumed lifetime. Individual risk estimates in these studies are usually based on average or median exposures for a wide population distribution.These estimates generally assume continuous exposure over an entire lifetime to levels estimated for 1 or a few years and do not account for expected changes in exposure over time. For example, risk estimates in U.S. EPA's recent National Scale Air Toxics Assessment assume individuals will be exposed to 1996 levels over a 70‐year lifetime. However, exposures to most air toxics are expected to change over time as a result of mobile and stationary source emission control programs.In this paper, a cohort‐based approach, which estimates individual lifetime cancer risk based on time‐weighted exposure over a lifetime, is presented. This approach accounts for changes in exposure level over time, including decreases anticipated as a result of regulatory programs. It also incorporates differences in exposures to children and adults that result from certain differences in time–activity patterns, integrating them into a single value for a cohort. Moreover, this paper presents a case study applying this approach to estimate average nationwide individual cancer risks from exposure to the highway mobile source contribution to ambient benzene. The case study includes estimates for the general population and a highly exposed demographic group, outdoor workers. © 2004 American Institute of Chemical Engineers Environ Prog, 23: 120–125, 2004

One-hour and eight-hour average ozone in the California South Coast air quality management district: trends in peak values and sensitivity to precursors

Exceedences of the 1 and 8 h O3 air quality standard were identified for 24 routine air quality monitor stations in the California South Coast Air Quality Management District (AQMD) from 1980 to 2001. Yearly trends, temporal and spatial distributions of O3 exceedences and ‘‘weekend effect’’ on O3 exceedences are presented. There were considerably more exceedences of the 8 h O3 standard than exceedences of the 1 h standard in the period of 1997–2001. Prescursor control strategies in the AQMD were very successful in controlling O3 with dramatic reductions in the frequency of days on which both the 1 and 8 h O3 standards were exceeded in 1990s. However, there was less reduction in frequency of moderate exceedences of the 8 h standard, where ‘‘moderate’’ was defined as the day on which 8 h average O3 exceeded 80 ppb but the peak hour O3 was o120 ppb. Observation-Based Methods (OBMs) were used to determine a possible shift in O3 control strategies for attaining the 8 h standard. The photochemical indicator, extent of reaction, was calculated for the days with exceedence of the 1 or 8 h O3 standards. Analysis of the results indicates that the promulgation of an 8 h standard would significantly increase the number of non-attainment in station days in the AQMD. The O3 control in the AQMD was general VOCs control benefit. The new 8 h O3 standard would lend the O3 control strategy little more VOCs control benefit. r 2004 Elsevier Ltd. All rights reserved.